Matrix metalloproteinase-10 effectively reduces infarct size in experimental stroke by enhancing fibrinolysis via a thrombin-activatable fibrinolysis inhibitor-mediated mechanism

BACKGROUND

The fibrinolytic and matrix metalloproteinase (MMP) systems cooperate in thrombus dissolution and extracellular matrix proteolysis. The plasminogen/plasmin system activates MMPs, and some MMPs have been involved in the dissolution of fibrin by targeting fibrin(ogen) directly or by collaborating with plasmin. MMP-10 has been implicated in inflammatory/thrombotic processes and vascular integrity, but whether MMP-10 could have a profibrinolytic effect and represent a promising thrombolytic agent is unknown.

METHODS AND RESULTS

The effect of MMP-10 on fibrinolysis was studied in vitro and in vivo, in MMP-10-null mice (Mmp10(-/-)), with the use of 2 different murine models of arterial thrombosis: laser-induced carotid injury and ischemic stroke. In vitro, we showed that MMP-10 was capable of enhancing tissue plasminogen activator-induced fibrinolysis via a thrombin-activatable fibrinolysis inhibitor inactivation-mediated mechanism. In vivo, delayed fibrinolysis observed after photochemical carotid injury in Mmp10(-/-) mice was reversed by active recombinant human MMP-10. In a thrombin-induced stroke model, the reperfusion and the infarct size in sham or tissue plasminogen activator-treated animals were severely impaired in Mmp10(-/-) mice. In this model, administration of active MMP-10 to wild-type animals significantly reduced blood reperfusion time and infarct size to the same extent as tissue plasminogen activator and was associated with shorter bleeding time and no intracranial hemorrhage. This effect was not observed in thrombin-activatable fibrinolysis inhibitor-deficient mice, suggesting thrombin-activatable fibrinolysis inhibitor inactivation as one of the mechanisms involved in the MMP-10 profibrinolytic effect.

CONCLUSIONS

A novel profibrinolytic role for MMP-10 in experimental ischemic stroke is described, opening new pathways for innovative fibrinolytic strategies in arterial thrombosis.

Matrix metalloproteinases in lung biology

Despite much information on their catalytic properties and gene regulation, we actually know very little of what matrix metalloproteinases (MMPs) do in tissues. The catalytic activity of these enzymes has been implicated to function in normal lung biology by participating in branching morphogenesis, homeostasis, and repair, among other events. Overexpression of MMPs, however, has also been blamed for much of the tissue destruction associated with lung inflammation and disease. Beyond their role in the turnover and degradation of extracellular matrix proteins, MMPs also process, activate, and deactivate a variety of soluble factors, and seldom is it readily apparent by presence alone if a specific proteinase in an inflammatory setting is contributing to a reparative or disease process. An important goal of MMP research will be to identify the actual substrates upon which specific enzymes act. This information, in turn, will lead to a clearer understanding of how these extracellular proteinases function in lung development, repair, and disease.

Regulation of matrilysin expression in airway epithelial cells by Pseudomonas aeruginosa flagellin

Matrilysin (matrix metalloproteinase-7) is expressed by mucosal epithelia throughout the body and functions in host defense by activating murine intestinal alpha-defensins. In normal adult human lung, matrilysin is expressed at low levels in the airway epithelium, but is markedly up-regulated in cystic fibrosis (CF). Because CF lungs support a heavy bacterial load, we assessed if relevant CF pathogens regulate matrilysin expression in human lung epithelial cells. Indeed, acute infection with Pseudomonas aeruginosa (but not Staphylococcus aureus, Haemophilus influenzae, or Klebsiella pneumoniae) induced the expression of matrilysin in Calu-3 lung epithelial cells. Increased matrilysin mRNA levels were detectable at 3 h post-infection and peaked at a 25-fold induction between 6 and 8 h. Both P. aeruginosa CF isolates and laboratory strains induced matrilysin expression to similar levels. Flagellin, the monomeric precursor of bacterial flagella, was identified as the inductive factor released by P. aeruginosa that regulated matrilysin expression. In addition, flagellin-null mutants failed to stimulate matrilysin expression in cultured cells or in lungs infected in vivo. These data show that P. aeruginosa (and specifically flagellin) potently stimulates matrilysin expression in lung epithelial cells and may mediate the overexpression of this proteinase in CF lungs.

Hypochlorous acid oxygenates the cysteine switch domain of pro-matrilysin (MMP-7). A mechanism for matrix metalloproteinase activation and atherosclerotic plaque rupture by myeloperoxidase

Myeloperoxidase uses hydrogen peroxide (H2O2) to generate hypochlorous acid (HOCl), a potent cytotoxic oxidant. We demonstrate that HOCl regulates the activity of matrix metalloproteinase-7 (MMP-7, matrilysin) in vitro, suggesting that this oxidant activates MMPs in the artery wall. Indeed, both MMP-7 and myeloperoxidase were colocalized to lipid-laden macrophages in human atherosclerotic lesions. A highly conserved domain called the cysteine switch has been proposed to regulate MMP activity. When we exposed a synthetic peptide that mimicked the cysteine switch to HOCl, HPLC analysis showed that the thiol residue reacted rapidly, generating a near-quantitative yield of products. Tandem mass spectrometric analysis identified the products as sulfinic acid, sulfonic acid, and a dimer containing a disulfide bridge. In contrast, the peptide reacted slowly with H2O2, and the only product was the disulfide. Moreover, HOCl markedly activated pro-MMP-7, an MMP expressed at high levels in lipid-laden macrophages in vivo. Tandem mass spectrometric analysis of trypsin digests revealed that the thiol residue of the enzyme's cysteine switch domain had been converted to sulfinic acid. Thiol oxidation was associated with autolytic cleavage of pro-MMP-7, strongly suggesting that oxygenation activates the latent enzyme. In contrast, H2O2 failed to oxidize the thiol residue of the protein or activate the enzyme. Thus, HOCl activates pro-MMP-7 by converting the thiol residue of the cysteine switch to sulfinic acid. This activation mechanism is distinct from the well-studied proteolytic cleavage of MMP pro-enzymes. Our observations raise the possibility that HOCl generated by myeloperoxidase contributes to MMP activation, and therefore to plaque rupture, in the artery wall. HOCl and other oxidants might regulate MMP activity by the same mechanism in a variety of inflammatory conditions.

Structural Analysis of the α2 Integrin I Domain/Procollagenase-1 (Matrix Metalloproteinase-1) Interaction

Previous studies have established that ligation of keratinocyte alpha(2)beta(1) integrin by type I collagen induces expression of matrix metalloproteinase-1 (MMP-1) and that MMP-1 activity is required for the alpha(2)beta(1) integrin-dependent migration of primary keratinocytes across collagenous matrices. We now present evidence that MMP-1 binds the alpha(2)beta(1) integrin via the I domain of the alpha(2) integrin subunit. Using an enzyme-linked immunosorbent assay with purified human MMP-1 and recombinant alpha(2) integrin I domain, we showed that the alpha(2) integrin I domain specifically bound in a divalent cation-dependent manner to both the pro and active forms of MMP-1, but not to MMP-3 or MMP-13. Although both the I domain and MMP-1 bind divalent cations, MMP-1 bound, in a divalent cation-dependent manner, to alpha(2) integrin I domains containing metal ion-dependent adhesion sites motif mutations that prevent divalent cation binding to the I domain, demonstrating that the metal ion dependence is a function of MMP-1. Using a series of MMP-1-MMP-3 and MMP-1-MMP-13 chimeras, we determined that both the linker domain and the hemopexin-like domain of MMP-1 were required for optimal binding to the I domain. The alpha(2) integrin/MMP-1 interaction described here extends an emerging paradigm in matrix biology involving anchoring of proteinases to the cell surface to regulate their biological activities.

Pro-collagenase-1 (Matrix Metalloproteinase-1) Binds the α2β1 Integrin upon Release from Keratinocytes Migrating on Type I Collagen

In injured skin, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is induced in migrating keratinocytes. This site-specific expression is regulated by binding of the alpha(2)beta(1) integrin with dermal type I collagen, and the catalytic activity of MMP-1 is required for keratinocyte migration. Because of this functional association among substrate/ligand, receptor, and proteinase, we assessed whether the integrin also directs the compartmentalization of MMP-1 to its matrix target. Indeed, pro-MMP-1 co-localized to sites of alpha(2)beta(1) contacts in migrating keratinocytes. Furthermore, pro-MMP-1 co-immunoprecipitated with alpha(2)beta(1) from keratinocytes, and alpha(2)beta(1) co-immunoprecipitated with pro-MMP-1. No other MMPs bound alpha(2)beta(1), and no other integrins interacted with MMP-1. Pro-MMP-1 also provided a substrate for alpha(2)beta(1)-dependent adhesion of platelets. Complex formation on keratinocytes was most efficient on native type I collagen and reduced or ablated on denatured or cleaved collagen. Competition studies suggested that the alpha(2) I domain interacts with the linker and hemopexin domains of pro-MMP-1, not with the pro-domain. These data indicate that the interaction of pro-MMP-1 with alpha(2)beta(1) confines this proteinase to points of cell contact with collagen and that the ternary complex of integrin, enzyme, and substrate function together to drive and regulate keratinocyte migration.

Matrilysin in epithelial repair and defense

Repair involves an orderly progression of events to reestablish the integrity of the injured tissue. During each stage in this process, secreted proteinases are needed to remodel extracellular matrix, facilitate cell migration, and process latent proteins, among other functions. In lung epithelium, several of these processes are mediated by matrilysin, a matrix metalloproteinase (MMP). Unlike most MMPs, matrilysin is produced by intact, noninjured airway and peribronchial epithelial cells. In other intact epithelial tissues, namely the small intestine, matrilysin functions in host defense by activating the latent form of defensins, a family of antimicrobial peptides. This metalloproteinase may serve a similar function in the lung. Furthermore, in models of airway injury, matrilysin expression is upregulated in migrating epithelial cells, and the activity of this proteinase is required for repair of airway wounds. These observations indicate that matrilysin serves key functions in both epithelial defense and repair.

p38 mitogen-activated kinase is a bidirectional regulator of human fibroblast collagenase-1 induction by three-dimensional collagen lattices

When fibroblasts are cultured in contracting collagen matrices, matrix metalloproteinase-1 (MMP-1, collagenase-1) is induced. In the present study we demonstrate that p38alpha mitogen-activated protein kinase (p38alpha MAPK) plays a bi-directional role in the MMP-1 response to contracting floating collagen lattices (fl-coll). fl-coll, but not attached collagen lattices (att-coll), co-ordinately increased expression of MMP-1 and activities of p38alpha and MKK3/6 (MAPK kinase 3/6). However, treatment of primary fibroblasts cultured in fl-coll with increasing doses of SB203580, an inhibitor of p38alpha and p38beta, caused a bipolar pattern of MMP-1 expression. Partial inhibition of p38 MAPK activity resulted in the lowest level of MMP-1 expression, whereas total inhibition of p38 activity led to MMP-1 levels as high as in the absence of inhibitor. The activation/inhibition of p38alpha was apparently responsible for the observed phenomena, as supported by three lines of evidence. (1) p38alpha was the predominant isoform sensitive to SB203580 in primary fibroblasts. (2) Fibroblasts transfected with increasing dose of a dominant negative p38alpha (p38DN) similarly demonstrated the bipolar pattern of MMP-1 expression induced by fl-coll. (3) The bipolar MMP-1 expression occurred during the gradual, linear inhibition of p38alpha kinase activity by both inhibitors, SB203580 and p38DN. Nuclear factor-kappaB (NF-kappaB), a previously identified positive regulator of MMP-1 expression induced by fl-coll [Xu, Zutter, Santoro and Clark (1998) J. Cell Biol. 140, 709-719] was mediated by fl-coll-activated p38alpha. However, the fl-coll-induced expression of MMP-1 facilitated by p38alpha suppression was maintained independent of NF-kappaB activity, suggesting the existence of a p38alpha-dependent antagonistic pathway. We conclude that fl-coll-induced MMP-1 expression is the net outcome of opposing effects mediated by p38alpha. Therefore, the level of p38alpha kinase activity may provide a fine-tuned control of MMP-1 gene expression in response to biomechanical signals.

Epilysin, a novel human matrix metalloproteinase (MMP-28) expressed in testis and keratinocytes and in response to injury

We have cloned a new human matrix metalloproteinase (MMP-28, epilysin) from human keratinocyte and testis cDNA libraries. Like most MMPs, epilysin contains a signal sequence, a prodomain with a PRCGVTD sequence, a zinc-binding catalytic domain with an HEIGHTLGLTH sequence, and a hemopexin-like domain. In addition, epilysin has a furin activation sequence (RRKKR) but has no transmembrane sequence. The exon-intron organization and splicing pattern of epilysin differ from that of other MMP genes. It has only 8 exons, and 5 exons are spliced at sites not used by other MMPs. Another novel feature of epilysin is that exon 4 is alternatively spliced to a transcript that does not encode the N-terminal half of the catalytic domain. Northern hybridization of tissue RNA indicated that epilysin is expressed at high levels in testis and at lower levels in lungs, heart, colon, intestine, and brain. RNase protection assay with various cell lines indicated that epilysin was selectively expressed in keratinocytes. Recombinant epilysin degraded casein in a zymography assay, and its proteolytic activity was inhibited by EDTA and by batimastat, a selective MMP inhibitor. Immunohistochemical staining showed expression of epilysin protein in the basal and suprabasal epidermis of intact skin. In injured skin, prominent staining for epilysin was seen in basal keratinocytes both at and some distance from the wound edge, a pattern that is quite distinct from that of other MMPs expressed during tissue repair. These findings suggest that this new MMP functions in several tissues both in tissue homeostasis and in repair.

Bromination of deoxycytidine by eosinophil peroxidase: a mechanism for mutagenesis by oxidative damage of nucleotide precursors

Oxidants generated by eosinophils during chronic inflammation may lead to mutagenesis in adjacent epithelial cells. Eosinophil peroxidase, a heme enzyme released by eosinophils, generates hypobromous acid that damages tissue in inflammatory conditions. We show that human eosinophils use eosinophil peroxidase to produce 5-bromodeoxycytidine. Flow cytometric, immunohistochemical, and mass spectrometric analyses all demonstrated that 5-bromodeoxycytidine generated by eosinophil peroxidase was taken up by cultured cells and incorporated into genomic DNA as 5-bromodeoxyuridine. Although previous studies have focused on oxidation of chromosomal DNA, our observations suggest another mechanism for oxidative damage of DNA. In this scenario, peroxidase-catalyzed halogenation of nucleotide precursors yields products that subsequently can be incorporated into DNA. Because the thymine analog 5-BrUra mispairs with guanine in DNA, generation of brominated pyrimidines by eosinophils might constitute a mechanism for cytotoxicity and mutagenesis at sites of inflammation.

Secretion of microbicidal alpha-defensins by intestinal Paneth cells in response to bacteria

Paneth cells in mouse small intestinal crypts secrete granules rich in microbicidal peptides when exposed to bacteria or bacterial antigens. The dose-dependent secretion occurs within minutes and alpha-defensins, or cryptdins, account for 70% of the released bactericidal peptide activity. Gram-negative bacteria, Gram-positive bacteria, lipopolysaccharide, lipoteichoic acid, lipid A and muramyl dipeptide elicit cryptdin secretion. Live fungi and protozoa, however, do not stimulate degranulation. Thus intestinal Paneth cells contribute to innate immunity by sensing bacteria and bacterial antigens, and discharge microbicidal peptides at effective concentrations accordingly.

Gelatinase B is required for alveolar bronchiolization after intratracheal bleomycin

Increased expression of matrix metalloproteinases, particularly gelatinase B (MMP-9), has been described in the lungs in pulmonary fibrosis. Intratracheal bleomycin is often used experimentally to produce lesions resembling human fibrosing alveolitis. To assess the role of gelatinase B in bleomycin-induced fibrosing alveolitis, we instilled bleomycin intratracheally into gelatinase B-deficient mice and gelatinase B+/+ littermates. Twenty-one days after bleomycin the two groups of mice were indistinguishable in terms of pulmonary histology and total lung collagen and elastin. However, the lungs of gelatinase B-deficient mice showed minimal alveolar bronchiolization, whereas bronchiolization was prominent in the lungs of gelatinase B+/+ mice. Gelatinase B was identified immunohistochemically in terminal bronchiolar cells and bronchiolized cells 7 and 14 days after bleomycin in gelatinase B+/+ mice, and whole lung gelatinase B mRNA was increased at the same times. Many bronchiolized cells displayed Clara cell features by electron microscopy. Some bronchiolized cells stained with antibody to helix transcription factor 4, a factor associated with the ciliated cell phenotype. Thus, fibrosing alveolitis develops after intratracheal bleomycin irrespective of gelatinase B. However, gelatinase B is required for alveolar bronchiolization, perhaps by facilitating migration of Clara cells and other bronchiolar cells into the regions of alveolar injury.

Structural analysis and promoter characterization of the human membrane-type matrix metalloproteinase-1 (MT1-MMP) gene

Membrane type-1 matrix metalloproteinase (MT1-MMP) degrades extracellular matrix components directly and indirectly by activation of other matrix metalloproteinases (MMPs). In the present study, we have isolated and characterized the human MT1-MMP gene and its promoter. The gene consists of 10 exons and nine introns spanning more than 10 kilobases (kb). The locations of two exon-intron splicing sites are distinct from the preserved positions among other known MMP genes. Primer extension and RNAse and S1 nuclease protection analyses indicated that there are four major and several minor transcription start sites. The 5'-flanking sequence of the gene contains putative regulatory elements, including one Sp-1 site and four CCAAT-boxes, whereas there is no TATA-box. The Sp-1 binding site was functional, as shown by gel shift and supershift analyses. Transfection studies with promoter constructs containing 0.1 to 7.2 kb of 5'-flanking sequence coupled to a luciferase reporter gene indicated that the promoter contains additional positive and negative regulatory sequences. Deletion of the Sp-1 binding site by site-directed mutagenesis reduced luciferase activity by about 90%, demonstrating the crucial role of this element in maintaining MT1-MMP transcription. Our findings indicate that the human MT1-MMP promoter has distinctive structural and functional features compared with other MMP genes, which may lead to a unique expression pattern and regulation during physiological and pathological processes.

An open reading frame element mediates posttranscriptional regulation of tropoelastin and responsiveness to transforming growth factor beta1

Elastin, an extracellular component of arteries, lung, and skin, is produced during fetal and neonatal growth. We reported previously that the cessation of elastin production is controlled by a posttranscriptional mechanism. Although tropoelastin pre-mRNA is transcribed at the same rate in neonates and adults, marked instability of the fully processed transcript bars protein production in mature tissue. Using RNase protection, we identified a 10-nucleotide sequence in tropoelastin mRNA near the 5' end of the sequences coded by exon 30 that interacts specifically with a developmentally regulated cytosolic 50-kDa protein. Binding activity increased as tropoelastin expression dropped, being low in neonatal fibroblasts and high in adult cells, and treatment with transforming growth factor beta1 (TGF-beta1), which stimulates tropoelastin expression by stabilizing its mRNA, reduced mRNA-binding activity. No other region of tropoelastin mRNA interacted with cellular proteins, and no binding activity was detected in nuclear extracts. The ability of the exon-30 element to control mRNA decay and responsiveness to TGF-beta1 was assessed by three distinct functional assays: (i) insertion of exon 30 into a heterologous gene conferred increased reporter activity after exposure to TGF-beta1; (ii) addition of excess exon 30 RNA slowed tropoelastin mRNA decay in an in vitro polysome degradation assay; and (iii) a mutant tropoelastin cDNA lacking exon 30, compared to wild-type cDNA, produced a stable transcript whose levels were not affected by TGF-beta1. These findings demonstrate that posttranscriptional regulation of elastin production in mature tissue is conferred by a specific element within the open reading frame of tropoelastin mRNA.

Matrix metalloproteinases in repair

During repair, many different matrix metalloproteinases are produced by multiple cell types residing in various compartments within the wound environment. This diversity of enzymes, coupled with discreet cellular expression, implies that different matrix metalloproteinases serve different functions, acting on a variety of substrates, during wound healing. With few exceptions, however, the actual function and spectrum of functions of matrix metalloproteinases in vivo is not known. Even with the advent of genetically defined animal models, few studies have rigorously addressed the substrates and role of matrix metalloproteinases in wound repair. Before we can understand the role of matrix metalloproteinases in ulceration and disease, we need to determine the function these enzymes serve in normal tissues and repair.

Regulation of intestinal alpha-defensin activation by the metalloproteinase matrilysin in innate host defense

Precursors of alpha-defensin peptides require activation for bactericidal activity. In mouse small intestine, matrilysin colocalized with alpha-defensins (cryptdins) in Paneth cell granules, and in vitro it cleaved the pro segment from cryptdin precursors. Matrilysin-deficient (MAT-/-) mice lacked mature cryptdins and accumulated precursor molecules. Intestinal peptide preparations from MAT-/- mice had decreased antimicrobial activity. Orally administered bacteria survived in greater numbers and were more virulent in MAT-/- mice than in MAT+/+ mice. Thus, matrilysin functions in intestinal mucosal defense by regulating the activity of defensins, which may be a common role for this metalloproteinase in its numerous epithelial sites of expression.

Role of matrix metalloproteinases and their inhibition in cutaneous wound healing and allergic contact hypersensitivity

Normal wounds can heal by secondary intention (epidermal migration to cover a denuded surface) or by approximation of the wound edges (e.g., suturing). In healing by secondary intention, epidermis-derived MMPs are important. Keratinocyte migration begins within 3-6 hr post injury, as basal cells detach from underlying basal lamina and encounter a dermal substratum rich in type I collagen. Cell contact with type I collagen in vitro stimulates collagenase-1 expression, which is mediated by the alpha 2 beta 1 integrin, the major keratinocyte collagen-binding receptor. Collagenase-1 activity alone is necessary and sufficient for keratinocyte migration over a collagen subsurface. Stromelysins-1 and -2 are also found in the epidermis of normal acute wounds. Stromelysin-2 co-localizes with collagenase-1 and may facilitate cell migration over non-collagenous matrices of the dermis. In contrast, stromelysin-1 is expressed by keratinocytes behind the migrating front and which remain on basal lamina, i.e., the proliferative cell population. Studies with stromelysin-1-deficient mice that suggest this MMP plays a role in keratinocyte detachment from underlying basement membrane to initiate cell migration. In chronic ulcers, MMP levels are markedly elevated, in contrast to their precise temporal and spatial expression in acute wounds. Both collagenase-1 and stromelysin-1 are found in fibroblasts underlying the nonhealing epithelium, and stromelysin-1 expression is especially prominent. Two key questions underlie the use of MMP inhibitors and wound healing: (1) will these agents impair normal reepithelialization in wounds that heal by secondary intention; and (2) can MMP inhibitors be effective therapy for chronic ulcers? The answer to neither is known. Batimastat and marimastat appear not to interfere with normal wound healing, but only in sutured surgical wounds, a situation in which MMP expression has practically no role. We also show the first example of an in vivo immune response, contact hypersensitivity, which is dependent upon MMP activity. Using gene-deficient mice, we demonstrate that stromylysin-1 (MMP-3) is required for sensitization, whereas gelatinase B (MMP-9) is required for timely resolution of the reaction to antigenic challenge.

Keratinocyte collagenase-1 expression requires an epidermal growth factor receptor autocrine mechanism

In response to cutaneous injury, expression of collagenase-1 is induced in keratinocytes via alpha2beta1 contact with native type I collagen, and enzyme activity is essential for cell migration over this substratum. However, the cellular mechanism(s) mediating integrin signaling remain poorly understood. We demonstrate here that treatment of keratinocytes cultured on type I collagen with epidermal growth factor receptor (EGFR) blocking antibodies or a specific receptor antagonist inhibited cell migration across type I collagen and the matrix-directed stimulation of collagenase-1 production. Additionally, stimulation of collagenase-1 expression by hepatocyte growth factor, transforming growth factor-beta1, and interferon-gamma was blocked by EGFR inhibitors, suggesting a required EGFR autocrine signaling step for enzyme expression. Collagenase-1 mRNA was not detectable in keratinocytes isolated immediately from normal skin, but increased progressively following 2 h of contact with collagen. In contrast, EGFR mRNA was expressed at high steady-state levels in keratinocytes isolated immediately from intact skin but was absent following 2 h cell contact with collagen, suggesting down-regulation following receptor activation. Indeed, tyrosine phosphorylation of the EGFR was evident as early as 10 min following cell contact with collagen. Treatment of keratinocytes cultured on collagen with EGFR antagonist or heparin-binding (HB)-EGF neutralizing antibodies dramatically inhibited the sustained expression (6-24 h) of collagenase-1 mRNA, whereas initial induction by collagen alone (2 h) was unaffected. Finally, expression of collagenase-1 in ex vivo wounded skin and re-epithelialization of partial thickness porcine burn wounds was blocked following treatment with EGFR inhibitors. These results demonstrate that keratinocyte contact with type I collagen is sufficient to induce collagenase-1 expression, whereas sustained enzyme production requires autocrine EGFR activation by HB-EGF as an obligatory intermediate step, thereby maintaining collagenase-1-dependent migration during the re-epithelialization of epidermal wounds.

Induction and evasion of host defenses by type 1-piliated uropathogenic Escherichia coli

Virtually all uropathogenic strains of Escherichia coli encode filamentous surface adhesive organelles called type 1 pili. High-resolution electron microscopy of infected mouse bladders revealed that type 1 pilus tips interacted directly with the lumenal surface of the bladder, which is embedded with hexagonal arrays of integral membrane glycoproteins known as uroplakins. Attached pili were shortened and facilitated intimate contact of the bacteria with the uroplakin-coated host cells. Bacterial attachment resulted in exfoliation of host bladder epithelial cells as part of an innate host defense system. Exfoliation occurred through a rapid apoptosis-like mechanism involving caspase activation and host DNA fragmentation. Bacteria resisted clearance in the face of host defenses within the bladder by invading into the epithelium.

Matrilysin expression and function in airway epithelium

We report that matrilysin, a matrix metalloproteinase, is constitutively expressed in the epithelium of peribronchial glands and conducting airways in normal lung. Matrilysin expression was increased in airway epithelial cells and was induced in alveolar type II cells in cystic fibrosis. Other metalloproteinases (collagenase-1, stromelysin-1, and 92-kD gelatinase) were not produced by normal or injured lung epithelium. These observations suggest that matrilysin functions in injury-mediated responses of the lung. Indeed, matrilysin expression was increased in migrating airway epithelial cells in wounded human and mouse trachea. In human tissue, epithelial migration was reduced by > 80% by a hydroxamate inhibitor, and in mouse tissue, reepithelialization in trachea from matrilysin-null mice was essentially blocked. In vivo observations and cell culture studies demonstrated that matrilysin was secreted lumenally by lung epithelium, but upon activation or while migrating over wounds, some matrilysin was released basally. The constitutive production of matrilysin in conducting airways, its upregulation after injury, its induction by alveolar epithelium, and its release into both lumenal and matrix compartments suggest that this metalloproteinase serves multiple functions in intact and injured lung, one of which is to facilitate reepithelialization.

Matrix metalloproteinases (MMPs) and their physiological inhibitors (TIMPs) are differentially expressed during excisional skin wound repair

During cutaneous wound healing a number of migratory and remodeling events occur that require the action of matrix metalloproteinases (MMPs) and their natural inhibitors (TIMPs). In this study, we analyzed the temporal and spatial expression patterns of these molecules during the healing of murine excisional skin wounds. Our data imply that defined phases of repair rely on distinct repertoires of MMP activity and TIMP counterregulation. Reepithelialization was found to be associated with active production of collagenase, 92-kDa gelatinase, and stromelysins-1 and -2 by distinct subpopulations of keratinocytes at the migrating border. Notably, no TIMP transcripts were expressed in the epidermis, but TIMP-1 expression in the wound colocalized with expression of collagenase, 92-kDa gelatinase, and stromelysin-1, albeit in distinct cells. Concomitant with the formation of an extensive hyperproliferative epithelium, TIMP-1 transcripts accumulated at the mesenchymal/epidermal border of the granulation tissue. During later phases of wound repair, we observed an increase in 72-kDa gelatinase and MT1-MMP expression, whereby the transcripts of these colocalizing MMPs were detected exclusively and at high levels in the granulation tissue. At completion of reepithelialization, the expression levels of the MMPs and TIMP-1 seen in epidermal and dermal compartments declined to near-basal levels, whereas the macrophage-specific metalloelastase (MME) reached maximum expression. In reepithelialized wound tissue, MME transcripts were detected in deep layers of reconstituted dermis and seemed to cluster around vascular structures. Systemic glucocorticoid treatment, which is known to result in impaired wound healing, led to a nearly complete shut-off of MME expression. These observations imply an additional role of macrophage-related proteolysis, independent of its classical roles during earlier, inflammatory phases of cutaneous wound repair.

Collagenase-1 and collagen in epidermal repair

An invariable feature of wounded skin, whether a normally healing or chronic lesion, is the expression of collagenase-1 by migrating basal keratinocytes. Collagenase-1 is a member of the matrix metalloproteinase family of enzymes and is the principal human enzyme which cleaves native fibrillar collagen. Following injury, basal keratinocytes move from the basement membrane and interact with new connective tissue proteins in the dermis and wound bed. Contact with native type I collagen, the most abundant protein in the dermis, induces expression of collagenase-1. This metalloproteinase cleaves collagen, thereby altering its structure and, hence, the affinity to which cells bind it. Thus, collagenase-1 serves a beneficial role in wound healing by facilitating the movement of keratinocytes over the collagen-rich dermis during reepithelialization.

Collagenase-1 complexes with alpha2-macroglobulin in the acute and chronic wound environments

The purpose of this study was to examine the appearance and activation of collagenase-1 (MMP-1) in the wound environment. We found that MMP-1 accumulates in the fluid phase of the burn wound environment within 2 d of injury and reaches maximal levels by day 4. Two forms of the enzyme were evident; one that corresponded to proMMP-1 and another that corresponded to a group of high molecular mass (approximately 200 kDa and >200 kDa doublet) MMP-1 containing complexes. ProMMP-1 and MMP-1 containing complexes also occurred in wound fluid from venous stasis ulcers, but neither was detected in mastectomy fluid or in plasma. Levels of the proteinase inhibitor alpha2-macroglobulin in burn fluid and chronic ulcer wound fluid were almost as high as in plasma, and the high molecular mass MMP-1 containing complexes in burn fluid appeared to result from binding between alpha2-macroglobulin and activated MMP-1. These observations provide direct evidence that active MMP-1 in the fluid phase of the wound environment becomes complexed to alpha2-macroglobulin.

Induction and repression of collagenase-1 by keratinocytes is controlled by distinct components of different extracellular matrix compartments

In all forms of cutaneous wounds, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is invariably expressed by basal keratinocytes migrating over the dermal matrix. We report that native type I collagen mediates induction of MMP-1 by primary human keratinocytes. Collagen-mediated induction of MMP-1 was rapid, being detected 2 h after plating, and was transcriptionally regulated. As demonstrated by in situ hybridization, only migrating keratinocytes expressed MMP-1, suggesting that contact with collagen is not sufficient to induce MMP-1 expression in keratinocytes; the cells must also be migrating. Upon denaturation, type I collagen lost its ability to induce MMP-1 expression but still supported cell adhesion. Other dermal or wound matrix proteins, such as type III collagen, fibrin, and fibronectin, and a mixture of basement membrane proteins did not induce MMP-1 production. In the presence of collagen, laminin-1 inhibited induction of MMP-1 but laminin-5 did not. Taken together, these observations suggest that as basal keratinocytes migrate from the basal lamina onto the dermal matrix contact with native type I collagen induces MMP-1 expression. In addition, our findings suggest that re-establishment of the basement membrane and, in particular, contact with laminin-1 provides a potent signal to down-regulate MMP-1 production as the epithelium is repaired.

Cell type-specific inhibition of keratinocyte collagenase-1 expression by basic fibroblast growth factor and keratinocyte growth factor. A common receptor pathway

Collagenase-1 is invariantly expressed by migrating basal keratinocytes in all forms of human skin wounds, and its expression is induced by contact with native type I collagen. However, net differences in enzyme production between acute and chronic wounds may be modulated by soluble factors present within the tissue environment. Basic fibroblast growth factor (bFGF, FGF-2) and keratinocyte growth factor (KGF, FGF-9), which are produced during wound healing, inhibited collagenase-1 expression by keratinocytes in a dose-dependent manner. However, KGF was >100-fold more effective than bFGF at inhibiting collagenase-1 expression, suggesting that this differential signaling is transduced via an FGF receptor that binds these ligands with different affinities. Reverse transcriptase-polymerase chain reaction analysis of human keratinocyte mRNA for fibroblast growth factor receptors (FGFRs) revealed expression of only FGFR-2 IIIb, the KGF-specific receptor, which also binds bFGF with low affinity, and FGFR-3 IIIb, which does not bind bFGF or KGF. FGFRs that bind bFGF with high affinity were not detected. Our results suggest that bFGF and KGF inhibit collagenase-1 expression through the KGF cell-surface receptor (FGFR-2 IIIb). Because bFGF induces collagenase-1 in most cell types, cell-specific expression of FGFR family members may dictate the regulation of matrix metalloproteinases in a tissue-specific manner.

The activity of collagenase-1 is required for keratinocyte migration on a type I collagen matrix

We have shown in a variety of human wounds that collagenase-1 (MMP-1), a matrix metalloproteinase that cleaves fibrillar type I collagen, is invariably expressed by basal keratinocytes migrating across the dermal matrix. Furthermore, we have demonstrated that MMP-1 expression is induced in primary keratinocytes by contact with native type I collagen and not by basement membrane proteins or by other components of the dermal or provisional (wound) matrix. Based on these observations, we hypothesized that the catalytic activity of MMP-1 is necessary for keratinocyte migration on type I collagen. To test this idea, we assessed keratinocyte motility on type I collagen using colony dispersion and colloidal gold migration assays. In both assays, primary human keratinocytes migrated efficiently on collagen. The specificity of MMP-1 in promoting cell movement was demonstrated in four distinct experiments. One, keratinocyte migration was completely blocked by peptide hydroxymates, which are potent inhibitors of the catalytic activity of MMPs. Two, HaCaTs, a line of human keratinocytes that do not express MMP-1 in response to collagen, did not migrate on a type I collagen matrix but moved efficiently on denatured type I collagen (gelatin). EGF, which induces MMP-I production by HaCaT cells, resulted in the ability of these cells to migrate across a type I collagen matrix. Three, keratinocytes did not migrate on mutant type I collagen lacking the collagenase cleavage site, even though this substrate induced MMP-1 expression. Four, cell migration on collagen was completely blocked by recombinant tissue inhibitor of metalloproteinase-1 (TIMP-1) and by affinity-purified anti-MMP-1 antiserum. In addition, the collagen-mediated induction of collagenase-1 and migration of primary keratinocytes on collagen was blocked by antibodies against the alpha2 integrin subunit but not by antibodies against the alpha1 or alpha3 subunits. We propose that interaction of the alpha2beta1 integrin with dermal collagen mediates induction of collagenase-1 in keratinocytes at the onset of healing and that the activity of collagenase-1 is needed to initiate cell movement. Furthermore, we propose that cleavage of dermal collagen provides keratinocytes with a mechanism to maintain their directionality during reepithelialization.

Transcriptional induction of collagenase-1 in differentiated monocyte-like (U937) cells is regulated by AP-1 and an upstream C/EBP-beta site

In this report, we demonstrate that the AP-1 site and a distal promoter element regulate transcriptional induction of collagenase-1 during monocytic differentiation. Chloramphenicol acetyltransferase expression constructs containing regions of the human collagenase-1 promoter were stably or transiently transfected into U937 cells, and reporter activity was assessed at various times after the onset of phorbol 12-myristate 13-acetate (PMA)-mediated differentiation. Rapid and strong induction of promoter activity was lost in constructs with a mutant AP-1 element; however, at 16-96 h post-PMA, the mutant collagenase-1 promoter displayed AP-1 independent PMA-mediated transactivation. The AP-1 mutant constructs also showed delayed transcriptional activation in PMA-treated fibroblasts. Western and supershift analyses indicated that functional Jun and Fos proteins were present in nuclear extracts of PMA-differentiated U937 cells. Promoter deletion constructs demonstrated the potential role of distal promoter sequences in regulating collagenase-1 transcription. In particular, Western, supershift, and promoter deletion analyses suggested a role for CCAAT/enhancer-binding protein-beta (C/EBP-beta) binding site between -2010 and -1954 in regulating transcription of collagenase-1 in monocytic cells. Our findings suggest that distinct regulatory elements, acting somewhat independently of each other, control expression of collagenase-1. In addition, our data suggests that the rapid PMA-mediated induction of collagenase-1 transcription is controlled by a mechanism distinct from that regulating the sustained expression of this proteinase in activated macrophages.

Spatial pattern of type I collagen expression in injured peripheral nerve

The authors studied the spatial expression and regulation of messenger RNA for the alpha subunit of collagen type I in crushed rat sciatic nerve to provide a basis for future therapeutic manipulation. Sciatic nerves in 20 male or female adult Lewis rats were crushed for 60 seconds; the unharmed contralateral sciatic nerves served as controls. Twenty-one days after injury the experimental animals were killed and their tissue was harvested. The spatial expression of collagen type I was determined by using in situ hybridization techniques. Quantification of fibroblast number and total signal was performed through computerized morphometry. Collagen upregulation was evident in epineurial and perineurial layers, with the epineurium displaying higher activity. The cells responsible for procollagen type I production were fibroblasts. No activity was seen in the endoneurium. Morphometric findings indicated that collagen upregulation in the epineurium and perineurium occurred at both pretranscriptional and posttranslational levels when compared to controls; a paired t-test analysis confirmed statistical significance for all comparisons between injured and control tissues. Epineurial fibroblasts are responsible for the collagen production associated with crushed peripheral nerve injury in the rat. Regulation occurs pretranscriptionally as well as posttranslationally. It is interesting to speculate that the delivery of agents directed against collagen production (such as neutralizing antibodies to growth factors) into epineurial tissues proximate to the time and location of clinical nerve injury might mitigate later deleterious effects of excess collagen production in axonal regeneration.

Modulation of intracellular calcium levels inhibits secretion of collagenase 1 by migrating keratinocytes

Calcium concentration influences keratinocyte differentiation, and, following injury, keratinocytes move through an environment of changing calcium levels. Because these migrating cells in wounds invariably express collagenase 1, we assessed if modulation of calcium levels regulates collagenase 1 production by primary human keratinocytes. Accurately reflecting the confined spatial pattern of enzyme production seen in vivo, collagenase 1 mRNA was expressed only by keratinocytes migrating from foci of differentiated cells. Treatment with calcium ionophores A23187 or thapsigargin markedly inhibited the basal and phorbol 12-myristate 13-acetate-(PMA) stimulated accumulation of keratinocyte collagenase 1 in the medium but did not affect collagenase 1 production by control or PMA-treated fibroblasts. A23187-mediated inhibition of collagenase 1 protein was not associated with a decrease in mRNA levels but rather was controlled by a selective and reversible block of enzyme secretion. This block in secretion was likely not due to altered protein folding as the proenzyme within A23187-treated cells remained capable of autolytic activation upon treatment with p-aminophenylmercuric acetate. In contrast, 92-kDa gelatinase mRNA and secreted protein levels were coordinately reduced by A23187. Keratin 14 expression, a basal keratinocyte marker, was reduced with PMA treatment, but A23187 did not affect keratin 14 expression. In human wounds, both basal and suprabasal keratinocytes at the migrating front of epidermis stained for keratin 14, but only the basal cells expressed collagenase 1. These data suggest that collagenase 1 production is not necessarily linked with expression of basal cell markers and that modulation of intracellular calcium levels can block secretion of collagenase 1 by keratinocytes which have moved away from the stratum basalis and from their natural substrate.

Distinct mechanisms regulate TIMP-1 expression at different stages of phorbol ester-mediated differentiation of U937 cells

Upon exposure to 12-O-tetradecanoylphorbol 13-acetate (PMA), promonocyte-like U937 cells differentiate into macrophage-like cells and begin to express certain metalloproteinases and TIMP-1. We report here that distinct mechanisms regulate TIMP-1 production in PMA-treated U937 cells. TIMP-1 protein and steady-state mRNA levels increased about 10-fold in PMA-differentiated cells compared to undifferentiated cells. TIMP-1 transcription increased about 2.5-fold, but this stimulation was not detected until at least 48 h post-PMA. In contrast, the half-life for TIMP-1 mRNA increased about 3-fold and was detected at 8 h post-PMA. Using in vitro translation assays, we found that TIMP-1 mRNA from PMA-differentiated cells translated about 5-fold less efficiently than that from basal cells, suggesting structural differences in TIMP-1 mRNA in basal and differentiated U937 cells. Although primer extension and RNase protection analyses showed 5' heterogeneity of TIMP-1 transcripts, all forms were equally stimulated in response to PMA-mediated differentiation. The poly(A) tail length of TIMP-1 mRNA, however, was longer in PMA-treated cells. Our findings suggested that up-regulation of TIMP-1 expression in PMA treated U937 cells is mediated early by enhanced TIMP-1 mRNA stability, possibly related to increased poly(A) tail length, and later by an increase in transcription rate.

Regulation of the expression of stromelysin-2 by growth factors in keratinocytes: implications for normal and impaired wound healing

Keratinocyte growth factor (KGF) has been implicated in wound re-epithelialization and branching morphogenesis of several organs. To determine whether KGF induces these effects via induction of matrix metalloproteinase expression we have analysed the effect of KGF on the expression of stromelysin-2 in cultured HaCaT keratinocytes. Here we show a strong induction of stromelysin-2 mRNA within 5-8 h of stimulation of these cells with KGF. The degree of induction was similar to that achieved by treatment with epidermal growth factor or tumour necrosis factor alpha, whereas the stimulatory effect of transforming growth factor beta 1 was even stronger. To determine whether the induction of stromelysin-2 expression by growth factors and cytokines might be important for wound healing, we analysed the expression of this gene during the healing process of full-thickness excisional wounds in mice. Whereas stromelysin-2 mRNA could hardly be detected in unwounded skin, a biphasic induction was seen after injury and highest levels were found at days 1 and 5 after wounding. Hybridization in situ revealed the presence of stromelysin-2 mRNA in basal keratinocytes at the wound edge but not in the underlying mesenchymal tissue. During impaired wound healing as seen in glucocorticoid-treated mice, stromelysin-2 expression was significantly increased compared with untreated control mice. Taken together, these results suggest that correct regulation of this broad-spectrum metalloproteinase might be important for normal repair.

Role of matrix metalloproteinases in abdominal aortic aneurysms

Considerable progress has been made toward characterizing the enzymes and proteolytic events that occur in established human abdominal aortic aneurysms (AAA). Through studies involving a number of different laboratories and various experimental approaches, enzymes of the matrix metalloproteinase (MMP) family have consistently emerged as important molecular participants in aneurysm disease. The finding that elastolytic MMPs, particularly MMP-9 and MMP-2, are expressed and produced in increased amounts in human aneurysm tissue, has led to the possibility that these enzymes might serve as rational targets for pharmacotherapy in this disease. Recent studies using MMP-inhibiting tetracycline derivatives in the elastase-induced rodent model of AAA indicate that metalloproteinase suppression is a feasible and successful approach in the experimental setting. The definitive proof-of-principle for the therapeutic efficacy of anti-MMP or other anti-proteinase strategies to limit the growth of small AAA, however, will remain unknown until specifically tested in clinical trials.

Collagenase-I, stromelysin-I, and matrilysin are expressed within the placenta during multiple stages of human pregnancy

Human pregnancy is associated with extensive growth and remodelling of the uterus and placenta, and restructuring of these tissues during specific stages of gestation likely involves the degradative activity of various matrix metalloproteinases (MMPs). In this investigation, we used in situ hybridization and immunohistochemistry to identify the sites and cell source of collagenase-1 (MMP-1), stromelysin-1 (MMP-3), matrilysin (MMP-7), and 92 kDa gelatinase (MMP-9), a subgroup of MMPs with the combined ability to degrade essentially all matrix proteins. Human tissues were recovered from uncomplicated pregnancies at various gestational ages and from pregnancies complicated by chorioamnionitis, pre-eclampsia, and placenta accreta. Our results show prominent expression of all four MMPs in specific cells of human placentae involved in trophoblast invasion and placental maturation. Collagenase-1 and stromelysin-1 were detected in cells of the amnion, decidua, and chorionic villi at all stages of pregnancy. Ninety-two kilodalton gelatinase was present in granulocytes whenever present. Matrilysin was seen in cytotrophoblasts and syncytiotrophoblasts during early pregnancy but only in cytotrophoblasts by the third trimester. In addition, we found that matrilysin is over expressed and is produced by more cell types in placentae from pregnancies complicated by pre-eclampsia suggesting that the proteolytic activity of this MMP contributes to the pathology of this condition. We conclude that certain MMPs produced by resident cells of the human placenta, and in particular trophoblasts, participate in the physiological progress human gestation and parturition.

Mechanisms of hepatocyte growth factor stimulation of keratinocyte metalloproteinase production

Matrix metalloproteinases participate in normal physiologic processes; however, their overproduction has been associated with connective tissue destruction in a variety of pathological states. Migrating basal keratinocytes transiently express collagenase-1 during normal cutaneous reepithelialization. However, the overexpression of both collagenase-1 and stromelysin-1 has been associated with the pathogenesis of chronic nonhealing ulcers. Aberrant expression of metalloproteinases in inflammation is mediated, at least in part, by soluble factors. Since hepatocyte growth factor/scatter factor (HGF/SF) has been reported to promote keratinocyte migration and proliferation, key events in wound repair, and since HGF/SF is produced by dermal fibroblasts and its c-Met receptor is expressed by basal keratinocytes in wounded skin, we have studied the effects of HGF/SF upon keratinocyte metalloproteinase expression. We have found that HGF/SF can stimulate keratinocyte collagenase-1 and stromelysin-1 production in a dose-dependent and matrix-dependent manner. Expression of 92-kDa gelatinase was not affected by HGF/SF. We determined that HGF/SF regulation of collagenase-1 expression is transcriptionally mediated and requires tyrosine kinase and protein kinase C activaties. HGF/NK1, a naturally occurring, truncated form of HGF/SF, also stimulates collagenase-1 production, but much less efficiently than does the parent molecule. However, HGF/NK2, another HGF/SF splice variant, as well as heparin, potently inhibit HGF/SF-induced collagenase-1 synthesis. These results indicate that HGF/SF and its naturally occurring splice variants have diverse biological effects on keratinocytes and suggest an additional mechanism whereby HGF/SF may regulate keratinocyte function during wound repair.

Role of matrix metalloproteinases in failure to re-epithelialize after corneal injury

Delayed re-epithelialization of the cornea after injury usually precedes stromal ulceration. Previous findings using a rat thermal injury model suggested that re-epithelialization is impeded by products of resident corneal cells, which destroy adhesive structures at the basement membrane zone. In this study, we provide additional evidence for this concept. Failure to re-epithelialize was found to correlate with an increase in the amounts of gelatinolytic matrix metalloproteinases present in the rat cornea. One of these gelatinases, gelatinase B, is synthesized by the resident corneal cells, and inhibitions of its synthesis correlated with inhibition of basement membrane dissolution. The matrix metalloproteinases collagenase and stromelysin are also synthesized by resident corneal cells in thermally injured corneas of rabbits, but the timing of bulk enzyme synthesis correlated more closely with deposition of repair tissue in the stroma than with failure to re-epithelialize. Nevertheless, in human corneas with repair defects, gelatinase B and collagenase are synthesized by cells in the basal layer of the epithelium directly adjacent to the basement membrane, suggesting that both could participate in dissolution of this structure. Importantly, treatment of thermally injured corneas with a synthetic inhibitor of matrix metalloproteinases significantly improved basement membrane integrity. These data support the concept that over-expression of matrix metalloproteinases by resident corneal cells impedes re-epithelialization after some types of corneal injury.

Angiotensin converting enzyme expression in primary pulmonary hypertension

We compared immunoreactivity for angiotensin converting enzyme (ACE) in pulmonary artery and lung parenchymal tissues (obtained at the time of resection for lung transplantation) from eight patients with Stage IV primary pulmonary hypertension (PPH) with the reactivity in similar tissues from eight normal donors. ACE immunoreactivity was markedly and consistently increased in the endothelium and subendothelial neointimal regions of elastic pulmonary arteries from patients with PPH as compared with normal pulmonary arteries. Immunoreactivity in normal muscular pulmonary arteries was usually less than in surrounding capillary endothelial cells, whereas it was usually of comparable intensity with that in surrounding alveolar capillaries in muscular pulmonary arteries of patients with PPH. These observations suggest that ACE may be involved in the pathogenesis of vascular remodeling associated with neointimal formation in pulmonary arteries.

Matrilysin is expressed by lipid-laden macrophages at sites of potential rupture in atherosclerotic lesions and localizes to areas of versican deposition, a proteoglycan substrate for the enzyme

Certain matrix metalloproteinases (MMP) are expressed within the fibrous areas surrounding acellular lipid cores of atherosclerotic plaques, suggesting that these proteinases degrade matrix proteins within these areas and weaken the structural integrity of the lesion. We report that matrilysin and macrophage metalloelastase, two broad-acting MMPs, were expressed in human atherosclerotic lesions in carotid endarterectomy samples (n = 18) but were not expressed in normal arteries (n = 7). In situ hybridization and immunohistochemistry revealed prominent expression of matrilysin in cells confined to the border between acellular lipid cores and overlying fibrous areas, a distribution distinct from other MMPs found in similar lesions. Metalloelastase was expressed in these same border areas. Matrilysin was present in lipid-laden macrophages, identified by staining with anti-CD-68 antibody. Furthermore, endarterectomy tissue in organ culture released matrilysin. Staining for versican demonstrated that this vascular proteoglycan was present at sites of matrilysin expression. Biochemical studies showed that matrilysin degraded versican much more efficiently than other MMPs present in atherosclerotic lesions. Our findings suggest that matrilysin, specifically expressed in atherosclerotic lesions, could cleave structural proteoglycans and other matrix components, potentially leading to separation of caps and shoulders from lipid cores.

Re-epithelialization of human oral keratinocytes in vitro

Re-epithelialization involves interactions between keratinocytes and the extracellular matrix upon which these cells move. It is hypothesized that keratinocytes are activated when wounded, and the resultant phenotypic change directs re-epithelialization. We have adapted organotypic cultures, in which oral gingival keratinocytes are fully differentiated, to study re-epithelialization following wounding. To elucidate keratinocyte behavior and phenotype during re-epithelialization, we have investigated this process in the presence and absence of the growth factor TGF-beta 1 and have monitored expression of MMP-1 (Type I collagenase) mRNA by in situ hybridization. In addition, we have followed proliferation and migration of wound keratinocytes by genetically marking these cells with a retroviral vector and by measuring their proliferative index. We found that keratinocytes grown without TGF-beta 1 were hyperproliferative in response to wounding, and re-epithelialization was complete by 24 h. However, 2.5 ng/mL TGF-beta 1 induced a transient delay in re-epithelialization, a reduction in proliferation, and fewer clusters of genetically marked cells. Keratinocytes expressed MMP-1 mRNA only when they covered the wounded surface, suggesting that the cells acquire a collagenolytic phenotype during re-epithelialization and that contact with different ECM components may modulate keratinocyte expression of MMP-1. We conclude that the phenotype of oral keratinocytes is altered during re-epithelialization in vitro and that this process is modulated by TGF-beta 1. Re-epithelialization occurs as keratinocytes are activated to move over the wound bed. Understanding the phenotype of wounded keratinocytes may facilitate treatment of chronic oral wounds and periodontal disease.

Doxycycline inhibition of aneurysmal degeneration in an elastase-induced rat model of abdominal aortic aneurysm: preservation of aortic elastin associated with suppressed production of 92 kD gelatinase

PURPOSE

Increased local production of matrix metalloproteinases (MMPs) is a potential mechanism underlying structural protein degradation in abdominal aortic aneurysms (AAA). With an elastase-induced rodent model of AAA, we determined whether pharmacologic treatment with an MMP-inhibiting tetracycline might limit the development of experimental AAA in vivo.

METHODS

Forty-eight Wistar rats underwent a 2-hour perfusion of the abdominal aorta with 50 U porcine pancreatic elastase and were then treated with either subcutaneous doxycycline (25 mg/day; n=24) or saline solution vehicle (n=24). Aortic diameter was measured before and after elastase perfusion was performed and before the rats were killed at 0, 2, 7, or 14 days, and AAAs were defined as an increase in aortic diameter to at least twice that before perfusion. At death the aortic tissues were either perfusion-fixed for histologic evaluation or extracted for substrate zymographic evaluation.

RESULTS

Aortic diameter was not different between groups at 0 or 2 days, but it was significantly less in animals treated with doxycycline at both 7 and 14 days (mean+/-SEM, p<0.01). After day 2 the incidence of AAA was reduced from 83% (10 of 12 rats treated with saline solution) to 8% (1 of 12 animals treated with doxycycline). By histologic assessment doxycycline prevented the structural deterioration of aortic elastin without decreasing the influx of inflammatory cells. Increased aortic wall production of 92 kD gelatinase observed in a saline solution-treated control group was markedly suppressed in animals treated with doxycycline.

CONCLUSIONS

Treatment with an MMP-inhibiting tetracycline inhibits the development of experimental AAA in vivo. This inhibition may be due to selective blockade of elastolytic MMP expression in infiltrating inflammatory cells. Additional experiments, however, are necessitated to fully delineate this process.

Enhanced expression of matrilysin, collagenase, and stromelysin-1 in gastrointestinal ulcers

Programmed expression of several matrix metalloproteinases is an important feature of cutaneous wound healing. To study whether this also applies to gastrointestinal ulcer healing, we used in situ hybridization with 35S-labeled probes to localize sites of collagenase, stromelysin-1, and matrilysin expression in 26 samples representing peptic ulcers, Crohn's disease, and ulcerative colitis. In contrast to skin wounds, collagenase mRNA was not detected in the surface epithelium bordering gastrointestinal ulcer areas. However, together with stromelysin-1 mRNA, it was abundantly expressed by the granulation tissue in all types of ulcers. Signal for matrilysin mRNA and protein was detected in the mucosal epithelium bordering the ulcerations but never in the ulcer stroma. The gut basement membrane was disrupted under the matrilysin-producing epithelial cells as assessed by immunostaining for laminin. Tissue inhibitor of metalloproteinases (TIMP-1) mRNA never co-localized with matrilysin-positive mucosal epithelial cells. These data indicate that matrilysin plays a significant role in epithelial remodelling occurring in gastrointestinal ulcerations whereas collagenase and stromelysin-1 are involved in the reparative processes in the ulcer bed.

Localization of type I procollagen gene expression in silica-induced granulomatous lung disease and implication of transforming growth factor-beta as a mediator of fibrosis

We have used the silica-induced model of pulmonary injury in the rat to study the pattern of collagen expression in granulomatous lung inflammation. A single intratracheal instillation of silica into adult rats resulted in granulomatous inflammation leading to fibrosis and alveolar proteinosis. The development of disease in these animals was characterized over a 27-day period after treatment by means of histological, biochemical, and molecular analyses. Biochemical analyses indicated that significant increases in the weights of silicotic lungs were due to elevated amounts of DNA and total protein. Analysis of hydroxyproline content showed a 15-fold increase in this amino acid in silicotic lungs, confirming the development of a fibrotic reaction. In situ hybridization for type I procollagen mRNA displayed increased gene expression in the parenchyma, conducting airways, and vasculature of silicotic rats. Within the parenchyma, type I procollagen was expressed uniquely within granulomatous lesions. Immunohistochemistry indicated type I procollagen was being expressed by an alpha-smooth muscle actin-negative population of cells. Immunolocalization of extra-cellular transforming growth factor-beta showed coincident temporal and spatial overlap with type I procollagen expression, implicating this cytokine as a mediator of collagen gene expression in this model.

In situ hybridization of human erythropoietin in pre- and postnatal kidneys

Due to the transient transcription of the gene of erythropoietin (EPO) in response to hypoxic stimuli, localization within the cell of origin in humans has not been possible. Under acutely induced transcription of the EPO gene, through severe bleeding (hematocrit < 10%), EPO transcripts were detected within renal interstitial cells in rodents. However, by immunohistochemistry or tissue culture, human tubular epithelial cells or glomerular mesangium have been shown to produce EPO, suggesting a species difference. Aiming to investigate the precise location of EPO in intact human kidneys, 38 fetal, infant, and adult kidneys were examined by in situ hybridization. Kidneys from patients with conditions predisposing to severe hypoxia and/or induced polycythemia were utilized, because under these conditions active EPO mRNA synthesis is expected. We found specific EPO mRNA transcripts within a small population of cortical interstitial cells of near-term or postnatal kidneys.

Osteopontin expression is increased in the heritable cardiomyopathy of Syrian hamsters

BACKGROUND

Osteopontin, a noncollagenous matrix protein, is transiently expressed in the heart after experimental cardiac injury, but its expression in states of continuing cardiac remodeling is unknown. We evaluated osteopontin expression in the heritable cardiomyopathy of the Syrian hamster.

METHODS AND RESULTS

Hamster hearts were obtained for RNA isolation and analysis and in situ hybridization from two groups: normal control animals (n = 4) and untreated cardiomyopathic hamsters (n = 5). Osteopontin mRNA was 12-fold greater in cardiomyopathic hearts compared with normal controls (1.76 +/- 0.31 versus 0.14 +/- 0.04 arbitrary units normalized to GAPDH, mean +/- SEM, P < .05). In situ hybridization was used to define the origin of osteopontin in the heart. Osteopontin mRNA above background levels was not detected in sections from noncardiomyopathic hamster hearts but was readily detected in sections from cardiomyopathic hamsters, in which it originated in cells morphologically consistent with tissue macrophages.

CONCLUSIONS

In the hamster, osteopontin is expressed in heritably cardiomyopathic hearts under conditions of chronic injury and repair, and the source of ostopontin message appears to be issue macrophage-like cells in foci of inflammation. This model could be used to evaluate the biological role of osteopontin in myocardial inflammation and remodeling.

Human dermal microvascular endothelial cells produce matrix metalloproteinases in response to angiogenic factors and migration

Matrix metalloproteinases (MMPs) are a family of inducible enzymes that degrade extracellular matrix components, allowing cells to traverse connective tissue structures efficiently. Specific tissue inhibitors (TIMPs) function as physiologic inhibitors of MMP activity. Because neovascularization may require various proteinases, we characterized the profile of metalloenzyme production by microvascular endothelial cells (MEC) and the modulation of expression by phorbol esters (PMA) and by the physiologically relevant cytokines tumor necrosis factor-alpha (TNF-alpha), basic fibroblast growth factor, and interferon-gamma. MMP expression by MEC and large-vessel human umbilical vein endothelial cells (HUVEC) was determined by enzyme-linked immunosorbent assay, immunoprecipitation, Northern hybridization, and transfection assays. Constitutive expression of MMPs by endothelial cells was low. PMA stimulated the production of collagenase, stromelysin, 92-kDa gelatinase, and TIMP-1 in both endothelial cell types. TIMP-2 was constitutively expressed by MEC and HUVEC, but was down-regulated by PMA. TNF-alpha induced an endothelial-cell-specific up-regulation of collagenase with a concomitant inhibition of PMA-induced TIMP-1 up-regulation, a response that is distinct from that of fibroblasts. Interferon-gamma up-regulated TIMP-1 production by MEC and blocked PMA and TNF-induced up-regulation of collagenase. Northern hybridization assays showed pretranslational control of PMA-, basic fibroblast growth factor-, and TNF-alpha-induced MMP expression. Collagenase-promoter CAT constructs containing 2.28 kb of the 5' region of the collagenase gene demonstrated transcriptional regulation. The potential physiologic relevance of such regulation was shown in an in vitro migration assay. MEC were stimulated to migrate by wounding and exposure to TNF-alpha. Collagenase mRNA was prominently expressed by the migrating cells, as shown by in situ hybridization. In sum, MEC have a unique profile of MMP expression and regulation compared with other cell types, which may be important for wound healing and angiogenesis, particularly during the early phase of migration.