Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Changes in the integrins expression are related with the osteoarthritis severity in an experimental animal model in rats

We identify changes in the expression and localization of α5, α4, and α2 integrins during osteoarthritis (OA) pathogenesis in a rat experimental model. The changes were concomitant with variations in the extracellular matrix (ECM) content and the increase of metalloproteinases (MMPs) activity during OA pathogenesis, which were analyzed by immunofluorescence and Western blot assays. Our results showed an increased expression of α5 and α2 integrins at OA late stages, which was co-related with changes in the ECM content, as a consequence of the MMPs activity. In addition, this is the first report that has shown the presence of α4 integrin since OA early stages, which was co-related with the loss of proteoglycans and clusters formation. However, at late OA stages, the increased expression of α4 integrin in the middle and deep zones of the cartilage was also co-related with the abnormal endochondral ossification of the cartilage through its interaction with osteopontin. Finally, we conclude that ECM-chondrocytes interaction through specific cell receptors is essential to maintain the cartilage homeostasis. However, due to integrins cell signaling is ligand-dependent; changes in the ECM contents could induce activation of either anabolic or catabolic processes, which limits the reparative capacity of chondrocytes, favoring OA severity.

COMP does not directly modify the expression of genes involved in cartilage homeostasis in contrast to several other cartilage matrix proteins

OBJECTIVE

We investigated whether COMP may modify cartilage metabolism and play a role as an endogenous disease aggravating factor in OA.

MATERIALS AND METHODS

Full-length and momomeric COMP was recombinantly expressed in human embryonic kidney cells and purified it via affinity chromatography. Purified COMP was used to stimulate either primary human chondrocytes or cartilage explants. Changes in the expression profiles of inflammatory genes, differentiation markers and growth factors were examined by immunoassay and by quantitative real-time reverse-transcription polymerase chain reaction.

RESULTS

Incubation of primary human chondrocytes or cartilage explants in the presence of COMP did not induce statistically significant changes in the expression of IL-6, MMP1, MMP13, collagen I, collagen II, collagen X, TGF-β1 and BMP-2.

CONCLUSIONS

In contrast to collagen II and matrilin-3, COMP lacks the ability to trigger a proinflammatory response in chondrocytes, although it carries an RGD motif and can bind to integrins. COMP is a well-accepted biomarker for osteoarthritis but increased COMP levels do not necessarily correlate with inflammation.

Regulation of the innate immune response by fibronectin: synergism between the III-1 and EDA domains

Fibronectin is a critical component of the extracellular matrix and alterations to its structure will influence cellular behavior. Matrix fibronectin is subjected to both mechanical and biochemical regulation. The Type III domains of fibronectin can be unfolded in response to increased cellular contractility, included or excluded from the molecule by alternative splicing mechanisms, or released from the matrix by proteolysis. Using Inflammatory Cytokine microarrays we found that the alternatively spliced fibronectin Type III domain, FnEDA, and the partially unfolded III-1 domain, FnIII-1c, induced the expression of a multitude of pro-inflammatory cytokines in human dermal fibroblasts, most notably CXCL1-3, IL-8 and TNF-α. FnIII-1c, a peptide representing an unfolded intermediate structure of the first Type III domain has been shown to initiate the toll-like receptor-4 (TLR4)-NFκB-dependent release of cytokines from human dermal fibroblasts (You, et al., J. Biol. Chem., 2010). Here we demonstrate that FnIII-1c and the alternatively spliced FnEDA domain induce a TLR4 dependent activation of p38 MAP kinase and its downstream effector, MAPKAP Kinase-2 (MK-2), to regulate cytokine expression in fibroblasts. RT-qPCR analysis indicated that the p38-MK-2 pathway regulates IL-8 mRNA stability. Interestingly, addition of FnIII-1c and FnEDA synergistically enhanced TLR4-dependent IL-8 release. These data indicate that Fn contains two Type III domains which can activate TLR signaling to induce an inflammatory response in fibroblasts. Furthermore, our data identifies the NF-κB and p38/MK2 signaling pathways as transducers of signals initiated in response to structural changes in fibronectin.

Expression and regulation of toll-like receptors (TLRs) in human intervertebral disc cells

PURPOSE

Although inflammatory processes play an essential role in painful intervertebral disc (IVD) degeneration, the underlying regulatory mechanisms are not well understood. This study was designed to investigate the expression, regulation and importance of specific toll-like receptors (TLRs)--which have been shown to play an essential role e.g. in osteoarthritis--during degenerative disc disease.

METHODS

The expression of TLRs in human IVDs was measured in isolated cells as well as in normal or degenerated IVD tissue. The role of IL-1β or TNF-α in regulating TLRs (expression/activation) as well as in regulating activity of down-stream pathways (NF-κB) and expression of inflammation-related genes (IL-6, IL-8, HSP60, HSP70, HMGB1) was analyzed.

RESULTS

Expression of TLR1/2/3/4/5/6/9/10 was detected in isolated human IVD cells, with TLR1/2/4/6 being dependent on the degree of IVD degeneration. Stimulation with IL-1β or TNF-α moderately increased TLR1/TLR4 mRNA expression (TNF-α only), and strongly increased TLR2 mRNA expression (IL-1β/TNF-α), with the latter being confirmed on the protein level. Stimulation with IL-1β, TNF-α or Pam3CSK4 (a TLR2-ligand) stimulated IL-6 and IL-8, which was inhibited by a TLR2 neutralizing antibody for Pam3CSK4; IL-1β and TNF-α caused NF-κB activation. HSP60, HSP70 and HMGB1 did not increase IL-6 or IL-8 and were not regulated by IL-1β/TNF-α.

CONCLUSION

We provide evidence that several TLRs are expressed in human IVD cells, with TLR2 possibly playing the most crucial role. As TLRs mediate catabolic and inflammatory processes, increased levels of TLRs may lead to aggravated disc degeneration, chronic inflammation and pain development. Especially with the identification of more endogenous TLR ligands, targeting these receptors may hold therapeutic promise.

An intron polymorphism of the fibronectin gene is associated with end-stage knee osteoarthritis in a Han Chinese population: two independent case-control studies

Background

Knee osteoarthritis (OA) is a complex disease involving both biomechanical and metabolic factors that alter the tissue homeostasis of articular cartilage and subchondral bone. The catabolic activities of extracellular matrix degradation products, especially fibronectin (FN), have been implicated in mediating cartilage degradation. Chondrocytes express several members of the integrin family which can serve as receptors for FN including integrins α5β1, αvβ3, and αvβ5. The purpose of this study was to determine whether polymorphisms in the FN (FN-1) and integrin genes are markers of susceptibility to, or severity of, knee OA in a Han Chinese population.

Methods

Two independent case–control studies were conducted on 928 patients with knee OA and 693 healthy controls. Ten single nucleotide polymorphisms (SNPs) of FN-1 and the integrin αV gene (ITGAV) were detected using the ABI 7500 real-time PCR system.

Results

The AT heterozygote in FN-1 (rs940739A/T) was found to be significantly associated with knee OA (adjusted OR = 1.44; 95% CI = 1.16–1.80) in both stages of the study. FN-1 rs6725958C/A and ITGAV rs10174098A/G SNPs were only associated with knee OA when both study groups were combined. Stratifying the participants by Kellgren-Lawrence (KL) score identified significant differences in the FN-1 rs6725958C/A and rs940739 A/T genotypes between patients with grade 4 OA and controls. Haplotype analyses revealed that TGA and TAA were associated with a higher risk of OA, and that TAG conferred a lower risk of knee OA in the combined population.

Conclusions

Our study suggests that the FN-1 rs940739A/T polymorphism may be an important risk factor of genetic susceptibility to knee OA in the Han Chinese population.

Homeostatic mechanisms in articular cartilage and role of inflammation in osteoarthritis

Osteoarthritis (OA) is a whole joint disease, in which thinning and disappearance of cartilage is a critical determinant in OA progression. The rupture of cartilage homeostasis whatever its cause (aging, genetic predisposition, trauma or metabolic disorder) induces profound phenotypic modifications of chondrocytes, which then promote the synthesis of a subset of factors that induce cartilage damage and target other joint tissues. Interestingly, among these factors are numerous components of the inflammatory pathways. Chondrocytes produce cytokines, chemokines, alarmins, prostanoids, and adipokines and express numerous cell surface receptors for cytokines and chemokines, as well as Toll-like receptors. These receptors activate intracellular signaling pathways involved in inflammatory and stress responses of chondrocytes in OA joints. This review focuses on mechanisms responsible for the maintenance of cartilage homeostasis and highlights the role of inflammatory processes in OA progression.

Expression of ADAMTs-5 and TIMP-3 in the condylar cartilage of rats induced by experimentally created osteoarthritis

OBJECTIVE

To study the expression of ADAMTs-5 and TIMP-3 in temporomandibular joint osteoarthritis (TMJOA) model rats, to explore and confer the possible effects of ADAMTs-5 and TIMP-3 involved in the degradation of the early stage of OA.

DESIGN

32 SD rats were divided into four groups: 2-week control group (NC1), 2-week OA group (OA1), 4-week control group (NC2) and 4-week OA group (OA2). Each group had 8 rats. Injection of collagenase was used to build up the TMJOA model. HE staining was used to analyze the structural change of condyle cartilage. Western blot and RT-PCR were used to measure the expression of ADAMTs-5 and TIMP-3 in protein and mRNA levels respectively.

RESULTS

HE analysis revealed that no significant changes were observed in NC1, NC2 and OA1 groups, while mild damages appeared in OA2 group. No significant differences were achieved in the expression of ADAMTs-5 in protein levels between NC1 and OA1, but the expression of ADAMTs-5 in 4-week group increased significantly compared to that in the NC2 group. On mRNA level, the expression of ADAMTs-5 in 2-week and 4-week OA groups increased significantly compared to that in the matched control group. Meanwhile, the expression of TIMP-3 decreased significantly, showing a completely different trend.

CONCLUSIONS

The expression of ADAMTs-5 and TIMP-3 changed significantly in the early stage of TMJOA, which indicated that ADAMTs-5 and TIMP-3 may be play an important part in the initial stage of condylar cartilage degradation.

Fibronectin in tissue regeneration: timely disassembly of the scaffold is necessary to complete the build

Tissue injury initiates extracellular matrix molecule expression, including fibronectin production by local cells and fibronectin leakage from plasma. To benefit tissue regeneration, fibronectin promotes opsonization of tissue debris, migration, proliferation, and contraction of cells involved in the healing process, as well as angiogenesis. When regeneration proceeds, the fibronectin matrix is fully degraded. However, in a diseased environment, fibronectin clearance is often disturbed, allowing structural variants to persist and contribute to disease progression and failure of regeneration. Here, we discuss first how fibronectin helps tissue regeneration, with a focus on normal cutaneous wound healing as an example of complete tissue recovery. Then, we continue to argue that, although the fibronectin matrix generated following cartilage and central nervous system white matter (myelin) injury initially benefits regeneration, fibronectin clearance is incomplete in chronic wounds (skin), osteoarthritis (cartilage), and multiple sclerosis (myelin). Fibronectin fragments or aggregates persist, which impair tissue regeneration. The similarities in fibronectin-mediated mechanisms of frustrated regeneration indicate that complete fibronectin clearance is a prerequisite for recovery in any tissue. Also, they provide common targets for developing therapeutic strategies in regenerative medicine.

Absolute quantification of selected proteins in the human osteoarthritic secretome

Osteoarthritis (OA) is characterized by a loss of extracellular matrix which is driven by catabolic cytokines. Proteomic analysis of the OA cartilage secretome enables the global study of secreted proteins. These are an important class of molecules with roles in numerous pathological mechanisms. Although cartilage studies have identified profiles of secreted proteins, quantitative proteomics techniques have been implemented that would enable further biological questions to be addressed. To overcome this limitation, we used the secretome from human OA cartilage explants stimulated with IL-1β and compared proteins released into the media using a label-free LC-MS/MS-based strategy. We employed QconCAT technology to quantify specific proteins using selected reaction monitoring. A total of 252 proteins were identified, nine were differentially expressed by IL-1 β stimulation. Selected protein candidates were quantified in absolute amounts using QconCAT. These findings confirmed a significant reduction in TIMP-1 in the secretome following IL-1β stimulation. Label-free and QconCAT analysis produced equivocal results indicating no effect of cytokine stimulation on aggrecan, cartilage oligomeric matrix protein, fibromodulin, matrix metalloproteinases 1 and 3 or plasminogen release. This study enabled comparative protein profiling and absolute quantification of proteins involved in molecular pathways pertinent to understanding the pathogenesis of OA.

Synovium and the innate inflammatory network in osteoarthritis progression

This review focuses on the recent advancements in the understanding of innate immunity in the pathogenesis of osteoarthritis, particularly with attention to the roles of damage-associated molecular patterns (DAMPs), pattern recognition receptors (PPRs), and complement in synovitis development and cartilage degradation. Endogenous molecular products derived from cellular stress and extracellular matrix disruption can function as DAMPs to induce inflammatory responses and pro-catabolic events in vitro and promote synovitis and cartilage degradation in vivo via PRRs. Some of the DAMPs and PRRs display various capacities in driving synovitis and/or cartilage degradation in different models of animal studies. New findings reveal that the inflammatory complement cascade plays a key in the pathogenesis of OA. Crosstalk between joint tissues such as synovium and cartilage communicated at the cellular level within the innate immune inflammatory network is implicated to play an important role in OA progression. Further studies on how the innate immune inflammatory network impacts the OA disease process at different stages of progression will lead to the development of new therapeutic strategies.

Pain treatment for patients with osteoarthritis and central sensitization

Osteoarthritis is one of the most frequent, disabling, and costly pathologies of modern society. Among the main aims of osteoarthritis management are pain control and functional ability improvement. The exact cause of osteoarthritis pain remains unclear. In addition to the pathological changes in articular structures, changes in central pain processing or central sensitization appear to be involved in osteoarthritis pain. The latter calls for a broader approach to the management of patients with osteoarthritis. Yet, the scientific literature offers scant information addressing the treatment of central sensitization, specifically in patients with osteoarthritis. Interventions such as cognitive-behavioral therapy and neuroscience education potentially target cognitive-emotional sensitization (and descending facilitation), and centrally acting drugs and exercise therapy can improve endogenous analgesia (descending inhibition) in patients with osteoarthritis. Future studies should assess these new treatment avenues.

The potential protective effects of calcitonin involved in coordinating chondrocyte response, extracellular matrix, and subchondral trabecular bone in experimental osteoarthritis

Previous reports indicate a potential role for calcitonin (CT) in the treatment of osteoarthritis (OA). To evaluate this potential therapeutic role, we investigated the effect of CT pretreatment on the activation of mitogen-activated protein kinase (MAPK) signaling and the expression of matrix metalloproteinase-13 (MMP-13) in interleukin-1β (IL-1β)-induced chondrocytes, and further assessed its protective effect in a rat model of anterior cruciate ligament transection (ACLT), using sham-operated and saline-treated controls. Using western blotting in vitro, we found that CT pretreatment inhibited the IL-1β-induced phosphorylation of 38,000-dalton protein (p38) and extracellular regulated protein 1/2 (ERK1/2) and reduced the expression of MMP-13 protein. For the in vivo experiment, 30 male rats were randomly divided into three groups of 10, subjected to bilateral ACLT or sham surgery, and then treated for 12 weeks with subcutaneous injections of CT or normal saline. Histological observations showed that CT treatment reduced the severity of the cartilage lesions stemming from the ACLT surgery and provided a lower Mankin score when compared with that determined for rats in the saline-treated ACLT group. Immunohistochemical staining revealed that CT treatment increased type II collagen expression and decreased MMP-3 and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) expression when compared with the saline-treated group. Subchondral bone analysis indicated that CT treatment inhibited the reduction in bone mineral density observed in the saline-treated ACLT group and reduced the ACLT-induced destruction to the subchondral trabecular microstructure. Our data demonstrate that CT induces its protective effects by reducing the chondrocyte response to inflammatory stimuli, cartilage extracellular matrix degradation, and subchondral trabecular microstructure damages brought on by OA.

Matrilin-3 switches from anti- to pro-anabolic upon integration to the extracellular matrix

The extracellular matrix (ECM) has long been viewed primarily as an organized network of solid-phase ligands for integrin receptors. During degenerative processes, such as osteoarthritis, the ECM undergoes deterioration, resulting in its remodeling and in the release of some of its components. Matrilin-3 (MATN3) is an almost cartilage specific, pericellular protein acting in the assembly of the ECM of chondrocytes. In the past, MATN3 was found required for cartilage homeostasis, but also involved in osteoarthritis-related pro-catabolic functions. Here, to better understand the pathological and physiological functions of MATN3, its concentration as a circulating protein in articular fluids of human osteoarthritic patients was determined and its functions as a recombinant protein produced in human cells were investigated with particular emphasis on the physical state under which it is presented to chondrocytes. MATN3 down-regulated cartilage extracellular matrix (ECM) synthesis and up-regulated catabolism when administered as a soluble protein. When artificially immobilized, however, MATN3 induced chondrocyte adhesion via a α5β1 integrin-dependent mechanism, AKT activation and favored survival and ECM synthesis. Furthermore, MATN3 bound directly to isolated α5β1 integrin in vitro. TGFβ1 stimulation of chondrocytes allowed integration of exogenous MATN3 into their ECM and ECM-integrated MATN3 induced AKT phosphorylation and improved ECM synthesis and accumulation. In conclusion, the integration of MATN3 to the pericellular matrix of chondrocytes critically determines the direction toward which MATN3 regulates cartilage metabolism. These data explain how MATN3 plays either beneficial or detrimental functions in cartilage and highlight the important role played by the physical state of ECM molecules.

Protein modification by deamidation indicates variations in joint extracellular matrix turnover

As extracellular proteins age, they undergo and accumulate nonenzymatic post-translational modifications that cannot be repaired. We hypothesized that these could be used to systemically monitor loss of extracellular matrix due to chronic arthritic diseases such as osteoarthritis (OA). To test this, we predicted sites of deamidation in cartilage oligomeric matrix protein (COMP) and confirmed, by mass spectroscopy, the presence of deamidated (Asp(64)) and native (Asn(64)) COMP epitopes (mean 0.95% deamidated COMP (D-COMP) relative to native COMP) in cartilage. An Asp(64), D-COMP-specific ELISA was developed using a newly created monoclonal antibody 6-1A12. In a joint replacement study, serum D-COMP (p = 0.017), but not total COMP (p = 0.5), declined significantly after replacement demonstrating a joint tissue source for D-COMP. In analyses of 450 participants from the Johnston County Osteoarthritis Project controlled for age, gender, and race, D-COMP was associated with radiographic hip (p < 0.0001) but not knee (p = 0.95) OA severity. In contrast, total COMP was associated with radiographic knee (p < 0.0001) but not hip (p = 0.47) OA severity. D-COMP was higher in soluble proteins extracted from hip cartilage proximal to OA lesions compared with remote from lesions (p = 0.007) or lesional and remote OA knee (p < 0.01) cartilage. Total COMP in cartilage did not vary by joint site or proximity to the lesion. This study demonstrates the presence of D-COMP in articular cartilage and the systemic circulation, and to our knowledge, it is the first biomarker to show specificity for a particular joint site. We believe that enrichment of deamidated epitope in hip OA cartilage indicates a lesser repair response of hip OA compared with knee OA cartilage.

Differential protein profiling of synovial fluid from rheumatoid arthritis and osteoarthritis patients using LC-MALDI TOF/TOF

The purpose of this study was to identify those proteins relatively more abundant in the synovial fluid (SF) of patients suffering from rheumatoid arthritis (RA) and osteoarthritis (OA) using high performance liquid chromatography coupled to mass spectrometry. 20 individual SF samples from each disease were pooled into two groups (RA and OA) to reduce the contribution of extreme individual values. Prior to the proteomic analysis, samples were immunodepleted from the top 20 most abundant plasma proteins, to enrich the lower-abundance protein fractions. Then, they were subjected to protein size fractioning and in-gel digestion, followed by reversed-phase peptide separation in a nano-LC system and subsequent peptide identification by MALDI-TOF/TOF. This strategy led to the identification of 136 different proteins in SF, which is the largest number of SF proteins described up to date by proteomics. A relative quantification of the proteins between RA and OA was carried out by spectral counting analysis. In RA, our results show a greater relative abundance of proteins related to complement activation, inflammation and the immune response, such as the major matrix metalloproteinases and several neutrophil-related proteins. In OA, we detected an increase in proteins involved in the formation and remodeling of the extracellular matrix (ECM), such as fibronectin, kininogen-1, cartilage acidic protein 1 and cartilage oligomeric matrix protein. The results obtained for MMP-1, BGH3, fibronectin and gelsolin were verified by immunoblotting analyses. Some of the novel proteins identified in this work might be relevant not only for increasing knowledge on the etiopathogenesis of RA and OA processes, but also as putative disease biomarkers, as their presence in SF is a prior step to their dilution in serum. This article is part of a Special Issue entitled: Proteomics: The clinical link.

Plasma proteins present in osteoarthritic synovial fluid can stimulate cytokine production via Toll-like receptor 4

Introduction

Osteoarthritis (OA) is a degenerative disease characterized by cartilage breakdown in the synovial joints. The presence of low-grade inflammation in OA joints is receiving increasing attention, with synovitis shown to be present even in the early stages of the disease. How the synovial inflammation arises is unclear, but proteins in the synovial fluid of affected joints could conceivably contribute. We therefore surveyed the proteins present in OA synovial fluid and assessed their immunostimulatory properties.

Methods

We used mass spectrometry to survey the proteins present in the synovial fluid of patients with knee OA. We used a multiplex bead-based immunoassay to measure levels of inflammatory cytokines in serum and synovial fluid from patients with knee OA and from patients with rheumatoid arthritis (RA), as well as in sera from healthy individuals. Significant differences in cytokine levels between groups were determined by significance analysis of microarrays, and relations were determined by unsupervised hierarchic clustering. To assess the immunostimulatory properties of a subset of the identified proteins, we tested the proteins' ability to induce the production of inflammatory cytokines by macrophages. For proteins found to be stimulatory, the macrophage stimulation assays were repeated by using Toll-like receptor 4 (TLR4)-deficient macrophages.

Results

We identified 108 proteins in OA synovial fluid, including plasma proteins, serine protease inhibitors, proteins indicative of cartilage turnover, and proteins involved in inflammation and immunity. Multiplex cytokine analysis revealed that levels of several inflammatory cytokines were significantly higher in OA sera than in normal sera, and levels of inflammatory cytokines in synovial fluid and serum were, as expected, higher in RA samples than in OA samples. As much as 36% of the proteins identified in OA synovial fluid were plasma proteins. Testing a subset of these plasma proteins in macrophage stimulation assays, we found that Gc-globulin, α₁-microglobulin, and α₂-macroglobulin can signal via TLR4 to induce macrophage production of inflammatory cytokines implicated in OA.

Conclusions

Our findings suggest that plasma proteins present in OA synovial fluid, whether through exudation from plasma or production by synovial tissues, could contribute to low-grade inflammation in OA by functioning as so-called damage-associated molecular patterns in the synovial joint.

Regulation of MMP-3 expression and secretion by the chemokine eotaxin-1 in human chondrocytes

BACKGROUND

Osteoarthritis (OA) is characterized by the degradation of articular cartilage, marked by the breakdown of matrix proteins. Studies demonstrated the involvement of chemokines in this process, and some may potentially serve as diagnostic markers and therapeutic targets; however, the underlying signal transductions are not well understood.

METHODS

We investigated the effects of the CC chemokine eotaxin-1 (CCL11) on the matrix metalloproteinase (MMP) expression and secretion in the human chondrocyte cell line SW1353 and primary chondrocytes.

RESULTS

Eotaxin-1 significantly induced MMP-3 mRNA expression in a dose-dependent manner. Inhibitors of extracellular signal-regulated kinase (ERK) and p38 kinase were able to repress eotaxin-1-induced MMP-3 expression. On the contrary, Rp-adenosine-3',5'-cyclic monophosphorothioate (Rp-cAMPs), a competitive cAMP antagonist for cAMP receptors, and H-89, a protein kinase A (PKA) inhibitor, markedly enhanced eotaxin-1-induced MMP-3 expression. These results suggest that MMP-3 expression is specifically mediated by the G protein-coupled eotaxin-1 receptor activities. Interestingly, little amount of MMP-3 protein was detected in the cell lysates of eotaxin-1-treated SW1353 cells, and most of MMP-3 protein was in the culture media. Furthermore we found that the eotaxin-1-dependent MMP-3 protein secretion was regulated by phospholipase C (PLC)-protein kinase C (PKC) cascade and c-Jun N-terminal kinase (JNK)/mitogen-activated protein (MAP) kinase pathways. These data indicate a specific regulation of MMP-3 secretion also by eotaxin-1 receptor activities.

CONCLUSIONS

Eotaxin-1 not only induces MMP-3 gene expression but also promotes MMP-3 protein secretion through G protein-coupled eotaxin-1 receptor activities. Chemokines, such as eotaxin-1, could be a potential candidate in the diagnosis and treatment of arthritis.

Identification of a central role for complement in osteoarthritis

Osteoarthritis, characterized by the breakdown of articular cartilage in synovial joints, has long been viewed as the result of “wear and tear”¹. Although low-grade inflammation is detected in osteoarthritis, its role is unclear^2–4. Here we identify a central role for the inflammatory complement system in the pathogenesis of osteoarthritis. Through proteomic and transcriptomic analyses of synovial fluids and membranes from individuals with osteoarthritis, we find that expression and activation of complement is abnormally high in human osteoarthritic joints. Using mice genetically deficient in C5, C6, or CD59a, we show that complement, and specifically the membrane attack complex (MAC)-mediated arm of complement, is critical to the development of arthritis in three different mouse models of osteoarthritis. Pharmacological modulation of complement in wild-type mice confirmed the results obtained with genetically deficient mice. Expression of inflammatory and degradative molecules was lower in chondrocytes from destabilized joints of C5-deficient mice than C5-sufficient mice, and MAC induced production of these molecules in cultured chondrocytes. Furthermore, MAC co-localized with matrix metalloprotease (MMP)-13 and with activated extracellular signal-regulated kinase (ERK) around chondrocytes in human osteoarthritic cartilage. Our findings indicate that dysregulation of complement in synovial joints plays a critical role in the pathogenesis of osteoarthritis.

Fibronectin III 13-14 domains induce joint damage via Toll-like receptor 4 activation and synergize with interleukin-1 and tumour necrosis factor

Cartilage loss is a feature of chronic arthritis. It results from degradation of the extracellular matrix which is composed predominantly of aggrecan and type II collagen. Extracellular matrix degradation is mediated by aggrecanases and matrix metalloproteinases (MMPs). Recently, a number of endogenous matrix molecules, including fibronectin (FN), have been implicated in mediating cartilage degradation. We were interested in studying the C-terminal heparin-binding region of FN since it mediates aggrecan and type II collagen breakdown in cartilage, but the specific FN domains responsible for proteolytic enzyme activity and their receptors in cartilage are unknown. In this study, the ability of recombinant FN domains to induce cartilage breakdown was tested. We found that the FN III 13-14 domains in the C-terminal heparin-binding region of FN are potent inducers of aggrecanase activity in articular cartilage. In murine studies, the FN III 13-14-induced aggrecanase activity was inhibited in Toll-like receptor 4 (TLR4) knockout mice but not wild-type mice. FN III 13-14 domains also synergized with the known catabolic cytokines interleukin-1α and tumour necrosis factor and induced secretion of MMP-1, MMP-3, gp38 and serum amyloid-like protein A in chondrocytes. Our studies provide a mechanistic link between the innate immune receptor TLR4 and sterile arthritis induced by the FN III 13-14 domains of the endogenous matrix molecule FN.

Association analysis of polymorphisms in lumican gene and systemic lupus erythematosus in a Taiwan Chinese Han population

OBJECTIVE

Lumican (LUM) is predominantly localized in areas of pathological fibrosis. To determine whether polymorphisms in LUM gene are associated with development of systemic lupus erythematosus (SLE), we analyzed 2 single-nucleotide polymorphisms (SNP) of LUM in a Taiwan Chinese Han population.

METHODS

Participants included 168 patients with SLE and 192 age-matched controls in whom examinations had excluded SLE. Genotyping of -628 A/-(rs17018757) and c.1567 T/C polymorphisms in LUM were carried out in each patient and control using the polymerase chain reaction-restriction fragment-length polymorphism method, and validated by Taqman SNP genotyping assay. Data were correlated with the development of SLE and various clinical symptoms by chi-square analysis.

RESULTS

Frequencies of C/C genotype and the C allele at c.1567 T/C were significantly higher in patients than controls. Polymorphism at c.1567 C/T was found to be associated with arthritis and photosensitivity in patients with SLE, which are both connective tissue-related symptoms.

CONCLUSION

The c.1567 T/C polymorphism of LUM is related to the development and clinical symptoms of SLE.

Tenascin-C fragments are endogenous inducers of cartilage matrix degradation

Cartilage destruction is a hallmark of osteoarthritis (OA) and is characterized by increased protease activity resulting in the degradation of critical extracellular matrix (ECM) proteins essential for maintaining cartilage integrity. Tenascin-C (TN-C) is an ECM glycoprotein, and its expression is upregulated in OA cartilage. We aimed to investigate the presence of TN-C fragments in arthritic cartilage and establish whether they promote cartilage degradation. Expression of TN-C and its fragments was evaluated in cartilage from subjects undergoing joint replacement surgery for OA and RA compared with normal subjects by western blotting. The localization of TN-C in arthritic cartilage was also established by immunohistochemistry. Recombinant TN-C fragments were then tested to evaluate which regions of TN-C are responsible for cartilage-degrading activity in an ex vivo cartilage explant assay measuring glycosaminoglycan (GAG) release, aggrecanase and matrix metalloproteinase (MMP) activity. We found that specific TN-C fragments are highly upregulated in arthritic cartilage. Recombinant TN-C fragments containing the same regions as those identified from OA cartilage mediate cartilage degradation by the induction of aggrecanase activity. TN-C fragments mapping to the EGF-L and FN type III domains 3–8 of TN-C had the highest levels of aggrecan-degrading ability that was not observed either with full-length TN-C or with other domains of TN-C. TN-C fragments represent a novel mechanism for cartilage degradation in arthritis and may present new therapeutic targets for the inhibition of cartilage degradation.

Expression of Toll-like receptors and their signaling pathways in rheumatoid synovitis

OBJECTIVE

Toll-like receptors (TLR) recognizing endogenous and exogenous danger signals could play a role in rheumatoid arthritis (RA). Our aim was to describe the presence, localization, and extent of expression of TLR and their adapters.

METHODS

TLR 1, 2, 3, 4, 5, 6, and 9 receptors, and myeloid differentiation primary response protein 88, Toll/interleukin receptor (TIR) domain-containing adapter protein MyD88 adapter-like, and TIR domain-containing adapter-inducing interferon/TIR-containing adapter molecule-1 adapters were analyzed in RA (n = 10) and osteoarthritis (OA; n = 5) samples using real-time polymerase chain reaction (PCR). Their colocalization with cellular markers CD68, CD15, CD3, CD4, CD8, CD20, dendritic cell lysosomal-associated membrane protein (DC-LAMP), CD123, and 5B5 was analyzed in double immunofluorescence staining.

RESULTS

In RA, ß-actin standardized messenger RNA of TLR 2, 3, and 9 (p < 0.001) were particularly high. TLR 5 and 6 were also elevated (p < 0.05), but TLR 1 and 4 and adapters did not differ between RA and OA. In double-staining, TLR and adapters were strongly labeled in myeloid and plasmacytoid dendritic cells (DC), moderately in CD68+ type A lining cells/macrophages, and weakly to moderately in 5B5+ type B lining cells/fibroblasts. CD3+/CD4+ and CD3+/CD8+ T cells and CD20+ B cells in perivenular areas and in lymphoid follicles were moderately TLR- and weakly adapter-positive. In OA, TLR and adapters were weakly immunolabeled in vascular, lining, and inflammatory cells.

CONCLUSION

RA synovium showed abundant expression of TLR. RA synovitis tissue seems to be responsive to TLR ligands. DC, type A cells/macrophages, and type B cells/fibroblasts are, in that order from highest to lowest, equipped with TLR, suggesting a hierarchical responsiveness. In RA, danger-associated molecular patterns to TLR interactions may particularly drive DC to autoinflammatory and autoimmune cascades/synovitis.

Receptor Activator for Nuclear Factor kappa B Ligand (RANKL) as an osteoimmune key regulator in bone physiology and pathology

The strength and integrity of the human skeleton depends on a delicate equilibrium between bone resorption and bone formation. Bone resorption is an elementary cellular activity in the modelling of the skeleton during growth and development. Later in life a most important physiological process in the skeleton is bone remodelling, which is locally initiated by resorption. During remodelling bone resorption is coupled to new bone formation that ensures renewal of bone with only minor local and temporary bone loss. Cells responsible for bone resorption and subsequent bone formation are the osteoclasts and osteoblasts, respectively. The osteoclast is derived from the pluripotent hematopoietic stem cell, which gives rise to a myeloid stem cell that can further differentiate into megakaryocytes, granulocytes, monocytes/macrophages and osteoclasts. The respective bone resorbing and forming actions of osteoclasts and osteoblasts are finely coupled, so that bone mass remains remarkably stable in a healthy adult. Imbalance between osteoclast and osteoblast activities can arise from a wide variety of hormonal changes or perturbations of inflammatory and growth factors resulting in postmenopausal osteoporosis, Paget's disease, lytic bone metastases, or rheumatoid arthritis, leading to increased bone resorption and crippling bone damage. In view of the critical role of osteoclasts in diverse pathology, there has been immense effort aimed at understanding the biology of this unique cell. The present review is focused on the current knowledge of the mechanisms that regulate the functional links between bone turnover and the immune system helping us to understand the main factors that lead to bone loss observed in osteoporosis, cancer and in rheumatoid arthritis. The aim of this review paper is to consider the key molecular interactions involved in the formation of osteoclast cells in normal and pathological conditions.

Intra-articular injections for the treatment of osteoarthritis: focus on the clinical use of hyaluronic acid

Osteoarthritis (OA), also called degenerative joint disease, is the most frequently occurring chronic musculoskeletal disease, particularly affecting the aging population. The use of viscosupplementation, i.e. intra-articular (IA) hyaluronic acid (HA) drug therapy, to treat OA, is growing worldwide, due to important results obtained from several clinical trials, which reported IA HA-related improvements in functional activity and pain management. This review is an update of the IA use of this compound in the treatment of OA, with clinical evidence from the last few years being discussed and used to delineate new trends for the future.

Mechanical impact induces cartilage degradation via mitogen activated protein kinases

OBJECTIVE

To determine the activation of Mitogen activated protein (MAP) kinases in and around cartilage subjected to mechanical damage and to determine the effects of their inhibitors on impaction-induced chondrocyte death and cartilage degeneration.

DESIGN

The phosphorylation of MAP kinases was examined with confocal microscopy and immunoblotting. The effects of MAP kinase inhibitors on impaction-induced chondrocyte death and proteoglycan (PG) loss were determined with fluorescent microscopy and 1, 9-Dimethyl-Methylene Blue (DMMB) assay. The expression of catabolic genes at mRNA levels was examined with quantitative real-time PCR.

RESULTS

Early p38 activation was detected at 20 min and 1h post-impaction. At 24h, enhanced phosphorylation of p38 and extracellular signal-regulated protein kinase (ERK)1/2 was visualized in chondrocytes from in and around impact sites. The phosphorylation of p38 was increased by 3.0-fold in impact sites and 3.3-fold in adjacent cartilage. The phosphorylation of ERK-1 was increased by 5.8-fold in impact zone and 5.4-fold in adjacent cartilage; the phosphorylation of ERK-2 increased by 4.0-fold in impacted zone and 3.6-fold in adjacent cartilage. Furthermore, the blocking of p38 pathway did not inhibit impaction-induced ERK activation. The inhibition of p38 or ERK pathway significantly reduced injury-related chondrocyte death and PG losses. Quantitative Real-time PCR analysis revealed that blunt impaction significantly up-regulated matrix metalloproteinase (MMP)-13, Tumor necrosis factor (TNF)-α, and ADAMTS-5 expression.

CONCLUSION

These findings implicate p38 and ERK mitogen activated protein kinases (MAPKs) in the post-injury spread of cartilage degeneration and suggest that the risk of post-traumatic osteoarthritis (PTOA) following joint trauma could be decreased by blocking their activities, which might be involved in up-regulating expressions of MMP-13, ADAMTS-5, and TNF-α.