Molecular cloning, chromosomal localization, and bacterial expression of a murine macrophage metalloelastase

Implications of MMP-12 in the pathophysiology of ischaemic stroke

This article focuses on the emerging role of matrix metalloproteinase-12 (MMP-12) in ischaemic stroke (IS). MMP-12 expression in the brain increases dramatically in animal models of IS, and its suppression reduces brain damage and promotes neurological, sensorimotor and cognitive functional outcomes. Thus, MMP-12 could represent a potential target for the management of IS. This article provides an overview of MMP-12 upregulation in the brain following IS, its deleterious role in the post-stroke pathogenesis (blood-brain barrier disruption, inflammation, apoptosis and demyelination), possible molecular interactions and mechanistic insights, its involvement in post-ischaemic functional deficits and recovery as well as the limitations, perspectives, challenges and future directions for further research. Prior to testing any MMP-12-targeted therapy in patients with acute IS, additional research is needed to establish the effectiveness of MMP-12 suppression against IS in older animals and in animals with comorbidities. This article also examines the clinical implications of suppressing MMP-12 alone or in combination with MMP-9 for extending the currently limited tissue plasminogen activator therapy time window. Targeting of MMP-12 is expected to have a profound influence on the therapeutic management of IS in the future.

Tensin 2-deficient nephropathy - mechanosensitive nephropathy, genetic susceptibility

Tensin 2 (TNS2), a focal adhesion protein, is considered to anchor focal adhesion proteins to β integrin as an integrin adaptor protein and/or serve as a scaffold to facilitate the interactions of these proteins. In the kidney, TNS2 localizes to the basolateral surface of glomerular epithelial cells, i.e., podocytes. Loss of TNS2 leads to the development of glomerular basement membrane lesions and abnormal accumulation of extracellular matrix in maturing glomeruli during the early postnatal stages. It subsequently results in podocyte foot process effacement, eventually leading to glomerulosclerosis. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation. In this review, we provide an overview of TNS2-deficient nephropathy and discuss the potential mechanism underlying this mechanosensitive nephropathy, which may be applicable to other glomerulonephropathies, such as CD151-deficient nephropathy and Alport syndrome. The onset of TNS2-deficient nephropathy strictly depends on the genetic background, indicating the presence of critical modifier genes. A better understanding of molecular mechanisms of mechanosensitive nephropathy may open new avenues for the management of patients with glomerulonephropathies.

Novel Matrix Metalloproteinase 12 Selective Radiotracers for Vascular Molecular Imaging

Matrix metalloproteinase-12 (MMP-12) is highly upregulated in several inflammatory diseases, including abdominal aortic aneurysm (AAA). Here we report four novel ^99mTc-labeled radiotracers derived from a highly selective competitive MMP-12 inhibitor. These tracers in their ^99gTc version were assessed in vitro on a set of human metalloproteases and displayed high affinity and selectivity toward MMP-12. Their radiolabeling with ^99mTc was shown to be efficient and stable in both buffer and mouse blood. The tracers showed major differences in their biodistribution and blood clearance. On the basis of its in vivo performance, [^99mTc]-1 was selected for evaluation in murine AAA, where MMP-12 gene expression is upregulated. Autoradiography of aortae at 2 h postinjection revealed high uptake of [^99mTc]-1 in AAA relative to adjacent aorta. Tracer uptake specificity was demonstrated through in vivo competition. This study paves the way for further evaluation of [^99mTc]-1 for imaging AAA and other MMP-12-associated diseases.

MMP-12-Induced Pro-osteogenic Responses in Human Aortic Valve Interstitial Cells

BACKGROUND

Calcific aortic valve disease (CAVD) is an age-related and slowly progressive valvular disorder. Overexpression of matrix metalloproteinase 12 (MMP-12) has been found in atherosclerosis, stiffed vascular tissue, and calcified aortic valves. We hypothesized that MMP-12 may induce the pro-osteogenic responses in human aortic valve interstitial cells (AVICs).

METHODS

Human AVICs were isolated from normal and calcified aortic valves. Cells were treated with MMP-12. The pro-osteogenic marker Runt-related transcription factor 2 (RUNX-2), bone morphogenetic protein 2 (BMP-2), and alkaline phosphatase (ALP), as well as MMP-12-associated signaling molecules, were analyzed.

RESULTS

Human calcified aortic valves expressed significantly higher MMP-12 than normal human aortic valves. MMP-12-induced the expression of RUNX-2, BMP-2, ALP, and calcium deposit formation. Suppression of MMP-12 by its inhibitor decreased the expression of RUNX-2, BMP-2, and ALP. MMP-12-induced osteogenic responses were associated with higher levels of phosphorylation of p38 mitogen-activated protein kinases (MAPK), low density lipoprotein-related protein 6 (LRP-6), and β-catenin signaling molecules. Calcified aortic valves exhibited markedly higher levels of LRP-6 and β-catenin levels. Inhibition of either p38 MAPK or LRP-6 attenuated MMP-12-induced expression of RUNX-2, BMP-2, and ALP. Suppression of p38 MAPK abrogated MMP-12-induced activation of LRP-6 and β-catenin signaling pathways.

CONCLUSIONS

MMP-12 induces pro-osteogenic responses in AVICs by activation of p38 MAPK-mediated LRP-6 and β-catenin signaling pathways. The study revealed that the potential role of MMP-12 in the pathogenesis of CAVD and therapeutically targeting MMP-12 may suppress the development of CAVD.

Distinct Requirements for Extracellular and Intracellular MMP12 in the Development of the Adult V-SVZ Neural Stem Cell Niche

The regulatory mechanisms that control neural stem cell (NSC) activation in the adult ventricular-subventricular zone (V-SVZ) stem cell niche have been the focus of intense investigation, yet how the niche first develops and organizes is poorly understood. Here, we examined matrix metalloproteinases (MMPs) for potential roles in V-SVZ stem cell niche development. MMP12 was found to promote appropriate niche cellular arrangements, the formation of specialized niche extracellular matrix, and the translational planar cell polarity of ependymal cells that surround and support niche NSCs. Surprisingly, ependymal cells were found to have an intracellular pool of MMP12 that promoted ependymal cell ciliogenesis by upregulating FOXJ1. In addition, both extracellular and intracellular MMP12 were found to regulate V-SVZ niche output by promoting NSC quiescence. These findings reveal that extracellular and intracellular MMP12 have both unique and overlapping roles that help orchestrate the development of the adult V-SVZ stem cell niche.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

MMP-12, a Promising Therapeutic Target for Neurological Diseases

The role of matrix metalloproteinase-12 (MMP-12) in the pathogenesis of several inflammatory diseases such as chronic obstructive pulmonary disease, emphysema, and asthma is well established. Several new studies and recent reports from our laboratory and others highlighted the detrimental role of MMP-12 in the pathogenesis of several neurological diseases. In this review, we discuss in detail the pathological role of MMP-12 and the possible underlying molecular mechanisms that contribute to disease pathogenesis in the context of central nervous system diseases such as stroke, spinal cord injury, and multiple sclerosis. The available information on the specific MMP-12 inhibitors used in several preclinical and clinical studies is also reviewed. Based on the reported studies to date, MMP-12 suppression could emerge as a promising therapeutic target for several CNS diseases that were discussed in this review.

The Role of Matrix Metalloproteinase Polymorphisms in Ischemic Stroke

Stroke remains the fifth leading cause of mortality in the United States with an annual rate of over 128,000 deaths per year. Differences in incidence, pathogenesis, and clinical outcome have long been noted when comparing ischemic stroke among different ethnicities. The observation that racial disparities exist in clinical outcomes after stroke has resulted in genetic studies focusing on specific polymorphisms. Some studies have focused on matrix metalloproteinases (MMPs). MMPs are a ubiquitous group of proteins with extensive roles that include extracellular matrix remodeling and blood-brain barrier disruption. MMPs play an important role in ischemic stroke pathophysiology and clinical outcome. This review will evaluate the evidence for associations between polymorphisms in MMP-1, 2, 3, 9, and 12 with ischemic stroke incidence, pathophysiology, and clinical outcome. The role of polymorphisms in MMP genes may influence the presentation of ischemic stroke and be influenced by racial and ethnic background. However, contradictory evidence for the role of MMP polymorphisms does exist in the literature, and further studies will be necessary to consolidate our understanding of these multi-faceted proteins.

Matrix metalloproteinase 12 modulates high-fat-diet induced glomerular fibrogenesis and inflammation in a mouse model of obesity

Obesity-induced kidney injury contributes to albuminuria, which is characterized by a progressive decline in renal function leading to glomerulosclerosis and renal fibrosis. Matrix metalloproteinases (MMPs) modulate inflammation and fibrosis by degrading a variety of extracellular matrix and regulating the activities of effector proteins. Abnormal regulation of MMP-12 expression has been implicated in abdominal aortic aneurysm, atherosclerosis, and emphysema, but the underlying mechanisms remain unclear. The present study examined the function of MMP-12 in glomerular fibrogenesis and inflammation using apo E^−/− or apo E^−/−MMP-12^−/− mice and maintained on a high-fat-diet (HFD) for 3, 6, or 9 months. MMP-12 deletion reduced glomerular matrix accumulation, and downregulated the expression of NADPH oxidase 4 and the subunit-p67^phox, indicating the inhibition of renal oxidative stress. In addition, the expression of the inflammation-associated molecule MCP-1 and macrophage marker-CD11b was decreased in glomeruli of apo E^−/−MMP-12^−/− mice fed HFD. MMP-12 produced by macrophages infiltrating into glomeruli contributed to the degradation of collagen type IV and fibronectin. Crescent formation due to renal oxidative stress in Bowman’s space was a major factor in the development of fibrogenesis and inflammation. These results suggest that regulating MMP-12 activity could be a therapeutic strategy for the treatment of crescentic glomerulonephritis and fibrogenesis.

A QSAR study on the inhibition mechanism of matrix metalloproteinase-12 by arylsulfone analogs based on molecular orbital calculations

The inhibition mechanism of matrix metalloproteinase-12 by arylsulfone analogs is revealed using a comprehensive computational approach including docking simulations, molecular orbital calculations, and QSAR.

Ambidextrous binding of cell and membrane bilayers by soluble matrix metalloproteinase-12

Matrix metalloproteinases (MMPs) regulate tissue remodelling, inflammation and disease progression. Some soluble MMPs are inexplicably active near cell surfaces. Here we demonstrate the binding of MMP-12 directly to bilayers and cellular membranes using paramagnetic NMR and fluorescence. Opposing sides of the catalytic domain engage spin-labelled membrane mimics. Loops project from the β-sheet interface to contact the phospholipid bilayer with basic and hydrophobic residues. The distal membrane interface comprises loops on the other side of the catalytic cleft. Both interfaces mediate MMP-12 association with vesicles and cell membranes. MMP-12 binds plasma membranes and is internalized to hydrophobic perinuclear features, the nuclear membrane and inside the nucleus within minutes. While binding of TIMP-2 to MMP-12 hinders membrane interactions beside the active site, TIMP-2-inhibited MMP-12 binds vesicles and cells, suggesting compensatory rotation of its membrane approaches. MMP-12 association with diverse cell membranes may target its activities to modulate innate immune responses and inflammation.

Administration of bleomycin via the oropharyngeal aspiration route leads to sustained lung fibrosis in mice and rats as quantified by UTE-MRI and histology

Pulmonary fibrosis can be experimentally induced in small rodents by bleomycin. The antibiotic is usually administered via the intratracheal or intranasal routes. In the present study, we investigated the oropharyngeal aspiration of bleomycin as an alternative route for the induction of lung fibrosis in rats and mice. The development of lung injury was followed in vivo by ultrashort echo time magnetic resonance imaging (UTE-MRI) and by post-mortem analyses (histology of collagen, hydroxyproline determination, and qRT-PCR). In C57BL/6 mice, oropharyngeal aspiration of bleomycin led to more prominent lung fibrosis as compared to intranasal administration. Consequently, the oropharyngeal aspiration route allowed a dose reduction of bleomycin and, therewith, a model refinement. Moreover, the distribution of collagen after oropharyngeal aspiration of bleomycin was more homogenous than after intranasal administration: for the oropharyngeal aspiration route, fibrotic areas appeared all over the lung lobes, while for the intranasal route fibrotic lesions appeared mainly around the largest superior airways. Thus, oropharyngeal aspiration of bleomycin induced morphological changes that were more comparable to the human disease than the intranasal administration route did. Oropharyngeal aspiration of bleomycin led to a homogeneous fibrotic injury also in rat lungs. The present data suggest oropharyngeal aspiration of bleomycin as a less invasive means to induce homogeneous and sustained fibrosis in the lungs of mice and rats.

Detection of endogenous matrix metalloprotease-12 active form with a novel broad spectrum activity-based probe

Matrix metalloproteases (MMPs) have attracted considerable attention as critical mediators of pathological tissue remodeling processes. However it remains an unresolved challenge to detect their active forms in biological samples. To prove the efficacy of a recently developed MMP activity-based probe, we examined the content in MMP active forms of bronchoalveolar lavage fluids (BALf) from male C57BL/6 mice exposed to ultrafine carbon black nanoparticles, a model of chronic obstructive pulmonary disease. This probe was shown to label proteins, mostly expressed in BALf of mice exposed to nanoparticles. Using competition assays with a selective MMP-12 inhibitor as well as MMP-12 knock-out mice, one of these proteins was identified as the active form of the catalytic domain of MMP-12. This new probe can detect the active form of MMP-12 down to a threshold of 1 fmol. Radioactive counting showed the concentration of the active form of MMP-12 to be around 1 fmol/μl in BALf from nanoparticle-treated mice. A less sensitive probe would therefore not have detected MMP-12. As the probe can detect other MMPs in the femtomolar range, it is a potentially powerful tool for monitoring the levels of MMP active forms in various diseases.

Macrophage infiltration and renal damage are independent of matrix metalloproteinase 12 in the obstructed kidney

AIM

To determine whether matrix metalloproteinase-12 (MMP-12) plays a functional role in renal interstitial macrophage accumulation, interstitial fibrosis or tubular apoptosis in the unilateral ureteric obstruction (UUO) model.

BACKGROUND

MMP-12 is an enzyme that can cleave a number of extracellular matrix proteins and plays a role in macrophage-mediated injury in experimental models of emphysema and antibody-dependent glomerular disease. Macrophages are thought to promote renal fibrosis and tubular damage in the obstructed kidney. Furthermore, upregulation of MMP-12 expression by infiltrating macrophages in the obstructed kidney has been described, but the potential role of MMP-12 in renal injury induced by this non-immune insult is unknown.

METHODS

Groups of eight MMP-12 gene deficient (MMP-12(-/-)) and wild type (WT) C57BL/6J mice were killed 3, 7 or 14 days after UUO.

RESULTS

Analysis of three different lineage markers found no difference in the degree of interstitial macrophage accumulation between MMP-12(-/-) and WT UUO groups at any time point. Examination of renal fibrosis by total collagen staining, α-SMA + myofibroblast accumulation, and TGF-β1, PAI-1 and collagen IV mRNA levels showed no difference between MMP-12(-/-) and WT UUO groups. Finally, tubular damage (KIM-1 levels) and tubular apoptosis (cleaved caspase-3) in the obstructed kidney was not affected by MMP-12 gene deletion.

CONCLUSION

In contrast to lung injury and antibody-dependent glomerular injury, MMP-12 is not required for renal interstitial macrophage accumulation, interstitial fibrosis or tubular damage in the obstructed kidney.

Influence of matrix metalloproteinase-12 on fibrinogen level

In vitro studies have shown that matrix metalloproteinase-12 (MMP12) can degrade fibrinogen, a clotting factor whose level predicts risk of advanced atherosclerosis and myocardial infarction. In this study, we found that mean plasma fibrinogen level was approximately 10-fold higher in MMP12 knockout mice than wildtype mice (p=0.0006). Differential allelic expression analysis of human MMP12 gene polymorphism rs17368582 in human vascular tissues showed an allele-specific effect on MMP12 expression, with one allele (T) having 1.6 fold higher expression level than the other allele (C) (p=0.0006). In a population cohort, we found that individuals homozygous for the MMP12 low expression allele had higher plasma fibrinogen levels (2.95 mg/mL compared with 2.61 mg/mL in other individuals, p=0.029) and increased risk of advanced atherosclerosis [odds ratio 6.3 (95% CI 1.9-20.8), p=0.003] and myocardial infarction [hazard ratio 5.6 (95% CI 1.7-18.3), p=0.005]. In summary, our study in mouse and humans provides in vivo evidence of an effect of MMP12 on fibrinogen level.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Evidence for early fibrosis and increased airway resistance in bone marrow transplant recipient mice deficient in MMP12

Idiopathic pneumonia syndrome (IPS) is a significant cause of morbidity and mortality post-bone marrow transplantation (BMT) in humans. In our established murine IPS model in which lethally conditioned recipients are given allogeneic bone marrow and splenocytes, recruitment of host monocytes occurs early post-BMT, followed by donor T cells concomitant with development of severe lung dysfunction. Because matrix metalloproteinase 12 (MMP12) is important for macrophage infiltration and injury in other mouse models of lung disease such as emphysema, lethally conditioned MMP12(-/-) mice were used as allogeneic recipients to determine whether MMP12 plays a similar role in potentiating lung injury in IPS. Surprisingly, MMP12(-/-) mice developed IPS and exhibited an accelerated allogeneic T cell-dependent decrease in compliance compared with wild-type (WT) recipients. MMP12(-/-), but not WT, mice also had allogeneic T cell-dependent elevated lung resistance post-BMT. Recruitment of monocytes and T cells into the lungs was not altered on day 7 post-BMT, but the lungs of MMP12(-/-) recipients had increased collagen deposition, a feature normally not seen in our IPS model. MMP12(-/-) mice had a compensatory increase in MMP2 in the lungs post-BMT, as well as increased β6-integrin compared with WT recipients, and only in the presence of allogeneic T cells. Levels of total transforming growth factor (TGF)-β1 protein in the lungs were elevated compared with WT recipients, consistent with the profibrotic function of β6-integrin as an activator of TGF-β. These data indicate that host-derived MMP12 may be important in limiting development of IPS by allowing proper remodeling of extracellular matrix and effective repair of BMT-related injury.

Characterization of peptide fragments from lung elastin degradation in chronic obstructive pulmonary disease

This study presents a method for detecting and characterizing peptides of elastin that result from lung matrix injury in chronic obstructive pulmonary disease (COPD). Lung elastin degradation was studied by two representative in vivo elastases, human neutrophil elastase (HNE) and macrophage metalloproteinase (MMP12). The resulting peptide mixtures were analyzed by high-performance liquid chromatography/electrospray tandem mass spectrometry (LC/MSMS) to characterize 40 elastin-derived peptides (EDPs), 24 from HNE and 16 from MMP12 digestions. The peptides constitute major EDPs that are solubilized by the enzymatic digestion. Using the selected reaction monitoring (SRM) from LC/MSMS analysis, the transition ions of the peptides were used to investigate the presence of the peptides in selected body fluids of chronic obstructive pulmonary disease (COPD) patients. Four peptides, GYPI, APGVGV, GLGAFPA, and VGVLPGVPT, were detected in plasma or sputum of some COPD patients but not in normal controls. A hexapeptide VGVAPG, which had been widely studied for its chemotactic activity for a possible pathogenic role in COPD, was not detected in lung EDPs by HNE or MMP12 digestion, but only by porcine pancreatic elastase (PPE) digestion. This study demonstrates a practical methodology to study peptides from matrix degradations in pulmonary disease and a means of investigating their pathogenesis.

Neprilysin is identical to skin fibroblast elastase: its role in skin aging and UV responses

Although human skin fibroblast (HSF) elastase has been characterized as a membrane-bound metalloproteinase, little is known about its structure, amino acid sequence, and encoding gene. As there are similarities in the molecular weights and inhibitory profiles of HSF elastase and neprilysin (neutral endopeptidase 24.11 (NEP)), in this study we tested the hypothesis that they are identical using immunoprecipitation and transfection methods. An immunoprecipitation study demonstrated that HSF elastase activity co-immunoprecipitated with anti-NEP in lysates of cultured HSF. Transfection of an NEP cDNA expression vector into COS-1 cells elicited the expression of HSF elastase and NEP activities in the transfected cells. These findings strongly suggest that HSF elastase is identical to NEP, which functions mainly in neuron-associated cells to degrade neuropeptides. Analysis of the expression pattern of NEP revealed that its expression was remarkably up-regulated at the gene, protein, and enzymatic activity levels during the replicative senescence of cultured HSF. Further, the activity of NEP was markedly enhanced in a pattern similar to elastase activity during the intrinsic aging of mouse skin, in UVA-exposed HSF as well as in HSF treated with conditioned medium from UVB-exposed human keratinocytes. Analysis of the cytokine profile for the stimulation of NEP and HSF elastase activities in HSF demonstrated that among the 11 cytokines tested, IL-1α, IL-1β, IL-6, IL-8, and GM-CSF had the potential to significantly stimulate both activities similarly, again supporting the identity of HSF elastase and NEP.

Physiology and pathophysiology of matrix metalloproteases

Matrix metalloproteases (MMPs) comprise a family of enzymes that cleave protein substrates based on a conserved mechanism involving activation of an active site-bound water molecule by a Zn(2+) ion. Although the catalytic domain of MMPs is structurally highly similar, there are many differences with respect to substrate specificity, cellular and tissue localization, membrane binding and regulation that make this a very versatile family of enzymes with a multitude of physiological functions, many of which are still not fully understood. Essentially, all members of the MMP family have been linked to disease development, notably to cancer metastasis, chronic inflammation and the ensuing tissue damage as well as to neurological disorders. This has stimulated a flurry of studies into MMP inhibitors as therapeutic agents, as well as into measuring MMP levels as diagnostic or prognostic markers. As with most protein families, deciphering the function(s) of MMPs is difficult, as they can modify many proteins. Which of these reactions are physiologically or pathophysiologically relevant is often not clear, although studies on knockout animals, human genetic and epigenetic, as well as biochemical studies using natural or synthetic inhibitors have provided insight to a great extent. In this review, we will give an overview of 23 members of the human MMP family and describe functions, linkages to disease and structural and mechanistic features. MMPs can be grouped into soluble (including matrilysins) and membrane-anchored species. We adhere to the 'MMP nomenclature' and provide the reader with reference to the many, often diverse, names for this enzyme family in the introduction.

Expression of recombinant matrix metalloproteinases in Escherichia coli

Matrix metalloproteinases (MMPs) are a group of zinc-dependent endopeptidases that are capable of cleaving all of the components of the extracellular matrix (ECM). The role that the MMPs play in normal and pathological conditions has long been of interest. The mechanisms by which the MMPs cleave the different components of the ECM have been examined extensively. Some of these studies have been made possible, in part, by the ability to express recombinant MMPs. These recombinant MMPs have been utilized in both structural and functional studies. In addition, future studies can benefit from the availability of recombinant MMPs. Recombinant MMPs have been expressed in mammalian and bacterial recombinant expression systems. The most common bacterial expression system employed for this has been the utilization of expression plasmids in Escherichia coli. This has resulted in the production of a large amount of protein in a short period of time. The expression of a recombinant truncated form of human stromelysin-1 (MMP-3) will be used to illustrate the methods utilized for the expression of a MMP in E. coli. This will include discussions about the expression vector, the cloning of the MMP cDNA into the expression vector, protein induction, protein extraction, protein refolding and purification, and protein characterization.

Macrophage metalloelastase (MMP-12) as a target for inflammatory respiratory diseases

BACKGROUND

MMPs are known to regulate the turnover of extracellular matrix and have been suggested to be important in lung disease associated with tissue remodeling. Macrophage elastase (MMP-12) is able to degrade extracellular matrix components such as elastin and is involved in tissue remodeling in inflammatory respiratory diseases such as chronic obstructive pulmonary diseases (COPD), including emphysema. Recent studies using MMP-12 inhibitors have demonstrated a reduction in both the inflammatory process and airspace enlargement in lung tissue.

OBJECTIVE/METHODS

This review discusses the potential involvement of MMP-12 in the pathophysiological process and proposes MMP-12 as a target for inflammatory disorders of the respiratory system.

RESULTS/CONCLUSIONS

MMP-12 plays a predominant role in the inflammatory process induced by cigarette smoke, and therefore is potentially an important therapeutic target for the treatment of COPD.

Matrix metalloproteinase 12 silencing: a therapeutic approach to treat pathological lung tissue remodeling?

Among the large matrix metalloproteinases (MMPs) family, MMP-12, also referred to as macrophage elastase, plays a significant role in chronic pulmonary pathologies characterized by an intense tissue remodeling such as asthma and COPD. This review will summarize knowledge about MMP-12 structure, functions and mechanisms of activation and regulation, including potential MMP-12 modulation by microRNA. As MMP-12 is involved in many tissue remodeling diseases, efforts have been made to develop specific synthetic inhibitors. However, at this time, very few chemical inhibitors have proved to be efficient and specific to a particular MMP. The relevance of silencing MMP-12 by RNA interference is highlighted. The specificity of this approach using siRNA or shRNA and the strategies to deliver these molecules in the lung are discussed.

The expression of macrophage and neutrophil elastases in rat periradicular lesions

Macrophage elastase and neutrophil elastase are involved in tissue destruction in periradicular lesions. The purpose of this study was to examine these elastases immunohistochemically during development of periradicular lesions induced in rat mandibular first molar by pulpal exposure for 7, 14, 21, 28, and 42 days. Histologically, periapical inflammation developed from 7 to 21 days and then subsided after 28 days. The area of these lesions gradually increased from 7 to 28 days and subsequently decreased at 42 days. Macrophage elastase was first detected at 7 days and predominantly shown from 14 to 28 days, whereas neutrophil elastase gradually increased from 14 to 28 days. Macrophage elastase was significantly greater than neutrophil elastase from 7 to 21 days. These results suggest that macrophage elastase was enhanced from an early stage during the development of these lesions and that neutrophil elastase was related to the expansion of periapical tissue destruction including bone resorption.

Solution structure of inhibitor-free human metalloelastase (MMP-12) indicates an internal conformational adjustment

Macrophage metalloelastase or matrix metalloproteinase-12 (MMP-12) appears to exacerbate atherosclerosis, emphysema, aortic aneurysm, rheumatoid arthritis, and inflammatory bowel disease. An inactivating E219A mutation, validated by crystallography and NMR spectra, prevents autolysis of MMP-12 and allows us to determine its NMR structure without an inhibitor. The structural ensemble of the catalytic domain without an inhibitor is based on 2813 nuclear Overhauser effects (NOEs) and has an average RMSD to the mean structure of 0.25 A for the backbone and 0.61 A for all heavy atoms for residues Trp109-Gly263. Compared to crystal structures of MMP-12, helix B (hB) at the active site is unexpectedly more deeply recessed under the beta-sheet. This opens a pocket between hB and beta-strand IV in the active-site cleft. Both hB and an internal cavity are shifted toward beta-strand I, beta-strand III, and helix A on the back side of the protease. About 25 internal NOE contacts distinguish the inhibitor-free solution structure and indicate hB's greater depth and proximity to the sheet and helix A. Line broadening and multiplicity of amide proton NMR peaks from hB are consistent with hB undergoing a slow conformational exchange among subtly different environments. Inhibitor-binding-induced perturbations of the NMR spectra of MMP-1 and MMP-3 map to similar locations across MMP-12 and encompass the internal conformational adjustments. Evolutionary trace analysis suggests a functionally important network of residues that encompasses most of the locations adjusting in conformation, including 18 residues with NOE contacts unique to inhibitor-free MMP-12. The conformational change, sequence analysis, and inhibitor perturbations of NMR spectra agree on the network they identify between structural scaffold and the active site of MMPs.

CD8+ T Cells are required for inflammation and destruction in cigarette smoke-induced emphysema in mice

Increased numbers of T lymphocytes are observed in the lungs of patients with chronic obstructive pulmonary disease, but their role in the disease process is not known. We investigated the role of CD8+ T cells in inflammatory cell recruitment and lung destruction in a cigarette smoke-induced murine model of emphysema. In contrast to wild-type C57BL/6J mice that displayed macrophage, lymphocyte, and neutrophil recruitment to the lung followed by emphysema in response to cigarette smoke, CD8+ T cell-deficient (CD8-/-) mice had a blunted inflammatory response and did not develop emphysema when exposed to long-term cigarette smoke. Further studies supported a pathogenetic pathway whereby the CD8+ T cell product, IFN-gamma-inducible protein-10, induces production of macrophage elastase (matrix metalloproteinase 12) that degrades elastin, both causing lung destruction directly and generating elastin fragments that serve as monocyte chemokines augmenting macrophage-mediated lung destruction. These studies demonstrate a requirement for CD8+ T cells for the development of cigarette smoke-induced emphysema and they provide a unifying pathway whereby CD8+ T cells are a central regulator of the inflammatory network in chronic obstructive pulmonary disease.

Over-expression and refolding of isotopically labeled recombinant catalytic domain of human macrophage elastase (MMP-12) for NMR studies

Human macrophage elastase (MMP-12) plays an important role in inflammatory processes and is involved in a number of physiological or pathological situations, such as conversion of plasminogen into angiostatin, allergic airway inflammation, vascular remodeling or alteration, as well as emphysema, and has been justified as a novel drug target. Here, we report the over-expression in Escherichia coil, purification and refolding of MMP-12 catalytic domain for NMR studies. The primary sequence of expressed protein was identified by means of MALDI-TOF MS, and was confirmed by the MALDI-TOF MS data of trypsin-digested peptides. A significantly optimized protocol has been worked out to prepare 15N and/or 13C-labeled MMP-12 catalytic domain, and the yield of the purified protein is estimated to 10-12 mg from 0.5L of M9 minimal media. Finally, the 15N-1H HSQC spectrum of uniformly 15N-labeled MMP-12 catalytic domain indicates the presence of well-ordered and properly folded protein in a monomeric form.

Essential role of MMP-12 in Fas-induced lung fibrosis

Acute lung injury (ALI) is characterized by an early inflammatory response followed by a late fibroproliferative phase, and by an increase in the bronchoalveolar lavage fluid (BALF) concentrations of bioactive soluble FasL (sFasL). Activation of Fas (CD95) has been associated with the development of lung fibrosis in mice. The goal of this study was to determine the mechanisms that link Fas activation with the development of fibrosis in the lungs. We treated mice with three daily intratracheal instillations of a Fas-activating monoclonal antibody (Jo2) or a control IgG, and studied the animals at sequential times. Mice treated with Jo2 had increased caspase-3 activation in alveolar wall cells on Days 2, 4, and 7; an inflammatory response peaking on Day 7, and increased total lung collagen on Day 21. Gene expression profiling performed on Days 2, 4, and 7 showed sequential activation of co-regulated profibrotic genes, including marked up-regulation of matrix metalloproteinase 12 (MMP-12). Targeted deletion of MMP-12 protected mice from Fas-induced pulmonary fibrosis, even though the inflammatory responses in the lungs were similar to those of wild-type mice. Compared with wild-type mice, the mmp12(-/-) mice showed decreased expression of the profibrotic genes egr1 and cyr61. We conclude that Fas activation in the lungs induces a complex response that includes apoptosis, inflammation, and eventually fibrosis, and that MMP-12 is essential for the fibrotic phenotype. We speculate that MMP-12 activity is required for activation of the profibrotic genes egr1 and cyr61.

Increase in the expression of matrix metalloproteinase-12 in the airways of rats with allergic bronchial asthma

Although an involvement of matrix metalloproteinase (MMP)-12 in the development of chronic obstructive pulmonary disease (COPD) and airway inflammation has been suggested, its detailed role in the airways is not well known now. In the present study, the changes in the expression and localization of MMP-12 in airways of repeatedly antigen-challenged rats were investigated to show an association of MMP-12 with allergic bronchial asthma. Rats sensitized by dinitrophenylated Ascaris antigen were 3 times repeatedly challenged with aerosolized antigen solution to induce an asthmatic reaction. Twenty-four hours after the last antigen challenge, marked airway inflammation and bronchial smooth muscle hyperresponsiveness were observed. In this animal model of allergic bronchial asthma, a significant increase in the expression/activity of MMP-12 was found: the peak was observed at 12 h after the last antigen challenge. Furthermore, mRNA expression of MMP-12 was also increased at the early phase (1-3 h) after the last antigen challenge. Immunohistochemical studies revealed that MMP-12 was mainly expressed in airway epithelia and alveolar macrophages. These findings suggest that MMP-12 is upregulated after the induction of asthmatic reaction. MMP-12 might be a new target for the therapy against allergic bronchial asthma.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.

Altered postnatal lung development in C3H/HeJ mice

C3H/HeJ mice develop an increase in terminal air space area detectable by postnatal d 14 that persists into adulthood compared with strain-matched controls (C3H/SnJ, C3H/OuJ). Morphometric quantification revealed a 50% increase in terminal air space area by postnatal d 14 and a 2.3-fold increase by 2 mo of age in C3H/HeJ mice. Bacteriologic cultures obtained from the left lung on postnatal d 7 revealed > 100 colony-forming units (CFU)/left lung of predominantly Gram-negative bacteria (GNB) (Escherichia coli and Proteus mirabilis) in 13 of the 14 C3H/HeJ mice compared with 0 of 12 controls demonstrating colonization of the developing lung in C3H/HeJ mice. An approximately threefold increase in macrophages from bronchoalveolar lavage, threefold increases in matrix metalloproteinase 12 (MMP-12) mRNA and protein levels and elevated levels of proinflammatory cytokines monocyte chemoattractant protein (MCP-1) and keratinocyte-derived cytokine (KC) were also found. P. mirabilis obtained from lung cultures in C3H/HeJ mice induced nuclear factor-kappaB (NF-kappaB) activation in human embryonic kidney 293 (HEK 293) cells transfected with TLR5. In C3H/HeJ mice lacking TLR4 signaling, bacterial colonization is associated with chronic inflammation and permanent changes in lung morphology.

Gelatinase B/matrix metalloproteinase-9 contributes to cellular infiltration in a murine model of zymosan peritonitis

Murine zymosan-induced peritonitis represents a well-defined model of acute inflammation. However, the molecular mechanisms by which leukocytes degrade basement membranes during extravasation into the peritoneum are not clear. Gelatinase B (MMP-9) is thought to participate in cellular migration, yet its role in leukocyte transmigration through endothelia during inflammation remains controversial. The aim of the present study was to evaluate the role of MMP-9 in the cell influx during zymosan-induced experimental peritonitis. In zymosan-treated Balb/c mice MMP-9 and its natural inhibitor (tissue inhibitor of metalloproteinase 1 - TIMP-1) were present in the peritoneal fluid and plasma at the time of peritoneal neutrophil (polymorphonuclear leukocyte - PMN) infiltration and persisted there until the time of monocytes/macrophages influx. To probe the function of gelatinases, gelatinase B-deficient mice (MMP-9(-/-)) were used as well as Balb/c mice treated with cyclic CTTHWGFTLC (INH), a specific peptide inhibitor of gelatinases. The studies revealed that in either group of mice deprived of MMP-9 activity, PMN infiltration was impaired at the time of their maximal extravasation (6h) while tumor necrosis factor alpha (TNF-alpha), cytokine-induced neutrophil chemoattractant (KC) and interleukin 10 (IL-10) levels were not changed. At later stages (24 h post-zymosan) a significant increase in PMNs was observed in MMP-9(-/-) mice, but not in the inhibitor-treated mice, in comparison to their respective controls. Moreover, intraperitoneal (i.p.) injection of recombinant mouse pro-MMP-9 induced leukocyte accumulation in peritoneum. Collectively, the findings indicate that gelatinase B participates in leukocyte transmigration; however, its function can be compensated by other mechanisms.

Transcriptional up‐regulation of MMPs 12 and 13 by asbestos occurs via a PKCδ‐dependent pathway in murine lung

Asbestos is a known inflammatory, carcinogenic, and fibrotic agent, but the mechanisms leading to asbestos-induced lung diseases are unclear. Using a murine inhalation model of fibrogenesis, we show that asbestos causes significant increases in mRNA levels of lung matrix metalloproteinases (MMPs 12 and 13) and tissue inhibitor of metalloproteinases (TIMP1), as well as increased activities of MMP 2, 9, and 12 in bronchoalveolar lavage fluids (BALF). Asbestos-exposed PKCdelta knockout (PKCdelta-/-) mice exhibited decreased expression of lung MMP12 and MMP13 compared with asbestos-exposed wild-type mice. Studies using small molecule inhibitors in murine alveolar epithelial type II cells (C10) and primary lung fibroblasts confirmed that asbestos transcriptionally up-regulates MMPs via an EGFR (or other growth factor receptors)/PI3K/PKCdelta/ERK1/2 pathway. Moreover, use of a broad-spectrum MMP inhibitor showed that MMPs play an important role in further enhancing asbestos-induced signaling events by activating EGFR. These data reveal a potentially important link between asbestos signaling and integrity of the extracellular matrix (ECM) that likely contributes to asbestos-induced lung remodeling and diseases.

Transfection of mouse macrophage metalloelastase gene into murine CT-26 colon cancer cells suppresses orthotopic tumor growth, angiogenesis and vascular endothelial growth factor expression

A cDNA fragment coding for domains I and II of mouse macrophage metalloelastase (MME) was transfected into murine CT-26 colon cancer cells that are MME deficient. An orthotopic implantation model was established by using MME-transfected cells. In MME-transfected primary tumors, it demonstrated that tumor growth and microvessel formation were significantly inhibited compared with the controls. The expression of vascular endothelial growth factor (VEGF) mRNA and protein was significantly lower in MME-transfected group compared with those in the controls. Our data show that both MME and VEGF gene expression is highly associated with the vascularity of tumors, which may depend on a balance between MME and VEGF expression.

Analysis of the inflammatory response induced by rhMMP-12 catalytic domain instilled in mouse airways

Macrophage elastase (MMP-12) is a metalloproteinase able to degrade extracellular matrix components such as elastin. As many MMPs, MMP-12 is involved in acute and chronic lung injury. However, its role in the inflammatory process of the lung parenchyma is not clearly understood. In this study, we have investigated the effects of airway instillation of rhMMP-12 on inflammatory cell recruitment, cytokine release and gelatinase expression in bronchoalveolar lavage fluid (BALF) or in lung homogenate supernatants in mice. Numbers of total and individual cell types were examined in BALF during the first 72 h following rhMMP-12 instillation. A marked recruitment of neutrophils was observed with a maximum increase at 18 h. This cellular recruitment was associated with a very transient increase in IL-6, TNF-alpha MIP-1alpha, MCP-1 and KC levels and gelatinase expression in BALF and in lung homogenate supernatants. From days 4 to 15, performing the same analyses, we observed an important and stable recruitment of macrophages in BALF in absence of the other studied inflammatory markers. These results demonstrate that rhMMP-12 itself is able to induce an early inflammatory response characterized by neutrophil infiltration, cytokine release and gelatinase activation followed by a later response composed mainly of macrophage recruitment.

A protective role for the A1 adenosine receptor in adenosine-dependent pulmonary injury

Adenosine is a signaling nucleoside that has been implicated in the regulation of asthma and chronic obstructive pulmonary disease. Adenosine signaling can serve both pro- and anti-inflammatory functions in tissues and cells. In this study we examined the contribution of A(1) adenosine receptor (A(1)AR) signaling to the pulmonary inflammation and injury seen in adenosine deaminase-deficient (ADA-deficient) mice, which exhibit elevated adenosine levels. Experiments revealed that transcript levels for the A(1)AR were elevated in the lungs of ADA-deficient mice, in which expression was localized predominantly to alveolar macrophages. Genetic removal of the A(1)AR from ADA-deficient mice resulted in enhanced pulmonary inflammation along with increased mucus metaplasia and alveolar destruction. These changes were associated with the exaggerated expression of the Th2 cytokines IL-4 and IL-13 in the lungs, together with increased expression of chemokines and matrix metalloproteinases. These findings demonstrate that the A(1)AR plays an anti-inflammatory and/or protective role in the pulmonary phenotype seen in ADA-deficient mice, which suggests that A(1)AR signaling may serve to regulate the severity of pulmonary inflammation and remodeling seen in chronic lung diseases by controlling the levels of important mediators of pulmonary inflammation and damage.

Induction of macrophage elastase (MMP-12) gene expression by statins

The statins (including mevastatin and lovastatin) are a widely prescribed class of serum-cholesterol lowering drugs that function by inhibiting 3-hydroxymethylglutaryl coenzyme A (HMG CoA) reductase activity and cellular sterol synthesis. Statins are also widely being appreciated for their inhibitory effects upon inflammation, primarily mediated through direct regulation of inflammatory gene expression. Here we report that statins are also capable of increasing the expression of macrophage elastase (MMP-12). The induction of MMP-12 in mouse macrophages by statins is specific for HMG CoA reductase inhibition, rescued by mevalonate and not observed after inhibition of subsequent steps in the cholesterol biosynthetic pathway. Modulation of cholesterol metabolism may lead to changes in MMP-12 expression and subsequent impacts during physiological and pathophysiological states. We conclude that statins, in addition to their previously described anti-inflammatory properties, may promote the production of some proteinases from activated macrophages.

Crystal structures of novel non-peptidic, non-zinc chelating inhibitors bound to MMP-12

Human macrophage elastase (MMP-12) plays an important role in inflammatory processes and has been implicated in diseases such as emphysema and chronic obstructive pulmonary disease (COPD). It is therefore an attractive target for therapeutic agents. As part of a structure-based drug design programme to find new inhibitors of MMP-12, the crystal structures of the MMP-12 catalytic domain (residues 106-268) complexed to three different non-peptidic small molecule inhibitors have been determined. The structures reveal that all three ligands bind in the S1' pocket but show varying degrees of interaction with the Zn atom. The structures of the complexes with inhibitors CP-271485 and PF-00356231 reveal that their central morpholinone and thiophene rings, respectively, sit over the Zn atom at a distance of approximately 5A, locating the inhibitors halfway down the S1' pocket. In both of these structures, an acetohydroxamate anion, an artefact of the crystallisation solution, chelates the zinc atom. By contrast, the acetohydroxamate anion is displaced by the ligand in the structure of MMP-12 complexed to PD-0359601 (Bayer), a potent zinc chelating N-substituted biaryl butyric acid, used as a reference compound for crystallisation. Although a racemate was used for the crystallisation, the S enantiomer only is bound in the crystal. Important hydrophobic interactions between the inhibitors and residues from the S1' pocket are observed in all of the structures. The relative selectivity displayed by these ligands for MMP-12 over other MMP family members is discussed.

Matrix metalloproteinase-12 (MMP-12) in osteoclasts: new lesson on the involvement of MMPs in bone resorption

Osteoclasts require matrix metalloproteinase (MMP) activity and cathepsin K to resorb bone, but the critical MMP has not been identified. Osteoclasts express MMP-9 and MMP-14, which do not appear limiting for resorption, and the expression of additional MMPs is not clear. MMP-12, also called metalloelastase, is reported only in a few cells, including tissue macrophages and hypertrophic chondrocytes. MMP-12 is critical for invasion and destruction in pathologies such as aneurysm and emphysema. In the present study, we demonstrate that osteoclasts express MMP-12, although only in some situations. Northern blots show that highly purified rabbit osteoclasts in culture express MMP-12 at the same level as macrophages, whereas in situ hybridizations performed on rabbit bone do not show any MMP-12 expression in osteoclasts whatever the bone type. In contrast, in situ hybridizations performed on mouse bone show MMP-12 expression in osteoclasts in calvariae and long bones. We also demonstrate that recombinant MMP-12 cleaves the putative functional domains of osteopontin and bone sialoprotein, two bone matrix proteins that strongly influence osteoclast activities, such as attachment, spreading and resorption. Furthermore, we investigated the role of MMP-12 in bone resorption and osteoclast recruitment by comparing MMP-12 knockout and wild-type mice in specialized culture models known to depend on MMP activity, as well as in the ovariectomy model, and we did not find any indication for a limiting role of MMP-12 in these processes. In conclusion, we found that osteoclasts are able to express MMP-12, but MMP-12 did not appear critical for osteoclast recruitment or resorption. The fact that none of the MMPs identified so far in osteoclasts appears limiting for resorption, gives strength to the hypothesis that the critical MMP for bone solubilization is produced by non-osteoclastic cells.

Inhibition of matrix metalloproteinase-14 in osteosarcoma cells by clodronate

BACKGROUND

Bisphosphonates reduce the bone metastasis formation and angiogenesis but the exact molecular mechanisms involved are unclear. Progelatinase A (proMMP-2; 78 KDa) is activated up during the tumor spread and metastasis by a cell surface-associated matrix metalloproteinase (membrane-type matrix metalloproteinase [MT1-MMP] or MMP-14).

MATERIAL AND METHODS

We evaluated the effects of a bisphosphonate (clodronate) on MT1-MMP mRNA expression and protein production, catalytic activity and proteolytic activation of proMMP-2 by cultured human MG-63 osteosarcoma cells.

RESULTS

Clodronate, at therapeutically attainable noncytotoxic concentrations, dose-dependently inhibited phorbol myristic acetate (PMA)-induced proteolytic activation of proMMP-2 by human MG-63 osteosarcoma cells. Clodronate also downregulated the PMA-induced expression of MT1-MMP mRNA and protein production in human MG-63 osteosarcoma cells, as evidenced by Northern analysis and fluorescent immunohistochemistry. Furthermore, clodronate inhibited directly and dose-dependently MT1-MMP activity, and the MT1-MMP inhibition by clodronate was reduced in the presence of an increased (5 mM) Ca(2+) concentrations when compared to physiological (1 mM) Ca(2+) concentrations.

CONCLUSION

We conclude that (1) the extracellular/cell-associated mechanism of bisphosphonate involves inhibition of MT1-MMP catalytic activity eventually by chelation, and that (2) intracellular mechanism involves downregulation of induced MT1-MMP mRNA and protein expression. The inhibition and downregulation of MT1-MMP by clodronate can be related to their ability to reduce MG-63 osteosarcoma cell invasion and spread. These findings may, at least in part, explain at molecular level the antitumor and antibone resorption activities of clodronate observed in clinical studies.

Macrophage metalloelastase as a major factor for glomerular injury in anti-glomerular basement membrane nephritis

Rat anti-glomerular basement membrane (GBM) nephritis is a model of crescentic glomerulonephritis induced by injection of anti-GBM antiserum. To elucidate the mechanism of glomerular injury, we analyzed the gene expression patterns in the kidneys of anti-GBM nephritis rats using DNA arrays, and found that macrophage metalloelastase/matrix metalloproteinase (MMP)-12 was one of the highly expressed genes in the kidneys on days 3 and 7 after the injection of anti-GBM antiserum. Enhancement of MMP-12 mRNA expression was confirmed by Northern blot analysis, and in situ hybridization revealed that MMP-12 mRNA was expressed in ED-1-positive macrophages and multinuclear giant cells in the glomeruli with crescent. Moreover, these cells were positive with anti-rat rMMP-12 Ab on the section of the kidneys of anti-GBM nephritis rats on day 7. To clarify the role of MMP-12, we conducted a neutralization experiment using anti-rat rMMP-12 Ab, which had an ability to inhibit rMMP-12 activity of degrading natural substrate such as bovine elastin or human fibronectin in vitro. Anti-rat rMMP-12 Ab or control Ig was injected in each of six rats on days 0, 2, 4, and 6 after the injection of anti-GBM antiserum. Consequently, crescent formation and macrophage infiltration in the glomeruli were significantly reduced in the rats treated with anti-rat rMMP-12 Ab, and the amount of urine protein was also decreased. These results disclosed that MMP-12 played an important role in glomerular injury in a crescentic glomerulonephritis model, and inhibition of MMP-12 may lead to a new therapeutic strategy for this disease.

Loss of integrin alpha(v)beta6-mediated TGF-beta activation causes Mmp12-dependent emphysema

Integrins are heterodimeric cell-surface proteins that regulate cell growth, migration and survival. We have shown previously that the epithelial-restricted integrin alpha(v)beta6 has another critical function; that is, it binds and activates latent transforming growth factor-beta (TGF-beta). Through a global analysis of pulmonary gene expression in the lungs of mice lacking this integrin (Itgb6 null mice) we have identified a marked induction of macrophage metalloelastase (Mmp12)--a metalloproteinase that preferentially degrades elastin and has been implicated in the chronic lung disease emphysema. Here we report that Itgb6-null mice develop age-related emphysema that is completely abrogated either by transgenic expression of versions of the beta6 integrin subunit that support TGF-beta activation, or by the loss of Mmp12. Furthermore, we show that the effects of Itgb6 deletion are overcome by simultaneous transgenic expression of active TGF-beta1. We have uncovered a pathway in which the loss of integrin-mediated activation of latent TGF-beta causes age-dependent pulmonary emphysema through alterations of macrophage Mmp12 expression. Furthermore, we show that a functional alteration in the TGF-beta activation pathway affects susceptibility to this disease.

Matrix metalloproteinase-12 gene expression in human vascular smooth muscle cells

BACKGROUND

Matrix metalloproteinases (MMPs) play an important role in smooth muscle cell (SMC) migration and proliferation during vascular remodelling. To investigate the expression of MMP-12 by SMCs, we examined the protein secretion and mRNA expression of MMP-12 by cultured medial SMCs and intimal SMCs derived from human aortic atherosclerotic lesions. To further elucidate the molecular mechanism for MMP-12 expression in SMCs, we determined the sequence requirements for MMP-12 gene transcriptional activity.

RESULTS

Cultured medial SMCs and intimal SMCs showed substantial MMP-12 expression at both the protein and mRNA levels. A series of 5'-deletion and site-directed mutants of the human MMP-12 promoter demonstrated that an AP-1 site spanning -81 to -75 bp was critical for the MMP-12 promoter activity in SMCs. An electrophoretic mobility shift assay confirmed the AP-1 binding activity in SMCs and showed that the protein bound to the AP-1 site consisted predominantly of c-Jun, JunD and Fra-1. Two structurally different inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002, inhibited MMP-12 transcriptional activity and AP-1 binding.

CONCLUSION

These results indicated the expression of MMP-12 in vascular SMCs and showed that the MMP-12 gene expression was dependent on the AP-1 binding activity. Phosphatidylinositol 3-kinase signalling may be involved in MMP-12 transcriptional activation through AP-1 binding activity.

Lefty contributes to the remodeling of extracellular matrix by inhibition of connective tissue growth factor and collagen mRNA expression and increased proteolytic activity in a fibrosarcoma model

Homeostasis of the extracellular matrix (ECM) of tissues is regulated by controlling deposition and degradation of ECM proteins. The breakdown of ECM is essential in blastocyst implantation and embryonic development, tissue morphogenesis, menstrual shedding, bone formation, tissue resorption after delivery, and tumor growth and invasion. TGF-beta family members are one of the classes of proteins that actively participate in the homeostasis of ECM. Here, we report on the effect of lefty, a novel member of the TGF-beta family, on the homeostasis of extracellular matrix in a fibrosarcoma model. Fibroblastic cells forced to express lefty by retroviral transduction lost their ability to deposit collagen in vivo. This event was associated with down-regulation of the steady-state level of connective tissue growth factor that induces collagen type I mRNA. In addition, lefty transduction significantly decreased collagen type I mRNA expression and simultaneously increased collagenolytic, gelatinolytic, elastolytic, and caseinolytic activities in vivo by the transduced fibroblasts. These findings provide a new insight on the actions of lefty and suggest that this cytokine plays an active role in remodeling of the extracellular matrix in vivo.