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

Establishment of a Posttraumatic Osteoarthritis Model in Mice Induced by Noninvasive Anterior Cruciate Ligament Tear

BACKGROUND

Animal models that use open surgical transection of the anterior cruciate ligament (ACL) do not accurately simulate the clinical condition regarding the pivot-shift mechanism and the associated inflammatory response that occurs before reconstruction.

PURPOSE/HYPOTHESIS

The purpose was to characterize a reproducible manual, nonsurgical method to mimic an isolated ACL tear in a clinically relevant model and to evaluate the development of progressive posttraumatic osteoarthritis due to ACL injury. It was hypothesized that the ACL could be reproducibly torn with minimal damage to other ligaments and that there would be progressive development of degenerative joint disease after ACL injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 37 mice (strain C57BL/6) were used to compare the manual procedure with sham surgery (sham group; n = 10) and with the established surgical ACL transection (ACLT) procedure (surgical group; n = 27). In the sham group, a closed manual procedure was performed on the right knee and sham surgery on the left knee. In the surgical group, the closed manual procedure was performed on the right knee and surgical ACLT on the left knee. Dissection using India ink, histological assessment with safranin O and hematoxylin-eosin staining, radiological evaluation through radiographs and microfocus computed tomography scans, and gait analyses were performed to assess cartilage/ligament status. Osteoarthritis Research Society International (OARSI) and synovitis scores, anterior tibial translation, range of motion, bone microstructure, osteophyte volume, and pain were assessed at 2, 4, and 8 weeks postoperatively.

RESULTS

The manual procedure successfully resulted in an ACL rupture and associated meniscal injury. The posterior cruciate, lateral collateral, and medial collateral ligaments were intact in all dissected knees. Two weeks after ACL tear, the surgical group showed a significantly higher synovitis score, whereas 8 weeks after ACL tear, the manual group showed a significantly higher volume of osteophytes. No significant differences were found between the groups in terms of OARSI score, anterior tibial translation, range of motion, bone microstructure computed tomography values, and stride distance/irregularity.

CONCLUSION

This procedure can be used to create an ACL tear model without causing grossly evident injuries to other ligaments and avoiding the risk of cartilage damage from surgical instruments.

CLINICAL RELEVANCE

This procedure offers a more clinically relevant ACL tear model and facilitates simple, inexpensive, and reproducible development of posttraumatic osteoarthritis.

Knee immobilization reproduces key arthrofibrotic phenotypes in mice

AIMS

As has been shown in larger animal models, knee immobilization can lead to arthrofibrotic phenotypes. Our study included 168 C57BL/6J female mice, with 24 serving as controls, and 144 undergoing a knee procedure to induce a contracture without osteoarthritis (OA).

METHODS

Experimental knees were immobilized for either four weeks (72 mice) or eight weeks (72 mice), followed by a remobilization period of zero weeks (24 mice), two weeks (24 mice), or four weeks (24 mice) after suture removal. Half of the experimental knees also received an intra-articular injury. Biomechanical data were collected to measure passive extension angle (PEA). Histological data measuring area and thickness of posterior and anterior knee capsules were collected from knee sections.

RESULTS

Experimental knees immobilized for four weeks demonstrated mean PEAs of 141°, 72°, and 79° after zero, two, and four weeks of remobilization (n = 6 per group), respectively. Experimental knees demonstrated reduced PEAs after two weeks (p < 0.001) and four weeks (p < 0.0001) of remobilization compared to controls. Following eight weeks of immobilization, experimental knees exhibited mean PEAs of 82°, 73°, and 72° after zero, two, and four weeks of remobilization, respectively. Histological analysis demonstrated no cartilage degeneration. Similar trends in biomechanical and histological properties were observed when intra-articular violation was introduced.

CONCLUSION

This study established a novel mouse model of robust knee contracture without evidence of OA. This was appreciated consistently after eight weeks of immobilization and was irrespective of length of remobilization. As such, this arthrofibrotic model provides opportunities to investigate molecular pathways and therapeutic strategies.Cite this article: Bone Joint Res 2023;12(1):58-71.

Contrast-enhanced micro-computed tomography of compartment and time-dependent changes in femoral cartilage and subchondral plate in a murine model of osteoarthritis

A lack of understanding of the mechanisms underlying osteoarthritis (OA) progression limits the development of effective long-term treatments. Quantitatively tracking spatiotemporal patterns of cartilage and bone degeneration is critical for assessment of more appropriately targeted OA therapies. In this study, we use contrast-enhanced micro-computed tomography (μCT) to establish a timeline of subchondral plate (SCP) and cartilage changes in the murine femur after destabilization of the medial meniscus (DMM). We performed DMM or sham surgery in 10-12-week-old male C57Bl/6J mice. Femora were imaged using μCT after 0, 2, 4, or 8 weeks. Cartilage-optimized scans were performed after immersion in contrast agent CA4+. Bone mineral density distribution (BMDD), cartilage attenuation, SCP, and cartilage thickness and volume were measured, including lateral and medial femoral condyle and patellar groove compartments. As early as 2 weeks post-DMM, cartilage thickness significantly increased and cartilage attenuation, SCP volume, and BMDD mean significantly decreased. Trends in cartilage and SCP metrics within each joint compartment reflected those seen in global measurements, and both BMDD and SCP thickness were consistently greater in the lateral and medial condyles than the patellar groove. Sham surgery also resulted in significant changes to SCP and cartilage metrics, highlighting a potential limitation of using surgical models to study tissue morphology or composition changes during OA progression. Contrast-enhanced μCT analysis is an effective tool to monitor changes in morphology and composition of cartilage, and when combined with bone-optimized μCT, can be used to assess the progression of degenerative changes after joint injury.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Therapeutic Potential Low-Intensity Pulsed Ultrasound for Osteoarthritis: Pre-clinical and Clinical Perspectives

Osteoarthritis (OA), degeneration of cartilage associated with aging, lifestyle, and trauma, is one of the most common diseases that leads to lower quality of life and socioeconomic burden in the United States. Clinically, OA is initially managed by non-steroidal anti-inflammatory drugs, but eventually requires surgical intervention to reduce pain and increase function. Cartilage is a mechanotransductive tissue and requires a mechanical stimulus to sustain its mechanical and physiologic properties. Low-intensity pulsed ultrasound (LIPUS) is a cyclic acoustic wave that can provide essential mechanical stimuli to activate molecular and cellular pathways leading to chondrocyte proliferation, differentiation and activity, as well as to inhibit inflammatory pathways associated with OA. The activation of chondrocyte proliferation and inhibition of anti-inflammatory cytokines make LIPUS a potential therapy for mild to moderate OA. Although a few review articles have described the effects of ultrasound on chondrocytes and cartilage, there remains a need for a comprehensive analysis of our current understanding of the basic science and clinical status of the effects of low-intensity ultrasound on chondrocytes and cartilage and the implications of these studies on LIPUS as a therapeutic option for OA. This review analyzes recent literature describing the results of LIPUS using in vitro and in vivo pre-clinical models and clinical studies, as well as future directions for research.

ADAMTS-5: A difficult teenager turning 20

A Disintegrin And Metalloproteinase with ThromboSpondin motif (ADAMTS)-5 was identified in 1999 as one of the enzymes responsible for cleaving aggrecan, the major proteoglycan in articular cartilage. Studies in vitro, ex vivo and in vivo have validated ADAMTS-5 as a target in osteoarthritis (OA), a disease characterized by extensive degradation of aggrecan. For this reason, it attracted the interest of many research groups aiming to develop a therapeutic treatment for OA patients. However, ADAMTS-5 proteoglycanase activity is not only involved in the dysregulated aggrecan proteolysis, which occurs in OA, but also in the physiological turnover of other related proteoglycans. In particular, versican, a major ADAMTS-5 substrate, plays an important structural role in heart and blood vessels and its proteolytic processing by ADAMTS-5 must be tightly regulated. On the occasion of the 20th anniversary of the discovery of ADAMTS-5, this review looks at the evidence for its detrimental role in OA, as well as its physiological turnover of cardiovascular proteoglycans. Moreover, the other potential functions of this enzyme are highlighted. Finally, challenges and emerging trends in ADAMTS-5 research are discussed.

Enhancement of autophagy flux by isopsoralen ameliorates interleukin-1β-stimulated apoptosis in rat chondrocytes

Chondrocyte apoptosis contributes to the pathogenesis of cartilage degeneration in osteoarthritis (OA). We found that isopsoralen pretreatment significantly reversed the increase in DNA fragmentation and apoptosis rate, and significantly decreased the caspase-3 activity and PARP cleavage in IL-1β-treated chondrocytes. Isopsoralen pretreatment markedly inhibited disruption of matrix proteins. Moreover, the expressions of LC3-II and LAMP-1 were markedly increased but the expression of p62/SQSTM1 was remarkably decreased by isopsoralen pretreatment. Importantly, the protective effects of isopsoralen against IL-1β were blocked by pretreatment with autophagy inhibitor 3-MA and bafilomycin A1. These results suggest that isopsoralen ameliorates chondrocyte apoptosis by promoting autophagy flux.[Formula: see text].

Matrix Metalloproteinase Inhibition With Doxycycline Affects the Progression of Posttraumatic Osteoarthritis After Anterior Cruciate Ligament Rupture: Evaluation in a New Nonsurgical Murine ACL Rupture Model

BACKGROUND

Doxycycline has broad-spectrum activity as a matrix metalloproteinase (MMP) inhibitor and thus could reduce the progression of posttraumatic osteoarthritis (PTOA) after anterior cruciate ligament (ACL) rupture.

HYPOTHESIS

Doxycycline would inhibit progression of PTOA in a murine ACL rupture model.

STUDY DESIGN

Controlled laboratory study.

METHODS

For the in vitro study, cadaveric C57BL/6 male mice knees (N = 108) were used for the development of a nonsurgical ACL rupture model. For the in vivo study, 24 C57BL/6 male mice then underwent ACL rupture with our manual procedure and were divided into 4 groups: untreated control; doxycycline, 10 mg/kg/d; doxycycline, 50 mg/kg/d; and doxycycline, 100 mg/kg/d. Doxycycline was administered in drinking water beginning immediately after ACL rupture. Radiographic imaging and paw prints were evaluated at 3, 7, 14, and 28 days. The foot length and toe spread were analyzed as measures of function. Histology and MMP-13 immunohistochemistry were done at 4 weeks.

RESULTS

Radiographs demonstrated anterior tibial subluxation and meniscal extrusion after ACL rupture, confirming knee joint instability without fractures. Statistically significant differences in gait were found between the intact and experimental groups. Histologic examination demonstrated cartilage damage, meniscal tears, and mild osteoarthritis after ACL rupture, similar to what occurs in human patients. Hypertrophy of the posterior horn of the medial and lateral meniscus was found, and tears of the posterior horn of the menisci were common. All doxycycline groups had a lower score than the untreated control group, indicating less cartilage damage. The posterior tibia of the untreated group had the most cartilage damage as compared with the 3 doxycycline groups, with a significant difference between the untreated and 50-mg/kg/d doxycycline groups, suggesting that the latter dose may protect against proteoglycan loss and decrease the progression of osteoarthritis. The nondoxycycline group had the highest synovial inflammation score among all groups, indicating that doxycycline has an inhibitory effect on synovitis. There was significantly lower MMP-13 expression on the tibia in the doxycycline-treated groups, with a positive correlation between doxycycline concentration and MMP-13 inhibition.

CONCLUSION

Modulation of MMP-13 activity by doxycycline treatment may offer a novel biological pathway to decrease the progression of PTOA after ACL rupture.

CLINICAL RELEVANCE

Doxycycline is an approved, readily available drug with infrequent side effects of photosensitivity and gastrointestinal symptoms. Future clinical trials could evaluate doxycycline to reduce or prevent progressive cartilage damage after ACL rupture.

Kartogenin enhances the therapeutic effect of bone marrow mesenchymal stem cells derived exosomes in cartilage repair

The effectiveness of mesenchymal stem cells (MSC) in the treatment of cartilage diseases has been demonstrated to be attributed to the paracrine mechanisms, especially the mediation of exosomes. But the exosomes derived from unsynchronized MSCs may be nonhomogeneous and the therapeutic effect varies between samples. Aim: To produce homogeneous and more effective exosomes for the regeneration of cartilage. Materials & methods: In this study we produced specific exosomes from bone marrow MSCs (BMSC) through kartogenin (KGN) preconditioning and investigated their performance in either in vitro or in vivo experiments. Results & conclusion: The exosomes derived from KGN-preconditioned BMSCs (KGN-BMSC-Exos) performed more effectively than the exosomes derived from BMSCs (BMSC-Exos). KGN preconditioning endowed BMSC-Exos with stronger chondral matrix formation and less degradation.

Two-photon fluorescence and second harmonic generation characterization of extracellular matrix remodeling in post-injury murine temporomandibular joint osteoarthritis

End stage temporomandibular joint osteoarthritis (TMJ-OA) is characterized by fibrillations, fissures, clefts, and erosion of the mandibular condylar cartilage. The goal of this study was to define changes in pericellular and interterritorial delineations of the extracellular matrix (ECM) that occur preceding and concurrent with the development of this end stage degeneration in a murine surgical instability model. Two-photon fluorescence (TPF) and second harmonic generation (SHG) microscopy was used to evaluate TMJ-OA mediated changes in the ECM. We illustrate that TPF/SHG microscopy reconstructs the three-dimensional network of key fibrillar and micro-fibrillar collagens altered during the progression of TMJ-OA. This method not only generates spatially distinct pericellular and interterritorial delineations of the ECM but distinguishes early and end stage TMJ-OA by signal organization, orientation, and composition. Early stage TMJ-OA at 4- and 8-weeks post-injury is characterized by two structurally distinct regions containing dense, large fiber collagens and superficial, small fiber collagens rich in types I, III, and VI collagen oriented along the mesiodistal axis of the condyle. At 8-weeks post-injury, type VI collagen is locally diminished on the central and medial condyle, but the type I/III rich superficial layer is still present. Twelve- and 16-weeks post-injury mandibular cartilage is characteristic of end-stage disease, with hypocellularity and fibrillations, fissures, and clefts in the articular layer that propagate along the mediolateral axis of the MCC. We hypothesize that the localized depletion of interterritorial and pericellular type VI collagen may signify an early marker for the transition from early to end stage TMJ-OA, influence the injury response of the tissue, and underlie patterns of degeneration that follow attritional modes of failure.

Genetic variation of aggrecanase-2 (ADAMTS5) in susceptibility to osteoarthritis

Aggrecanase-2 (ADAMTS5) gene is responsible for aggrecan degradation that may contribute to cartilage destruction in a mouse osteoarthritis (OA) model. We aimed to investigate the effects of ADAMTS5 gene polymorphisms on OA risk in a Chinese population. A total of 300 OA patients and 300 controls were recruited and their genotypes for ADAMTS5 gene rs226794 and rs2830585 polymorphisms were determined using a custom-by-design 48-Plex single nucleotide polymorphism Scan™ kit. ADAMTS5-associated genes were identified by co-expression analysis and their functions were investigated by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. Bioinformatics analysis showed that ADAMTS5 was significantly related to the components, structural constituent, and organization of the extracellular matrix. The rs2830585 polymorphism, but not rs226794 polymorphism, was significantly associated with an increased risk of knee OA. Stratified analysis further confirmed this significant association in patients at age ≥55 years. In conclusion, the ADAMTS5 rs2830585 polymorphism may be involved in the development of knee OA by destroying the extracellular matrix, but this finding should be further confirmed by larger studies.

High molecular weight hyaluronan protects cartilage from degradation by inhibiting aggrecanase expression

Hyaluronan (HA) is an extracellular matrix (ECM) component of articular cartilage and has been used to treat patients with osteoarthritis (OA). A disintegrin and metalloproteinases with thrombospondin motifs (ADAMTSs) play an important role in cartilage degradation in OA. We have previously reported that ADAMTS4 and ADAMTS9 were induced by cytokine stimulation. However, the effect of HA on the cytokine-inducible ADAMTS9 has never been investigated. Moreover, it is unclear whether HA protects cartilage by suppressing aggrecan degradation. Here, we examined the effects of HA on ADAMTS expression in vitro and on cartilage degradation in vivo. ADAMTS9 expression was higher than that of the other aggrecanases (ADAMTS4 and 5) in human chondrocytes, chondrocytic cells, and rat cartilage. ADAMTS4 and 9 mRNA levels were upregulated in cytokine-stimulated chondrocytes and chondrocytic cells. Pre-incubation with HA significantly inhibited ADAMTS9 mRNA expression in cytokine-stimulated cells. In a rat OA model, Adamts5 and 9 mRNA levels were transiently increased after surgery; intra-articular HA injections attenuated the induction of Adamts5 and 9 mRNA. HA also blocked aggrecan cleavage by aggrecanase in OA rats in a molecular size-dependent manner. These results demonstrate that HA attenuates induced aggrecanases expression in OA and thereby protects articular cartilage degradation by this enzyme. Our findings provide insight into the molecular basis for the beneficial effects of HA in OA. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 36:3247-3255, 2018.

Cardiac fibrosis in regenerative medicine: destroy to rebuild

The major limitations for cardiac regeneration in patients after myocardial infarction (MI) are the wide loss of cardiomyocytes and the adverse structural alterations of extracellular matrix (ECM). Cardiac fibroblast differentiation into myofibroblasts (MFB) leads to a huge deposition of ECM and to the subsequent loss of ventricular structural integrity. All these molecular events depict the fundamental features at the basis of the post-MI fibrosis and deserve in depth cellular and molecular studies to fill the gap in the clinical practice. Indeed, to date, there are no effective therapeutic approaches to limit the post-MI massive fibrosis development. In this review we describe the involvement of integrins and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)/ADAMTS-like (ADAMTSL) proteins in cardiac reparative pro-fibrotic response after MI, proposing some of them as novel potential pharmacological tools.

Dehydroepiandrosterone and Experimental Osteoarthritis

Despite an increased understanding of the pathogenesis of osteoarthritis (OA) and the availability of a number of drugs designed to ameliorate its symptoms, a successful disease-modifying therapy remains elusive. Recent lines of evidence suggest that dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone classified as an adrenal androgen, exerts a chondroprotective effect in OA patients, and it has been proven to be an effective DMOAD candidate that slows OA progression. However, the exact mechanisms underlying its anti-OA effect is largely unknown. This review summarizes emerging observations from studies of cell biology, preclinical animal studies, and preliminary clinical trials and describes the findings of investigations on this topic to develop an initial blueprint of the mechanisms by which DHEA slows OA progression. Presently, studies on DMOADs are increasing in importance but have met limited success. Encouragingly, the current data on DHEA are promising and may prove that DHEA-based treatment is efficacious for preventing and slowing human OA progression.

Advances for Treatment of Knee OC Defects

Osteochondral (OC) defects are prevalent among young adults and are notorious for being unable to heal. Although they are traumatic in nature, they often develop silently. Detection of many OC defects is challenging, despite the criticality of early care. Current repair approaches face limitations and cannot provide regenerative or long-standing solution. Clinicians and researchers are working together in order to develop approaches that can regenerate the damaged tissues and protect the joint from developing osteoarthritis. The current concepts of tissue engineering and regenerative medicine, which have brought many promising applications to OC management, are overviewed herein. We will also review the types of stem cells that aim to provide sustainable cell sources overcoming the limitation of autologous chondrocyte-based applications. The various scaffolding materials that can be used as extracellular matrix mimetic and having functional properties similar to the OC unit are also discussed.

A Highly Selective Hydantoin Inhibitor of Aggrecanase-1 and Aggrecanase-2 with a Low Projected Human Dose

Aggrecanase-1 and -2 (ADAMTS-4 and ADAMTS-5) are zinc metalloproteases involved in the degradation of aggrecan in cartilage. Inhibitors could provide a means of altering the progression of osteoarthritis. We report the identification of 7 which had good oral pharmacokinetics in rats and showed efficacy in a rat chemical model of osteoarthritis. The projected human dose required to achieve sustained plasma levels ≥10 times the hADAMTS-5 IC₅₀ is 5 mg q.d.

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.

Trauma and Stem Cells: Biology and Potential Therapeutic Implications

Trauma may cause irreversible tissue damage and loss of function despite current best practice. Healing is dependent both on the nature of the injury and the intrinsic biological capacity of those tissues for healing. Preclinical research has highlighted stem cell therapy as a potential avenue for improving outcomes for injuries with poor healing capacity. Additionally, trauma activates the immune system and alters stem cell behaviour. This paper reviews the current literature on stem cells and its relevance to trauma care. Emphasis is placed on understanding how stem cells respond to trauma and pertinent mechanisms that can be utilised to promote tissue healing. Research involving notable difficulties in trauma care such as fracture non-union, cartilage damage and trauma induced inflammation is discussed further.

Discoidin Domain Receptor 2 as a Potential Therapeutic Target for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is the most common form of arthritis disorders, but the identification of therapeutic targets to effectively prevent OA has been increasingly difficult. The goal of this investigation is to provide experimental evidence that discoidin domain receptor 2 (DDR2) may be an ideal target for the development of disease-modifying OA drugs. Ddr2 was conditionally deleted from articular cartilage of adult mouse knee joints. Aggrecan-CreERT2;floxed Ddr2 mice, which were generated by crossing Aggrecan-CreERT2 mice with floxed Ddr2 mice, then received tamoxifen injections at the age of 8 weeks. The mice were then subjected to destabilization of the medial meniscus (DMM) surgery. At 8 and 16 weeks after DMM, mice were euthanized for the collection of knee joints. In a separate experiment, Aggrecan-CreERT2;floxed Ddr2 mice were subjected to DMM at the age of 10 weeks. The mice then received tamoxifen injections at 8 weeks after DMM. The mice were euthanized for the collection of knee joints at 16 weeks after DMM. The progressive process of articular cartilage degeneration was significantly delayed in the knee joints of Ddr2-deficient mice in comparison to their control littermates. Articular cartilage damage in the knee joints of the mice was associated with increased expression profiles of both Ddr2 and matrix metalloproteinase 13. These findings suggest that DDR2 may be an ideal target for the development of disease-modifying OA drugs.

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.

Mesenchymal Stem Cells and Their Clinical Applications in Osteoarthritis

Osteoarthritis is a chronic degenerative joint disorder characterized by articular cartilage destruction and osteophyte formation. Chondrocytes in the matrix have a relatively slow turnover rate, and the tissue itself lacks a blood supply to support repair and remodeling. Researchers have evaluated the effectiveness of stem cell therapy and tissue engineering for treating osteoarthritis. All sources of stem cells, including embryonic, induced pluripotent, fetal, and adult stem cells, have potential use in stem cell therapy, which provides a permanent biological solution. Mesenchymal stem cells (MSCs) isolated from bone marrow, adipose tissue, and umbilical cord show considerable promise for use in cartilage repair. MSCs can be sourced from any or all joint tissues and can modulate the immune response. Additionally, MSCs can directly differentiate into chondrocytes under appropriate signal transduction. They also have immunosuppressive and anti-inflammatory paracrine effects. This article reviews the current clinical applications of MSCs and future directions of research in osteoarthritis.

Human genome-wide expression analysis reorients the study of inflammatory mediators and biomechanics in osteoarthritis

A major objective of this article is to examine the research implications of recently available genome-wide expression profiles of cartilage from human osteoarthritis (OA) joints. We propose that, when viewed in the light of extensive earlier work, this novel data provides a unique opportunity to reorient the design of experimental systems toward clinical relevance. Specifically, in the area of cartilage explant biology, this will require a fresh evaluation of existing paradigms, so as to optimize the choices of tissue source, cytokine/growth factor/nutrient addition, and biomechanical environment for discovery. Within this context, we firstly discuss the literature on the nature and role of potential catabolic mediators in OA pathology, including data from human OA cartilage, animal models of OA, and ex vivo studies. Secondly, due to the number and breadth of studies on IL-1β in this area, a major focus of the article is a critical analysis of the design and interpretation of cartilage studies where IL-1β has been used as a model cytokine. Thirdly, the article provides a data-driven perspective (including genome-wide analysis of clinical samples, studies on mutant mice, and clinical trials), which concludes that IL-1β should be replaced by soluble mediators such as IL-17 or TGF-β1, which are much more likely to mimic the disease in OA model systems. We also discuss the evidence that changes in early OA can be attributed to the activity of such soluble mediators, whereas late-stage disease results more from a chronic biomechanical effect on the matrix and cells of the remaining cartilage and on other local mediator-secreting cells. Lastly, an updated protocol for in vitro studies with cartilage explants and chondrocytes (including the use of specific gene expression arrays) is provided to motivate more disease-relevant studies on the interplay of cytokines, growth factors, and biomechanics on cellular behavior.

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.

Non-invasive mouse models of post-traumatic osteoarthritis

Animal models of osteoarthritis (OA) are essential tools for investigating the development of the disease on a more rapid timeline than human OA. Mice are particularly useful due to the plethora of genetically modified or inbred mouse strains available. The majority of available mouse models of OA use a joint injury or other acute insult to initiate joint degeneration, representing post-traumatic osteoarthritis (PTOA). However, no consensus exists on which injury methods are most translatable to human OA. Currently, surgical injury methods are most commonly used for studies of OA in mice; however, these methods may have confounding effects due to the surgical/invasive injury procedure itself, rather than the targeted joint injury. Non-invasive injury methods avoid this complication by mechanically inducing a joint injury externally, without breaking the skin or disrupting the joint. In this regard, non-invasive injury models may be crucial for investigating early adaptive processes initiated at the time of injury, and may be more representative of human OA in which injury is induced mechanically. A small number of non-invasive mouse models of PTOA have been described within the last few years, including intra-articular fracture of tibial subchondral bone, cyclic tibial compression loading of articular cartilage, and anterior cruciate ligament (ACL) rupture via tibial compression overload. This review describes the methods used to induce joint injury in each of these non-invasive models, and presents the findings of studies utilizing these models. Altogether, these non-invasive mouse models represent a unique and important spectrum of animal models for studying different aspects of PTOA.

Unravelling osteoarthritis-related synovial fibrosis: a step closer to solving joint stiffness

Synovial fibrosis is often found in OA, contributing heavily to joint pain and joint stiffness, the main symptoms of OA. At this moment the underlying mechanism of OA-related synovial fibrosis is not known and there is no cure available. In this review we discuss factors that have been reported to be involved in synovial fibrosis. The aim of the study was to gain insight into how these factors contribute to the fibrotic process and to determine the best targets for therapy in synovial fibrosis. In this regard, the following factors are discussed: TGF-β, connective tissue growth factor, procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2, tissue inhibitor of metalloproteinase 1, A disintegrin and metalloproteinase domain 12, urotensin-II, prostaglandin F2α and hyaluronan.

Mesenchymal stem cell therapy for knee osteoarthritis: 5 years follow-up of three patients

AIM

Osteoarthritis is a degenerative joint disease characterized by the destruction of joint cartilage. Mesenchymal stem cells (MSCs) are found in low numbers in normal cartilage, mainly in the superficial layer, acting as repairing agents. In OA, MSCs are seen in larger numbers, but act chaotic and are unable to repair the cartilage. The synovial membrane becomes inflamed and interacts with the cartilage. Transplanted MSC have the ability to normalize them, redirecting them to their normal function. In a preliminary study, we showed that MSC could improve knee OA in four patients at 6 months. This report shows their long-term follow-up at 5 years.

METHODS

One patient was lost to follow-up at 2 years and three were followed for 5 years. They were aged 55, 57, 65 and 54 years, and had moderate to severe knee osteoarthritis. The worse knee of each patient was injected with 8-9 × 10(6) MSC.

RESULTS

As previously reported, all parameters improved in transplant knees at 6 months (walking time, stair climbing, gelling pain, patella crepitus, flection contracture and the visual analogue score on pain). Then, they started gradually to deteriorate, but at 5 years they were still better than at baseline. PGA (Patient Global Assessment) improved from baseline to 5 years. The better knee at baseline (no MSC), continued its progression toward aggravation and at 5 years became the worse knee.

CONCLUSION

Transplant knees were all in a rather advanced stage of OA. Earlier transplantation may give better results in long-term follow-up. This is what future studies have to demonstrate.

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.

Nanomechanical phenotype of chondroadherin-null murine articular cartilage

Chondroadherin (CHAD), a class IV small leucine rich proteoglycan/protein (SLRP), was hypothesized to play important roles in regulating chondrocyte signaling and cartilage homeostasis. However, its roles in cartilage development and function are not well understood, and no major osteoarthritis-like phenotype was found in the murine model with CHAD genetically deleted (CHAD^−/−). In this study, we used atomic force microscopy (AFM)-based nanoindentation to quantify the effects of CHAD deletion on changes in the biomechanical function of murine cartilage. In comparison to wild-type (WT) mice, CHAD-deletion resulted in a significant≈70–80% reduction in the indentation modulus, E_ind, of the superficial zone knee cartilage of 11 weeks, 4 months and 1 year old animals. This mechanical phenotype correlates well with observed increases in the heterogeneity collagen fibril diameters in the surface zone. The results suggest that CHAD mainly plays a major role in regulating the formation of the collagen fibrillar network during the early skeletal development. In contrast, CHAD-deletion had no appreciable effects on the indentation mechanics of middle/deep zone cartilage, likely due to the dominating role of aggrecan in the middle/deep zone. The presence of significant rate dependence of the indentation stiffness in both WT and CHAD^−/− knee cartilage suggested the importance of both fluid flow induced poroelasticity and intrinsic viscoelasticity in murine cartilage biomechanical properties. Furthermore, the marked differences in the nanomechanical behavior of WT versus CHAD^−/− cartilage contrasted sharply with the relative absence of overt differences in histological appearance. These observations highlight the sensitivity of nanomechanical tools in evaluating structural and mechanical phenotypes in transgenic mice.

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.

TAK1 regulates SOX9 expression in chondrocytes and is essential for postnatal development of the growth plate and articular cartilages

TAK1 is a MAP3K that mediates non-canonical TGF-β and BMP signaling. During the embryonic period, TAK1 is essential for cartilage and joint development as deletion of Tak1 in chondro-osteo progenitor cells leads to severe chondrodysplasia with defects in both chondrocyte proliferation and maturation. We have investigated the role of TAK1 in committed chondrocytes during early postnatal development. Using the Col2a1-CreER(T2); Tak1(f/f) mouse model, we induced deletion of Tak1 at postnatal day 7 and characterized the skeletal phenotypes of these mice at 1 and 3 months of age. Mice with chondrocyte-specific Tak1 deletion exhibited severe growth retardation and reduced proteoglycan and type II collagen content in the extracellular matrix of the articular cartilage. We found reduced Col2a1 and Acan expression, but increased Mmp13 and Adamts5 expression, in Tak1-deficient chondrocytes along with reduced expression of the SOX trio of transcription factors, SOX9, SOX5 and SOX6. In vitro, BMP2 stimulated Sox9 gene expression and Sox9 promoter activity. These effects were reduced; however, following Tak1 deletion or treatment with a TAK1 kinase inhibitor. TAK1 affects both canonical and non-canonical BMP signal transduction and we found that both of these pathways contribute to BMP2-mediated Sox9 promoter activation. Additionally, we found that ATF2 directly binds the Sox9 promoter in response to BMP signaling and that this effect is dependent upon TAK1 kinase activity. These novel findings establish that TAK1 contributes to BMP2-mediated Sox9 gene expression and is essential for the postnatal development of normal growth plate and articular cartilages.

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.

Mesenchymal stem cells in joint disease and repair

Osteoarthritis (OA), a prevalent chronic condition with a striking impact on quality of life, represents an enormous societal burden that increases greatly as populations age. Yet no approved pharmacological intervention, biologic therapy or procedure prevents the progressive destruction of the OA joint. Mesenchymal stem cells (MSCs)-multipotent precursors of connective tissue cells that can be isolated from many adult tissues, including those of the diarthrodial joint-have emerged as a potential therapy. Endogenous MSCs contribute to maintenance of healthy tissues by acting as reservoirs of repair cells or as immunomodulatory sentinels to reduce inflammation. The onset of degenerative changes in the joint is associated with aberrant activity or depletion of these cell reservoirs, leading to loss of chondrogenic potential and preponderance of a fibrogenic phenotype. Local delivery of ex vivo cultures of MSCs has produced promising outcomes in preclinical models of joint disease. Mechanistically, paracrine signalling by MSCs might be more important than differentiation in stimulating repair responses; thus, paracrine factors must be assessed as measures of MSC therapeutic potency, to replace traditional assays based on cell-surface markers and differentiation. Several early-stage clinical trials, initiated or underway in 2013, are testing the delivery of MSCs as an intra-articular injection into the knee, but optimal dose and vehicle are yet to be established.

Sustained delivery of bioactive TGF-β1 from self-assembling peptide hydrogels induces chondrogenesis of encapsulated bone marrow stromal cells

Tissue engineering strategies for cartilage defect repair require technology for local targeted delivery of chondrogenic and anti-inflammatory factors. The objective of this study was to determine the release kinetics of transforming growth factor β1 (TGF-β1) from self-assembling peptide hydrogels, a candidate scaffold for cell transplant therapies, and stimulate chondrogenesis of encapsulated young equine bone marrow stromal cells (BMSCs). Although both peptide and agarose hydrogels retained TGF-β1, fivefold higher retention was found in peptide. Excess unlabeled TGF-β1 minimally displaced retained radiolabeled TGF-β1, demonstrating biologically relevant loading capacity for peptide hydrogels. The initial release from acellular peptide hydrogels was nearly threefold lower than agarose hydrogels, at 18% of loaded TGF-β1 through 3 days as compared to 48% for agarose. At day 21, cumulative release of TGF-β1 was 32-44% from acellular peptide hydrogels, but was 62% from peptide hydrogels with encapsulated BMSCs, likely due to cell-mediated TGF-β1 degradation and release of small labeled species. TGF-β1 loaded peptide hydrogels stimulated chondrogenesis of young equine BMSCs, a relevant preclinical model for treating injuries in young human cohorts. Self-assembling peptide hydrogels can be used to deliver chondrogenic factors to encapsulated cells making them a promising technology for in vivo, cell-based regenerative medicine.

Exome sequencing of senescence-accelerated mice (SAM) reveals deleterious mutations in degenerative disease-causing genes

BACKGROUND

Senescence-accelerated mice (SAM) are a series of mouse strains originally derived from unexpected crosses between AKR/J and unknown mice, from which phenotypically distinct senescence-prone (SAMP) and -resistant (SAMR) inbred strains were subsequently established. Although SAMP strains have been widely used for aging research focusing on their short life spans and various age-related phenotypes, such as immune dysfunction, osteoporosis, and brain atrophy, the responsible gene mutations have not yet been fully elucidated.

RESULTS

To identify mutations specific to SAMP strains, we performed whole exome sequencing of 6 SAMP and 3 SAMR strains. This analysis revealed 32,019 to 38,925 single-nucleotide variants in the coding region of each SAM strain. We detected Ogg1 p.R304W and Mbd4 p.D129N deleterious mutations in all 6 of the SAMP strains but not in the SAMR or AKR/J strains. Moreover, we extracted 31 SAMP-specific novel deleterious mutations. In all SAMP strains except SAMP8, we detected a p.R473W missense mutation in the Ldb3 gene, which has been associated with myofibrillar myopathy. In 3 SAMP strains (SAMP3, SAMP10, and SAMP11), we identified a p.R167C missense mutation in the Prx gene, in which mutations causing hereditary motor and sensory neuropathy (Dejerine-Sottas syndrome) have been identified. In SAMP6 we detected a p.S540fs frame-shift mutation in the Il4ra gene, a mutation potentially causative of ulcerative colitis and osteoporosis.

CONCLUSIONS

Our data indicate that different combinations of mutations in disease-causing genes may be responsible for the various phenotypes of SAMP strains.

New findings in osteoarthritis pathogenesis: therapeutic implications

This review focuses on the new perspectives which can provide insight into the crucial pathways that drive cartilage-bone physiopathology. In particular, we discuss the critical signaling and effector molecules that can activate cellular and molecular processes in both cartilage and bone cells and which may be relevant in cross talk among joint compartments: growth factors (bone morphogenetic proteins and transforming growth factor), hypoxia-related factors, cell-matrix interactions [discoidin domain receptor 2 (DDR2) and syndecan 4], signaling molecules [WNT, Hedgehog (Hh)]. With the continuous progression of our knowledge on the molecular pathways involved in cartilage and bone changes in osteoarthritis (OA), an increasing number of potentially effective candidates for OA therapy are already under scrutiny in clinical trials to ascertain their possible safe use in an attempt to identify molecules active in slowing or halting OA progression and reducing joint pain. We then review the principal molecules currently under clinical investigation.

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.

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.

Initial application of EPIC-μCT to assess mouse articular cartilage morphology and composition: effects of aging and treadmill running

OBJECTIVE

The current study was undertaken to adapt Equilibrium Partitioning of an Ionic Contrast agent via microcomputed tomography (EPIC-μCT) to mouse articular cartilage (AC), which presents a particular challenge because it is thin (30 μm) and has a small volume (0.2-0.4 mm(3)), meaning there is only approximately 2-4 μg of chondroitin sulfate (CS) glycosaminoglycan per joint surface cartilage.

DESIGN

Using 6 μm isotropic voxels and the negatively charged contrast agent ioxaglate (Hexabrix), we optimized contrast agent concentration and incubation time, assessed two methods of tissue preservation (formalin fixation and freezing), examined the effect of ex vivo chondroitinase ABC digestion on X-ray attenuation, assessed accuracy and precision, compared young and skeletally mature cartilage, and determined patterns of degradation in a murine cartilage damage model induced by treadmill running.

RESULTS

The optimal concentration of the contrast agent was 15%, formalin fixation was preferred to freezing, and 2 h of incubation was needed to reach contrast agent equilibrium with formalin-fixed specimens. There was good agreement with histologic measurements of cartilage thickness, although μCT over-estimated thickness by 13% (5 μm) in 6-week-old mice. Enzymatic release of 0.8 μg of chondrotin sulfate (about 40% of the total) increased X-ray attenuation by 17%. There was a 15% increase in X-ray attenuation in 14-week-old mice compared to 6-week-old mice (P < 0.001) and this corresponded to 65% decrease in CS content at 14 weeks. The older mice also had reductions of 33% in cartilage thickness and 44% in cartilage volume (P < 0.001). Treadmill running induced a 16% decrease in cartilage thickness (P = 0.012) and a 12% increase in X-ray attenuation (P = 0.006) in 14-week-old mice.

CONCLUSION

This technique enables non-destructive visualization and quantification of murine femoral AC in three dimensions with anatomic specificity and should prove to be a useful new tool in studying degeneration of cartilage in mouse models.

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.

Recent progress in understanding molecular mechanisms of cartilage degeneration during osteoarthritis

Osteoarthritis (OA) is a highly prevalent disease affecting more than 20% of American adults. Predispositions include joint injury, heredity, obesity, and aging. Biomechanical alterations are commonly involved. However, the molecular mechanisms of this disease are complex, and there is currently no effective disease-modifying treatment. The initiation and progression of OA subtypes is a complex process that at the molecular level probably involves many cell types, signaling pathways, and changes in extracellular matrix. Ex vivo studies with tissue derived from OA patients and in vivo studies with mutant mice have suggested that pathways involving receptor ligands such as TGF-β1, WNT3a, and Indian hedgehog; signaling molecules such as Smads, β-catenin, and HIF-2a; and peptidases such as MMP13 and ADAMTS4/5 are probably involved to some degree. This review focuses on molecular mechanisms of OA development related to recent findings.

Adamts5 (aggrecanase-2) is widely expressed in the mouse musculoskeletal system and is induced in specific regions of knee joint explants by inflammatory cytokines

ADAMTS5 (aggrecanase-2) is an extracellular matrix-degrading protease implicated in cartilage destruction in arthritis. Our goals were to determine expression sites of Adamts5 in the murine musculoskeletal system and in an ex vivo joint inflammation model. In mice with an intragenic LacZ reporter controlled by the Adamts5 promoter, β-galactosidase staining was used to identify Adamts5 expressing cells. Mice expressing one wild-type Adamts5 allele were used to determine distribution of Adamts5 mRNA, cleaved aggrecan and versican, and the ADAMTS5 activating enzymes furin and PACE4. Quantitative RT-PCR and immunoblotting were used to validate the immunohistochemistry results. Adamts5 was expressed in mouse synovium, tenosynovium, bone marrow sinusoids, tendons, ligaments, ligament insertions, periosteal cells, and bone vasculature. In knee joint explants treated with IL-1α and TNFα, Adamts5 expression was induced in tenocytes, synovium, and in patellar, but not femoral or tibial articular cartilage. In contrast, increased proteoglycan breakdown in tibial and femoral articular cartilage was associated with increased immunohistochemical staining of PACE4 and furin. These studies identify diverse cell types in the musculoskeletal system that express Adamts5. They also suggest that Adamts5 induction in joint components other than cartilage, and its post-translational activation by PACE4 and/or furin may be important in the pathophysiology of arthritis.

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.