Activation of collagen type II expression in osteoarthritic and rheumatoid cartilage

Advancing drug delivery to articular cartilage: From single to multiple strategies

Articular cartilage (AC) injuries often lead to cartilage degeneration and may ultimately result in osteoarthritis (OA) due to the limited self-repair ability. To date, numerous intra-articular delivery systems carrying various therapeutic agents have been developed to improve therapeutic localization and retention, optimize controlled drug release profiles and target different pathological processes. Due to the complex and multifactorial characteristics of cartilage injury pathology and heterogeneity of the cartilage structure deposited within a dense matrix, delivery systems loaded with a single therapeutic agent are hindered from reaching multiple targets in a spatiotemporal matched manner and thus fail to mimic the natural processes of biosynthesis, compromising the goal of full cartilage regeneration. Emerging evidence highlights the importance of sequential delivery strategies targeting multiple pathological processes. In this review, we first summarize the current status and progress achieved in single-drug delivery strategies for the treatment of AC diseases. Subsequently, we focus mainly on advances in multiple drug delivery applications, including sequential release formulations targeting various pathological processes, synergistic targeting of the same pathological process, the spatial distribution in multiple tissues, and heterogeneous regeneration. We hope that this review will inspire the rational design of intra-articular drug delivery systems (DDSs) in the future.

Elastin stabilization prevents impaired biomechanics in human pulmonary arteries and pulmonary hypertension in rats with left heart disease

Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.

Alterations in the chondrocyte surfaceome in response to pro-inflammatory cytokines

Background

Chondrocytes are exposed to an inflammatory micro-environment in the extracellular matrix (ECM) of articular cartilage in joint diseases such as osteoarthritis (OA) and rheumatoid arthritis (RA). In OA, degenerative changes and low-grade inflammation within the joint transform the behaviour and metabolism of chondrocytes, disturb the balance between ECM synthesis and degradation, and alter the osmolality and ionic composition of the micro-environment. We hypothesize that chondrocytes adjust their physiology to the inflammatory microenvironment by modulating the expression of cell surface proteins, collectively referred to as the ‘surfaceome’. Therefore, the aim of this study was to characterize the surfaceome of primary equine chondrocytes isolated from healthy joints following exposure to the pro-inflammatory cytokines interleukin-1-beta (IL-1β) and tumour necrosis factor-alpha (TNF-α). We employed combined methodology that we recently developed for investigating the surfaceome in stem cells. Membrane proteins were isolated using an aminooxy-biotinylation technique and analysed by mass spectrometry using high throughput shotgun proteomics. Selected proteins were validated by western blotting.

Results

Amongst the 431 unique cell surface proteins identified, a high percentage of low-abundance proteins, such as ion channels, receptors and transporter molecules were detected. Data are available via ProteomeXchange with identifier PXD014773. A high number of proteins exhibited different expression patterns following chondrocyte stimulation with pro-inflammatory cytokines. Low density lipoprotein related protein 1 (LPR-1), thrombospondin-1 (TSP-1), voltage dependent anion channel (VDAC) 1–2 and annexin A1 were considered to be of special interest and were analysed further by western blotting.

Conclusions

Our results provide, for the first time, a repository for proteomic data on differentially expressed low-abundance membrane proteins on the surface of chondrocytes in response to pro-inflammatory stimuli.

Targeting inflammatory sites through collagen affinity enhances the therapeutic efficacy of anti-inflammatory antibodies

Enhancing the therapeutic efficacy of drugs for inflammatory diseases is of high demand. One possible approach is targeting drugs to the extracellular matrix of the inflamed area. Here, we target collagens in the matrix, which are inaccessible in most tissues yet are exposed to the bloodstream in the inflamed area because of vascular hyperpermeability. We conferred collagen affinity to anti-tumor necrosis factor-α (α-TNF) antibody by conjugating a collagen-binding peptide (CBP) derived from the sequence of decorin. CBP-α-TNF accumulated in the inflamed paw of the arthritis model, and arthritis development was significantly suppressed by treatment with CBP-α-TNF compared with the unmodified antibody. Similarly, CBP-anti-transforming growth factor-β (α-TGF-β) accumulated in the inflamed lung of pulmonary fibrosis model and significantly suppressed pulmonary fibrosis compared with the unmodified antibody. Together, collagen affinity enables the anticytokine antibodies to target arthritis and pulmonary fibrosis accompanied by inflammation, demonstrating a clinically translational approach to treat inflammatory diseases.

Articular fibrocartilage - Why does hyaline cartilage fail to repair?

Once damaged, articular cartilage has a limited potential to repair. Clinically, a repair tissue is formed, yet, it is often mechanically inferior fibrocartilage. The use of monolayer expanded versus naïve cells may explain one of the biggest discrepancies in mesenchymal stromal/stem cell (MSC) based cartilage regeneration. Namely, studies utilizing monolayer expanded MSCs, as indicated by numerous in vitro studies, report as a main limitation the induction of type X collagen and hypertrophy, a phenotype associated with endochondral bone formation. However, marrow stimulation and transfer studies report a mechanically inferior collagen I/II fibrocartilage as the main outcome. Therefore, this review will highlight the collagen species produced during the different therapeutic approaches. New developments in scaffold design and delivery of therapeutic molecules will be described. Potential future directions towards clinical translation will be discussed. New delivery mechanisms are being developed and they offer new hope in targeted therapeutic delivery.

Non-Invasive Monitoring of Functional State of Articular Cartilage Tissue with Label-Free Unsupervised Hyperspectral Imaging

Damage and degradation of articular cartilage leads to severe pain and loss of mobility. The development of new therapies for cartilage regeneration for monitoring their effect requires further study of cartilage, ideally at a molecular level and in a minimally invasive way. Hyperspectral microscopy is a novel technology which utilises endogenous fluorophores to non-invasively assess the molecular composition of cells and tissue. In this study, we applied hyperspectral microscopy to healthy bovine articular cartilage and osteoarthritic human articular cartilage to investigate its capacity to generate informative molecular data and characterise disease state and treatment effects. We successfully demonstrated label-free fluorescence identification of collagen type I and II - isolated in cartilage here for the first time and the co-enzymes free NADH and FAD which together give the optical redox ratio that is an important measure of metabolic activity. The intracellular composition of chondrocytes was also examined. Differences were observed in the molecular ratios within the superficial and transitional zones of the articular cartilage which appeared to be influenced by disease state and treatment. These findings show that hyperspectral microscopy could be useful for investigating the molecular underpinnings of articular cartilage degradation and repair. As it is non-invasive and non-destructive, samples can be repeatedly assessed over time, enabling true time-course experiments with in-depth molecular data. Additionally, there is potential for the hyperspectral approach to be adapted for patient examination to allow the investigation of cartilage state. This could be of advantage for assessment and diagnosis as well as treatment monitoring.

Cellular and molecular changes to chondrocytes in an in vitro model of developmental dysplasia of the hip‑an experimental model of DDH with swaddling position

The aim of the present study was to assess the cellular and molecular changes to chondrocytes in a developmental dysplasia of the hip (DDH) model and to investigate the early metabolism of chondrocytes in DDH. Neonatal Wistar rats were used for the DDH model with swaddling position. Primary cultures of chondrocytes were prepared at serial interval stages (2, 4, 6 and 8 weeks) to investigate cellular proliferation. The expression of collagen II and aggrecan mRNA was detected to assess the anabolic ability of chondrocytes. The expression of matrix metallopeptidase (MMP)-13 and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5) mRNA was measured to investigate the degradation of collagen II and aggrecan, respectively. Morphological changes were observed in coronal dissection samples after the removal of fixation. Primary chondrocytes at serial intervals were assessed using a Cell Counting Kit-8 assay and the results revealed that DDH chondrocytes had more proliferative activity. The expression of collagen II mRNA was upregulated at 2 weeks and was more sensitive to mechanical loading compared with aggrecan. Similar changes occurred at 6 weeks. Furthermore, MMP-13 and ADAMTS-5 mRNA expression levels were upregulated at 2 weeks. It was also demonstrated that DDH chondrocytes exhibited high proliferative activity at the early stages and degeneration later.

Biomaterials for articular cartilage tissue engineering: Learning from biology

Articular cartilage is commonly described as a tissue that is made of up to 80% water, is devoid of blood vessels, nerves, and lymphatics, and is populated by only one cell type, the chondrocyte. At first glance, an easy tissue for clinicians to repair and for scientists to reproduce in a laboratory. Yet, chondral and osteochondral defects currently remain an open challenge in orthopedics and tissue engineering of the musculoskeletal system, without considering osteoarthritis. Why do we fail in repairing and regenerating articular cartilage? Behind its simple and homogenous appearance, articular cartilage hides a heterogeneous composition, a high level of organisation and specific biomechanical properties that, taken together, make articular cartilage a unique material that we are not yet able to repair or reproduce with high fidelity. This review highlights the available therapies for cartilage repair and retraces the research on different biomaterials developed for tissue engineering strategies. Their potential to recreate the structure, including composition and organisation, as well as the function of articular cartilage, intended as cell microenvironment and mechanically competent replacement, is described. A perspective of the limitations of the current research is given in the light of the emerging technologies supporting tissue engineering of articular cartilage.

STATEMENT OF SIGNIFICANCE

The mechanical properties of articular tissue reflect its functionally organised composition and the recreation of its structure challenges the success of in vitro and in vivo reproduction of the native cartilage. Tissue engineering and biomaterials science have revolutionised the way scientists approach the challenge of articular cartilage repair and regeneration by introducing the concept of the interdisciplinary approach. The clinical translation of the current approaches are not yet fully successful, but promising results are expected from the emerging and developing new generation technologies.

Extracellular Distribution of Collagen II and Perifibrillar Adapter Proteins in Healthy and Osteoarthritic Human Knee Joint Cartilage

Perifibrillar adapter proteins, interconnecting collagen fibrils, and linking the collagen network with the aggrecan matrix seem to play a crucial role in the pathogenesis of osteoarthritis (OA). Therefore, we examined immunohistochemically the extracellular distribution of collagen II and the main perifibrillar adapter proteins-collagen IX, decorin, cartilage oligomeric matrix protein (COMP), and matrilin-3-in human samples of healthy (n=4) and OA (n=42) knee joint cartilage. Histopathology assessment was performed using an OA score. Staining patterns were evaluated in relation to the disease stage. The perifibrillar adapter proteins were uniformly distributed in the upper zones of healthy cartilage. In moderate OA (n=8; score 14.3 ± 4.7), all proteins analyzed were locally absent in the fibrillated area or the superficial and upper mid zone. In advanced OA (n=20; score 18.9 ± 5.3), they were uniformly distributed in these zones and accumulated pericellularly. Perifibrillar adapter proteins are important for the stabilization of the collagen network in the upper zones of healthy cartilage. Their degradation might be a critical event in early OA. In advanced OA, there are indications for an increased synthesis in an attempt to regenerate the lost tissue and to protect the remaining cartilage from further destruction.

An evaluation of the delayed effect of intra-articular injections of lidocaine (2%) on articular cartilage: an experimental study in rabbits

Lidocaine is commonly injected into the joints as an analgesic. The aim of the present study was to evaluate the delayed effect of intra-articular injections of lidocaine (2%) on articular cartilage in rabbit knees. Ten rabbits were divided into two groups, each group containing five animals. Two milliliters of normal saline solution was injected into both knee joints of animals in group one (control group), and 2 ml of lidocaine was injected into both knee joints of animals in group two (case group). After 8 weeks, the articular cartilage of the distal femur was harvested and analyzed through confocal microscopy and real-time polymerase chain reaction to evaluate the viability and function of chondrocytes, respectively. Confocal microscopy showed a significant decrease in the number of live cells caused by lidocaine (P ≤ 0.001). The changes in gene expression of collagen types II (COL II) and aggrecan were significant in group two (P = 0.008 and P = 0.002, respectively). According to the results, the delayed in vivo effect of lidocaine on chondrocyte is to reduce live chondrocytes and change in the gene expression of COL II and aggrecan.

Low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic field (PEMF) treatments affect degeneration of cultured articular cartilage explants

PURPOSE

Articular cartilage has some capacity for self-repair. Clinically used low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic field (PEMF) treatments were compared in their potency to prevent degeneration using an explant model of porcine cartilage.

METHODS

Explants of porcine cartilage and human osteoarthritic cartilage were cultured for four weeks and subjected to daily LIPUS or PEMF treatments. At one, two, three and four weeks follow-up explants were prepared for histological assessment or gene expression (porcine only).

RESULTS

Non-treated porcine explants showed signs of atrophy of the superficial zone starting at one week. Treated explants did not. In LIPUS-treated explants cell clusters were observed. In PEMF-treated explants more hypertrophic-like changes were observed at later follow up. Newly synthesized tissue was present in treated explants. Gene expression profiles did indicate differences between the two methods. Both methods reduced expression of the aggrecan and collagen type II gene compared to the control. LIPUS treatment of human cartilage samples resulted in a reduction of degeneration according to Mankin scoring. PEMF treatment did not.

CONCLUSIONS

LIPUS or PEMF prevented degenerative changes in pig knee cartilage explants. LIPUS reduced degeneration in human cartilage samples. LIPUS treatment seems to have more potency in the treatment of osteoarthritis than PEMF treatment.

A three-dimensionally engineered biomimetic cartilaginous tissue model for osteoarthritic drug evaluation

Osteoarthritis (OA) is primarily characterized by focal cartilage destruction and synovitis. Presently, the pathogenesis of OA remains unclear, and an effective treatment methodology is an unmet need. To this end, a plethora of animal models and monolayer models have been developed, but they are faced with the limitation of high cost and inability to recapitulate a pure hyaline cartilaginous phenotype, which is important in studying the efficacy of therapeutic agents. We have previously developed a living hyaline cartilage graft (LhCG) that accurately presented a pure hyaline cartilage phenotype. Here, through the coculture of lipopolysaccharide (LPS)-activated macrophages with LhCG, we hypothesized that an accurate OA disease model may be developed. Subsequently, this model was evaluated for its accuracy for in vitro drug testing. Results indicated that chondrocyte proliferation and apoptosis were increased in the disease model. Additionally, extracellular matrix (ECM) synthesis increased as indicated by the increased anabolic gene expression levels, such as collagen type II and aggrecan. Up-regulation of matrix metalloproteinase-1 (MMP-1) and MMP-3 genes suggested increased degradative activity, while chondrocytic hypertrophic differentiation was observed. Furthermore, extensive degradation of collagen type II and glycosaminoglycans (GAGs) were also observed. The results of celecoxib treatment on our model showed inhibition of nitric oxide (NO) and prostaglandin E2 (PGE2) production, as well as down-regulation of MMP-1 and MMP-3 expression. Taken together, the results suggested that this coculture model was able to sufficiently mimic the native, diseased OA cartilage, while drug testing results confirmed its suitability as an in vitro model for predicting native cartilage response to drug treatment.

CCN family member 2/connective tissue growth factor (CCN2/CTGF) has anti-aging effects that protect articular cartilage from age-related degenerative changes

To examine the role of connective tissue growth factor CCN2/CTGF (CCN2) in the maintenance of the articular cartilaginous phenotype, we analyzed knee joints from aging transgenic mice (TG) overexpressing CCN2 driven by the Col2a1 promoter. Knee joints from 3-, 14-, 40-, and 60-day-old and 5-, 12-, 18-, 21-, and 24-month-old littermates were analyzed. Ccn2-LacZ transgene expression in articular cartilage was followed by X-gal staining until 5 months of age. Overexpression of CCN2 protein was confirmed through all ages in TG articular cartilage and in growth plates. Radiographic analysis of knee joints showed a narrowing joint space and other features of osteoarthritis in 50% of WT, but not in any of the TG mice. Transgenic articular cartilage showed enhanced toluidine blue and safranin-O staining as well as chondrocyte proliferation but reduced staining for type X and I collagen and MMP-13 as compared with those parameters for WT cartilage. Staining for aggrecan neoepitope, a marker of aggrecan degradation in WT articular cartilage, increased at 5 and 12 months, but disappeared at 24 months due to loss of cartilage; whereas it was reduced in TG articular cartilage after 12 months. Expression of cartilage genes and MMPs under cyclic tension stress (CTS) was measured by using primary cultures of chondrocytes obtained from wild-type (WT) rib cartilage and TG or WT epiphyseal cartilage. CTS applied to primary cultures of mock-transfected rib chondrocytes from WT cartilage and WT epiphyseal cartilage induced expression of Col1a1, ColXa1, Mmp-13, and Mmp-9 mRNAs; however, their levels were not affected in CCN2-overexpressing chondrocytes and TG epiphyseal cartilage. In conclusion, cartilage-specific overexpression of CCN2 during the developmental and growth periods reduced age-related changes in articular cartilage. Thus CCN2 may play a role as an anti-aging factor by stabilizing articular cartilage.

Mitochondrial haplogroups define two phenotypes of osteoarthritis

Objective: To assess a mitochondrion-related phenotype in patients with osteoarthritis (OA). Methods: Serum levels of the following OA-related biomarkers: matrix metalloproteinase-1 (MMP-1); MMP-3; MMP-13; myeloperoxidase (MPO); a peptide of the alpha-helical region of type II collagen, Coll2-1, and its nitrated form Coll2-1NO₂; a C-terminal neoepitope generated by the collagenase-mediated cleavage of collagen type II triple helix, C2C; the C-propeptide of collagen type II, CPII; hyaluronic acid (HA); human cartilage glycoprotein 39, YKL-40; cartilage oligomeric matrix protein; and cathepsin K were analyzed in 48 OA patients and 52 healthy controls carrying the haplogroups H and J. Logistic regression models and receiver operating characteristic (ROC) curves were performed to predict the onset of OA. Results: MMP-13 was the only biomarker significantly increased in OA patients compared to healthy controls in both haplogroups H and J. The collagen type II biomarkers, Coll2-1, Coll2-1NO₂, the Coll2-1NO₂/Coll2-1 ratio, C2C, CPII, and the C2C:CPII ratio were significantly increased in OA patients carrying haplogroup H compared to OA carriers of the haplogroup J. Two logistic regression models for diagnosis were constructed and adjusted for age, gender, and body mass index. For haplogroup H, the biomarkers significantly associated with OA were MMP-13 and Coll2-1; the area under the curve (AUC) of the ROC curve for this model was 0.952 (95% CI = 0.892–1.012). For haplogroup J, the only biomarker significantly associated with OA was MMP-13; the AUC for this model was 0.895 (95% CI = 0.801–0.989). Conclusion: The mitochondrial DNA haplogroups are potential complementary candidates for biomarkers of OA; their genotyping in conjunction with the assessment of classical protein molecular markers is recommended.

[Osteoarthritis. Etiology, typing, staging and histological grading]

Degenerative disorders of the musculoskeletal system, in particular osteoarthritis, are among the most common diseases of the elderly and their importance in an aging society is continuously increasing. Correspondingly, many surgical interventions are undertaken and pathological specimens submitted for histopathologic workup. The pathophysiology of osteoarthritis, which ultimately leads to joint destruction, is still poorly understood. The question remains as to whether the cause lies (mainly) within the chondrocytes themselves (e.g. cellular aging/senescence) or whether the synovial membrane or the subchondral bone are equally or even more important factors. The process of joint destruction can be evaluated in terms of pathogenesis (typing), extent (staging) and degree of the most extensive focal damage (grading). Because of the heterogeneity of the disease and substantial individual differences in progression, classification and grading of cartilage degeneration represents a complex task. Any pathology report should be concise and delineate only the essential features. Differentiating between primary osteoarthritis and secondary degenerative changes, e.g., due to previously unknown rheumatoid disease, bone necrosis or an infection of the joint, is of particular clinical interest.

The response to oestrogen deprivation of the cartilage collagen degradation marker, CTX-II, is unique compared with other markers of collagen turnover

INTRODUCTION

The urinary level of the type II collagen degradation marker CTX-II is increased in postmenopausal women and in ovariectomised rats, suggesting that oestrogen deprivation induces cartilage breakdown. Here we investigate whether this response to oestrogen is also true for other type II collagen turnover markers known to be affected in osteoarthritis, and whether it relates to its presence in specific areas of cartilage tissue.

METHODS

The type II collagen degradation markers CTX-II and Helix-II were measured in the body fluids of premenopausal and postmenopausal women and in those of ovariectomised rats receiving oestrogen or not. Levels of PIIANP, a marker of type II collagen synthesis, were also measured in rats. Rat knee cartilage was analysed for immunoreactivity of CTX-II and PIIANP and for type II collagen expression.

RESULTS

As expected, urinary levels of CTX-II are significantly increased in postmenopausal women and also in oestrogen deprived rats, although only transiently. However, in neither case were these elevations paralleled by a significant increase of Helix-II levels and PIIANP levels did not change at any time. CTX-II immunoreactivity and collagen expression were detected indifferent cartilage areas. The upper zone is the area where CTX-II immunoreactivity and collagen expression best reflected the differences in urinary levels of CTX-II measured in response to oestrogen. However, correlations between urinary levels of CTX-II and tissue immunostainings in individual rats were not statistically significant.

CONCLUSIONS

We found only a small effect of oestrogen deprivation on cartilage. It was detected by CTX-II, but not by other type II collagen turnover markers typically affected in osteoarthritis.

Proliferative remodeling of the spatial organization of human superficial chondrocytes distant from focal early osteoarthritis

OBJECTIVE

Human superficial chondrocytes show distinct spatial organizations, and they commonly aggregate near osteoarthritic (OA) fissures. The aim of this study was to determine whether remodeling or destruction of the spatial chondrocyte organization might occur at a distance from focal (early) lesions in patients with OA.

METHODS

Samples of intact cartilage (condyles, patellofemoral groove, and proximal tibia) lying distant from focal lesions of OA in grade 2 joints were compared with location-matched nondegenerative (grade 0-1) cartilage samples. Chondrocyte nuclei were stained with propidium iodide, examined by fluorescence microscopy, and the findings were recorded in a top-down view. Chondrocyte arrangements were tested for randomness or significant grouping via point pattern analyses (Clark and Evans Aggregation Index) and were correlated with the OA grade and the surface cell densities.

RESULTS

In grade 2 cartilage samples, superficial chondrocytes were situated in horizontal patterns, such as strings, clusters, pairs, and singles, comparable to the patterns in nondegenerative cartilage. In intact cartilage samples from grade 2 joints, the spatial organization included a novel pattern, consisting of chondrocytes that were aligned in 2 parallel lines, building double strings. These double strings correlated significantly with an increased number of chondrocytes per group and an increased corresponding superficial zone cell density. They were observed in all grade 2 condyles and some grade 2 tibiae, but never in grade 0-1 cartilage.

CONCLUSION

This study is the first to identify a distinct spatial reorganization of human superficial chondrocytes in response to distant early OA lesions, suggesting that proliferation had occurred distant from focal early OA lesions. This spatial reorganization may serve to recruit metabolically active units as an attempt to repair focal damage.

Expression of collagen types I and II on articular cartilage in a rat knee contracture model

The purpose of our study was to clarify the expression patterns of collagen types I and II on articular cartilage after immobilization in a rat knee contracture model in 3 specific areas (noncontact area, transitional area, contact area). The unilateral knee joints of adult male rats were rigidly immobilized at 150 degrees of flexion using screws and a rigid plastic plate. Sham-operated animals had holes drilled in the femur and the tibia and screws inserted but were not plated. The expression patterns of collagen types I and II in each area were evaluated by in situ hybridization (ISH), immunohistochemistry (IHC), and quantitative real-time polymerase chain reaction (qPCR). The expression of collagen type II in the noncontact area was decreased by ISH but appeared unchanged when examined by IHC. In the transitional and contact areas, the expression of collagen type II was initially shown to have decreased and then increased at the hypertrophic chondrocytes by ISH but appeared decreased by IHC. Quantitative PCR revealed the decreased expression of type II collagen in the contact area. Immunostaining of collagen type I was increased at the noncontact area and transitional areas. Alterations of collagen types I and II expression may also affect the degeneration of articular cartilage after immobilization and the changes were different in the three areas.

[Osteoarthritis--histopathologic diagnosis: typing, grading, and staging]

Osteoarthritis is one of the most common diseases in modern western societies, particularly in the elderly, but it is occurring more and more often in the younger and middle-aged population, especially after traumatic injuries. The classification and grading of changes during cartilage degeneration is difficult due to the notoriously high heterogeneity of the disease process and is only partly clinically relevant. Overall, the process of joint destruction can always be evaluated for the pathogenesis (typing), its extent (staging), and the degree of the most extensive focal damage (grading). However, in the clinical routine, description and reporting of the basic findings might be best restricted to specimens obtained from endoprosthetic surgery. Only the identification of previously unknown underlying conditions such as rheumatoid disease, gout, or extensive osteonecrosis is of particular clinical interest.

Over-expression of c-maf by chondrocytes in osteoarthritis

The c-maf gene expression profile was investigated in normal and osteoarthritic articular cartilage using in situ hybridization, qualitative reverse transcription-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR. Osteoarthritic samples were obtained from 10 patients undergoing total knee replacement for severe osteoarthritis of the knee joints, and control samples from 10 trauma patients undergoing amputation. Expression of c-maf was significantly up-regulated in osteoarthritic cartilage compared with normal cartilage. Using in situ hybridization, distribution of a specific c-maf mRNA signal was found in the top zone and a decreased signal was found in the lower middle zone and the deep zone in osteoarthritic cartilage. A prominent c-maf mRNA signal was seen particularly in proliferating 'chondrocyte clusters'. In contrast, in normal cartilage almost no c-maf-positive cells were found. These findings suggest that c-maf may be important in chondrocyte hypertrophy and terminal differentiation, and may be involved in the pathogenesis of osteoarthritis.

[Typing, grading and staging of osteoarthritis: histopathological assessment of joint degeneration]

Osteoarthritis (degenerative arthropathy) is one of the most common diseases particular in the elderly. Osteoarthritis can principally affect all joints, although the knee, hip and phalangeal joints are most commonly involved in a clinically relevant manner. The grading and classification of changes during cartilage degeneration is complex and only partly informative for clinical management. Overall, the process of joint destruction can always be evaluated for the pathogenesis ("typing"), extent ("staging") and the degree of focal damage ("grading"). However, particularly in the final stages of the disease (e. g. in connection with prosthetic surgery) a description and report should be limited to only the most essential features, because no specific clinical relevance exists for further evaluation. Only the identification of secondary types of degenerative changes, due to as yet unknown rheumatoid diseases, gout or extensive osteonecrosis is of particular interest to clinical colleagues (i.e. typing of the joint lesion).

Biochemical markers of type II collagen breakdown and synthesis are positioned at specific sites in human osteoarthritic knee cartilage

OBJECTIVE

To investigate whether type II collagen turnover markers used for osteoarthritis (OA) activity evaluation in body fluids can be detected at the level of specific histological features of OA cartilage tissue, as well as how they relate with each other at this level.

METHODS

Adjacent sections were obtained from full-depth cartilage biopsies from 32 OA knees. Immunohistochemistry was performed for Helix-II and CTX-II, which are type II collagen fragments originating from the triple helix and the telopeptide region, respectively, and believed to reflect distinct breakdown events, as well as for type IIA N propeptide (PIIANP), a biochemical marker reflecting synthesis of type IIA collagen.

RESULTS

Helix-II and CTX-II were detected in areas where collagen damage was reported previously, most frequently around chondrocytes, but also frequently in regions not previously investigated such as the margin area and close to subchondral bone, including vascularization sites and bone-cartilage interface. The latter is CTX-II's prevailing position and shows rarely Helix-II. PIIANP co-localized with Helix-II and CTX-II on a limited number of features, mainly in deep zone cartilage. Overall, our analysis highlights clear patterns of association of the markers with specific histological features, and shows that they spread to these features in an ordered way.

CONCLUSION

Helix-II and CTX-II show to some degree differential selectivity for specific features in cartilage tissue. CTX-II detection close to bone may be relevant to the possible role of subchondral bone in OA. The restricted co-localization of breakdown markers and PIIANP suggests that collagen fragments can result only partially from newly synthesized collagen. Our study strengthens the interest for the question whether combining several markers reflecting different regional cartilage contributions or metabolic processes should allow a broader detection of OA activity.

Identification of calponin 3 as a novel Smad-binding modulator of BMP signaling expressed in cartilage

Bone morphogenetic proteins (BMP) play a prominent role in cartilage tissue homeostasis and perturbations of BMP signaling contribute to pathological processes like osteoarthritis. The response to BMP is determined by intracellular proteins interacting with the signal mediators Smads 1 and 5. Applying the yeast two-hybrid technique we could identify the actin-binding protein calponin 3 as a novel Smad-binding protein expressed in chondrocytes. It interacted with Smads 1 and 5 and overexpression led to an attenuation of BMP-dependent transcription. Calponin 3 mRNA and protein were expressed in cartilage tissue and isolated chondrocytes and a slight, but statistically significant reduction of mRNA expression levels could be detected in osteoarthritic cartilage. Our results suggest a role of calponin 3 in the regulation of BMP-dependent cellular responses. By interaction with the Smad proteins 1 and 5 and the inhibition of BMP-induced transcription, calponin 3 provides a negative regulatory mechanism for the BMP signaling pathway. This inhibitory effect likely depends on a sequestration of the Smads to the cytoskeleton due to the actin-binding properties of calponin 3. The down-regulation of calponin 3 expression in osteoarthritic joints could contribute to the increased responsiveness to BMPs described previously. Furthermore, our data provide a possible explanation for the effect of the related protein calponin 1 on bone and cartilage development.

[Histopathological examination of joint degeneration: typing, grading and staging of osteoarthritis]

Degenerative arthropathy (osteoarthritis) is one of the most common diseases in modern western societies, in particular in the elderly. The classification and grading of changes during cartilage degeneration represent complex endeavors which are only of limited value in daily pathological practice. In general, the process of joint destruction can always be evaluated for the determining pathogenesis ("typing"), extent ("staging") and degree of the most extensive focal damage ("grading"). However, for routine use one might best restrict description and reporting to the most essential features. This is in particular true for specimens obtained from endoprosthetic surgery (hips and knees), because there is currently no specific clinical relevance for further evaluation. Only the identification of secondary types of degenerative changes, such as those due to unknown rheumatoid disease, gout or extensive osteonecrosis, is of particular interest to the clinical colleague (i.e. typing of the joint lesion).

Activation of interleukin-1 signaling cascades in normal and osteoarthritic articular cartilage

Interleukin (IL)-1 is one of the most important catabolic cytokines in rheumatoid arthritis. In this study, we were interested in whether we could identify IL-1 expression and activity within normal and osteoarthritic cartilage. mRNA expression of IL-1beta and of one of its major target genes, IL-6, was observed at very low levels in normal cartilage, whereas only a minor up-regulation of these cytokines was noted in osteoarthritic cartilage, suggesting that IL-1 signaling is not a major event in osteoarthritis. However, immunolocalization of central mediators involved in IL-1 signaling pathways [38-kd protein kinases, phospho (P)-38-kd protein kinases, extracellular signal-regulated kinase 1/2, P-extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase 1/2, P-c-Jun NH(2)-terminal kinase 1/2, and nuclear factor kappaB] showed that the four IL-1 signaling cascades are functional in normal and osteoarthritic articular chondrocytes. In vivo, we found that IL-1 expression and signaling mechanisms were detectible in the upper zones of normal cartilage, whereas these observations were more pronounced in the upper portions of osteoarthritic cartilage. Given these expression and distribution patterns, our data support two roles for IL-1 in the pathophysiology of articular cartilage. First, chondrocytes in the upper zone of osteoarthritic articular cartilage seem to activate catabolic signaling pathways that may be in response to diffusion of external IL-1 from the synovial fluid. Second, IL-1 seems to be involved in normal cartilage tissue homeostasis as shown by identification of baseline expression patterns and signaling cascade activation.

Phenotyping of chondrocytes in vivo and in vitro using cDNA array technology

The cDNA array technology is a powerful tool to analyze a high number of genes in parallel. We investigated whether large-scale gene expression analysis allows clustering and identification of cellular phenotypes of chondrocytes in different in vivo and in vitro conditions. In 100% of cases, clustering analysis distinguished between in vivo and in vitro samples, suggesting fundamental differences in chondrocytes in situ and in vitro regardless of the culture conditions or disease status. It also allowed us to differentiate between healthy and osteoarthritic cartilage. The clustering also revealed the relative importance of the investigated culturing conditions (stimulation agent, stimulation time, bead/monolayer). We augmented the cluster analysis with a statistical search for genes showing differential expression. The identified genes provided hints to the molecular basis of the differences between the sample classes. Our approach shows the power of modern bioinformatic algorithms for understanding and classifying chondrocytic phenotypes in vivo and in vitro. Although it does not generate new experimental data per se, it provides valuable information regarding the biology of chondrocytes and may provide tools for diagnosing and staging the osteoarthritic disease process.

Assessment of cartilage degradation effects of matrix metalloproteinase-13 in equine cartilage cocultured with synoviocytes

OBJECTIVE

To determine the effects of matrix metalloproteinase (MMP)-13, compared with interleukin (IL)-1alpha, on cartilage matrix molecule gene expression in a coculture system of equine cartilage explants and synoviocytes.

SAMPLE POPULATION

Articular cartilage and synovium specimens harvested from femoropatellar joints of 4 horses, aged 3 to 5 years.

PROCEDURES

Synoviocytes were isolated and cocultured with cartilage explants. Cultures were treated with human recombinant MMP-13 (1, 25, or 100 ng/mL) or IL-1alpha (0.01, 0.1, 1.0, or 10 ng/mL) for 96 hours, with medium exchange at 48 hours. Cartilage extracts and media were analyzed for glycosaminoglycan (GAG) content, and results were adjusted to cartilage DNA content. Quantitative PCR was performed on mRNA from cartilage (MMP-3, MMP-13, aggrecan, and collagen type IIB [COL2A1]) and synoviocytes (MMP-3 and MMP-13), and results were adjusted to 18S ribosomal subunit mRNA expression. Treatments were performed in triplicate, and the experiment was repeated 4 times.

RESULTS

Cultures treated with MMP-13 or IL-1alpha had increased media GAG concentration at 48 and 96 hours. Aggrecan and COL2A1 mRNA expression were increased by application of MMP-13 or IL-1alpha. Gene expression of the catabolic mediator, MMP-3, in cartilage and synoviocytes was increased in cultures treated with MMP-13 or IL-1alpha. Expression of MMP-13 mRNA in cartilage was increased by IL-1alpha, but decreased in synoviocytes by MMP-13 treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Results support the use of recombinant MMP-13 in a coculture system of synoviocytes and cartilage explants for the study of osteoarthritis.

Chondrocyte hypertrophy can be induced by a cryptic sequence of type II collagen and is accompanied by the induction of MMP-13 and collagenase activity: implications for development and arthritis

The objective of this study was to determine whether a peptide of type II collagen which can induce collagenase activity can also induce chondrocyte terminal differentiation (hypertrophy) in articulate cartilage. Full depth explants of normal adult bovine articular cartilage were cultured with or without a 24 mer synthetic peptide of type II collagen (residues 195-218) (CB12-II). Peptide CB12-II lacks any RGD sequence and is derived from the CB12 fragment of type II collagen. Type II collagen cleavage by collagenase was measured by ELISA in cartilage and medium. Real-time RT-PCR was used to analyze gene expression of the chondrocyte hypertrophy markers COL10A1 and MMP-13. Immunostaining for anti-Ki67, anti-PCNA, (proliferation markers), type X collagen, cleavage of type II collagen by collagenases (hypertrophy markers) and TUNEL staining (hypertrophy and apoptosis markers) were used to detect progressive maturational stages of chondrocyte hypertrophy. At high but naturally occurring concentrations (10 microM and up) the collagen peptide CB12-II induced an increase in the expression of MMP-13 (24 h) and cleavage of type II collagen by collagenase in the mid zone (day 4) and also in the superficial zone (day 6). Furthermore the peptide induced an increase in proliferation on day 1 in the mid and deep zones extending to the superficial zone by day 4. There was also upregulation of COL10A1 expression at day 4 and of type X staining in the mid zone extending to the superficial zone by day 6. Apoptotic cell death was increased by day 4 in the lower deep zone and also in the superficial zone at day 7. The increase in apoptosis in the deep zone was also seen in controls. Our results show that the induction of collagenase activity by a cryptic peptide sequence of type II collagen, is accompanied by chondrocyte hypertrophy and associated with cellular and matrix changes. This induction occurs in the mid and superficial zones of previously healthy articular cartilage. This response of the chondrocyte to a cryptic sequence of denatured type II collagen may play a role in naturally occurring hypertrophy in endochondral ossification and in the development of cartilage pathology in osteoarthritis.

Neutrophil gelatinase–associated lipocalin is expressed in osteoarthritis and forms a complex with matrix metalloproteinase 9

OBJECTIVE

Expression of matrix metalloproteinase 9 (MMP-9) is up-regulated in osteoarthritis (OA) and usually presents as multiple bands when synovial fluid (SF) from OA patients is analyzed by zymography. Among these bands is an approximately 125-130-kd band for high molecular weight (HMW) gelatinase, which has not been characterized. This study was undertaken to characterize the HMW MMP activity in OA SF.

METHODS

MMP activity in OA SF was determined by gelatin zymography. Recombinant MMPs were used to identify MMP activity on the zymogram. Western immunoblotting, immunoprecipitation, and immunodepletion analyses were performed using antibodies specific for human MMP-9 and human neutrophil gelatinase-associated lipocalin (NGAL). Human cartilage matrix degradation was determined by dimethylmethylene blue assay.

RESULTS

Zymographic analysis showed that the HMW gelatinase in OA SF comigrated with a purified NGAL-MMP-9 complex. Results of Western immunoblotting showed that the HMW gelatinase was also recognized by antibodies specific for human NGAL or human MMP-9. These same antibodies also immunoprecipitated the HMW gelatinase activity from OA SF. The NGAL-MMP-9 complex was reconstituted in vitro in gelatinase buffer. In the presence of NGAL, MMP-9 activity was stabilized; in the absence of NGAL, rapid loss of MMP-9 activity occurred. MMP-9-mediated release of cartilage matrix proteoglycans was significantly higher in the presence of NGAL (P < 0.05).

CONCLUSION

Our findings demonstrate that the HMW gelatinase activity in OA SF represents a complex of NGAL and MMP-9. The ability of NGAL to protect MMP-9 activity is relevant to cartilage matrix degradation in OA and may represent an important mechanism by which NGAL may contribute to the loss of cartilage matrix proteins in OA.

Bone morphogenetic protein 7 (bmp-7) stimulates Proteoglycan synthesis in human osteoarthritic chondrocytes in vitro

BMP-7 is a member of the TGF-beta superfamily which is supposed to be one of the most potent anabolic factors of chondrocytes. In this study we analysed the effect of BMP-7 on three dimensional cultured chondrocytes with and without serum. Cartilage samples from fourteen patients with osteoarthritis of the knee were harvested and chondrocytes were cultivated in alginate-beads with and without serum supplementation (10% FCS). BMP-7 was added in three different concentrations (200, 600 and 1000 ng/ml). After 4 and 21 days PG concentration was determined by a Blyscan-Assay. For gene expression analysis of aggrecan (AGG) quantitative Lightcycler-PCR was used to estimate the mRNA levels. Under serumfree culture conditions there was no stimulation after 4 days but there was a twofold increase of PG concentration after 21 days. Using BMP-7 together with serum supplemented medium we found comparable results, however not as pronounced. AGG expression was increased only after 4 days but not after 21 days. Beside a stimulatory effect under serumfree conditions we also found a stimulatory effect of BMP-7 in the presence of serum. This study pronounces that BMP-7 might be a suitable anabolic activator of osteoarthritic chondrocytes.

Large-scale gene expression profiling reveals major pathogenetic pathways of cartilage degeneration in osteoarthritis

OBJECTIVE

Despite many research efforts in recent decades, the major pathogenetic mechanisms of osteoarthritis (OA), including gene alterations occurring during OA cartilage degeneration, are poorly understood, and there is no disease-modifying treatment approach. The present study was therefore initiated in order to identify differentially expressed disease-related genes and potential therapeutic targets.

METHODS

This investigation consisted of a large gene expression profiling study performed based on 78 normal and disease samples, using a custom-made complementary DNA array covering >4,000 genes.

RESULTS

Many differentially expressed genes were identified, including the expected up-regulation of anabolic and catabolic matrix genes. In particular, the down-regulation of important oxidative defense genes, i.e., the genes for superoxide dismutases 2 and 3 and glutathione peroxidase 3, was prominent. This indicates that continuous oxidative stress to the cells and the matrix is one major underlying pathogenetic mechanism in OA. Also, genes that are involved in the phenotypic stability of cells, a feature that is greatly reduced in OA cartilage, appeared to be suppressed.

CONCLUSION

Our findings provide a reference data set on gene alterations in OA cartilage and, importantly, indicate major mechanisms underlying central cell biologic alterations that occur during the OA disease process. These results identify molecular targets that can be further investigated in the search for therapeutic interventions.

BAC constructs in transgenic reporter mouse lines control efficient and specific LacZ expression in hypertrophic chondrocytes under the complete Col10a1 promoter

During endochondral ossification hypertrophic chondrocytes in the growth plate of fetal long bones, ribs and vertebrae play a key role in preparing growth plate cartilage for replacement by bone. In order to establish a reporter gene mouse to facilitate functional analysis of genes expressed in hypertrophic chondrocytes in this process, Col10a1- BAC reporter gene mouse lines were established expressing LacZ specifically in hypertrophic cartilage under the control of the complete Col10a1 gene. For this purpose, a bacterial artificial chromosome (BAC RP23-192A7) containing the entire murine Col10a1 gene together with 200 kb flanking sequences was modified by inserting a LacZ-Neo cassette into the second exon of Col10a1 by homologous recombination in E. coli. Transgenic mice containing between one and seven transgene copies were generated by injection of the purified BAC-Col10a1- lLacZ DNA. X-gal staining of newborns and embryos revealed strong and robust LacZ activity exclusively in hypertrophic cartilage of the fetal and neonatal skeleton of the transgenic offspring. This indicates that expression of the reporter gene in its proper genomic context in the BAC Col10a1 environment is independent of the integration site and reflects authentic Col10a1 expression in vivo. The Col10a1 specific BAC recombination vector described here will enable the specific analysis of effector gene functions in hypertrophic cartilage during skeletal development, endochondral ossification, and fracture callus healing.

Optimized extraction of glycosaminoglycans from normal and osteoarthritic cartilage for glycomics profiling

Articular cartilage is a highly specialized smooth connective tissue whose proper functioning depends on the maintenance of an extracellular matrix consisting of an integrated assembly of collagens, glycoproteins, proteoglycans (PG), and glycosaminoglycans. Isomeric chondroitin sulfate glycoforms differing in position and degree of sulfation and uronic acid epimerization play specific and distinct functional roles during development and disease onset. This work introduces a novel glycosaminoglycan extraction method for the quantification of mixtures of chondroitin sulfate oligosaccharides from intact cartilage tissue for mass spectral analysis. Glycosaminoglycans were extracted from intact cartilage samples using a combination of ethanol precipitation and enzymatic release followed by reversed-phase and strong anion exchange solid-phase extraction steps. Extracted chondroitin sulfate glycosaminoglycans were partially depolymerized using chondroitinases, labeled with 2-anthranilic acid-d(4) (2-AA) and subjected to size exclusion chromatography with online electrospray ionization mass spectrometric detection in the negative ion mode. The method presented herein enabled simultaneous determination of sulfate position and uronic acid epimerization in juvenile bovine and adult human cartilage samples. The method was applied to a series of 13 adult human cartilage explants. Standard deviation of the mean for the measurements was 1.6 on average. Coefficients of variation were approximately 4% for all compositions of 40% or greater. These results show that the new method has sufficient accuracy to allow determination of topographical distribution of glycoforms in connective tissue.

The lack of effect of glucosamine sulphate on aggrecan mRNA expression and 35S-sulphate incorporation in bovine primary chondrocytes

Glucosamine and glucosamine sulphate have been promoted as a disease-modifying agent to improve the clinical symptoms of osteoarthritis. The precise mechanism of the action of the suggested positive effect of glucosamine or glucosamine sulphate on cartilage proteoglycans is not known, since the level of glucosamine in plasma remains very low after oral administration of glucosamine sulphate. We examined whether exogenous hexosamines or their sulphated forms would increase steady-state levels of aggrecan and hyaluronan synthase (HAS) or glycosaminoglycan synthesis using Northern blot and (35)S-sulphate incorporation analyses. Total RNA was extracted from bovine primary chondrocytes which were cultured either in 1 mM concentration of glucosamine, galactosamine, mannosamine, glucosamine 3-sulphate, glucosamine 6-sulphate or galactosamine 6-sulphate for 0, 4, 8 and 24 h, or in three different concentrations (control, 100 microM and 1 mM) of glucosamine sulphate salt or glucose for 24 or 72 h. Northern blot assay showed that neither hexosamines nor glucosamine sulphate salt stimulated aggrecan and HAS-2 mRNA expression. Glycosaminoglycan synthesis remained at a control level in the treated cultures, with the exception of mannosamine which inhibited (35)S-sulphate incorporation in low-glucose DMEM treatment. In our culture conditions, hexosamines or their sulphated forms did not increase aggrecan expression or (35)S-sulphate incorporation.

Hgs physically interacts with Smad5 and attenuates BMP signaling

Signaling by members of the bone morphogenetic protein family plays a critical role in cartilage development and differentiation. Recently, the potential involvement of BMPs in the maintenance and repair of damaged adult articular cartilage has initiated an interest in the role of BMP signaling and the involved signaling pathways in the adult tissue. In this study, we identified Hgs as a novel Smad5 interactor using a cDNA expression library constructed from human adult cartilage. This interaction was confirmed by coimmunoprecipitation experiments in 293 EBNA cells and the chondrocytic cell line T/C-28a2. Overexpression of Hgs resulted in an attenuation of BMP-dependent transcriptional responses suggesting that Hgs acts as an inhibitor of BMP signaling. Of note, osteoarthritic chondrocytes which have been suggested previously to show increased reactivity to BMP-stimulation showed less expression of Hgs. Thus, it is tempting to speculate that both might be related to each other given the suppressive effect of BMP signaling on Hgs shown in this study.

Type II collagen synthesis in the articular cartilage of a rabbit model of osteoarthritis: expression of type II collagen C-propeptide and mRNA especially during early-stage osteoarthritis

BACKGROUND

The aim of this study was to observe time course changes in type II collagen synthesis in various regions of articular cartilage affected with osteoarthritis (OA) by examining the expression of type II collagen C-propeptide (pCOL II-C) and mRNA in a rabbit OA model.

METHODS

Osteoarthritis was experimentally induced by partial lateral meniscectomy in the knees of Japanese white rabbits. The cartilage of the animals was then examined histologically over time. The degenerative area of articular cartilage was divided into three areas, according to the degree of degeneration. The ability to synthesize type II collagen was estimated by the immunohistological staining of pCOL II-C and the in situ hybridization of mRNA in type II collagen.

RESULTS

The positive rate of pCOL II-C immunostaining in chondrocytes was highest in the central-degenerative region 1 week after surgery, and the highest rate in the para-degenerative region was observed 2 and 4 weeks after surgery. The percentage of pCOL II-C positive cells increased as the histological degeneration score increased to moderate degeneration and then decreased with further progression of the severity of cartilage degeneration. Examination by in situ hybridization revealed that the regions marked by strong pCOL II-C mRNA expression were similar to those indicated by the immunohistology results.

CONCLUSIONS

These results suggest that the type II collagen-synthesizing potential of chondrocytes is highest in moderately degenerated areas of OA articular cartilage. Cartilage repair continues to be seen even as OA advances, although the reaction varies depending on the stage of OA.

Molecular characterization of spontaneous and growth-factor-augmented chondrogenesis in periosteum–bone tissue transferred into a joint

Multilineage potential of progenitor cells from periosteum is well established, but conditions for differentiation within their native niche are unclear. We evaluated at cellular and molecular levels whether chondrogenesis of periosteal progenitor cells is promoted spontaneously or by growth-factor mixture (GFM) application when transferring periosteum-bone cylinders into cartilage defects. Osteochondral defects in the patellar groove of minipigs were filled with periosteum-bone cylinders and randomly supplemented with GFM. Neochondrogenesis was characterized by histology, immunohistology, and quantitative gene expression analysis. According to morphology and glycosaminoglycan accumulation, spontaneous neocartilage formation occurred in the cambium layer already at 6 weeks, increased after 12 weeks, but declined until 52 weeks, independent of GFM. Multiple cartilage differentiation markers were induced after transfer. Expression of aggrecan, COMP, decorin, and Col10a1 increased significantly within 52 weeks. Sox 9 and Col2a1 mRNA levels were elevated at 6 versus 52 weeks in the GFM group and resulted in higher collagen type II protein accumulation. Neochondrogenesis was promoted in lower periosteum layers by transfer of periosteum-bone plugs into a joint, and collagen type II protein deposition was enhanced by GFM. The final tissue subsumed typical features of periosteum and fibrocartilage but lacked an intact tide mark and features of hyaline cartilage desired for cartilage repair.

Phenotypic characterization of human chondrocyte cell line C-20/A4: a comparison between monolayer and alginate suspension culture

DNA microarray analysis was used to investigate the molecular phenotype of one of the first human chondrocyte cell lines, C-20/A4, derived from juvenile costal chondrocytes by immortalization with origin-defective simian virus 40 large T antigen. Clontech Human Cancer Arrays 1.2 and quantitative PCR were used to examine gene expression profiles of C-20/A4 cells cultured in the presence of serum in monolayer and alginate beads. In monolayer cultures, genes involved in cell proliferation were strongly upregulated compared to those expressed by human adult articular chondrocytes in primary culture. Of the cell cycle-regulated genes, only two, the CDK regulatory subunit and histone H4, were downregulated after culture in alginate beads, consistent with the ability of these cells to proliferate in suspension culture. In contrast, the expression of several genes that are involved in pericellular matrix formation, including MMP-14, COL6A1, fibronectin, biglycan and decorin, was upregulated when the C-20/A4 cells were transferred to suspension culture in alginate. Also, nexin-1, vimentin, and IGFBP-3, which are known to be expressed by primary chondrocytes, were differentially expressed in our study. Consistent with the proliferative phenotype of this cell line, few genes involved in matrix synthesis and turnover were highly expressed in the presence of serum. These results indicate that immortalized chondrocyte cell lines, rather than substituting for primary chondrocytes, may serve as models for extending findings on chondrocyte function not achievable by the use of primary chondrocytes.

Freshly isolated osteoarthritic chondrocytes are catabolically more active than normal chondrocytes, but less responsive to catabolic stimulation with interleukin-1beta

OBJECTIVE

Interleukin-1beta (IL-1beta) is one potentially important cytokine during cartilage destruction. The aim of this study was to investigate whether there are different effects of low and high concentrations of IL-1beta on the expression level of anabolic genes (type II collagen, aggrecan), catabolic genes (matrix metalloproteinase 1 [MMP-1], MMP-2, MMP-3, MMP-13, and ADAMTS-4), and cytokines (IL-1beta, IL-6, and leukemia inhibitory factor [LIF]) by articular chondrocytes (normal and osteoarthritic). Determination of whether there was a difference in reactivity between normal and osteoarthritic chondrocytes was also a goal of this study.

METHODS

Gene expression levels were detected by real-time polymerase chain reaction from isolated (nonpassaged) chondrocytes (normal [n = 6]; osteoarthritic [n = 7]) after stimulation with 0.01 ng, 0.1 ng, 1 ng, and 10 ng/ml IL-1beta.

RESULTS

In normal adult articular chondrocytes the expression of both aggrecan and type II collagen genes was significantly down-regulated, whereas matrix-degrading proteases (except MMP-2), as well as the investigated cytokines, were induced by IL-1beta in a dose-dependent manner. The strongest regulation was found for IL-6 and LIF. Osteoarthritic chondrocytes showed strongly increased levels of catabolic enzymes and mediators, but were less responsive to further stimulation with IL-1beta.

CONCLUSION

Our study confirms that IL-1beta activity is critically dependent on both the applied concentration and the reactivity of the cells stimulated. The responsiveness appears to be significantly reduced in late-stage osteoarthritic chondrocytes. However, these cells show high basic expression levels of catabolic enzymes and mediators. Thus, it remains open whether our data indicate that osteoarthritic chondrocytes are per se not responsive to IL-1beta or are already so strongly stimulated (e.g., by IL-1) during the disease process that they are refractory to further stimulation.

Repression of anti-proliferative factor Tob1 in osteoarthritic cartilage

Osteoarthritis is the most common degenerative disorder of the modern world. However, many basic cellular features and molecular processes of the disease are poorly understood. In the present study we used oligonucleotide-based microarray analysis of genes of known or assumed relevance to the cellular phenotype to screen for relevant differences in gene expression between normal and osteoarthritic chondrocytes. Custom made oligonucleotide DNA arrays were used to screen for differentially expressed genes in normal (n = 9) and osteoarthritic (n = 10) cartilage samples. Real-time polymerase chain reaction (PCR) with gene-specific primers was used for quantification. Primary human adult articular chondrocytes and chondrosarcoma cell line HCS-2/8 were used to study changes in gene expression levels after stimulation with interleukin-1β and bone morphogenetic protein, as well as the dependence on cell differentiation. In situ hybridization with a gene-specific probe was applied to detect mRNA expression levels in fetal growth plate cartilage. Overall, more than 200 significantly regulated genes were detected between normal and osteoarthritic cartilage (P < 0.01). One of the significantly repressed genes, Tob1, encodes a protein belonging to a family involved in silencing cells in terms of proliferation and functional activity. The repression of Tob1 was confirmed by quantitative PCR and correlated to markers of chondrocyte activity and proliferation in vivo. Tob1 expression was also detected at a decreased level in isolated chondrocytes and in the chondrosarcoma cell line HCS-2/8. Again, in these cells it was negatively correlated with proliferative activity and positively with cellular differentiation. Altogether, the downregulation of the expression of Tob1 in osteoarthritic chondrocytes might be an important aspect of the cellular processes taking place during osteoarthritic cartilage degeneration. Activation, the reinitiation of proliferative activity and the loss of a stable phenotype are three major changes in osteoarthritic chondrocytes that are highly significantly correlated with the repression of Tob1 expression.

Enhanced concentration of COMP (cartilage oligomeric matrix protein) in osteochondral fractures from racing Thoroughbreds

The aim of the present study was to correlate the levels of COMP and aggrecan as indicators of tissue damage, in synovial fluid (sf) from carpal joints of acutely lame racehorses, with macroscopical lesions of articular cartilage (OA), osteochondral fractures and ligament tears found at arthroscopy. Sixty-three lame horses [49 Standardbred trotters (STB) and 14 Thoroughbreds (TB)] in conventional training and racing that underwent arthroscopy of their middle carpal or radiocarpal joints were included in the study. Intact as well as fragmented COMP and aggrecan released into the synovial fluid were quantified by western blot analyses and ELISA. The expression of COMP in tissues was estimated by mRNA in situ hybridisation and protein immunolocalisation in cartilage and osteochondral fractures. The concentration of sf-COMP was higher in TB with an osteochondral fracture than in STB with osteochondral fractures and TB and STB with OA. The chondrocytes in middle and deep zones of the articular cartilage of the osteochondral fragments (from a TB) expressed COMP mRNA, in contrast to the cartilage on the opposite side of the fracture where no expression was detected. In the synovial fluid from a joint (TB) with osteochondral fractures only intact COMP was present, whereas, fragmented COMP was more prominent in synovial fluid from a joint with OA. The concentration of sf-aggrecan did not differ between the two breeds, or between different lesions. The increased concentration of sf-COMP in TB with osteochondral fractures, but not in synovial fluid from equine joints with OA, is a novel finding. The results from this study indicate that elevated sf-COMP concentration in the joints of Thoroughbreds may be a useful marker for carpal joint osteochondral fragments.

Perlecan in late stages of osteoarthritis of the human knee joint

OBJECTIVE

Disturbances of the proteoglycan metabolism play an essential role in the pathology of osteoarthritis. The extracellular matrix proteoglycan, perlecan, has lately been identified as a cell biological factor in cartilage development and maintenance. We investigated the tissue distribution of perlecan, the relation between the level of the protein and its mRNA and which type of cell, type 1 chondrocytes or elongated secretory type 2 cells, produces perlecan in late stages of osteoarthritis.

METHODS

In 10 patients suffering from late-stage osteoarthritis tissue samples taken from a macroscopically intact area and the area adjacent to the main cartilage defect were investigated. We performed quantitative immunogold histochemistry and in situ hybridization in vivo and determined the level of perlecan mRNA with the help of real-time RT-PCR in native cartilage tissue and in cultured cells.

RESULTS

In vivo, an increased level of perlecan protein was found in the area adjacent to the main defect. A 45% rise in the level of perlecan mRNA secreted by elongated secretory type 2 cells in comparison to type 1 chondrocytes was detected. Type 2 cells also translated the highest levels of perlecan to be deposited mainly in the pericellular matrix, and also in the interterritorial matrix in late stages of osteoarthritis. Also in vitro, type 2 cells showed a 50% higher level of mRNA for perlecan.

CONCLUSION

We found evidence that perlecan is involved in the pathogenesis of late stages of osteoarthritis. The levels of perlecan protein and mRNA are up-regulated especially by the elongated secretory type 2 cells in the area adjacent to the main cartilage defect. This might be seen as an attempt on the part of the cartilage tissue to stabilize the extracellular matrix.

Aging theories of primary osteoarthritis: from epidemiology to molecular biology

Osteoarthritis is the most common disabling condition of humans in the western world. It has been known for a very long time that aging is the most prominent risk factor for the initiation and progression of the disease, but the explanations for this phenomenon have changed over time. The most longstanding theory is that osteoarthritis develops because of continuous mechanical wear and tear. However, osteoarthritis can also be the result of time/age-related modifications to cartilage matrix components. One of the simplest biological explanations for the initiation and progression of osteoarthritic cartilage degeneration is a mere loss of viable cells, due to apoptosis or other mechanisms. Overall, the most likely scenario is that the cells and the matrix of articular cartilage get older over time, and eventually the tissue enters a senescence-like state that makes it more prone to enter the osteoarthritic degeneration pathway. Thus, patients with osteoarthritis might progress more quickly to the senescence phenotype compared to others. Moreover, stressful conditions associated with the osteoarthritic disease process might further promote chondrocyte senescence. Primary osteoarthritis in this model would be a "premature" degeneration of the joint due to a premature chondrocyte senescence. By analogy to neurodegenerative disorders, one could refer to osteoarthritis as the "M. Alzheimer" of articular cartilage. One of the most important implications of this hypothesis is that it points to issues of cellular degeneration as the basis for understanding the initiation and progression of osteoarthritis. Equally important, it emphasizes that whatever treatment we envisage for osteoarthritis, we must take into account that we are dealing with aged/(pre)senescent cells that no longer have the ability of their juvenile counterparts to counteract the many mechanical, inflammatory, and/or other assaults to the tissue.