T.E. Swingler

The regulation of matrix metalloproteinases and their inhibitors

The matrix metalloproteinases (MMP) are a family of 23 enzymes in man. These enzymes were originally described as cleaving extracellular matrix (ECM) substrates with a predominant role in ECM homeostasis, but it is now clear that they have much wider functionality. Control over MMP and/or tissue inhibitor of metalloproteinases (TIMP) activity in vivo occurs at different levels and involves factors such as regulation of gene expression, activation of zymogens and inhibition of active enzymes by specific inhibitors. Whilst these enzymes and inhibitors have clear roles in physiological tissue turnover and homeostasis, if control of their expression or activity is lost, they contribute to a number of pathologies including e.g. cancer, arthritis and cardiovascular disease. The expression of many MMPs and TIMPs is regulated at the level of transcription by a variety of growth factors, cytokines and chemokines, though post-transcriptional pathways may contribute to this regulation in specific cases. The contribution of epigenetic modifications has also been uncovered in recent years. The promoter regions of many of these genes have been, at least partly, characterised including the role of identified single nucleotide polymorphisms. This article aims to review current knowledge across these gene families and use a bioinformatic approach to fill the gaps where no functional data are available.

Superoxide dismutase downregulation in osteoarthritis progression and end-stage disease

Background Oxidative stress is proposed as an important factor in osteoarthritis (OA). Objective To investigate the expression of the three superoxide dismutase (SOD) antioxidant enzymes in OA. Methods SOD expression was determined by real-time PCR and immunohistochemistry using human femoral head cartilage. SOD2 expression in Dunkin–Hartley guinea pig knee articular cartilage was determined by immunohistochemistry. The DNA methylation status of the SOD2 promoter was determined using bisulphite sequencing. RNA interference was used to determine the consequence of SOD2 depletion on the levels of reactive oxygen species (ROS) using MitoSOX and collagenases, matrix metalloproteinase 1 (MMP-1) and MMP-13, gene expression. Results All three SOD were abundantly expressed in human cartilage but were markedly downregulated in end-stage OA cartilage, especially SOD2. In the Dunkin–Hartley guinea pig spontaneous OA model, SOD2 expression was decreased in the medial tibial condyle cartilage before, and after, the development of OA-like lesions. The SOD2 promoter had significant DNA methylation alterations in OA cartilage. Depletion of SOD2 in chondrocytes increased ROS but decreased collagenase expression. Conclusion This is the first comprehensive expression profile of all SOD genes in cartilage and, importantly, using an animal model, it has been shown that a reduction in SOD2 is associated with the earliest stages of OA. A decrease in SOD2 was found to be associated with an increase in ROS but a reduction of collagenase gene expression, demonstrating the complexities of ROS function.

Analyzing mRNA expression identifies Smad3 as a microRNA-140 target regulated only at protein level

mRNA profiling is routinely used to identify microRNA targets, however, this high-throughput technology is not suitable for identifying targets regulated only at protein level. Here, we have developed and validated a novel methodology based on computational analysis of promoter sequences combined with mRNA microarray experiments to reveal transcription factors that are direct microRNA targets at the protein level. Using this approach we identified Smad3, a key transcription factor in the TGFbeta signaling pathway, as a direct miR-140 target. We showed that miR-140 suppressed the TGFbeta pathway through repression of Smad3 and that TGFbeta suppressed the accumulation of miR-140 forming a double negative feedback loop. Our findings establish a valid strategy for the discovery of microRNA targets regulated only at protein level, and we propose that additional targets could be identified by re-analysis of existing microarray datasets.

Review: The Role of MicroRNAs in Osteoarthritis and Chondrogenesis

The etiology of osteoarthritis (OA) is complex, with genetic, developmental, biochemical, and biomechanical factors contributing to the disease process. Chondrocytes in articular cartilage must express appropriate genes to achieve tissue homeostasis, and this is altered in OA. One facet of the aberrant gene expression in OA is the replay of chondrocyte differentiation with the expression of genes associated with chondrocyte hypertrophy. The pattern of gene expression and the transcription factors that control chondrogenesis are known in some detail. Mechanisms that lead to altered gene expression in OA, however, are less well understood. MicroRNAs (miRNAs) are small noncoding RNAs that have recently been recognized as important regulators of gene expression in human cells. A number of miRNAs are regulated across chondrogenesis, and their function is beginning to be delineated. Similarly, miRNAs are differentially expressed in OA cartilage compared to normal tissue. MicroRNA-140 (miR-140), which is highly and selectively expressed in cartilage, has been the focus of much work to date, though the full gamut of its actions is still to be defined. Many other regulated miRNAs likely act as a network to control cartilage homeostasis, catabolism, and repair. Chondrocytes are the sole cell type in cartilage, and they produce and maintain the extracellular matrix (ECM) that gives the tissue its load-bearing function (1). Chondrocytes originate from mesenchymal stem cells (MSCs) through chondrogenic differentiation (2). Investigation of the mechanisms mediating chondrogenic differentiation of MSCs as well as regulation of their functions will contribute to a better understanding of skeletal development and new strategies for treating diseases such as OA. Chondrogenesis and chondrocyte function are highly regulated by transcription and growth factors. The SOX family members SOX9, L-SOX5, and SOX6 are necessary for chondrogenic differentiation (see, for example, ref. 3). Many family members of the bone morphogenetic protein (BMP) and transforming growth factor (TGF ) signaling pathways have also been shown to control chondrogenesis (2). An additional level of regulation mediated by miRNAs has been identified (4), and miRNAs may represent novel therapeutic targets for pharmacologic control of skeletal diseases. OA, the most prevalent degenerative joint disease, causes pain, tenderness, limitation of movement, and a variable degree of inflammation (5). OA is characterized by articular cartilage destruction due to an imbalance between the synthesis and degradation of ECM components, mainly type II collagen and the proteoglycan aggrecan. Matrix-degrading enzymes, e.g., the matrix metalloproteinases (MMPs) and ADAMTS, play important roles (1). The pathogenesis of OA is complex and poorly understood but involves the interaction of multiple factors, ranging from genetic predisposition to mechanical and environmental components (5). Studies are in progress to define molecular mechanisms underlying OA, including the roles of specific miRNAs in, e.g., phenotype shift, apoptosis, and regulation of gene expression in chondrocytes (6). MicroRNA-140, the major miRNA implicated in OA to date, plays a role in chondrogenesis and cartilage development (7–9). The knockout or overexpression of miR140 in vivo has profound effects on the development of OA (10,11). Other miRNAs appear to follow this pattern (see, for example, ref. 12), but it is likely that further miRNAs that contribute to OA play a role in, for example, mechanotransduction or inflammation. The utility of miRNAs may be in the diagnosis of OA, tissue Supported by the Vietnamese Ministry of Education and Training (Project 322 grant to Ms Le) and Arthritis Research UK (program grant 19424 to Drs. Swingler and Clark). Linh T. T. Le, MSc, Tracey E. Swingler, PhD, Ian M. Clark, PhD: University of East Anglia, Norwich, UK. Address correspondence to Ian M. Clark, PhD, Biomedical Research Centre, School of Biological Sciences, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, UK. E-mail: i.clark@uea.ac.uk. Submitted for publication September 11, 2012; accepted in revised form April 23, 2013.

Matriptase is a novel initiator of cartilage matrix degradation in osteoarthritis

OBJECTIVE Increasing evidence implicates serine proteinases in pathologic tissue turnover. The aim of this study was to assess the role of the transmembrane serine proteinase matriptase in cartilage destruction in osteoarthritis (OA). METHODS Serine proteinase gene expression in femoral head cartilage obtained from either patients with hip OA or patients with fracture to the neck of the femur (NOF) was assessed using a low-density array. The effect of matriptase on collagen breakdown was determined in cartilage degradation models, while the effect on matrix metalloproteinase (MMP) expression was analyzed by real-time polymerase chain reaction. ProMMP processing was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis/N-terminal sequencing, while its ability to activate proteinase-activated receptor 2 (PAR-2) was determined using a synovial perfusion assay in mice. RESULTS Matriptase gene expression was significantly elevated in OA cartilage compared with NOF cartilage, and matriptase was immunolocalized to OA chondrocytes. We showed that matriptase activated proMMP-1 and processed proMMP-3 to its fully active form. Exogenous matriptase significantly enhanced cytokine-stimulated cartilage collagenolysis, while matriptase alone caused significant collagenolysis from OA cartilage, which was metalloproteinase-dependent. Matriptase also induced MMP-1, MMP-3, and MMP-13 gene expression. Synovial perfusion data confirmed that matriptase activates PAR-2, and we demonstrated that matriptase-dependent enhancement of collagenolysis from OA cartilage is blocked by PAR-2 inhibition. CONCLUSION Elevated matriptase expression in OA and the ability of matriptase to activate selective proMMPs as well as induce collagenase expression make this serine proteinase a key initiator and inducer of cartilage destruction in OA. We propose that the indirect effects of matriptase are mediated by PAR-2, and a more detailed understanding of these mechanisms may highlight important new therapeutic targets for OA treatment.

Class I Histone Deacetylase Inhibition Modulates Metalloproteinase Expression and Blocks Cytokine‐Induced Cartilage Degradation

OBJECTIVE To examine the ability of a broad-spectrum histone deacetylase (HDAC) inhibitor to protect cartilage in vivo, and to explore the effects of class-selective HDAC inhibitors and small interfering RNA (siRNA)-induced knockdown of HDACs on metalloproteinase expression and cartilage degradation in vitro. METHODS A destabilization of the medial meniscus (DMM) model was used to assess the in vivo activity of the HDAC inhibitor trichostatin A (TSA). Human articular chondrocytes (HACs) and SW-1353 chondrosarcoma cells were treated with cytokines and TSA, valproic acid, MS-275, or siRNA, and quantitative reverse transcription-polymerase chain reaction was performed to determine the effect of treatment on metalloproteinase expression. HDAC inhibitor activity was detected by Western blotting. A bovine nasal cartilage (BNC) explant assay was performed to measure cartilage resorption in vitro. RESULTS Systemically administered TSA protected cartilage in the DMM model. TSA, valproic acid, and MS-275 repressed cytokine-induced MMP1 and MMP13 expression in HACs. Knockdown of each class I HDAC diminished interleukin-1-induced MMP13 expression. All of the HDAC inhibitors prevented degradation of BNC, in which TSA and MS-275 repressed cytokine-induced MMP expression. CONCLUSION Inhibition of class I HDACs (HDAC-1, HDAC-2, HDAC-3) by MS-275 or by specific depletion of HDACs is capable of repressing cytokine-induced metalloproteinase expression in cartilage cells and BNC explants, resulting in inhibition of cartilage resorption. These observations indicate that specific inhibition of class I HDACs is a possible therapeutic strategy in the arthritides.

Degradome expression profiling in human articular cartilage

IntroductionThe molecular mechanisms underlying cartilage destruction in osteoarthritis are poorly understood. Proteolysis is a key feature in the turnover and degradation of cartilage extracellular matrix where the focus of research has been on the metzincin family of metalloproteinases. However, there is strong evidence to indicate important roles for other catalytic classes of proteases, with both extracellular and intracellular activities. The aim of this study was to profile the expression of the majority of protease genes in all catalytic classes in normal human cartilage and that from patients with osteoarthritis (OA) using a quantitative method.MethodsHuman cartilage was obtained from femoral heads at joint replacement for either osteoarthritis or following fracture to the neck of femur (NOF). Total RNA was purified, and expression of genes assayed using Taqman® low-density array quantitative RT-PCR.ResultsA total of 538 protease genes were profiled, of which 431 were expressed in cartilage. A total of 179 genes were differentially expressed in OA versus NOF cartilage: eight aspartic proteases, 44 cysteine proteases, 76 metalloproteases, 46 serine proteases and five threonine proteases. Wilcoxon ranking as well as the LogitBoost-NR machine learning approach were used to assign significance to each gene, with the most highly ranked genes broadly similar using each method.ConclusionsThis study is the most complete quantitative analysis of protease gene expression in cartilage to date. The data help give direction to future research on the specific function(s) of individual proteases or protease families in cartilage and may help to refine anti-proteolytic strategies in OA.

Expression and function of matrix metalloproteinase (MMP)-28.

Matrix metalloproteinase-28 (MMP-28, epilysin) is highly expressed in the skin by keratinocytes, the developing and regenerating nervous system and a number of other normal human tissues. In epithelial cells, over-expression of MMP-28 mediates irreversible epithelial to mesenchymal transition concomitant with loss of E-cadherin from the cell surface and an increase in active transforming growth factor beta. We recently reported the expression of MMP-28 in both cartilage and synovium where expression is increased in patients with osteoarthritis. In human chondrosarcoma cells MMP-28 was activated by proprotein convertases and the active form of the enzyme preferentially associated with the extracellular matrix in a C-terminal independent manner. over-expression of MMP-28 in chondrosarcoma cells led to altered cell morphology with increased organisation of actin. Adhesion to type II collagen and fibronectin was increased, and migration across the former was decreased. MMP-28 was localised to the cell surface, at least transiently, in a C-terminal dependent manner. Heparin prevented both extracellular matrix association and cell surface binding of MMP-28 suggesting that both are via heparan sulphate proteoglycans. Over-expression of activatable MMP-28, but not catalytically inactive EA mutant increased the expression and activity of MMP-2, and all forms of MMP-28 tested increased expression of MMP19 and TIMP3 mRNA. These data demonstrate that expression of MMP28 alters cell phenotype towards a more adhesive, less migratory behaviour. Further, MMP-28 activity may reside predominantly in the extracellular matrix, and we are currently searching for substrates in this compartment.

MMP28 gene expression is regulated by Sp1 transcription factor acetylation

MMP-28 (epilysin) is a recently cloned member of the MMP (matrix metalloproteinase) family. It is highly expressed in the skin by keratinocytes, the developing and regenerating nervous system and a number of other normal human tissues, as well as a number of carcinomas. The MMP28 promoter has previously been cloned and characterized identifying a conserved GT-box that binds Sp1/Sp3 (specificity proteins 1 and 3) proteins and is essential for the basal expression of the gene. The present study demonstrates that MMP28 expression is induced by HDAC (histone deacetylase) inhibitors and that this effect is mediated through the GT-box. Transient transfection assays have shown that the induction of MMP28 expression by the HDAC inhibitior TSA (trichostatin A) is mediated via Sp1 at the GT-box. Immunoprecipitation experiments have shown that the acetylation of Sp1 and Sp3 is increased by TSA treatment; however, no effect on DNA binding was observed. Histone acetyltransferases such as p300 and P/CAF [p300/CREB (cAMP-response-element-binding protein)-binding protein-associated factor] increased induction of the MMP28 promoter by Sp1. Knockdown of HDAC1 using siRNA (small interfering RNA) also induces the MMP28 promoter. Oligonucleotide pulldown identified STRAP (serine/threonine kinase receptor-associated protein) as a further protein recruited to the MMP28 promoter and acting functionally with Sp1.

Acetylation in the regulation of metalloproteinase and tissue inhibitor of metalloproteinases gene expression.

Together, the matrix metalloproteinases (MMPs) are capable of degrading every component of the extracellular matrix (ECM). Besides degradation of the ECM, MMPs release bioactive molecules from the matrix or cell surface and play important role in tissue repair after injury, development and in a number of pathologies including arthritis and cancer metastasis. Small molecules that inhibit a broad spectrum of metalloproteinases have not proved useful in the treatment of various diseases, probably due to the diverse roles of this large family of enzymes. An alternative therapeutic approach for a number of pathologies is to modulate the expression of specific metalloproteinase genes. Acetylation represents a recently identified covalent protein modification that is strongly implicated in transcriptional regulation. Histones were the first proteins demonstrated to show variable acetylation leading to gene activation. Subsequently, a large number of molecules including structural proteins, intracellular signaling molecules, nuclear membrane receptors and transcription factors were shown to be acetylated. Acetylation, like phosphorylation, is a reversible modification. Acetyl groups are added by a family of histone acetyl transferase enzymes (HATs) and are removed by histone deacetylases (HDACs). Inhibitors of HDACs (HDACi) have potent anti-proliferative and pro-apoptotic activities in cancer cells and may be used as cancer therapeutics. In this review, we examine the impact of changes in acetylation on the expression of the MMPs and their inhibitors (tissue inhibitors of metalloproteinases, TIMPs). We discuss the suggestion that HDACi may act in a dual fashion: selectively decreasing cancer cell viability and reducing metastatic potential by decreasing stromal cell expression of specific metalloproteinases. Furthermore, we consider the possibility that selective HDACi have a potential as anti-inflammatory agents and in a range of degradative diseases such as arthritis.