The expression of collagenase 3 (MMP-13) mRNA in the synovial tissue is associated with histopathologic type II synovitis in rheumatoid arthritis

LncRNA HOTAIR-mediated Wnt/β-catenin network modeling to predict and validate therapeutic targets for cartilage damage

BACKGROUND

Cartilage damage is a crucial feature involved in several pathological conditions characterized by joint disorders, such as osteoarthritis and rheumatoid arthritis. Accumulated evidences showed that Wnt/β-catenin pathway plays a role in the pathogenesis of cartilage damage. In addition, it is experimentally documented that lncRNA (long non-coding RNA) HOTAIR plays a key role in the regulation of Wnt/β-catenin pathway based on directly decreased WIF-1 expression. Further, it is reported that Wnt/β-catenin pathway is a potent pathway to regulate the expression of MMP-13, which is responsible for degradation of collagen type II in articular cartilage. It is increasingly recognized that systems modeling approach provides an opportunity to understand the complex relationships and direct quantitative analysis of dynamic network in various diseases.

RESULTS

A dynamic network of lncRNA HOTAIR-mediated Wnt/β-catenin pathway regulating MMP-13 is developed to investigate the dynamic mechanism of the network involved in the pathogenesis of cartilage damage. Based on the network modeling, the potential therapeutic intervention point Axin is predicted and confirmed by the experimental validation.

CONCLUSIONS

Our study provides a promising strategy for revealing potential dynamic mechanism and assessing potential targets which contribute to the prevention of the pathological conditions related to cartilage damage.

Treatment Effects of the Second-Generation Tyrosine Kinase Inhibitor Dasatinib on Autoimmune Arthritis

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease that primarily manifests as persistent synovitis and progressive joint destruction. Imatinib exhibited a therapeutic effect in murine collagen-induced arthritis (CIA) via selective inhibition tyrosine kinases. The second-generation tyrosine kinase inhibitor dasatinib exhibits more durable hematological and cytogenetic effects and more potency compared to imatinib. However, the effect of dasatinib on CIA is poorly understood. The present study investigated the treatment effect of dasatinib on autoimmune arthritis. We demonstrated that dasatinib alleviated arthritis symptoms and histopathological destruction in CIA mice. Dasatinib treatment inhibited the production of proinflammatory cytokines including IL-1β, TNF-α, and IL-6, and promoted the production of the anti-inflammatory cytokine IL-10. Dasatinib treatment also suppressed the expression of anti-mouse CII antibodies including total IgG, IgG1, IgG2, and IgG2b, in CIA mice. We further demonstrated that dasatinib inhibited the migration and proliferation of fibroblast-like synoviocytes (FLS) from RA patients and promoted FLS apoptosis. The mRNA expression of MMP13, VEGF, FGF, and DKK1 was down-regulated in FLS treated with dasatinib. Our findings suggest that dasatinib exhibited treatment effects on CIA mice and that FLS are an important target cell of dasatinib treatment in autoimmune arthritis.

Increased succinate receptor GPR91 involved in the pathogenesis of Mooren's ulcer

AIM

To investigate the expression of succinate receptor GPR91 and its pathogenic roles in Mooren's ulcer (MU).

METHODS

Biopsy specimens were obtained from 7 patients with MU and 6 healthy donors. The expression of GPR91 in MU tissues was evaluated using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC). Succinate was used to activate GPR91 signaling, and the effect of GPR91 on the expression of interleukin-1β (IL-1β), NLRP3, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-13 (MMP-13) in human peripheral blood mononuclear cells (PBMCs) was determined. The influence of GPR91 on the nuclear factor-κB (NF-κB) signaling in PBMCs was investigated by detecting the phosphorylation of p65. Moreover, the expression of IL-1β, VEGF, MMP-13 and phosphorylated p65 (p-p65) in the tissues of MU was examined by qRT-PCR or IHC.

RESULTS

GPR91 mRNA expression showed a higher level in the MU group than in the healthy control group. IHC analysis also revealed that the expression of GPR91 was elevated in patients with MU compared with healthy controls. Moreover, ligation of GPR91 with succinate promoted the lipopolysaccharide-induced production of NLRP3, IL-1β, VEGF and MMP-13 in PBMCs through increased phosphorylation of p65. Pharmacological inhibition of the NF-κB signaling reversed GPR91 induced production of NLRP3, IL-1β, VEGF and MMP-13. These findings, coupled with the elevated amounts of IL-1β, VEGF, MMP-13 and p-p65 observed in the MU biopsies, constituted a rational basis for the involvement of GPR91 in the pathogenesis of MU.

CONCLUSION

This study indicates the increased succinate receptor GPR91 in conjunctival or corneal tissues is involved in the pathogenesis of MU through elevated NF-κB activity, which may provide a new therapeutic target for MU.

Network Intervention, a Method to Address Complex Therapeutic Strategies

Objective: Network-based approaches emerged as powerful tools for studying complex diseases. Our intention in this article was to raise awareness of the benefits of new therapeutic strategy in biological networks context and provide an introduction to this topic.

Methods: This article will discuss the rational for network intervention, and outline some of the important aspects of deciphering targets activities in the network and future embodiments of network intervention. We also present examples of network intervention based on the strategies these approaches use.

Results: Network intervention seeks for target combinations to perturb a specific subset of nodes in disease networks to inhibit the bypass mechanisms at systems level. Experimental results derived from our studies are discussed, with conclusions that lead to future research directions. A simple diagram is designed to give a way to find the minimum number of external input required for a network intervention based on the graph theory and get the analytical value of the least input.

Conclusion: Creating network intervention that addresses blindness and unthinking action in this way could, therefore, provide more benefit than multi-target therapy. We hope that this article will give readers an appreciation for a new therapeutic strategy that has been proposed for improving clinical benefit by adopting network-based approaches as well as insight into their properties.

CXCL10 suppression of hem- and lymph-angiogenesis in inflamed corneas through MMP13

Though not present in the normal adult cornea, both hem- and lymph-angiogenesis can be induced in this tissue after an inflammatory, infectious, or traumatic insult. We previously showed that the chemokine CXCL10 plays a key role in eradicating invading Candida (C.) albicans in C57BL6 mouse corneas. However, even after the clearance of pathogens, infection-induced inflammation and angiogenesis continue to progress in the cornea. The aim of this study is define the role of CXCL10 as a major angiostatic factor in modulating cornea angiogenesis in B6 mouse corneas under pathogenic conditions. We showed that epithelial expression of CXCL10, driven by AAV9 vector, suppressed both infection- and inflammation-induced hem and lymph angiogenesis, whereas the neutralization of CXCL10 as well as its receptor CXCR3 greatly promoted these processes. The inhibitory effect of CXCL10 was unrelated to its antimicrobial activity, but through the suppression of the expression of many angiogenic factors, including VEGFa and c, and MMP-13 in vivo. Inhibition of MMP13 but not TIMPs, attenuated suture-induced neovascularization but had no effects on CXCL10 expression. Strikingly, topical application of CXCL10 post-C. albicans infection effectively blocked both hem- and lymph-angiogenesis and preserved the integrity of sensory nerves in the cornea. Taken together, CXCL10 has strong inhibitory effects on neovascularization, whereas MMP13 is required for neovascularization in C. albicans-infected corneas and the local application of CXCL10 or MMP13 inhibitors, alone or as adjuvant therapy, may target hem- and lymph-angiogenesis in the inflamed corneas.

Matrix Metalloproteinases and Synovial Joint Pathology

Matrix metalloproteinases (MMPs) are zinc-dependent enzymes. These enzymes play a critical role in the destruction of articular cartilage in rheumatoid arthritis (RA), osteoarthritis (OA), psoriatic arthritis (PsA), and the spondyloarthropathies. MMP gene expression is upregulated in these synovial joint pathologies in response to elevated levels of proinflammatory cytokines and soluble mediators such as tumor necrosis factor-α, interleukin-1 (IL-1), IL-6, IL-17, and interferon-γ. These molecules are capable of activating the mitogen-activated protein kinase and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways by binding the cytokine to their respective receptors on immune cells, macrophages, chondrocytes, synoviocytes, and osteocytes leading to increased synthesis of MMPs. Biologic drugs and/or small-molecule inhibitors designed to block cytokine to cytokine receptor interactions or to selectively inhibit JAKs have clinical efficacy in RA, PsA, and ankylosing spondylitis which correlated with a reduction in MMPs. Although there are currently no OA-selective drugs, it is likely that such a drug would have to reduce MMP gene expression to have clinical efficacy.

Gene expression study in positron emission tomography-positive abdominal aortic aneurysms identifies CCL18 as a potential biomarker for rupture risk

Rupture of abdominal aortic aneurysm (AAA) is a cause of significant mortality and morbidity in aging populations. Uptake of 18-fluorodeoxyglucose (FDG) detected by positron emission tomography (PET) is observed in the wall of 12% of AAA (A+), with most of them being symptomatic. We previously showed that the metabolically active areas displayed adventitial inflammation, medial degeneration and molecular alterations prefacing wall rupture. The aim of this study was to identify new factors predictive of rupture. Transcriptomic analyses were performed in the media and adventitia layers from three types of samples: AAA with-out FDG uptake (A0) and with FDG uptake (A+), both at the positive spot (A+(Pos)) and at a paired distant negative site (A+(Neg)) of the same aneurysm. Follow-up studies included reverse-transcriptase-polymerase chain reaction (RT-PCR), immunohistochemical staining and enzyme-linked immunosorbent assay (ELISA). A large number of genes, including matrix metalloproteinases, collagens and cytokines as well as genes involved in osteochondral development, were differentially expressed in the A+(Pos) compared with A+(Neg). Moreover, a series of genes (notably CCL18) was differentially expressed both in the A+(Neg) and A+(Pos) compared with the A0. A significant increase of CCL18 was also found at the protein level in the aortic wall and in peripheral blood of A+ patients compared with A0. In conclusion, new factors, including CCL18, involved in the progression of AAA and, potentially, in their rupture were identified by a genome-wide analysis of PET-positive and -negative human aortic tissue samples. Further work is needed to study their role in AAA destabilization and weakening.

Matrix Metalloproteinase-13 as a Target for Suppressing Corneal Ulceration Caused by Pseudomonas aeruginosa Infection

PURPOSE

Pseudomonas aeruginosa keratitis is characterized by severe corneal ulceration. This study investigated whether matrix metalloproteinase-13 (MMP13) is involved in P. aeruginosa-induced corneal ulceration and whether it therefore can be targeted for preventing P. aeruginosa keratitis.

METHODS

MMP13 expression in P. aeruginosa-infected C57BL/6 mouse corneas was assessed by quantitative polymerase chain reaction and immunohistochemistry analyses. An MMP13-inhibitor (MMP13i) was either injected subconjunctivally prior to or coapplied topically with gatifloxacin 16 hours after infection. Disease severity was assessed by corneal imaging, clinical scoring, bacterial burden, neutrophil infiltration, and CXCL2 expression. Corneal damage and infiltration were also determined by immunohistochemistry analysis and whole-mount confocal microscopy.

RESULTS

P. aeruginosa infection induced an increased expression of MMP13 in mouse corneas from 6 to 24 hours after infection in a Toll-liked receptor 5-dependent manner. Subconjunctival injection of MMP13i prior to P. aeruginosa inoculation significantly decreased keratitis severity, as evidenced by preserved epithelium integrity and intact basement membrane, leading to reduced bacterial dissemination to the stroma. Furthermore, topical coapplication of MMP13i with gatifloxacin greatly improved disease outcomes, including accelerated opacity dissolution; decreased inflammation, cellular infiltration, and collagen disorganization; and basement membrane preservation.

CONCLUSIONS

Elevated MMP13 activity may contribute to P. aeruginosa keratitis through basement membrane degradation, and its inhibition could potentially be used as an adjunctive therapy to treat microbial keratitis and other mucosal infections.

Effect of qubi zhentong recipe on synovial gene expression in collagen-induced arthritis in rats

OBJECTIVE

To investigate the effect of the Chinese medical formula Qubi Zhentong Recipe(, QZR) on the synovial gene expression profile in collagen-induced arthritis (CIA) rats.

METHODS

Ten rats were randomly chosen from 60 rats as the control group, and the other 50 rats were used for the CIA models. The CIA model group was constructed by bovine injection of type II collagen through the rats' neck and tail. Twenty rats were randomly chosen from 34 successful CIA models and randomly assigned into two groups: the model group (n =10) and the QZR group (n=10). The QZR group was fed intragastrically with QZR 22.9 g/(kg·d) (10 times the clinical adult dose), and the CIA model group was given the same dose of normal saline. Both model and QZR groups were administered treatment once a day. Total RNA was collected from the knee joint synovium after 30 days. The change in gene expression profile was analyzed by a whole gene chip.

RESULTS

A total of 76 genes showed a difference in expression between CIA model group and the control group; 35 genes were down-regulated and 41 were up-regulated. A total of 67 genes showed a difference in expression between the model group and the QZR group; 48 genes were down-regulated and 19 were upregulated.

CONCLUSIONS

QZR may affect CIA by stimulating multiple genes and targets, which are related to oncogenes, apoptosis, metabolism, the immune system, ion channels, and transport proteins.

Gene expression profiling of macrophages: implications for an immunosuppressive effect of dissolucytotic gold ions

Background

Gold salts has previously been used in the treatment of rheumatoid arthritis but have been replaced by biologicals such as TNF-α inhibitors. The mechanisms behind the anti-inflammatory effect of metallic gold ions are still unknown, however, recent data showed that charged gold atoms are released from pure metallic gold implants by macrophages via a dissolucytosis membrane, and that gold ions are taken up by local macrophages, mast cells and to some extent fibroblasts. These findings open the question of possible immunomodulatory effects of metallic gold and motivate efforts on a deeper understanding of the effect of metallic gold on key inflammatory cells as macrophages.

Methods

Human macrophage cells (cell line THP-1) were grown on gold foils and intracellular uptake was analysed by autometallography. The impact of phagocytised gold ions on viability of THP-1 cells was investigated by trypan blue staining and TUNEL assay. The global gene expression profile of THP-1 cells after incorporation of gold ions was studied using microarray analysis comprising approximately 20,000 genes. The gene expression data was confirmed by measurement of secreted proteins.

Results

Autometallography showed intracellular uptake of gold ions into THP-1 cells. No significant effect on viability of THP-1 cells was demonstrated. Our data revealed a unique gene expression signature of dissolucytotic THP-1 cells that had taken up gold ions. A large number of regulated genes were functionally related to immunomodulation. Gold ion uptake induced downregulation of genes involved in rheumatoid arthritis such as hepatocyte growth factor, tenascin-C, inhibitor of DNA binding 1 and 3 and matrix metalloproteinase 13.

Conclusion

The data obtained in this study offer new insights into the mode of action of gold ions and suggest for the investigation of effects on other key cells and a possible future role of metallic gold as implants in rheumatoid arthritis or other inflammatory conditions.

MALDI MS imaging as a powerful tool for investigating synovial tissue

OBJECTIVE

To identify and image protein biomarker candidates in the synovial tissue of patients with rheumatoid arthritis (RA) and patients with osteoarthritis (OA).

METHODS

A novel matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) technique was applied to the analysis of synovial tissue. Patients were classified according to the American College of Rheumatology (ACR) criteria for RA. Frozen sections were stained to obtain morphological data. Serial sections were desiccated, and spotted with matrix for MALDI analysis. Ions generated by laser irradiation of the tissue were separated in time, based on their m/z ratio, and were subsequently detected. IMS was used in a 'profiling' mode to detect discrete spots for rapid evaluation of proteomic patterns in various tissue compartments. Photomicrographs of the stained tissue images were reviewed by a pathologist. Areas of interest (10 discrete areas/compartment) were marked digitally and the histology-annotated images were merged to form a photomicrograph of the section taken before the MALDI measurement. Pixel coordinates of these areas were transferred to a robotic spotter, the matrix was spotted, and the coordinates of the spots were transferred to a mass spectrometer for spectral acquisition. The data generated were then subjected to biocomputation analysis to reveal the biomarker candidates.

RESULTS

Several peaks (m/z) consistent in mass with calgranulins, defensins, and thymosins were detected and their distribution in various synovial compartments (synovial lining and sublining layer) was demonstrated.

CONCLUSION

MALDI IMS is a powerful tool for the rapid detection of numerous proteins (in situ proteomics) and was applied here for the analysis of the distribution of proteins in synovial tissue sections.

Kinetics and thermodynamics of irreversible inhibition of matrix metalloproteinase 2 by a Co(III) Schiff base complex

Cobalt(III) Schiff base complexes have been used as potent inhibitors of protein function through the coordination to histidine residues essential for activity. The kinetics and thermodynamics of the binding mechanism of Co(acacen)(NH(3))(2)Cl [Co(acacen); where H(2)acacen is bis(acetylacetone)ethylenediimine] enzyme inhibition has been examined through the inactivation of matrix metalloproteinase 2 (MMP-2) protease activity. Co(acacen) is an irreversible inhibitor that exhibits time- and concentration-dependent inactivation of MMP-2. Co(acacen) inhibition of MMP-2 is temperature-dependent, with the inactivation increasing with temperature. Examination of the formation of the transition state for the MMP-2/Co(acacen) complex was determined to have a positive entropy component indicative of greater disorder in the MMP-2/Co(acacen) complex than in the reactants. With further insight into the mechanism of Co(acacen) complexes, Co(III) Schiff base complex protein inactivators can be designed to include features regulating activity and protein specificity. This approach is widely applicable to protein targets that have been identified to have clinical significance, including matrix metalloproteinases. The mechanistic information elucidated here further emphasizes the versatility and utility of Co(III) Schiff base complexes as customizable protein inhibitors.

An MMP13-selective inhibitor delays primary tumor growth and the onset of tumor-associated osteolytic lesions in experimental models of breast cancer

We investigated the effects of the matrix metalloproteinase 13 (MMP13)-selective inhibitor, 5-(4-{4-[4-(4-fluorophenyl)-1,3-oxazol-2-yl]phenoxy}phenoxy)-5-(2-methoxyethyl) pyrimidine-2,4,6(1H,3H,5H)-trione (Cmpd-1), on the primary tumor growth and breast cancer-associated bone remodeling using xenograft and syngeneic mouse models. We used human breast cancer MDA-MB-231 cells inoculated into the mammary fat pad and left ventricle of BALB/c Nu/Nu mice, respectively, and spontaneously metastasizing 4T1.2-Luc mouse mammary cells inoculated into mammary fat pad of BALB/c mice. In a prevention setting, treatment with Cmpd-1 markedly delayed the growth of primary tumors in both models, and reduced the onset and severity of osteolytic lesions in the MDA-MB-231 intracardiac model. Intervention treatment with Cmpd-1 on established MDA-MB-231 primary tumors also significantly inhibited subsequent growth. In contrast, no effects of Cmpd-1 were observed on soft organ metastatic burden following intracardiac or mammary fat pad inoculations of MDA-MB-231 and 4T1.2-Luc cells respectively. MMP13 immunostaining of clinical primary breast tumors and experimental mice tumors revealed intra-tumoral and stromal expression in most tumors, and vasculature expression in all. MMP13 was also detected in osteoblasts in clinical samples of breast-to-bone metastases. The data suggest that MMP13-selective inhibitors, which lack musculoskeletal side effects, may have therapeutic potential both in primary breast cancer and cancer-induced bone osteolysis.

Hyaluronan inhibits matrix metalloproteinase-13 in human arthritic chondrocytes via CD44 and P38

We investigated the effects of hyaluronan (HA) on interleukin-1β (IL-1β)-stimulated matrix metalloproteinase (MMP)-13 production in human chondrocytes from patients with osteoarthritis (OA) or rheumatoid arthritis (RA). Secreted levels of MMP-13 in conditioned media were detected by immunoblotting, while intracellular MMP-13 synthesis in articular cartilage was evaluated by immunofluorescence microscopic analysis. Mitogen-activated protein kinases (MAPKs), p38, extracellular signal-regulated kinases (ERK), and c-jun NH2-terminal kinase (JNK) were assessed by Western blotting. IL-1β (2 ng/ml) stimulates the secretion of MMP-13 in both OA and RA chondrocytes. Inhibition studies using specific MAPK inhibitors revealed that IL-1β induced MMP-13 via p38 in both OA and RA chondrocytes. HA down-regulates IL-1β-stimulated MMP-13 and phosphorylated p38 (p-p38) in a dose-dependent manner (0.1, 1, 2, and 4 mg/ml). When used at 4 mg/ml, HA inhibits p-p38 phosphorylation by more than 60%. In response to IL-1β, RA chondrocytes express a higher level of p-p38 than that of OA chondrocytes. Inhibition of CD44, using a blocking antibody, significantly reversed the inhibitory effect of HA on both MMP-13 and p-p38. Our study clearly shows that HA inhibits IL-1β-induced MMP-13 via its principal receptor, CD44, and subsequent intracellular p38 MAPK signaling in OA and RA chondrocytes.

Discoidin domain receptor 2 is associated with the increased expression of matrix metalloproteinase-13 in synovial fibroblasts of rheumatoid arthritis

Regulation of matrix metalloproteinase-13 (MMP-13) by collagen matrix in the synovial fibroblasts of rheumatoid arthritis (RA) is critical event in the progressive joint destruction. Our previous study indicated that a collagen receptor, discoidin receptor 2 (DDR2), was highly expressed in the synovial fibroblasts of RA. However, the functional role of DDR2 in the regulation of MMP-13 production in synovial fibroblasts has not been elucidated. In this study, we initially demonstrated that the DDR2 and MMP-13 proteins are both highly expressed in the synovial lining layer of RA. MMP-13 mRNA and protein in synovial fibroblasts of RA were preferentially induced by collagen type II compared with MMP-1. Furthermore, stable overexpression of wild type DDR2 in murine synoviocytes dramatically augments the production of MMP-13. The activation of DDR2 also mediates the up-regulation of MMP-13 promoter activity in 293T cells. Inhibitor specific for extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) cascade was shown to decrease MMP-13 level induced by collagen II in RA synovial fibroblasts and DDR2-induced MMP-13 promoter activity. Runx2 and activator protein-1 (AP-1) binding sites in MMP-13 promoter region are required for DDR2-induced transcription. The data in this study suggest that DDR2-mediated MMP-13 induction by collagen matrix in synovial fibroblasts of RA contributed to articular cartilage destruction.

[Association between histopathologic type II synovitis and increased amounts of pyridinoline in synovial tissue samples in rheumatoid arthritis]

OBJECTIVE

To investigate the association between immunohistopathological and morphological features of synovitis in rheumatoid arthritis and the amounts of collagen degradation products pyridinoline and deoxypyridinoline in the synovial tissue and in body fluids in order to discover potential markers of erosive disease.

METHODS

Histopathological analysis of synovial tissue samples from 22 patients with RA was performed according to the histopathologic scoring system of RA synovitis by P. Stiehl. Accordingly, the samples were (a) classified into type I synovitis, type II synovitis, or undifferentiated synovitis and were (b) characterized for local features of disease activity, including basic activity and actual activity. The contents of pyridinoline and deoxypyridinoline were measured in the synovial tissue, the synovial fluid, serum and urine by HPLC analysis.

RESULTS

The amounts of pyridinoline in synovial tissue samples characterized by type II synovitis were 1.7-fold and 2.7-fold higher compared with those with type I synovitis and undifferentiated synovitis, respectively. In contrast, the content of deoxypyridinoline was not different between the histopathologic types of synovitis. At the same time, increased amounts of pyridinoline, but not deoxypyridinoline, were detected in synovial tissue samples with basic activity or actual activity grade II compared with synovial tissue samples with basic activity or actual activity grade I. The concentrations of both collagen degradation products in the synovial fluid, serum and urine did not differ between patients when they were analyzed either for histopathologic types of synovitis or local disease activity.

CONCLUSION

The amount of cartilage collagen degradation product pyridinoline in synovial tissue is positively correlated with the histopathological grading of local disease activity. Furthermore, the increased amounts of pyridinoline in synovial tissue samples with type II synovitis suggest a more erosive course of RA in patients with this type of synovitis.

Discovery and Characterization of a Novel Inhibitor of Matrix Metalloprotease-13 That Reduces Cartilage Damage in Vivo without Joint Fibroplasia Side Effects

Matrix metalloproteinase-13 (MMP13) is a Zn(2+)-dependent protease that catalyzes the cleavage of type II collagen, the main structural protein in articular cartilage. Excess MMP13 activity causes cartilage degradation in osteoarthritis, making this protease an attractive therapeutic target. However, clinically tested MMP inhibitors have been associated with a painful, joint-stiffening musculoskeletal side effect that may be due to their lack of selectivity. In our efforts to develop a disease-modifying osteoarthritis drug, we have discovered MMP13 inhibitors that differ greatly from previous MMP inhibitors; they do not bind to the catalytic zinc ion, they are noncompetitive with respect to substrate binding, and they show extreme selectivity for inhibiting MMP13. By structure-based drug design, we generated an orally active MMP13 inhibitor that effectively reduces cartilage damage in vivo and does not induce joint fibroplasias in a rat model of musculoskeletal syndrome side effects. Thus, highly selective inhibition of MMP13 in patients may overcome the major safety and efficacy challenges that have limited previously tested non-selective MMP inhibitors. MMP13 inhibitors such as the ones described here will help further define the role of this protease in arthritis and other diseases and may soon lead to drugs that safely halt cartilage damage in patients.

MyD88, IRAK1 and TRAF6 knockdown in human chondrocytes inhibits interleukin-1-induced matrix metalloproteinase-13 gene expression and promoter activity by impairing MAP kinase activation

Interleukin-1 (IL-1) is the major prototypic proinflammatory cytokine that stimulates degradation of cartilage in arthritis by inducing prominent collagen II-degrading matrix metalloproteinase-13 (MMP-13). Nothing is known about the involvement of adaptor proteins, MyD88, IRAK1 and TRAF6 in MMP-13 regulation. Here we investigated for the first time the role of these proteins in IL-1-regulated MMP-13 expression in chondrocytes. MyD88 homodimerization inhibitory peptide diminished the expression of MMP-13 gene, promoter activity, phosphorylation of mitogen-activated protein kinases (MAPKs), c-Jun and activating protein 1 (AP-1) activity. Knockdown of MyD88, IRAK1 and TRAF6 by RNA interference (RNAi) drastically down-regulated the expression of IL-1-induced MMP-13 mRNA and protein levels and MMP-13 promoter-driven luciferase activity. Non-specific control siRNA had no effect. Mechanisms of MMP-13 inhibition involved reduced phosphorylation of ERK, p38, JNK and c-Jun as well as AP-1 transcription factor binding activity. The genetic evidence presented here demonstrates that MyD88, IRAK1 and TRAF6 proteins are crucial early mediators for the IL-1-induced MMP-13 regulation through MAPK pathways and AP-1 activity. These proteins could constitute important therapeutic targets for arthritis-associated cartilage loss by MMP-13.

Identification of genomic targets downstream of p38 mitogen-activated protein kinase pathway mediating tumor necrosis factor-alpha signaling

Inhibition of p38 MAPK suppresses the expression of proinflammatory cytokines such as TNF-alpha and IL-1 beta in macrophages and fibroblast-like synoviocytes (FLS). However, there have been no genomewide studies on the gene targets of p38 MAPK signaling in synoviocytes. Microarray technology was applied to generate a comprehensive analysis of all genes regulated by the p38 MAPK signaling pathway in FLS. Gene expression levels were measured with Agilent oligonucleotide microarrays. Four independent sets of mRNA modulated by TNF-alpha and vehicle were used to measure the change of gene expression due to TNF-alpha, and three experiments were done to ascertain the effect of SB-203580, a p38 MAPK inhibitor, on TNF-alpha-induced genes. Microarray data were validated by RT-quantitative polymerase chain reaction. One hundred forty-one significantly expressed genes were more than twofold upregulated by TNF-alpha. Thirty percent of these genes were downregulated by the p38 inhibitor SB-203580, whereas 67% of these genes were not significantly changed. The SB-203580-inhibited genes include proinflammatory cytokines such as interleukins and chemokines, proteases including matrix metallopeptidases, metabolism-related genes such as cyclooxygenases and phosphodiesterase, genes involved in signal transduction, and genes encoding for transcription factors, receptors, and transporters. Approximately one-third of the TNF-alpha-induced genes in FLS are regulated by the p38 MAPK signal pathway, showing that p38 MAPK is a possible target for suppressing proinflammatory gene expressions in rheumatoid arthritis.

Active Expression of Matrix Metalloproteinase-13 mRNA in the Granulation Tissue of Equine Superficial Digital Flexor Tendinitis

The DNA microarray analysis for matrix metalloproteinase (MMP)-related mRNA expression in equine superficial digital flexor tendinitis indicated that mRNA level of MMP-13 was apparently up-regulated in the tendinitis as compared to normal tendon. In situ hybridization also revealed that fibroblastic cells proliferated in the granulation tissue generated in the tendinitis actively expressed MMP-13 mRNA. On the other hand, in normal tendon, a few fibroblastic cells and vascular components lied in the endotenon barely expressed its mRNA, but other cellular components in the tendon bundle were not positively hybridized. As mentioned above, MMP-13 but not other collagenases or gelatinases, may play an important role in tendon injuries in the racehorses.