Comparison of the catabolic effects of fibronectin fragments in human knee and ankle cartilages

Attenuative Effects of Platelet-Rich Plasma on 30 kDa Fibronectin Fragment-Induced MMP-13 Expression Associated with TLR2 Signaling in Osteoarthritic Chondrocytes and Synovial Fibroblasts

Proteolytic fragments of fibronectin can have catabolic effects on cartilage, menisci, and synovium. Previous studies have reported that Toll-like receptor (TLR) signaling pathways might be associated with joint inflammation and joint destruction. Platelet-rich plasma (PRP) is increasingly being used to treat a range of joint conditions; however, it has yet to be determined whether PRP influences fibronectin fragment (FN-f) procatabolic activity and TLRs. In this study, human primary culture cells were treated with 30 kDa FN-f with/without PRP co-incubation, and then analyzed using real-time PCR to determine gene expression levels in articular chondrocytes, meniscal fibrochondrocytes, and synovial fibroblasts. Protein levels were evaluated by Western immunoblotting. This study observed an increase in the protein expression of matrix metalloproteinases (MMPs), Toll-like receptor 2 (TLR2), nitric oxide synthase 2 (NOS2), prostaglandin-endoperoxide synthase (PTGS2), and cyclooxygenase 2 (COX2) in articular chondrocytes, meniscal fibrochondrocytes, and synovial fibroblasts following insult with 30 kDa FN-f. Upregulation of these genes was significantly attenuated by PRP treatment. TLR2 and matrix metalloproteinase 13 (MMP-13) were also significantly attenuated by cotreatment with 30 kDa FN-f + PRP + TLR2 inhibitor. PRP treatment was shown to attenuate the 30 kDa FN-f-induced MMP-13 expression associated with the decreased expression of TLR2 in osteoarthritic chondrocytes and synovial fibroblasts. PRP treatment was also shown to attenuate procatabolic activity associated with MMP-13 expression via the TLR2 signaling pathway.

Toll-like receptor involvement in adolescent scoliotic facet joint degeneration

Facet joint osteoarthritis is prevalent in young patients with adolescent idiopathic scoliosis (AIS) and might contribute to back pain. Toll-like receptors (TLR) have been linked to cartilaginous tissue degeneration but their involvement in facet joint osteoarthritis in AIS patients is still unknown. We compared baseline gene expression levels of TLRs -1, -2, -4, and -6 in scoliotic and non-scoliotic chondrocytes and found higher expression levels in scoliotic chondrocytes with significantly higher TLR2 levels. Furthermore, TLR expression correlated strongly and significantly with inflammatory and catabolic markers in scoliotic but not in non-scoliotic chondrocytes. TLR activation with a synthetic TLR2/6 agonist resulted in a robust induction and release of pro-inflammatory and catabolic factors which exacerbated proteoglycan loss in scoliotic but not in non-scoliotic cartilage. We also detected a higher abundance of alarmins including S100A8/9 and biglycan in scoliotic cartilage. Finally, the small-molecule antagonists Sparstolonin B and o-Vanillin reduced catabolism following induction with naturally occurring alarmins and the synthetic TLR2/6 agonist. The high baseline expression, robust responsiveness and strong and significant correlation with proteases and pro-inflammatory cytokines suggest that TLRs are key regulators of facet joint degeneration in AIS. Blocking their activity could therefore potentially modify disease progression.

Agili-C implant promotes the regenerative capacity of articular cartilage defects in an ex vivo model

PURPOSE

Osteochondral implants are currently adopted for the treatment of symptomatic full-thickness chondral and osteochondral defects. Agili-C™ is a cell-free aragonite-based scaffold which aims to reproduce the original structure and function of the articular joint while directing the growth and regeneration of both cartilage and its underlying subchondral bone. The goal of the present study was to investigate the ex vivo mechanisms of action (MOA) of the Agili-C™ implant in the repair of full-thickness cartilage defects. In particular, we tested whether Agili-C™ implant has the potential to stimulate cartilage ingrowth through chondrocytes migration into the 3D interconnected porous structure of the scaffold, along with maintaining their viability and phenotype and the deposition of hyaline cartilage matrix.

METHODS

Articular cartilage samples were collected through the Gift of Hope Organ and Tissue Donor Network (Itasca, IL) within 24 h from death. For this study, cartilage from a total of 14 donors was used. To model a chondral defect, donut-shaped cartilage explants were prepared from each tissue specimen. The chondral phase of the Agili-C™ implant was placed inside the tissue in full contact and press fit manner. Cartilage explants with the Agili-C™ implant inside were cultured for 60 days. As a control, the same donut-shaped cartilage explants were cultured without Agili-C™, under the same culture conditions.

RESULTS

Using fresh human cadaveric articular cartilage tissue in a 60-day culture, it was demonstrated that chondrocytes were able to migrate into the Agili-C™ scaffold and contribute to the deposition of the extracellular matrix (ECM) rich in collagen type II and aggrecan, and lacking collagen type I. Additionally, we were able to show the formation of a layer populated by progenitor-like cells on the articular surface of the implant.

CONCLUSIONS

The analysis of samples taken from knee and ankle joints of human donors with a wide age range and both genders supports the potential of Agili-C™ scaffold to stimulate cartilage regeneration and repair. Based on these results, the present scaffold can be used in the clinical practice as a one-step procedure to treat full-thickness chondral defects.

Articular chondrocytes isolated from the knee and ankle joints of human tissue donors demonstrate similar redox-regulated MAP kinase and Akt signaling

OBJECTIVE

To compare key intracellular redox-regulated signaling pathways in chondrocytes derived from knee joint femoral cartilage and ankle joint talar cartilage in order to determine if differences exist that might contribute to the lower prevalence of ankle osteoarthritis (OA).

METHODS

Femoral and talar chondrocytes were treated with H₂O₂ generators (menadione or 2-3-dimethoxy-1,4-napthoquinone (DMNQ), fragments of fibronectin (FN-f)) to stimulate MAP kinase signaling (MAPK), or with IGF-1 to stimulate the Akt signaling pathway. Hyperoxidation of the peroxiredoxins, used as a measure of redox status, and phosphorylation of proteins pertinent to MAPK (p38, ERK, JNK, c-Jun) and Akt (Akt, PRAS40) signaling cascades were detected by immunoblotting.

RESULTS

Treatment of femoral and talar chondrocytes with menadione, DMNQ or FN-f led to a time dependent increase in extracellular-regulated kinase (ERK) and p38 phosphorylation. DMNQ and FN-f stimulation enhanced phosphorylation of JNK and its downstream substrate, c-Jun. Menadione treatment did not stimulate JNK activity but hyperoxidized the peroxiredoxins and inhibited IGF-1-induced Akt activation. In all experiments, chondrocytes derived from the femur and talar joints displayed comparable MAP kinase responses after treatment with various catabolic stimuli, as well as similar Akt signaling responses after IGF-1 treatment.

CONCLUSIONS

MAP kinase and Akt signaling in response to factors that modulate the intracellular redox status were similar in chondrocytes from knee and ankle joints suggesting that redox signaling differences do not explain differences in OA prevalence. Talar chondrocytes, when isolated from their native matrix, can be used to examine redox-regulated cell signaling events relevant to OA in either joint.

Establishment of rat ankle post-traumatic osteoarthritis model induced by malleolus fracture

BACKGROUND

Malleolar fracture, which is present in 37-53% of human ankle osteoarthritis (OA), is the most common type of fracture in the ankle joint. In spite of this, no rat animal model has been developed for this type of injury to date. Here, we established a rat ankle post-traumatic OA (PTOA) model induced by malleolar fracture; this model will be useful in ankle OA research.

METHODS

Two-month-old male Sprague Dawley (SD) rats were randomized into 2 groups (n = 19 per group): 1) malleolus articular fracture, dislocation, and immediate reduction on the right joints and 2) malleolus articular fracture on the right ankle. The contralateral ankle joints were used as controls. The fracture and healing processes were confirmed and monitored by radiography. Changes in inflammation were monitored in vivo by fluorescence molecular tomography (FMT). Cartilage damage and changes in expression of OA-related genes were analyzed by histology, immunohistochemistry, Real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA) at 8 weeks post-surgery.

RESULTS

X-rays showed that all fractures were healed at 8 weeks post-surgery. A reproducible, mild to moderate degree of OA cartilage damage with reduced aggrecan was detected by histology in all animals in both groups but there was no significant difference between the two groups. Decreased Col-II and increased Col-X and MMP-13 levels were detected by qPCR, immunohistochemistry, ELISA and FMT from both groups cartilage.

CONCLUSIONS

Malleolus articular fracture alone induces ankle OA with lesions on the central weight bearing area of the tibiotalar joint in rats. This model will provide a reproducible and useful tool for researchers to study ankle OA.

Post-traumatic osteoarthritis of the ankle: A distinct clinical entity requiring new research approaches

The diagnosis of ankle osteoarthritis (OA) is increasing as a result of advancements in non-invasive imaging modalities such as magnetic resonance imaging, improved arthroscopic surgical technology and heightened awareness among clinicians. Unlike OA of the knee, primary or age-related ankle OA is rare, with the majority of ankle OA classified as post-traumatic (PTOA). Ankle trauma, more specifically ankle sprain, is the single most common athletic injury, and no effective therapies are available to prevent or slow progression of PTOA. Despite the high incidence of ankle trauma and OA, ankle-related OA research is sparse, with the majority of clinical and basic studies pertaining to the knee joint. Fundamental differences exist between joints including their structure and molecular composition, response to trauma, susceptibility to OA, clinical manifestations of disease, and response to treatment. Considerable evidence suggests that research findings from knee should not be extrapolated to the ankle, however few ankle-specific preclinical models of PTOA are currently available. The objective of this article is to review the current state of ankle OA investigation, highlighting important differences between the ankle and knee that may limit the extent to which research findings from knee models are applicable to the ankle joint. Considerations for the development of new ankle-specific, clinically relevant animal models are discussed. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:440-453, 2017.

Peculiarities in Ankle Cartilage

Posttraumatic osteoarthritis (PTOA) is the most common form of osteoarthritis (OA) of the ankle joint. PTOA occurs as a result of several factors, including the poor regenerative capacity of hyaline articular cartilage as well as increased contact stresses following trauma. The purpose of this article is to review the epidemiology, pathogenesis, and potential targets for treatment of PTOA in the ankle joint. Previous reviews primarily addressed clinical approaches to ankle PTOA, while the focus of the current article will be specifically on the newly acquired knowledge of the cellular mechanisms that drive PTOA in the ankle joint and means for potential targeted therapeutics that might halt the progression of cartilage degeneration and/or improve the outcome of surgical interventions. Three experimental treatment strategies are discussed in this review: (1) increasing the anabolic potential of chondrocytes through treatment with growth factors such as bone morphogenetic protein-7; (2) limiting chondrocyte cell death either through the protection of cell membrane with poloxamer 188 or inhibiting activity of intracellular proteases, caspases, which are responsible for cell death by apoptosis; and (3) inhibiting catabolic/inflammatory responses of chondrocytes by treating them with anti-inflammatory agents such as tumor necrosis factor-α antagonists. Future studies should focus on identifying the appropriate timing for treatment and an appropriate combination of anti-inflammatory, chondro- and matrix-protective biologics to limit the progression of trauma-induced cartilage degeneration and prevent the development of PTOA in the ankle joint.

Platelet-Rich Plasma Attenuates 30-kDa Fibronectin Fragment-Induced Chemokine and Matrix Metalloproteinase Expression by Meniscocytes and Articular Chondrocytes

BACKGROUND

Proteolytic fragments of fibronectin have catabolic effects on cartilage and menisci. Platelet-rich plasma (PRP) is increasingly being used to treat a range of joint conditions, but it is unknown whether PRP influences fibronectin fragment (FN-f) procatabolic activity.

HYPOTHESES

The procatabolic activity of FN-f on meniscocytes and articular chondrocytes is attenuated by cotreatment with PRP.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human meniscocytes were treated with FN-f (30 kDa) with or without PRP coincubation, and gene expression was analyzed by complementary DNA microarray analysis. Validation of altered expression of known and novel chemokine and protease genes was undertaken by real-time polymerase chain reaction (RT-PCR) in articular chondrocytes and meniscocytes. Chemokine release was assayed by enzyme-linked immunosorbent assay, and intracellular pathway signaling was evaluated by Western immunoblotting.

RESULTS

Microarray analysis and RT-PCR showed increased expression of matrix metalloproteinase (MMP)1, MMP2, MMP3, MMP9, MMP13, interleukin (IL)-6, IL-8 (CXCL8), CCL5, CCL20, and CXCL10 chemokines in meniscocytes after treatment with FN-f. Upregulation of these genes was significantly attenuated by PRP. Similar results were seen with articular chondrocytes, although no changes in MMP2 or MMP9 levels were identified. PRP-induced suppression of gene expression was associated with activation of Akt and p44/p42.

CONCLUSION

PRP treatment attenuates the 30-kDa FN-f-induced expression of a range of proinflammatory chemokines and MMPs, including IL-8, IL-6, CCL20, CCL5, CXCL10, MMP1, MMP3, and MMP13, by both meniscocytes and articular chondrocytes.

CLINICAL RELEVANCE

These observations provide support for the use and further trials of PRP in management of cartilage and meniscal injuries.

Fibronectin molecular status determination useful to differentiate between rheumatoid arthritis and systemic lupus erythematosus patients

To find whether the plasma fibronectin (FN) molecular status can be useful to differentiate between rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). The expression of plasma FN domains was determined by ELISA using monoclonal domain-specific antibodies. FN molecular forms were revealed by immunoblotting and analyzed by densitometry. The following findings were found: (1) Mean values of ^{Fibrin–Heparin}FN concentration were lower in SLE and RA patients than in normal plasmas. The cut off points at 31 mg/l in SLE and at 45 mg/l in RA showed a sensitivity and specificity of 54, 55 and 75%, respectively. (2) Mean values of concentrations of ^CBDFN and ^CtFN were lower in SLE than those in normal and RA plasmas. Quantified data showed the cut off points of ^CBDFN and ^CtFN at 200 mg/l (58% of sensitivity, 56% of specificity) and 350 mg/l (58% of sensitivity, 58% of specificity) in SLE, as well as at 295 mg/l (52% of sensitivity, 51% of specificity) and 460 mg/l in RA (70% of sensitivity, 73% of specificity). (3) The plasma FN immunopatterns, characterized by the presence of high-molecular (260–310 kDa) and/or low-molecular (158–209 kDa) FN bands, were specific only for SLE samples. The analysis of plasma FN status revealed by its Fibrin-Heparin-, CBD- and Ct-domain reactivity with monoclonal antibody and immunoblotting can be helpful to differentiate the SLE in respect to RA and normal plasmas.

MR imaging of the articular cartilage of the knee and ankle

Cartilage abnormalities in the knee and ankle are a common source of pain and are often difficult to diagnose clinically or radiographically. MR imaging is a valuable tool for diagnosing and characterizing cartilage lesions of both the knee and ankle. An understanding of the appearance of cartilage, and an understanding of how and when to report cartilage injury in the knee and ankle based on current grading systems allows the radiologist to provide the most helpful reports to referring clinicians. This article presents the range of cartilage pathologies in the knee and ankle and provides clinically relevant guidelines.

Variations in chondrocyte apoptosis may explain the increased prevalence of osteoarthritis in some joints

OBJECTIVES

To investigate whether there are any variations in chondrocyte susceptibility to an apoptotic stimulus between cells of articular cartilage (AC) from equine joints that differ in prevalence of osteoarthritis (OA).

METHODS

Cartilage from macroscopically normal equine metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints was used. Prior to culture, chondrocyte viability was assessed using the fluorescein diacetate (FDA) and propidium iodide paravital staining method. AC explants were subsequently treated with tumour necrosis factor-α (TNF-α) in combination with Actinomycin D to induce apoptosis. Apoptosis of chondrocytes in cartilage sections was assessed by expression of active caspase-3 using indirect immunohistochemistry and sections also histologically graded using a 'modified' Mankin scoring system.

RESULTS

Prior to culture (mean ± standard deviation) chondrocyte viability was 80.7% (3.5). The extent of chondrocyte apoptosis induced by TNF-α/Actinomycin D varied markedly according to the joint type that the cartilage was sampled from. For MCP joints, the extent of overall chondrocyte apoptosis was significantly higher (P < 0.001) in stimulated explants (26.7%, 10.3) than that observed in unstimulated control samples (9.6%, 7.5). Conversely, chondrocytes from PIP and DIP joint cartilage did not respond significantly to apoptotic stimulation (P > 0.05). Significant variations in cellularity and thickness were also evident between cartilages of different joint types.

CONCLUSIONS

Data in this study demonstrate that chondrocytes from three equine joint types with varying prevalences of OA differ significantly in terms of susceptibility to apoptosis induction. This may provide a possible explanation for the joint-specific nature of the disease.

A review of the differences between normal and osteoarthritis articular cartilage in human knee and ankle joints

BACKGROUND

Osteoarthritis (OA) is the most common joint disease yet its pathophysiology is still poorly understood. It is more prevalent in some lower limb joints than others; in particular the knee is more commonly affected than the ankle. Research into articular cartilage and OA has primarily focussed on using animal models. However, it is apparent that articular cartilage differs between species, so more research is concentrating on human cartilage.

OBJECTIVE

This paper reviews recent studies that have been undertaken to elucidate the reasons for this, and to discover if the findings would alter the conception that articular cartilage is not capable of repair.

METHOD

Primary research papers into human knee and ankle cartilage published since 1997 have been reviewed.

RESULTS

Differences in the structure, metabolism, physical properties and response to trauma have been found, implying that ankle cartilage may be more resistant to damage.

CONCLUSIONS

More research is needed before definitive conclusions can be reached, but the findings so far suggest that OA should not be accepted as the inevitable outcome of joint injury and individuals and practitioners, such as podiatrists, may be able to use simple measures to prevent or delay its onset.

Osteoarthritis of the ankle: bridging concepts in basic science with clinical care

Trends in science are beginning to suggest that cartilage degeneration may be related to a chronic imbalance in extracellular matrix metabolism. In cartilage, a combination of biomechanical, biochemical, and matrix-related signaling pathways regulates the equilibrium between cartilage anabolism and catabolism. A potential limitation of many current treatments of osteoarthritis is that they may not comprehensively restore regulation of a balance between cartilage anabolism and catabolism.

[Autologous chondrocyte transplantation in the ankle joint. Rational or irrational?]

Ankle sprains are one the most common injuries of the lower limb. Fractures, ligamentous lesions, and cartilaginous damage are often associated. Nevertheless the injury is often misjudged and concomitant chondral lesions are assessed late. In the case of a symptomatic osteocartilaginous lesion of the talus, which can be illustrated by MRI or X-ray, operative intervention is indicated. Methods such as microfracturing, mosaicplasty, and autologous chondrocyte transplantation (ACT) are in clinical use. The latter is well known and being established as the treatment of choice for large cartilage defects in the knee. Due to the good results in the knee and the technological improvements (three-dimensional tissue constructs seeded with autologous chondrocytes) this method is being increasingly applied for cartilage lesions of the talus. In contrast to the mosaicplasty donor site morbidity is low and the size of the defect is not a limiting factor. The current studies about ACT of the talus show a stable repair of the defect with mostly hyaline-like cartilage and high patient satisfaction. Therefore, the procedure can be recommended for lesions>1 cm2. Concomitant treatment of posttraumatic deformities (malalignment), ligamentous instabilities, and especially the reconstruction of bony defects are compulsory.

Factor Xa stimulates proinflammatory and profibrotic responses in fibroblasts via protease-activated receptor-2 activation

Coagulation proteases have been suggested to play a role in the pathogenesis of tissue remodeling and fibrosis. We therefore assessed the proinflammatory and fibroproliferative effects of coagulation protease factor (F)Xa. We show that FXa elicits a signaling response in C2C12 and NIH3T3 fibroblasts. FXa-induced ERK1/2 phosphorylation was dependent on protease-activated receptor (PAR)-2 cleavage because desensitization with a PAR-2 agonist (trypsin) but not a PAR-1 agonist (thrombin) abolished FXa-induced signal transduction and PAR-2 siRNA abolished FXa-induced ERK1/2 phosphorylation. The PAR-2-dependent cellular effects of FXa led to fibroblast proliferation, migration, and differentiation into myofibroblasts, as demonstrated by the expression of alpha-smooth muscle actin and desmin, followed by the secretion of the cytokines monocyte chemotactic protein-1 and interleukin-6 as well as the expression of the fibrogenic proteins transforming growth factor-beta and fibronectin. To assess the relevance of FXa-induced proliferation and cell migration, we examined the effect of FXa in a wound scratch assay. Indeed, FXa facilitated wound healing in a PAR-2- and ERK1/2-dependent manner. Taken together, these results support the notion that, beyond its role in coagulation, FXa-dependent PAR-2 cleavage might play a role in the progression of tissue fibrosis and remodeling.

Large-scale gene expression profiles, differentially represented in osteoarthritic synovium of the knee joint using cDNA microarray technology

Osteoarthritis (OA) is one of the most common age-related chronic disorders of articular cartilage, joints and bone tissue. Diagnosis of OA commonly depends on clinical and radiographic findings. However, changes in cartilage associated with the early stage of OA cannot be detected using radiographs, because significant cartilage degeneration must occur before radiographic findings show alterations of the appearance of cartilage. To identify new biomarkers of OA, we analysed gene expression profiles of synovium from 43 patients with OA, ten patients with rheumatoid arthritis (RA), and eight non-OA/non-RA patients using a novel cDNA microarray chip. We identified 21 genes with simultaneous significant differences in expression between OA and non-OA/non-RA groups and between OA and RA groups. Linear discriminant analysis showed that the three groups could be well separated using those 21 genes. Statistical analysis also revealed that several of the 21 genes were associated with disease progression and clinical presentation. The graphical modelling method indicated that some of the 21 genes are significantly associated with a particular clinical presentation, suggesting biological relationships among those genes. This is the first report of the use of cDNA microarray technology to create large-scale gene expression profiles differentially expressed in situ in OA synovium of the knee joint.

[Ankle chondrocytes are more resistant to Interleukin-1 than chondrocytes derived from the knee]

BACKGROUND

The incidence of degenerative changes and osteoarthritis is lower in the ankle than in the knee joints. This cannot be explained exclusively with differences in anatomy and biomechanical properties of these two synovial joints. Previous studies have indicated distinct differences in the biochemical composition of the extracellular matrix of articular cartilage from knee and ankle joints. The aim of this study was to identify potential metabolic differences between knee and ankle joint chondrocytes using isolated cells to distinguish the secondary effects of the resident extracellular matrix from the primary matrix-independent effects of cellular differentiation.

METHOD

Isolated knee and ankle chondrocytes from the same human donor were cultured in alginate beads and subsequently exposed to a three-day pulse of the catabolic cytokine interleukin-1 (IL-1) as a model of an inflammatory episode. The metabolism of proteoglycans (PG's) was analyzed as expressed changes in 35S-sulfate incorporation into glycosaminoglycans (GAG's).

RESULTS

The presence of IL-1 induced an inhibition of PG synthesis in knee and ankle articular chondrocytes. The 50% inhibitory concentration (IC50) of IL-1 was about 5 times lower for knee than for ankle chondrocytes.

CONCLUSION

Ankle chondrocytes are more resistant to IL-1 induced inhibition of PG synthesis than chondrocytes from the knee.

Mixtures of glucosamine and chondroitin sulfate reverse fibronectin fragment mediated damage to cartilage more effectively than either agent alone

OBJECTIVE

To test the effectiveness of glucosamine (GluNH(2))-HCl, chondroitin sulfate (CS) and mixtures in protecting cartilage exposed to fibronectin fragments (Fn-fs), an exposure known to enhance catabolic cytokines and matrix metalloproteinases (MMPs).

METHODS

Pharmacologic formulations of GluNH(2) (FCHG49) and CS (TRH122) (Nutramax Laboratories, Inc.) were added at 1, 10 or 100 microg/ml singly or in mixtures to bovine cartilage cultures in serum or serum-free conditions with or without Fn-f. Proteoglycan (PG) release into media and remaining cartilage PG content were measured by dye binding analysis and effects on PG synthesis by assays of 35-sulfate incorporation. Effects on MMP-3 and -13 expression were measured by Western blotting of conditioned media.

RESULTS

In serum-free conditions, the agents singly or as mixtures did not block Fn-f mediated matrix degradation. In serum, single agents were weakly effective at 100 microg/ml, while the mixture of each agent at 0.1 microg/ml decreased PG loss by about 50% by day 7 and at 1 microg/ml restored nearly 50% of the PG after 7 days in Fn-f pretreated cartilage. However, both agents singly and as mixtures at 0.1-100 microg/ml decreased MMP release. In serum, the single agents at 1-10 microg/ml weakly reversed Fn-f mediated PG synthesis suppression, while the mixtures were 100% effective at 1 microg/ml.

CONCLUSIONS

GluNH(2) and CS act synergistically in reversing damage and promoting repair at concentrations found in plasma after oral ingestion of these agents. Reversal of PG synthesis suppression correlates more with these activities than suppression of MMP-3 or -13 expression.

Analysis of the relationship between peak stress and proteoglycan loss following injurious compression of human post-mortem knee and ankle cartilage

While traumatic joint injuries are known to increase the risk of osteoarthritis (OA), the mechanism is not known. Models for injurious compression of cartilage may identify predictors of injury that suggest a clinical mechanism. We investigated the relationship between peak stress during compression and glycosaminoglycan (GAG) loss after injury for knee and ankle cartilages. Human cartilage explant disks were harvested post-mortem from the knee and ankle of three organ donors with no history of OA and subjected to injurious compression to 65% strain in uniaxial unconfined compression at 2 mm/s (400%/s). The GAG content of the conditioned medium was measured 3 days after injury. After injury of knee cartilage disks, damage was visible in 18 of 39 disks (36%). Three days after injury, the increase in GAG loss to the medium (GAG loss from injured disks minus GAG loss from location-matched uncompressed controls) was 1.5+/-0.3 microg/disk (mean +/- SEM). With final strain and compression velocity held constant, we observed that increasing peak stress during injury was associated with less GAG loss after injury (P<0.001). In contrast, ankle cartilage appeared damaged after injury in only 1 of 16 disks (6%), there was no increase in GAG loss (0.0+/-0.3 microg/disk), and no relationship between peak stress and increase in GAG loss was detected (P=0.51). By itself, increasing peak stress did not appear to be an important cause of GAG loss from human cartilage in our injurious compression model. However, we observed further evidence for differences in the response of knee and ankle cartilages to injury.

Expression and regulation of Toll-like receptor 2 by IL-1beta and fibronectin fragments in human articular chondrocytes

OBJECTIVE

The objective of this study was to examine expression and regulation of Toll-like receptor 2 (TLR2) in human articular chondrocytes.

METHODS

Human articular chondrocytes were enzymatically isolated from normal and osteoarthritic knee cartilage. Immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to assess the expression of toll-like receptors. Following stimulation of chondrocytes in vitro by IL-1beta and fibronectin proteolytic fragments, the relative levels of mRNA for TLR2 were determined by quantitative real-time PCR. MyD88 activation and nuclear factor-kappaB (NF-kappaB) translocation were evaluated by immunoprecipitation and electrophoretic mobility shift assay, respectively.

RESULTS

Human articular chondrocytes mainly expressed TLR1, 2, 5 by RT-PCR. Protein expression of TLR2 was also identified in adult human articular cartilage. TLR2 was upregulated following IL-1beta and fibronectin proteolytic fragments stimulation in primary cultures of osteoarthritic articular chondrocytes. Fibronectin proteolytic fragments-induced TLR2 upregulation involved an IL-1beta autocrine/paracrine pathway.

CONCLUSIONS

TLR2 is expressed in human articular cartilage and is upregulated by proarthritic agents including IL-1beta and fibronectin fragments. Signaling through TLR is a novel pro-inflammatory mechanism in osteoarthritis and targeting of these signaling pathways may be of value in treatment of degenerative joint disease.

Cartilage degeneration in different human joints

Variations among joints in the initiation and progression of degeneration may be explained, in part, by metabolic, biochemical and biomechanical differences. Compared to the cartilage in the knee joint, ankle cartilage has a higher content of proteoglycans and water, as well as an increased rate of proteoglycan turnover and synthesis, all of which are responsible for its increased stiffness and reduced permeability. Chondrocytes within ankle cartilage have a decreased response to catabolic factors such as interleukin-1 and fibronectin fragments, compared to the chondrocytes of knee cartilage. Moreover, in response to damage, ankle chondrocytes synthesize proteoglycans at a higher rate than that found in knee cartilage chondrocytes, which suggests a greater capacity for repair. In addition to the cartilages of the two joints, the underlying bones also respond differently to degenerative changes. Taken together, these metabolic, biochemical and biomechanical differences may provide protection to the ankle.

Differential matrix degradation and turnover in early cartilage lesions of human knee and ankle joints

OBJECTIVE

To determine whether there are differences in matrix turnover within early cartilage lesions of the ankle (talocrural) joint compared with the knee (tibiofemoral) joint that may help explain differences in the prevalence of osteoarthritis in these 2 joints.

METHODS

Cartilage removed from lesions of the tali and femoral condyles was analyzed for type IIB collagen messenger RNA, C-terminal type II procollagen propeptide (CPII), the collagenase cleavage neoepitope (Col2-3/4C(short)), and the denaturation epitope (Col2-3/4m). The content of collagen, glycosaminoglycan, and epitope 846 of aggrecan was quantitated.

RESULTS

In ankle lesions, there was an up-regulation of markers of synthesis (CPII [P = 0.07]; epitope 846 [P < or = 0.0001]), but these were down-regulated in the knee (CPII [P = 0.1]; epitope 846 [P = 0.004]). In lesions of the knee, but not the ankle, there was an up-regulation of collagen degradation markers (P = 0.008). On a molar basis, there was 24 times more cleavage epitope than denaturation epitope in knee lesions compared with ankle lesions.

CONCLUSION

The up-regulation of matrix turnover that is seen in early cartilage lesions of the ankle would appear to represent an attempt to repair the damaged matrix. The increase in collagen synthesis and aggrecan turnover seen in ankle lesions is absent from knee lesions. Instead, there is an increase in type II collagen cleavage. Together with the differences in collagen denaturation, these changes point to an emphasis on matrix assembly during early lesion development in the ankle and to degradation in the knee, resulting in fundamental differences in matrix turnover in these lesions.

Synovial lining macrophages mediate osteophyte formation during experimental osteoarthritis

OBJECTIVE

In human osteoarthritis (OA), various forms of pathology are observed. Besides cartilage damage and fibrosis, neogenesis of bone, osteophyte formation, also occurs. Osteophytes are thought to limit joint movement and cause pain. The objective of this study was to investigate whether synovial macrophages are involved in osteophyte formation in experimental OA, and if they are, to study which mechanism may be involved.

DESIGN

Experimental OA was induced by two intra-articular injections of collagenase on alternate days into murine knee joints. The role of synovial lining macrophages in this model was studied by selective removal of these cells prior to OA induction using clodronate liposomes. After 1 and 2 weeks, knee joints were dissected and examined (immuno)histologically.

RESULTS

At days 7 and 14 after induction of OA, osteophyte formation and fibrosis were observed. Depletion of synovial macrophages resulted in spectacular reduction of osteophyte formation, 84% and 66%, respectively, at days 7 and 14. Fibrosis and synovial activation, measured by MRP8/14 expression, were also ameliorated (40-60%). In addition, production of growth factors (TGFbeta, BMP-2 and BMP-4) in the lining was largely prevented but production of these growth factors in deeper layers of the synovium and the periosteum did not differ from controls.

CONCLUSIONS

These results indicate the synovial macrophage to be a pivotal cell in the synovium mediating osteophyte formation and other OA-related pathology, like fibrosis, during experimental OA. Production of growth factors and induction of synovial activation by these cells may play a crucial role in this event.