Proteoglycan degradation after injurious compression of bovine and human articular cartilage in vitro: interaction with exogenous cytokines

The regional sensitivity of chondrocyte gene expression to coactive mechanical load and exogenous TNF-α stimuli

Both mechanical load and elevated levels of proinflammatory cytokines have been associated with the risk for developing osteoarthritis (OA), yet the potential interaction of these mechanical and biological factors is not well understood. The purpose of this study was to evaluate the response of chondrocytes to the effects of dynamic unconfined compression, TNF-α, and the simultaneous effects of dynamic unconfined compression and TNF-α. The response to these three treatments was markedly different and, taken together, the response in the gene expression of chondrocytes to the different treatment conditions suggest a complex interaction between structure, biology, and mechanical loading.

Enhanced cell-induced articular cartilage regeneration by chondrons; the influence of joint damage and harvest site

OBJECTIVE

Interactions between chondrocytes and their native pericellular matrix provide optimal circumstances for regeneration of cartilage. However, cartilage diseases such as osteoarthritis change the pericellular matrix, causing doubt to them as a cell source for autologous cell therapy.

METHODS

Chondrons and chondrocytes were isolated from stifle joints of goats in which cartilage damage was surgically induced in the right knee. After 4 weeks of regeneration culture, DNA content and proteoglycan and collagen content and release were determined.

RESULTS

The cartilage regenerated by chondrons isolated from the damaged joint contained less proteoglycans and collagen compared to chondrons from the same harvest site in the nonoperated knee (P < 0.01). Besides, chondrons still reflected whether they were isolated from a damaged joint, even if they where isolated from the opposing or adjacent condyle. Although chondrocytes did not reflect this diseased status of the joint, chondrons always outperformed chondrocytes, even when isolated from the damaged joints (P < 0.0001). Besides increased cartilage production, the chondrons showed less collagenase activity compared to the chondrocytes.

CONCLUSION

Chondrons still outperform chondrocytes when they were isolated from a damaged joint and they might be a superior cell source for articular cartilage repair and cell-induced cartilage formation.

Quantitative evaluation of in vitro effects and interactions of active fractions in a Chinese medicinal formula (Yaotongning Capsule) on rat chondrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Yaotongning Capsule (YTNC) is a Traditional Chinese Medicinal (TCM) formula that has been demonstrated to be effective for osteoarthritis (OA) treatment in clinical use. Many compounds and 10 component medicinal materials (CMMs for short, i.e., the fundamental elements used in TCM formulas) in YTNC are challenging to study the pharmacological effects and interactions of the CMMs. Besides, it is difficult to know whether the YTNC formula is reasonable, and if YTNC formula could be improved without comparing YTNC with other TCM formulas of treating OA. Based on different combinations of the active fractions from the 10 CMMs of YTNC and eight additional herbs frequently used in the TCM formulas of treating OA, the present study evaluated systematically the in vitro effects of these active fractions and the interactions among the active fractions from YTNC on rat chondrocytes to find possible solutions of the above questions.

MATERIALS AND METHODS

Based on the formulation of YTNC and the concept of combinatorial chemistry, the active fractions were applied to form the whole YTNC prescription (i.e., the combination of all YTNC active fractions and the extract of YTNC׳s vehicle), five disassembled formulas of YTNC (i.e., the combinations of some active fractions in YTNC) and 21 TCM samples consisted of different kinds of active fractions. The degenerated chondrocytes were induced with interleukin-1β (IL-1β), and then the half-effective concentration (EC50) value of the proliferation activity was analyzed to evaluate the 27 TCM samples. Nine samples were screened for the following evaluation on glycosaminoglycan (GAG) synthesis. Rat articular cartilage was obtained from six Sprague-Dawley rats (seven days of age), and then chondrocytes were isolated through enzymatic digestion with 0.2% Collagenase II. Proliferations of chondrocytes were examined through Cell Counting Kit-8 assay, when the intracellular levels of GAG were detected by 1,9-Dimethylmethylene blue staining. The interactions between the active fractions in YTNC were evaluated by comparing experimental EC50 values of the YTNC formulas with their additive EC50 values. The effects of every active fraction were estimated by comparing the EC50 values of the TCM sample containing the active fraction with that of the initial sample without the active fraction.

RESULTS

The whole formula of YTNC was very good at promoting the proliferation and GAG synthesis among all the 27 TCM samples. The vehicle of YTNC (Chinese rice wine) strengthened the two activities of YTNC. Refer to promoting the proliferation in chondrocytes, Davallia mariesii flavonoids (not belong to YTNC) were more potent than Glycyrrhiza uralensis flavonoids in YTNC, while the saponins, volatile oils and polysaccharides of YTNC were more potent than those from the eight additional herbs. Some samples including fewer active fractions were as good as YTNC. The YTNC formula and its disassembled formulas exhibited good activities both in promoting the proliferation and GAG synthesis, and the whole formula was most potent among the six YTNC formulas.

CONCLUSIONS

The YTNC formula is reasonable and has advantage in promoting the proliferation and GAG synthesis in IL-1β induced chondrocytes. YTNC׳s vehicle Chinese rice wine plays an important role in strengthening the activity of YTNC. YTNC may have the potential activity on treating chondrocytes degeneration caused by OA. However, the formula still can be simplified based on the combination of alkaloids, flavonoids and 50% of saponins from Glycyrrhiza uralensis to improve its quality controllability and safety. The present study can be a quite purposeful work for developing new YTNC-based formulas with maximal therapeutic efficacy and minimal adverse effects.

Influence of TNF-α and biomechanical stress on matrix metalloproteinases and lysyl oxidases expressions in human knee synovial fibroblasts

PURPOSE

It was reported that not only ACL but also the synovium may be the major regulator of matrix metalloproteinases (MMPs) in synovial fluids after ACL injury. In order to further confirm whether synovium is capable of regulating the microenvironment in the process of ACL injury, the complicated microenvironment of joint cavity after ACL injury was mimicked and the combined effects of mechanical injury and inflammatory factor [tumour necrosis factor-α (TNF-α)] on expressions of lysyl oxidases (LOXs) and MMPs in synovial fibroblasts derived from normal human synovium were studied.

METHODS

Human normal knee joint synovial fibroblasts were stimulated for 1-6 h with mechanical stretch and inflammatory factor (TNF-α). Total RNA was harvested, reverse transcribed and assessed by real-time polymerase chain reaction for the expression of LOXs and MMP-1, 2, 3 messenger RNAs. MMP-2 activity was assayed from the collected culture media samples using zymography.

RESULTS

Compared to control group, our results showed that 6% physiological stretch increased MMP-2 and LOXs (except LOXL-3), decreased MMP-1 and MMP-3; injurious stretch (12%) decreased LOXs (except LOXL-2)and increased MMP-1, 2 and 3; the combination of injurious stretch and TNF-α decreased LOXs and increased MMP-1, 2 and 3 in synovial fibroblasts in a synergistical manner.

CONCLUSION

This study demonstrated that combination of mechanical injury and inflammatory factors up-regulated the expressions of MMPs and down-regulated the expressions of LOXs in synovial fibroblasts, eventually alter the balance of tissue healing. Thus, synovium may be involved in regulating the microenvironment of joint cavity. Based on the mechanism, early interventions to inhibit the production of MMPs or promote the production of LOXs in the synovial fibroblasts should be performed to facilitate the healing of tissue.

A high-throughput model of post-traumatic osteoarthritis using engineered cartilage tissue analogs

OBJECTIVE

A number of in vitro models of post-traumatic osteoarthritis (PTOA) have been developed to study the effect of mechanical overload on the processes that regulate cartilage degeneration. While such frameworks are critical for the identification therapeutic targets, existing technologies are limited in their throughput capacity. Here, we validate a test platform for high-throughput mechanical injury incorporating engineered cartilage.

METHOD

We utilized a high-throughput mechanical testing platform to apply injurious compression to engineered cartilage and determined their strain and strain rate dependent responses to injury. Next, we validated this response by applying the same injury conditions to cartilage explants. Finally, we conducted a pilot screen of putative PTOA therapeutic compounds.

RESULTS

Engineered cartilage response to injury was strain dependent, with a 2-fold increase in glycosaminoglycan (GAG) loss at 75% compared to 50% strain. Extensive cell death was observed adjacent to fissures, with membrane rupture corroborated by marked increases in lactate dehydrogenase (LDH) release. Testing of established PTOA therapeutics showed that pan-caspase inhibitor [Z-VAD-FMK (ZVF)] was effective at reducing cell death, while the amphiphilic polymer [Poloxamer 188 (P188)] and the free-radical scavenger [N-Acetyl-L-cysteine (NAC)] reduced GAG loss as compared to injury alone.

CONCLUSIONS

The injury response in this engineered cartilage model replicated key features of the response of cartilage explants, validating this system for application of physiologically relevant injurious compression. This study establishes a novel tool for the discovery of mechanisms governing cartilage injury, as well as a screening platform for the identification of new molecules for the treatment of PTOA.

Targeted delivery to cartilage is critical for in vivo efficacy of insulin-like growth factor 1 in a rat model of osteoarthritis

OBJECTIVE

Acute articular injuries lead to an increased risk of progressive joint damage and osteoarthritis (OA), and no therapies are currently available to repair or protect the injured joint tissue. Intraarticular delivery of therapeutic proteins has been limited by their rapid clearance from the joint space and lack of retention within cartilage. The aim of this study was to test whether targeted delivery to cartilage by fusion with a heparin-binding domain would be sufficient to prolong the in vivo function of the insulin-like growth factor 1 (IGF-1).

METHODS

We produced a humanized and optimized recombinant HB-IGF-1 fusion protein. By injecting HB-IGF-1, IGF-1, or saline alone into the knee joints of adult Lewis rats, we tested whether fusion with a heparin-binding domain 1) altered the kinetics of retention in joint tissues, 2) prolonged functional stimulation as measured by radiolabel incorporation, and 3) enhanced efficacy in a rat model of surgically induced OA, using weekly injections.

RESULTS

Fusion of heparin-binding domain with IGF-1 prolonged retention in articular and meniscal cartilage from <1 day to 8 days after injection. Unmodified IGF-1 had no functional effect 2 days after injection, whereas HB-IGF-1 stimulated meniscal cartilage at least 4 days after injection. HB-IGF-1, but not IGF-1, significantly slowed cartilage damage in a rat model of OA.

CONCLUSION

Heparin-binding domain fusions can transform rapidly cleared proteins into potential intraarticular therapies by targeting them to cartilage.

Stem cells catalyze cartilage formation by neonatal articular chondrocytes in 3D biomimetic hydrogels

Cartilage loss is a leading cause of disability among adults and effective therapy remains elusive. Neonatal chondrocytes (NChons) are an attractive allogeneic cell source for cartilage repair, but their clinical translation has been hindered by scarce donor availability. Here we examine the potential for catalyzing cartilage tissue formation using a minimal number of NChons by co-culturing them with adipose-derived stem cells (ADSCs) in 3D hydrogels. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation are dependent on the intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and resulted in the formation of large neocartilage nodules. This work raises the potential of utilizing stem cells to catalyze tissue formation by neonatal chondrocytes via paracrine signaling, and highlights the importance of controlling cell distribution in 3D matrices to achieve optimal synergy.

Moderate dynamic compression inhibits pro-catabolic response of cartilage to mechanical injury, tumor necrosis factor-α and interleukin-6, but accentuates degradation above a strain threshold

OBJECTIVE

Traumatic joint injury can initiate early cartilage degeneration in the presence of elevated inflammatory cytokines (e.g., tumor necrosis factor (TNF)-α and interleukin (IL)-6). The positive/negative effects of post-injury dynamic loading on cartilage degradation and repair in vivo are not well-understood. This study examined the effects of dynamic strain on immature bovine cartilage in vitro challenged with TNF-α + IL-6 and its soluble receptor (sIL-6R) with/without initial mechanical injury.

METHODS

Groups of mechanically injured or non-injured explants were cultured in TNF-α + IL-6/sIL-6R for 8 days. Intermittent dynamic compression was applied concurrently at 10%, 20%, or 30% strain amplitude. Outcome measures included sulfated glycosaminoglycan (sGAG) loss (dimethylmethylene blue (DMMB)), aggrecan biosynthesis ((35)S-incorporation), aggrecanase activity (Western blot), chondrocyte viability (fluorescence staining) and apoptosis (nuclear blebbing via light microscopy), and gene expression (qPCR).

RESULTS

In bovine explants, cytokine alone and injury-plus-cytokine treatments markedly increased sGAG loss and aggrecanase activity, and induced chondrocyte apoptosis. These effects were abolished by moderate 10% and 20% strains. However, 30% strain amplitude greatly increased apoptosis and had no inhibitory effect on aggrecanase activity. TNF + IL-6/sIL-6R downregulated matrix gene expression and upregulated expression of inflammatory genes, effects that were rescued by moderate dynamic strains but not by 30% strain.

CONCLUSIONS

Moderate dynamic compression inhibits the pro-catabolic response of cartilage to mechanical injury and cytokine challenge, but there is a threshold strain amplitude above which loading becomes detrimental to cartilage. Our findings support the concept of appropriate loading for post-injury rehabilitation.

Autologous solution protects bovine cartilage explants from IL-1α- and TNFα-induced cartilage degradation

Osteoarthritis (OA) is characterized by deterioration of articular cartilage driven by an imbalance of pro- and anti-inflammatory cytokines. To address the cartilage deterioration observed in OA, an autologous protein solution (APS) has been developed which has been shown to inhibit the production of destructive proteases and inflammatory cytokines from chondrocytes and monocytes, respectively. The purpose of this study was to determine the chondroprotective effect of APS on IL-1α- or TNFα-challenged bovine articular cartilage explants. Cartilage explants were cultured in the presence or absence of recombinant inflammatory cytokines, IL-1α and TNFα. Explants under equivalent inflammatory conditions were pretreated with recombinant antagonists IL-1ra, sTNF-RI, or APS to measure their inhibition of matrix degradation. Explants were further evaluated with Safranin-O, Masson's Trichrome, and Hematoxylin and Eosin histological staining. APS was more effective than recombinant antagonists in preventing cartilage matrix degradation and inhibited any measurable IL-1α-induced collagen release over a 21-day culture period. APS treatment reduced the degree of Safranin-O staining loss when cartilage explants were cultured with IL-1α or TNFα. Micrographs of APS treated cartilage explants showed an increase in observed cellularity and apparent cell division. APS may have the potential to prevent cartilage loss associated with early OA.

Matrix metalloproteases and tissue inhibitors of metalloproteinases in medial plica and pannus-like tissue contribute to knee osteoarthritis progression

Osteoarthritis (OA) is characterized by degradation of the cartilage matrix, leading to pathologic changes in the joints. However, the pathogenic effects of synovial tissue inflammation on OA knees are not clear. To investigate whether the inflammation caused by the medial plica is involved in the pathogenesis of osteoarthritis, we examined the expression of matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α in the medial plica and pannus-like tissue in the knees of patients with medial compartment OA who underwent either arthroscopic medial release (stage II; 15 knee joints from 15 patients) or total knee replacement (stage IV; 18 knee joints from 18 patients). MMP-2, MMP-3, MMP-9, IL-1β, and TNF-α mRNA and protein levels measured, respectively, by quantitative real-time PCR and Quantibody human MMP arrays, were highly expressed in extracts of medial plica and pannus-like tissue from stage IV knee joints. Immunohistochemical staining also demonstrated high expression of MMP-2, MMP-3, and MMP-9 in plica and pannus-like tissue of stage IV OA knees and not in normal cartilage. Some TIMP/MMP ratios decreased significantly in both medial plica and pannus-like tissue as disease progressed from stage II to stage IV. Furthermore, the migration of cells from the pannus-like tissue was enhanced by IL-1β, while plica cell migration was enhanced by TNF-α. The results suggest that medial plica and pannus-like tissue may be involved in the process of cartilage degradation in medial compartment OA of the knee.

Avidin as a model for charge driven transport into cartilage and drug delivery for treating early stage post-traumatic osteoarthritis

Local drug delivery into cartilage remains a challenge due to its dense extracellular matrix of negatively charged proteoglycans enmeshed within a collagen fibril network. The high negative fixed charge density of cartilage offers the unique opportunity to utilize electrostatic interactions to augment transport, binding and retention of drug carriers. With the goal of developing particle-based drug delivery mechanisms for treating post-traumatic osteoarthritis, our objectives were, first, to determine the size range of a variety of solutes that could penetrate and diffuse through normal cartilage and enzymatically treated cartilage to mimic early stages of OA, and second, to investigate the effects of electrostatic interactions on particle partitioning, uptake and binding within cartilage using the highly positively charged protein, Avidin, as a model. Results showed that solutes having a hydrodynamic diameter ≤10 nm can penetrate into the full thickness of cartilage explants while larger sized solutes were trapped in the tissue's superficial zone. Avidin had a 400-fold higher uptake than its neutral same-sized counterpart, NeutrAvidin, and >90% of the absorbed Avidin remained within cartilage explants for at least 15 days. We report reversible, weak binding (K(D) ~ 150 μM) of Avidin to intratissue sites in cartilage. The large effective binding site density (N(T) ~ 2920 μM) within cartilage matrix facilitates Avidin's retention, making its structure suitable for particle based drug delivery into cartilage.

Curcumin reduces prostaglandin E2, matrix metalloproteinase-3 and proteoglycan release in the secretome of interleukin 1β-treated articular cartilage

Objective:Curcumin (diferuloylmethane) is a phytochemical with potent anti-inflammatory and anti-oxidant properties, and has therapeutic potential for the treatment of a range of inflammatory diseases, including osteoarthritis (OA). The aim of this study was to determine whether non-toxic concentrations of curcumin can reduce interleukin-1beta (IL-1β)-stimulated inflammation and catabolism in an explant model of cartilage inflammation.

Methods:Articular cartilage explants and primary chondrocytes were obtained from equine metacarpophalangeal joints. Curcumin was added to monolayer cultured primary chondrocytes and cartilage explants in concentrations ranging from 3μM-100μM. Prostaglandin E ₂ (PGE ₂) and matrix metalloproteinase (MMP)-3 release into the secretome of IL-1β-stimulated explants was measured using a competitive ELISA and western blotting respectively. Proteoglycan (PG) release in the secretome was measured using the 1,9-dimethylmethylene blue (DMMB) assay. Cytotoxicity was assessed with a live/dead assay in monolayer cultures after 24 hours, 48 hours and five days, and in explants after five days.

Results:Curcumin induced chondrocyte death in primary cultures (50μM p<0.001 and 100μM p<0.001) after 24 hours. After 48 hours and five days, curcumin (≥25μM) significantly increased cell death ( p<0.001 both time points). In explants, curcumin toxicity was not observed at concentrations up to and including 25μM after five days. Curcumin (≥3μM) significantly reduced IL-1β-stimulated PG ( p<0.05) and PGE ₂ release ( p<0.001) from explants, whilst curcumin (≥12μM) significantly reduced MMP-3 release ( p<0.01).

Conclusion: Non-cytotoxic concentrations of curcumin exert anti-catabolic and anti-inflammatory effects in cartilage explants.

Tensile strain increases expression of CCN2 and COL2A1 by activating TGF-β-Smad2/3 pathway in chondrocytic cells

Physiologic mechanical stress stimulates expression of chondrogenic genes, such as multifunctional growth factor CYR61/CTGF/NOV (CCN) 2 and α1(II) collagen (COL2A1), and maintains cartilage homeostasis. In our previous studies, cyclic tensile strain (CTS) induces nuclear translocation of transforming growth factor (TGF)-β receptor-regulated Smad2/3 and the master chondrogenic transcription factor Sry-type HMG box (SOX) 9. However, the precise mechanism of stretch-mediated Smad activation remains unclear in transcriptional regulation of CCN2 and COL2A1. Here we hypothesized that CTS may induce TGF-β1 release and stimulate Smad-dependent chondrogenic gene expression in human chondrocytic SW1353 cells. Uni-axial CTS (0.5Hz, 5% strain) stimulated gene expression of CCN2 and COL2A1 in SW1353 cells, and induced TGF-β1 secretion. CCN2 synthesis and nuclear translocalization of Smad2/3 and SOX9 were stimulated by CTS. In addition, CTS increased the complex formation between phosphorylated Smad2/3 and SOX9. The CCN2 promoter activity was cooperatively enhanced by CTS and Smad3 in luciferase reporter assay. Chromatin immunoprecipitation revealed that CTS increased Smad2/3 interaction with the CCN2 promoter and the COL2A1 enhancer. Our results suggest that CTS epigenetically stimulates CCN2 transcription via TGF-β1 release associated with Smad2/3 activation and enhances COL2A1 expression through the complex formation between SOX9 and Smad2/3.

Synoviocytes protect cartilage from the effects of injury in vitro

Background

It is well documented that osteoarthritis (OA) can develop following traumatic joint injury and is the leading cause of lameness and subsequent wastage of equine athletes. Although much research of injury induced OA has focused on cartilage, OA is a disease that affects the whole joint organ.

Methods

In this study, we investigated the impact of synovial cells on the progression of an OA phenotype in injured articular cartilage. Injured and control cartilage were cultured in the presence of synoviocytes extracted from normal equine synovium. Synoviocytes and cartilage were evaluated for catabolic and anabolic gene expression. The cartilage was also evaluated histologically for loss of extracellular matrix molecules, chondrocyte cell death and chondrocyte cluster formation.

Results

The results indicate synoviocytes exert both positive and negative effects on injured cartilage, but ultimately protect injured cartilage from progressing toward an OA phenotype. Synoviocytes cultured in the presence of injured cartilage had significantly reduced expression of aggrecanase 1 and 2 (ADAMTS4 and 5), but also had increased expression of matrix metalloproteinase (MMP) -1 and reduced expression of tissue inhibitor of metalloproteinases 1 (TIMP-1). Injured cartilage cultured with synoviocytes had increased expression of both collagen type 2 and aggrecanase 2. Histologic examination of cartilage indicated that there was a protective effect of synoviocytes on injured cartilage by reducing the incidence of both focal cell loss and chondrocyte cluster formation, two major hallmarks of OA.

Conclusions

These results support the importance of evaluating more than one synovial joint tissue when investigating injury induced OA.

Transport of anti-IL-6 antigen binding fragments into cartilage and the effects of injury

The efficacy of biological therapeutics against cartilage degradation in osteoarthritis is restricted by the limited transport of macromolecules through the dense, avascular extracellular matrix. The availability of biologics to cell surface and matrix targets is limited by steric hindrance of the matrix, and the microstructure of matrix itself can be dramatically altered by joint injury and the subsequent inflammatory response. We studied the transport into cartilage of a 48 kDa anti-IL-6 antigen binding fragment (Fab) using an in vitro model of joint injury to quantify the transport of Fab fragments into normal and mechanically injured cartilage. The anti-IL-6 Fab was able to diffuse throughout the depth of the tissue, suggesting that Fab fragments can have the desired property of achieving local delivery to targets within cartilage, unlike full-sized antibodies which are too large to penetrate beyond the cartilage surface. Uptake of the anti-IL-6 Fab was significantly increased following mechanical injury, and an additional increase in uptake was observed in response to combined treatment with TNFα and mechanical injury, a model used to mimic the inflammatory response following joint injury. These results suggest that joint trauma leading to cartilage degradation can further alter the transport of such therapeutics and similar-sized macromolecules.

Response of mature meniscal tissue to a single injurious compression and interleukin-1 in vitro

OBJECTIVE

To study mechanical overload of mature meniscal tissue under normal and pro-inflammatory conditions in vitro.

METHOD

Three days after a single unconfined compression (strain: 25-75%, strain rate 1/s) of meniscal explants from 16 to 24 months-old cattle combined with interleukin-1-treatment (IL-1, 10 ng/ml) release of glycosaminoglycans (GAGs; dimethylmethylene blue (DMMB) assay), lactate dehydrogenase (LDH; cytotoxicity detection kit), and nitric oxide (NO; Griess assay), as well as gene transcription (quantitative reverse transcription polymerase chain reaction (RT-PCR)) and numbers of cells with condensed nuclei (CN; histomorphometry) were determined.

RESULTS

Mean peak stresses during compression were about five (25%), 11 (50%), and 30 MPa (75%), respectively. GAG and LDH release and numbers of CN increased whereas NO production and mRNA levels of matrix metalloproteinase (MMP)-2, -3 and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 decreased strain-dependently after compression. IL-1 induced an increase in GAG and NO release as well as MMP-2, -3 and ADAMTS-4 levels, but had no impact on the LDH release and slightly increased numbers of CN. However, in combination with compression the tissue responses were reduced and LDH and CN levels were increased compared to IL-1 alone.

CONCLUSION

Our data suggest that a single impact compression induces cell damage and release of GAG and reduces the NO production and transcription of certain matrix-degrading enzymes. It also reduces the capacity of meniscal tissue to respond to IL-1, which might be related to the cell damage and suggests that the compression-related GAG release might rather be the result of immediate extracellular matrix-damage than a cell-mediated event. This, however, needs to be confirmed in future studies.

Single impact cartilage trauma and TNF-α: interactive effects do not increase early cell death and indicate the need for bi-/multidirectional therapeutic approaches

Blunt trauma of articular cartilage, often resulting from accidents or sports injuries, is associated with local inflammatory reactions and represents a major risk factor for development of post-traumatic osteoarthritis. TNF-α is increased in synovial fluid early after trauma, potentiates injury-induced proteoglycan degradation and may act proapoptotic under permissive conditions. We asked whether TNF-α also influences chondrocyte death, gene expression of catabolic and anabolic markers and the release of proinflammatory mediators in the early post-traumatic phase. Interactive effects of a defined single impact trauma (0.59 J) and TNF-α (100 ng/ml) on human early-stage osteoarthritic cartilage were investigated in vitro over 24 h. Exposure of traumatized cartilage to TNF-α did not increase chondrocyte death. IL-6-synthesis was augmented by trauma, TNF-α and combined treatment. The impact increased the release of PGE2 and PGD2 in the presence and absence of TNF-α to a similar extent while TNF-α alone showed no effect. In contrast, NOS2A-expression and nitric oxide (NO)-release were not affected by trauma but significantly increased by TNF-α. Expression of OPG and RANKL was not affected by TNF-α but modulated by trauma. TNF-α with and without trauma significantly induced MMP1 gene expression. These results indicate that TNF-α does not potentiate early cell death in early-stage osteoarthritic cartilage after blunt injury. However, trauma and TNF-α showed independent and interactive effects concerning prostaglandin and NO release. TNF-α probably contributes to cartilage degradation after trauma by an early induction of MMP1 gene expression. Our study confirms that an anti-TNF-α therapy may have inhibitory effects on catabolic and, partly, on inflammatory processes after a single impact trauma. As TNF-α does not contribute to the loss of chondrocytes in the initial post-traumatic phase, a combination with pharmaco-therapeutic strategies reducing early cell death could be reasonable.

Cannabinoids: novel therapies for arthritis?

A key feature of osteoarthritis and rheumatoid arthritis is the loss of articular cartilage. Cartilage breakdown is mediated by complex interactions of proinflammatory cytokines, such as IL-1, inflammatory mediators, including nitric oxide and prostaglandin E2, and proteases, including matrix metalloproteinases and aggrecanases, such as ADAMTS-4 and -5. Cannabinoids have been shown to reduce joint damage in animal models of arthritis. They have also been shown to prevent IL-1-induced matrix breakdown of collagen and proteoglycan, indicating that cannabinoids may mediate chondroprotective effects. Cannabinoids produce their effects via several cannabinoid receptors and it is important to identify the key cannabinoids and their receptors that are involved in chondroprotection. This review aims to outline the current and future prospects of cannabinoids as anti-arthritic therapeutics, in terms of their ability to prevent cartilage breakdown.

Repeated measurement of mechanical properties in viable osteochondral explants following a single blunt impact injury

The objective of this work was to develop a method for repeated same-site measurement of mechanical properties suitable for the detection of degenerative changes in a biologically active explant model after a single blunt impact injury. Focal blunt impact injuries to articular surfaces lead to local cartilage degeneration and loss of mechanical properties. We employed a repeated measurement methodology to determine variations in mechanical same-site properties before and after injury in living cartilage, with the hypothesis that normalization with initial mechanical properties may provide a clearer evaluation of impact effects and improve our understanding of the biologic responses to impact injury. Bovine osteochondral explants were cultured for up to 14 days after impact injury. Indentation tests were performed before and after impact injury to assess relative changes in mechanical properties. Creep strain increased significantly in impacted explants after 7 days and in both impacted and control explants after 14 days. Further analysis at 14 days revealed decreases in stretch factor beta, creep time constant and local compressive modulus. A repeated measures methodology reliably detected changes in the mechanical behaviour of viable osteochondral explants after a single impact injury.

Effects of Wnt3A and mechanical load on cartilage chondrocyte homeostasis

Introduction

Articular cartilage functions in withstanding mechanical loads and provides a lubricating surface for frictionless movement of joints. Osteoarthritis, characterised by cartilage degeneration, develops due to the progressive erosion of structural integrity and eventual loss of functional performance. Osteoarthritis is a multi-factorial disorder; two important risk factors are abnormal mechanical load and genetic predisposition. A single nucleotide polymorphism analysis demonstrated an association of hip osteoarthritis with an Arg324Gly substitution mutation in FrzB, a Wnt antagonist. The purpose of this study was two-fold: to assess whether mechanical stimulation modulates β-catenin signalling and catabolic gene expression in articular chondrocytes, and further to investigate whether there is an interplay of mechanical load and Wnt signalling in mediating a catabolic response.

Methods

Chondrocytes were pre-stimulated with recombinant Wnt3A for 24 hours prior to the application of tensile strain (7.5%, 1 Hz) for 30 minutes. Activation of Wnt signalling, via β-catenin nuclear translocation and downstream effects including the transcriptional activation of c-jun, c-fos and Lef1, markers of chondrocyte phenotype (type II collagen (col2a1), aggrecan (acan), SOX9) and catabolic genes (MMP3, MMP13, ADAMTS-4, ADAMTS-5) were assessed.

Results

Physiological tensile strain induced col2a1, acan and SOX9 transcription. Load-induced acan and SOX9 expression were repressed in the presence of Wnt3A. Load induced partial β-catenin nuclear translocation; there was an additive effect of load and Wnt3A on β-catenin distribution, with both extensive localisation in the nucleus and cytoplasm. Immediate early response (c-jun) and catabolic genes (MMP3, ADAMTS-4) were up-regulated in Wnt3A stimulated chondrocytes. With load and Wnt3A there was an additive up-regulation of c-fos, MMP3 and ADAMTS-4 transcription, whereas there was a synergistic interplay on c-jun, Lef1 and ADAMTS-5 transcription.

Conclusion

Our data suggest that load and Wnt, in combination, can repress transcription of chondrocyte matrix genes, whilst enhancing expression of catabolic mediators. Future studies will investigate the respective roles of abnormal loading and genetic predisposition in mediating cartilage degeneration.

Mechanical injury suppresses autophagy regulators and pharmacologic activation of autophagy results in chondroprotection

OBJECTIVE

Mechanical injury induces cell death in cartilage and triggers a remodeling process that ultimately can manifest as osteoarthritis. Autophagy is a process for turnover of intracellular organelles and macromolecules that protects cells during stress responses. This study was undertaken to determine changes in and functions of autophagy following mechanical injury to cartilage.

METHODS

Bovine and human cartilage explants were subjected to mechanical impact (40% strain for 500 msec). Cell viability, sulfated glycosaminoglycan (sGAG) release, and changes in the levels of the autophagy markers ULK1, beclin 1, and microtubule-associated protein 1 light chain 3 (LC3) were evaluated. Cartilage explants were treated with the mammalian target of rapamycin complex 1 (mTORC-1) inhibitor and the autophagy inducer rapamycin and tested for protective effects against mechanical injury. Explants were also treated with the cell death inducers nitric oxide and tumor necrosis factor α (TNFα) plus actinomycin D, and the proinflammatory cytokine interleukin-1α (IL-1α).

RESULTS

Mechanical injury induced cell death and loss of sGAG in a time-dependent manner. This was associated with significantly decreased ULK1, beclin 1, and LC3 expression in the cartilage superficial zone (P < 0.05) 48 hours after injury. The levels of LC3-II were increased 24 hours after injury but decreased at 48 and 96 hours. Rapamycin enhanced expression of autophagy regulators and prevented cell death and sGAG loss in mechanically injured explants. Rapamycin also protected against cell death induced by sodium nitroprusside and TNFα plus actinomycin D and prevented sGAG loss induced by IL-1α.

CONCLUSION

Our findings indicate that mechanical injury leads to suppression of autophagy, predominantly in the superficial zone where most of the cell death occurs. Pharmacologic inhibition of mTORC-1, at least in part by enhancement of autophagy, prevents cell and matrix damage, suggesting a novel approach for chondroprotection.

Effects of short-term glucocorticoid treatment on changes in cartilage matrix degradation and chondrocyte gene expression induced by mechanical injury and inflammatory cytokines

Introduction

Traumatic joint injury damages cartilage and causes adjacent joint tissues to release inflammatory cytokines, increasing the risk of developing osteoarthritis. The main objective of this study was to determine whether the combined catabolic effects of mechanical injury, tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6)/soluble IL-6 receptor (sIL-6R) on cartilage could be abolished by short-term treatment with glucocorticoids such as dexamethasone.

Methods

In an initial dexamethasone-dose-response study, bovine cartilage explants were treated with TNFα and increasing concentrations of dexamethasone. Bovine and human cartilage explants were then subjected to individual and combined treatments with TNFα, IL-6/sIL-6R and injury in the presence or absence of dexamethasone. Treatment effects were assessed by measuring glycosaminoglycans (GAG) release to the medium and synthesis of proteoglycans. Additional experiments tested whether pre-exposure of cartilage to dexamethasone could prevent GAG loss and inhibition of biosynthesis induced by cytokines, and whether post-treatment with dexamethasone could diminish the effects of pre-established cytokine insult. Messenger ribonucleic acid (mRNA) levels for genes involved in cartilage homeostasis (proteases, matrix molecules, cytokines, growth and transcription factors) were measured in explants subjected to combined treatments with injury, TNFα and dexamethasone. To investigate mechanisms associated with dexamethasone regulation of chondrocyte metabolic response, glucocorticoid receptor (GR) antagonist (RU486) and proprotein convertase inhibitor (RVKR-CMK) were used.

Results

Dexamethasone dose-dependently inhibited GAG loss and the reduction in biosynthesis caused by TNFα. The combination of mechanical injury, TNFα and IL-6/sIL-6R caused the most severe GAG loss; dexamethasone reduced this GAG loss to control levels in bovine and human cartilage. Additionally, dexamethasone pre-treatment or post-treatment of bovine explants lowered GAG loss and increased proteoglycan synthesis in cartilage explants exposed to TNFα. Dexamethasone did not down-regulate aggrecanase mRNA levels. Post-transcriptional regulation by dexamethasone of other genes associated with responses to injury and cytokines was noted. GR antagonist reversed the effect of dexamethasone on sulfate incorporation. RVKR-CMK significantly reduced GAG loss caused by TNFα + IL-6 + injury.

Conclusions

Short-term glucocorticoid treatment effectively abolished the catabolic effects exerted by the combination of pro-inflammatory cytokines and mechanical injury: dexamethasone prevented proteoglycan degradation and restored biosynthesis. Dexamethasone appears to regulate the catabolic response of chondrocytes post-transcriptionally, since the abundance of transcripts encoding aggrecanases was still elevated in the presence of dexamethasone.

Volumetric stress-strain analysis of optohydrodynamically suspended biological cells

Ongoing investigations are exploring the biomechanical properties of isolated and suspended biological cells in pursuit of understanding single-cell mechanobiology. An optical tweezer with minimal applied laser power has positioned biologic cells at the geometric center of a microfluidic cross-junction, creating a novel optohydrodynamic trap. The resulting fluid flow environment facilitates unique multiaxial loading of single cells with site-specific normal and shear stresses resulting in a physical albeit extensional state. A recent two-dimensional analysis has explored the cytoskeletal strain response due to these fluid-induced stresses [Wilson and Kohles, 2010, "Two-Dimensional Modeling of Nanomechanical Stresses-Strains in Healthy and Diseased Single-Cells During Microfluidic Manipulation," J Nanotechnol Eng Med, 1(2), p. 021005]. Results described a microfluidic environment having controlled nanometer and piconewton resolution. In this present study, computational fluid dynamics combined with multiphysics modeling has further characterized the applied fluid stress environment and the solid cellular strain response in three dimensions to accompany experimental cell stimulation. A volumetric stress-strain analysis was applied to representative living cell biomechanical data. The presented normal and shear stress surface maps will guide future microfluidic experiments as well as provide a framework for characterizing cytoskeletal structure influencing the stress to strain response.

A Distinct Catabolic to Anabolic Threshold Due to Single-Cell Static Nanomechanical Stimulation in a Cartilage Biokinetics Model

Understanding physicochemical interactions during biokinetic regulation will be critical for the creation of relevant nanotechnology supporting cellular and molecular engineering. The impact of nanoscale influences in medicine and biology can be explored in detail through mathematical models as an in silico testbed. In a recent single-cell biomechanical analysis, the cytoskeletal strain response due to fluid-induced stresses was characterized (Wilson, Z. D., and Kohles, S. S., 2010, "Two-Dimensional Modeling of Nanomechanical Strains in Healthy and Diseased Single-Cells During Microfluidic Stress Applications," J. Nanotech. Eng. Med., 1(2), p. 021005). Results described a microfluidic environment having controlled nanometer and piconewton resolution for explorations of multiscale mechanobiology. In the present study, we constructed a mathematical model exploring the nanoscale biomolecular response to that controlled microenvironment. We introduce mechanical stimuli and scaling factor terms as specific input values for regulating a cartilage molecule synthesis. Iterative model results for this initial multiscale static load application have identified a transition threshold load level from which the mechanical input causes a shift from a catabolic state to an anabolic state. Modeled molecule homeostatic levels appear to be dependent upon the mechanical stimulus as reflected experimentally. This work provides a specific mathematical framework from which to explore biokinetic regulation. Further incorporation of nanomechanical stresses and strains into biokinetic models will ultimately lead to refined mechanotransduction relationships at the cellular and molecular levels.

Oxidant conditioning protects cartilage from mechanically induced damage

Articular cartilage degeneration in osteoarthritis has been linked to abnormal mechanical stresses that are known to cause chondrocyte apoptosis and metabolic derangement in in vitro models. Evidence implicating oxidative damage as the immediate cause of these harmful effects suggests that the antioxidant defenses of chondrocytes might influence their tolerance for mechanical injury. Based on evidence that antioxidant defenses in many cell types are stimulated by moderate oxidant exposure, we hypothesized that oxidant preconditioning would reduce acute chondrocyte death and proteoglycan depletion in cartilage explants after exposure to abnormal mechanical stresses. Porcine cartilage explants were treated every 48 h with tert-butyl hydrogen peroxide (tBHP) at nonlethal concentrations (25, 100, 250, and 500 microM) for a varying number of times (one, two, or four) prior to a bout of unconfined axial compression (5 MPa, 1 Hz, 1800 cycles). When compared with untreated controls, tBHP had significant positive effects on post-compression viability, lactate production, and proteoglycan losses. Overall, the most effective regime was 100 microM tBHP applied four times. RNA analysis revealed significant effects of 100 microM tBHP on gene expression. Catalase, hypoxia-inducible factor-1alpha (HIF-1alpha), and glyceraldehyde 6-phosphate dehydrogenase (GAPDH) were significantly increased relative to untreated controls in explants treated four times with 100 microM tBHP, a regime that also resulted in a significant decrease in matrix metalloproteinase-3 (MMP-3) expression. These findings demonstrate that repeated exposure of cartilage to sublethal concentrations of peroxide can moderate the acute effects of mechanical stress, a conclusion supported by evidence of peroxide-induced changes in gene expression that could render chondrocytes more resistant to oxidative damage.

New developments in osteoarthritis. Posttraumatic osteoarthritis: pathogenesis and pharmacological treatment options

Joint trauma can lead to a spectrum of acute lesions, including osteochondral fractures, ligament or meniscus tears and damage to the articular cartilage. This is often associated with intraarticular bleeding and causes posttraumatic joint inflammation. Although the acute symptoms resolve and some of the lesions can be surgically repaired, joint injury triggers a chronic remodeling process in cartilage and other joint tissues that ultimately manifests as osteoarthritis in a majority of cases. The objective of the present review is to summarize information on pathogenetic mechanisms involved in the acute and chronic consequences of joint trauma and discuss potential pharmacological interventions. The focus of the review is on the early events that follow joint trauma since therapies for posttraumatic joint inflammation are not available and this represents a unique window of opportunity to limit chronic consequences.

Joint aging and chondrocyte cell death

Articular cartilage extracellular matrix and cell function change with age and are considered to be the most important factors in the development and progression of osteoarthritis. The multifaceted nature of joint disease indicates that the contribution of cell death can be an important factor at early and late stages of osteoarthritis. Therefore, the pharmacologic inhibition of cell death is likely to be clinically valuable at any stage of the disease. In this article, we will discuss the close association between diverse changes in cartilage aging, how altered conditions influence chondrocyte death, and the implications of preventing cell loss to retard osteoarthritis progression and preserve tissue homeostasis.

Mechanical load inhibits IL-1 induced matrix degradation in articular cartilage

OBJECTIVE

Osteoarthritis is a disease process of cellular degradation of articular cartilage caused by mechanical loads and inflammatory cytokines. We studied the cellular response in native cartilage subjected to a mechanical load administered simultaneously with an inflammatory cytokine interleukin-1 (IL-1), hypothesizing that the combination of load and cytokine would result in accelerated extracellular matrix (ECM) degradation.

METHODS

Mature bovine articular cartilage was loaded for 3 days (stimulation) with 0.2 and 0.5 MPa stresses, with and without IL-1 (IL-1alpha, 10 ng/ml), followed by 3 days of no stimulation (recovery). Aggrecan and collagen loss were measured as well as aggrecan cleavage using monoclonal antibodies AF-28 and BC-3 for cleavage by aggrecanases (ADAMTS) and matrix metalloproteinases (MMPs), respectively.

RESULTS

Incubation with IL-1 caused aggrecan cleavage by aggrecanases and MMPs during the 3 days of stimulation. A load of 0.5 MPa inhibited the IL-1-induced aggrecan loss while no inhibition was found for the 0.2 MPa stress. There was no collagen loss during the treatments but upon load and IL-1 removal proteoglycan and collagen loss increased. Load itself under these conditions was found to have no effect when compared to the unloaded controls.

CONCLUSIONS

A mechanical load of sufficient magnitude can inhibit ECM degradation by chondrocytes when stimulated by IL-1. The molecular mechanisms involved in this process are not clear but probably involve altered mechanochemical signal transduction between the ECM and chondrocyte.

Mechanical injury potentiates proteoglycan catabolism induced by interleukin-6 with soluble interleukin-6 receptor and tumor necrosis factor alpha in immature bovine and adult human articular cartilage

OBJECTIVE

Traumatic joint injury can damage cartilage and release inflammatory cytokines from adjacent joint tissue. The present study was undertaken to study the combined effects of compression injury, tumor necrosis factor alpha (TNFalpha), and interleukin-6 (IL-6) and its soluble receptor (sIL-6R) on immature bovine and adult human knee and ankle cartilage, using an in vitro model, and to test the hypothesis that endogenous IL-6 plays a role in proteoglycan loss caused by a combination of injury and TNFalpha.

METHODS

Injured or uninjured cartilage disks were incubated with or without TNFalpha and/or IL-6/sIL-6R. Additional samples were preincubated with an IL-6-blocking antibody Fab fragment and subjected to injury and TNFalpha treatment. Treatment effects were assessed by histologic analysis, measurement of glycosaminoglycan (GAG) loss, Western blot to determine proteoglycan degradation, zymography, radiolabeling to determine chondrocyte biosynthesis, and Western blot and enzyme-linked immunosorbent assay to determine chondrocyte production of IL-6.

RESULTS

In bovine cartilage samples, injury combined with TNFalpha and IL-6/sIL-6R exposure caused the most severe GAG loss. Findings in human knee and ankle cartilage were strikingly similar to those in bovine samples, although in human ankle tissue, the GAG loss was less severe than that observed in human knee tissue. Without exogenous IL-6/sIL-6R, injury plus TNFalpha exposure up-regulated chondrocyte production of IL-6, but incubation with the IL-6-blocking Fab significantly reduced proteoglycan degradation.

CONCLUSION

Our findings indicate that mechanical injury potentiates the catabolic effects of TNFalpha and IL-6/sIL-6R in causing proteoglycan degradation in human and bovine cartilage. The temporal and spatial evolution of degradation suggests the importance of transport of biomolecules, which may be altered by overload injury. The catabolic effects of injury plus TNFalpha appeared partly due to endogenous IL-6, since GAG loss was partially abrogated by an IL-6-blocking Fab.

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.

Co-culture of mechanically injured cartilage with joint capsule tissue alters chondrocyte expression patterns and increases ADAMTS5 production

We studied changes in chondrocyte gene expression, aggrecan degradation, and aggrecanase production and activity in normal and mechanically injured cartilage co-cultured with joint capsule tissue. Chondrocyte expression of 21 genes was measured at 1, 2, 4, 6, 12, and 24h after treatment; clustering analysis enabled identification of co-expression profiles. Aggrecan fragments retained in cartilage and released to medium and loss of cartilage sGAG were quantified. Increased expression of MMP-13 and ADAMTS4 clustered with effects of co-culture, while increased expression of ADAMTS5, MMP-3, TGF-beta, c-fos, c-jun clustered with cartilage injury. ADAMTS5 protein within cartilage (immunohistochemistry) increased following injury and with co-culture. Cartilage sGAG decreased over 16-days, most severely following injury plus co-culture. Cartilage aggrecan was cleaved at aggrecanase sites in the interglobular and C-terminal domains, resulting in loss of the G3 domain, especially after injury plus co-culture. Together, these results support the hypothesis that interactions between injured cartilage and other joint tissues are important in matrix catabolism after joint injury.

Mechanical compression of articular cartilage induces chondrocyte proliferation and inhibits proteoglycan synthesis by activation of the ERK pathway: implications for tissue engineering and regenerative medicine

Articular cartilage is recalcitrant to endogenous repair and regeneration and is thus a focus of tissue engineering and regenerative medicine strategies. A prerequisite for articular cartilage tissue engineering is an understanding of the signal transduction pathways involved in mechanical compression during trauma or disease. We sought to explore the role of the extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway in chondrocyte proliferation and proteoglycan synthesis following acute mechanical compression. Bovine articular cartilage explants were cultured with and without the ERK 1/2 pathway inhibitor PD98059. Cartilage explants were statically loaded to 40% strain at a strain rate of 1/s for 5 s. Control explants were cultured under similar conditions but were not loaded. There were four experimental groups: (a) no load, without inhibitor; (b) no load, with the inhibitor PD98059; (c) loaded, without the inhibitor; and (d) loaded, with the inhibitor PD98059. The explants were cultured for varying durations from 5 min to 5 days and were then analysed by biochemical and immunohistochemical methods. Mechanical compression induced phosphorylation of ERK 1/2, and this was attenuated with the ERK 1/2 pathway inhibitor PD98059 in a dose-dependent manner. Chondrocyte proliferation was increased by mechanical compression. This effect was blocked by the inhibitor of the ERK 1/2 pathway. Mechanical compression also led to a decrease in proteoglycan synthesis that was reversed with inhibitor PD98059. In conclusion, the ERK 1/2 pathway is involved in the proliferative and biosynthetic response of chondrocytes following acute static mechanical compression.

Potent inhibition of cartilage biosynthesis by coincubation with joint capsule through an IL-1-independent pathway

The reason for the increased risk for development of osteoarthritis (OA) after acute joint trauma is not well understood, but the mechanically injured cartilage may be more susceptible to degradative mediators secreted by other tissues in the joint. To establish a model for such interactions, we coincubated bovine cartilage tissue explants together with normal joint capsule and found a profound ( approximately 70%) reduction in cartilage proteoglycan biosynthesis. This reduction is due to release by the joint capsule of a heat-labile and non-toxic factor. Surprisingly, while cultured synovium is a canonical source of interleukin-1 (IL-1), blockade either by soluble IL-1 type II receptor (sIL-1r) or IL-1 receptor antagonist (IL-1RA) had no effect. Combined blockade of IL-1 and tumor necrosis factor alpha (TNF-alpha) also had no effect. To support the clinical relevance of the findings, we harvested joint capsule from post-mortem human knees. Human joint capsule from a normal adult knee also released a substance that caused an approximately 40% decrease in cartilage proteoglycan biosynthesis. Furthermore, this inhibition was not affected by IL-1 blockade with either sIL-1r or IL-1RA. These results suggest that joint capsule tissue from a normal knee joint can release an uncharacterized cytokine that potently inhibits cartilage biosynthetic activity by an IL-1- and TNF-independent pathway.

Modulation of lubricin biosynthesis and tissue surface properties following cartilage mechanical injury

OBJECTIVE

To evaluate the effects of injurious compression on the biosynthesis of lubricin at different depths within articular cartilage and to examine alterations in structure and function of the articular surface following mechanical injury.

METHODS

Bovine cartilage explants were subdivided into level 1, with intact articular surface, and level 2, containing middle and deep zone cartilage. Following mechanical injury, lubricin messenger RNA (mRNA) levels were monitored by quantitative reverse transcriptase-polymerase chain reaction, and soluble or cartilage-associated lubricin protein was analyzed by Western blotting and immunohistochemistry. Cartilage morphology was assessed by histologic staining, and tissue functionality was assessed by friction testing.

RESULTS

Two days after injury, lubricin mRNA expression was up-regulated approximately 3-fold for level 1 explants and was down-regulated for level 2 explants. Lubricin expression in level 1 cartilage returned to control levels after 6 days in culture. Similarly, lubricin protein synthesis and secretion increased in response to injury for level 1 explants and decreased for level 2 cartilage. Histologic staining revealed changes in the articular surface of level 1 explants following injury, with respect to glycosaminoglycan and collagen content. Injured level 1 explants displayed an increased coefficient of friction relative to controls.

CONCLUSION

Our findings indicate that increased lubricin biosynthesis appears to be an early transient response of surface-layer cartilage to injurious compression. However, distinct morphologic changes occur with injury that appear to compromise the frictional properties of the tissue.

Mechanical injury and cytokines cause loss of cartilage integrity and upregulate proteins associated with catabolism, immunity, inflammation, and repair

The objectives of this study were to perform a quantitative comparison of proteins released from cartilage explants in response to treatment with IL-1beta, TNF-alpha, or mechanical compression injury in vitro and to interpret this release in the context of anabolic-catabolic shifts known to occur in cartilage in response to these insults in vitro and their implications in vivo. Bovine calf cartilage explants from 6-12 animals were subjected to injurious compression, TNF-alpha (100 ng/ml), IL-1beta (10 ng/ml), or no treatment and cultured for 5 days in equal volumes of medium. The pooled medium from each of these four conditions was labeled with one of four iTRAQ labels and subjected to nano-2D-LC/MS/MS on a quadrupole time-of-flight instrument. Data were analysed by ProQuant for peptide identification and quantitation. k-means clustering and biological pathways analysis were used to identify proteins that may correlate with known cartilage phenotypic responses to such treatments. IL-1beta and TNF-alpha treatment caused a decrease in the synthesis of collagen subunits (p < 0.05) as well as increased release of aggrecan G2 and G3 domains to the medium (p < 0.05). MMP-1, MMP-3, MMP-9, and MMP-13 were significantly increased by all treatments compared with untreated samples (p < 0.10). Increased release of proteins involved in innate immunity and immune cell recruitment were noted following IL-1beta and TNF-alpha treatment, whereas increased release of intracellular proteins was seen most dramatically with mechanical compression injury. Proteins involved in insulin-like growth factor and TGF-beta superfamily pathway modulation showed changes in pro-anabolic pathways that may represent early repair signals. At the systems level, two principal components were sufficient to describe 97% of the covariance in the data. A strong correlation was noted between the proteins released in response to IL-1beta and TNF-alpha; in contrast, mechanical injury resulted in both similarities and unique differences in the groups of proteins released compared with cytokine treatment.

Interleukin-1 inhibits osmotically induced calcium signaling and volume regulation in articular chondrocytes

OBJECTIVE

Articular chondrocytes respond to osmotic stress with transient changes in cell volume and the intracellular concentration of calcium ion ([Ca(2+)](i)). The goal of this study was to examine the hypothesis that interleukin-1 (IL-1), a pro-inflammatory cytokine associated with osteoarthritis, influences osmotically induced Ca(2+) signaling.

METHODS

Fluorescence ratio imaging was used to measure [Ca(2+)](i) and cell volume in response to hypo- or hyper-osmotic stress in isolated porcine chondrocytes, with or without pre-exposure to 10-ng/ml IL-1alpha. Inhibitors of IL-1 (IL-1 receptor antagonist, IL-1Ra), Ca(2+) mobilization (thapsigargin, an inhibitor of Ca-ATPases), and cytoskeletal remodeling (toxin B, an inhibitor of the Rho family of small GTPases) were used to determine the mechanisms involved in increased [Ca(2+)](i), F-actin remodeling, volume adaptation and active volume recovery.

RESULTS

In response to osmotic stress, chondrocytes exhibited transient increases in [Ca(2+)](i), generally followed by decaying oscillations. Pre-exposure to IL-1 significantly inhibited regulatory volume decrease (RVD) following hypo-osmotic swelling and reduced the change in cell volume and the time to peak [Ca(2+)](i) in response to hyper-osmotic stress, but did not affect the peak magnitudes of [Ca(2+)](i) in those cells that did respond. Co-treatment with IL-1Ra, thapsigargin, or toxin B restored these responses to control levels. The effects were associated with alterations in F-actin organization.

CONCLUSIONS

IL-1 alters the normal volumetric and Ca(2+) signaling response of chondrocytes to osmotic stress through mechanisms involving F-actin remodeling via small Rho GTPases. These findings provide further insights into the mechanisms by which IL-1 may interfere with normal physiologic processes in the chondrocyte, such as the adaptation or regulatory responses to mechanical or osmotic loading.

IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains

OBJECTIVE

Partial meniscectomy is known to cause osteoarthritis (OA) of the underlying cartilage as well as alter the load on the remaining meniscus. Removal of 30-60% of the medial meniscus increases compressive strains from a maximum of approximately 10% to almost 20%. The goal of this study is to determine if meniscal cells produce catabolic molecules in response to the altered loading that results from a partial meniscectomy.

METHOD

Relative changes in gene expression of interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and subsequent changes in the concentration of nitric oxide (NO) released by meniscal tissue in response to compression were measured. Porcine meniscal explants were dynamically compressed for 2 h at 1 Hz to simulate physiological stimulation at either 10% strain or 0.05 MPa stress. Additional explants were pathologically stimulated to either 0% strain, 20% strain or, 0.1 MPa stress.

RESULTS

iNOS and IL-1 gene expression and NO release into the surrounding media were increased at 20% compressive strain compared to other conditions. Pathological unloading (0% compressive strain) of meniscal explants did not significantly change expression of IL-1 or iNOS genes, but did result in an increased amount of NO released compared to physiological strain of 10%.

CONCLUSION

These data suggest that meniscectomies which reduce the surface area of the meniscus by 30-60% will increase the catabolic activity of the meniscus which may contribute to the progression of OA.

Effects of doxycycline on articular cartilage GAG release and mechanical properties following impact

The effects of doxycycline were examined on articular cartilage glycosaminoglycan (GAG) release and biphasic mechanical properties following two levels of impact loading at 1 and 2 weeks post-injury. Further, treatment for two continuous weeks was compared to treatment for only the 1st week of a 2-week culture period. Following impact at two levels, articular cartilage explants were cultured for 1 or 2 weeks with 0, 50, or 100 microM doxycycline. Histology, GAG release to the media, and creep indentation biomechanical properties were examined. The "High" (2.8 J) impact level had gross surface damage, whereas "Low" (1.1 J) impact was indiscernible from non-impacted controls. GAG staining decreased after High impact, but doxycycline did not visibly affect staining. High impact resulted in decreased aggregate moduli at both 1 and 2 weeks and increased permeability at 2 weeks, but tissue mechanical properties were not affected by doxycycline treatment. At 1 week, High impact resulted in more GAG release compared to non-impacted controls. However, following High impact, 100 microM doxycycline reduced cumulative GAG release at 1 and 2 weeks by 30% and 38%, respectively, compared to no treatment. Interestingly, there was no difference in GAG release comparing 2 weeks continuous treatment with 1 week on, 1 week off. These results support the hypothesis that doxycycline can mitigate GAG release from articular cartilage following impact loads. However, doxycycline was unable to prevent the loss of tissue stiffness observed post-impact, presumably due to initial matrix damage resulting solely from mechanical trauma.

Galectin-1 in cartilage: expression, influence on chondrocyte growth and interaction with ECM components

Galectin-1 is a 14 kDa beta-galactoside binding protein, capable of forming lattice-like structures with glycans of cellular glycoconjugates and inducing intracellular signaling. The expression of Galectin-1 in porcine cartilage is described in this work for the first time. Immunocytochemical methods revealed distinct distribution patterns for both articular and growth plate cartilage. In articular cartilage, the highest reactivity for Galectin-1 was found in all chondrocytes at the superficial zone and in most of those at the lower layer of the middle zone. In the growth plate, marked reactivity was seen in chondrocytes at the proliferative zone and reached a maximum level for the column-forming cells at the hypertrophic zone. In addition, different Galectin-1 distribution patterns were observed at the subcellular level. With regards to the metabolic effects of Galectin-1, the results in vitro seem to indicate an inhibitory effect of Galectin-1 on articular chondrocyte anabolism (i.e. inhibition of cell proliferation and anabolic gene expression) and a stimulation of catabolic processes (i.e. induction of matrix degradation and hypertrophy marker expression). These data represent a starting point for the understanding the molecular mechanisms underlining ECM-Galectin-1 interaction and the subsequent signaling-cell transduction processes involving cartilage formation and maturation.

A sodium dodecyl sulfate-polyacrylamide gel electrophoresis-liquid chromatography tandem mass spectrometry analysis of bovine cartilage tissue response to mechanical compression injury and the inflammatory cytokines tumor necrosis factor alpha and interleukin-1beta

OBJECTIVE

To compare the response of chondrocytes and cartilage matrix to injurious mechanical compression and treatment with interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha), by characterizing proteins lost to the medium from cartilage explant culture.

METHODS

Cartilage explants from young bovine stifle joints were treated with 10 ng/ml of IL-1beta or 100 ng/ml of TNFalpha or were subjected to uniaxial, radially-unconfined injurious compression (50% strain; 100%/second strain rate) and were then cultured for 5 days. Pooled media were subjected to gel-based separation (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and analysis by liquid chromatography tandem mass spectrometry, and the data were analyzed by Spectrum Mill proteomics software, focusing on protein identification, expression levels, and matrix protein proteolysis.

RESULTS

More than 250 proteins were detected, including extracellular matrix (ECM) structural proteins, pericellular matrix proteins important in cell-cell interactions, and novel cartilage proteins CD109, platelet-derived growth factor receptor-like, angiopoietin-like 7, and adipocyte enhancer binding protein 1. IL-1beta and TNFalpha caused increased release of chitinase 3-like protein 1 (CHI3L1), CHI3L2, complement factor B, matrix metalloproteinase 3, ECM-1, haptoglobin, serum amyloid A3, and clusterin. Injurious compression caused the release of intracellular proteins, including Grp58, Grp78, alpha4-actinin, pyruvate kinase, and vimentin. Injurious compression also caused increased release and evidence of proteolysis of type VI collagen subunits, cartilage oligomeric matrix protein, and fibronectin.

CONCLUSION

Overload compression injury caused a loss of cartilage integrity, including matrix damage and cell membrane disruption, which likely occurred through strain-induced mechanical disruption of cells and matrix. IL-1beta and TNFalpha caused the release of proteins associated with an innate immune and stress response by the chondrocytes, which may play a role in host defense against pathogens or may protect cells against stress-induced damage.

Temporal effects of impact on articular cartilage cell death, gene expression, matrix biochemistry, and biomechanics

Articular cartilage injury can cause post-traumatic osteoarthritis, but early processes leading to the disease are not well understood. The objective of this study was to characterize two levels of impact loading at 24 h, 1 week, and 4 weeks in terms of cell death, gene expression, extracellular matrix biochemistry, and tissue biomechanical properties. The data show cell death increased and tissue stiffness decreased by 24 h following High impact (2.8 J). These degradative changes persisted at 1 and 4 weeks, and were further accompanied by measurable changes in ECM biochemistry. Moreover, following High impact at 24 h there were specific changes in gene expression that distinguished injured tissue from adjacent tissue that was not loaded. In contrast, Low impact (1.1 J) showed little change from control specimens at 24 h or 1 week. However, at 4 weeks, a significant increase in cell death and significant decrease in tissue stiffness were present. The constellation of findings indicates Low impacted tissue exhibited a delayed biological response. The study characterizes a model system for examining the biology of articular cartilage post-impact, as well as identifies possible time points and success criteria to be used in future studies employing intervention agents.

Comparison of marker gene expression in chondrocytes from patients receiving autologous chondrocyte transplantation versus osteoarthritis patients

Currently, autologous chondrocyte transplantation (ACT) is used to treat traumatic cartilage damage or osteochondrosis dissecans, but not degenerative arthritis. Since substantial refinements in the isolation, expansion and transplantation of chondrocytes have been made in recent years, the treatment of early stage osteoarthritic lesions using ACT might now be feasible. In this study, we determined the gene expression patterns of osteoarthritic (OA) chondrocytes ex vivo after primary culture and subculture and compared these with healthy chondrocytes ex vivo and with articular chondrocytes expanded for treatment of patients by ACT. Gene expression profiles were determined using quantitative RT-PCR for type I, II and X collagen, aggrecan, IL-1β and activin-like kinase-1. Furthermore, we tested the capability of osteoarthritic chondrocytes to generate hyaline-like cartilage by implanting chondrocyte-seeded collagen scaffolds into immunodeficient (SCID) mice. OA chondrocytes ex vivo showed highly elevated levels of IL-1β mRNA, but type I and II collagen levels were comparable to those of healthy chondrocytes. After primary culture, IL-1β levels decreased to baseline levels, while the type II and type I collagen mRNA levels matched those found in chondrocytes used for ACT. OA chondrocytes generated type II collagen and proteoglycan-rich cartilage transplants in SCID mice. We conclude that after expansion under suitable conditions, the cartilage of OA patients contains cells that are not significantly different from those from healthy donors prepared for ACT. OA chondrocytes are also capable of producing a cartilage-like tissue in the in vivo SCID mouse model. Thus, such chondrocytes seem to fulfil the prerequisites for use in ACT treatment.

The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis

The objectives of this study are to review the long-term consequences of injuries to the anterior cruciate ligament and menisci, the pathogenic mechanisms, and the causes of the considerable variability in outcome. Injuries of the anterior cruciate ligament and menisci are common in both athletes and the general population. At 10 to 20 years after the diagnosis, on average, 50% of those with a diagnosed anterior cruciate ligament or meniscus tear have osteoarthritis with associated pain and functional impairment: the young patient with an old knee. These individuals make up a substantial proportion of the overall osteoarthritis population. There is a lack of evidence to support a protective role of repair or reconstructive surgery of the anterior cruciate ligament or meniscus against osteoarthritis development. A consistent finding in a review of the literature is the often poor reporting of critical study variables, precluding data pooling or a meta-analysis. Osteoarthritis development in the injured joints is caused by intra-articular pathogenic processes initiated at the time of injury, combined with long-term changes in dynamic joint loading. Variation in outcome is reinforced by additional variables associated with the individual such as age, sex, genetics, obesity, muscle strength, activity, and reinjury. A better understanding of these variables may improve future prevention and treatment strategies. In evaluating medical treatment, we now expect large randomized clinical trials complemented by postmarketing monitoring. We should strive toward a comparable level of quality of evidence in surgical treatment of knee injuries. In instances in which a randomized clinical trial is not feasible, natural history and other observational cohort studies need to be as carefully designed and reported as the classic randomized clinical trial, to yield useful information.

Analysis of cartilage matrix fixed charge density and three-dimensional morphology via contrast-enhanced microcomputed tomography

Small animal models of osteoarthritis are often used for evaluating the efficacy of pharmacologic treatments and cartilage repair strategies, but noninvasive techniques capable of monitoring matrix-level changes are limited by the joint size and the low radiopacity of soft tissues. Here we present a technique for the noninvasive imaging of cartilage at micrometer-level resolution based on detecting the equilibrium partitioning of an ionic contrast agent via microcomputed tomography. The approach exploits electrochemical interactions between the molecular charges present in the cartilage matrix and an ionic contrast agent, resulting in a nonuniform equilibrium partitioning of the ionic contrast agent reflecting the proteoglycan distribution. In an in vitro model of cartilage degeneration we observed changes in x-ray attenuation magnitude and distribution consistent with biochemical and histological analyses of sulfated glycosaminoglycans, and x-ray attenuation was found to be a strong predictor of sulfated glycosaminoglycan density. Equilibration with the contrast agent also permits direct in situ visualization and quantification of cartilage surface morphology. Equilibrium partitioning of an ionic contrast agent via microcomputed tomography thus provides a powerful approach to quantitatively assess 3D cartilage composition and morphology for studies of cartilage degradation and repair.

Cellular events leading to chondrocyte death after cartilage impact injury

OBJECTIVE

We undertook this study to test our postulate that leukocytes extend the zone of injury in cartilage after acute mechanical trauma.

METHODS

Fresh cadaveric canine femoral condyles were subjected to 20-25-MPa impact injury. Condyle explants or dispersed chondrocytes were cultured with autologous blood mononuclear leukocytes (MNLs). Viability of chondrocytes at varying distances from the impact site was assessed by trypan blue exclusion.

RESULTS

Mechanical injury caused a significant loss of viable chondrocytes over 7 days, even in cartilage >10 mm from the impact site. After biomechanical stress, death of cells within 10 mm of the impact could be largely prevented by addition of N(G)-monomethyl-L-arginine to inhibit nitric oxide (NO) generation. Chondrocytes within 10 mm of the impact were also susceptible to killing by living MNLs, but not by incubation with the supernatants of endotoxin-activated MNLs. Chondrocytes in this vulnerable zone expressed intercellular adhesion molecule 1 (ICAM-1) (CD54), facilitating attachment of MNLs that localized adjacent to the chondrocytes. Leukocytes killed dispersed chondrocytes harvested from the impact zone by generation of reactive oxygen species. Leukocyte-mediated killing could be blocked by desferoxamine or by antibodies to CD18, which prevent attachment of leukocytes to ICAM-1-expressing chondrocytes.

CONCLUSION

Our data suggest that after mechanical injury, chondrocytes distant from the site may be killed through the generation of NO. Inflammatory leukocytes further extend the zone of chondrocyte death by adhering to chondrocytes expressing ICAM-1 and by inducing the accumulation of free oxygen radicals in the chondrocyte cytoplasm. Patients may benefit from therapies that reduce infiltration of inflammatory leukocytes into acutely injured cartilage.

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.

Current concepts and techniques in posttraumatic arthritis

Posttraumatic arthrosis is a commonly encountered clinical problem, but the pathoetiology of its development is not yet clarified. Many contributing mechanical biologic factors interplay with the traumatic event that necessarily precedes the posttraumatic syndrome. New biologic concepts involving the ability of the cartilage to repair and how such healing can be promoted are being realized in new modalities of treatment. The traumatic event as such and the resulting pathomechanical consequences require new ways of evaluation.