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

The Role of Matrix Metalloproteinase in Inflammation with a Focus on Infectious Diseases

Matrix metalloproteinases (MMPs) are involved in extracellular matrix remodeling through the degradation of extracellular matrix components and are also involved in the inflammatory response by regulating the pro-inflammatory cytokines TNF-α and IL-1β. Dysregulation in the inflammatory response and changes in the extracellular matrix by MMPs are related to the development of various diseases including lung and cardiovascular diseases. Therefore, numerous studies have been conducted to understand the role of MMPs in disease pathogenesis. MMPs are involved in the pathogenesis of infectious diseases through a dysregulation of the activity and expression of MMPs. In this review, we discuss the role of MMPs in infectious diseases and inflammatory responses. Furthermore, we present the potential of MMPs as therapeutic targets in infectious diseases.

An Unexplored Role for MMP-7 (Matrix Metalloproteinase-7) in Promoting Gut Permeability After Ischemic Stroke

Poststroke infections are common complications of stroke and are highly associated with poor outcomes for patients. Stroke induces profound immunodepression coupled with alterations to autonomic signaling, which together render the body more susceptible to infection from without (nosocomial/community-acquired infection) and from within (commensal bacterial infection). Critical to the hypothesis of commensal infection is the phenomenon of poststroke gut permeability and gut dysbiosis. Few studies have provided adequate explanations for the mechanisms underlying the molecular alterations that produce a more permeable gut and perturbed gut microbiota after stroke. A dysregulation in the production of matrix MMP-7 (metalloproteinase-7) may play a critical role in the progression of gut permeability after stroke. By cleaving junctional and extracellular matrix proteins, MMP-7 is capable of compromising gut barrier integrity. Because of MMP-7's unique abundance in the small intestine and its capacity to be induced in states of bacterial invasion and inflammation, along with its unique degradative capability, MMP-7 may be crucially important to the progression of gut permeability after ischemic stroke.

MMP-7 marks severe pancreatic cancer and alters tumor cell signaling by proteolytic release of ectodomains

Pancreatic cancer incurs the worst survival rate of the major cancers. High levels of the protease matrix metalloproteinase-7 (MMP-7) in circulation correlate with poor prognosis and limited survival of patients. MMP-7 is required for a key path of pancreatic tumorigenesis in mice and is present throughout tumor progression. Enhancements to chemotherapies are needed for increasing the number of pancreatic tumors that can be removed and for preventing relapses after surgery. With these ends in mind, selective inhibition of MMP-7 may be worth investigation. An anti-MMP-7 monoclonal antibody was recently shown to increase the susceptibility of several pancreatic cancer cell lines to chemotherapeutics, increase their apoptosis, and decrease their migration. MMP-7 activities are most apparent at the surfaces of innate immune, epithelial, and tumor cells. Proteolytic shedding of multiple protein ectodomains by MMP-7 from such cell surfaces influence apoptosis, proliferation, migration, and invasion. These activities warrant targeting of MMP-7 selectively in pancreatic cancer and other tumors of mucosal epithelia. Competitive and non-competitive modes of MMP-7 inhibition are discussed.

Shedding of Syndecan-1/CXCL1 Complexes by Matrix Metalloproteinase 7 Functions as an Epithelial Checkpoint of Neutrophil Activation

Although neutrophils play critical roles in innate immunity, in excess these cells cause severe tissue damage. Thus, neutrophil activation must be tightly regulated to prevent indiscriminant damage. Previously, we reported that mice lacking matrix metalloproteinase (MMP) 7 are protected from lung injury owing to markedly impaired neutrophil movement from the interstitium into mucosal lumenal spaces. This phenotype resulted from a lack of MMP7 shedding of syndecan-1, a heparan sulfate proteoglycan that carries the neutrophil chemokine CXCL1 as cargo. Here, we assessed if shedding syndecan-1/CXCL1 complexes affects neutrophil activation. Whereas injured monolayers of wild-type alveolar type II cells potently stimulated neutrophil activation, as gauged by release of myeloperoxidase, cells from Mmp7(-/-) or syndecan-1-null (Sdc1(-/-)) mice or human cells with MMP7 knockdown did not. In vivo, we observed reduced myeloperoxidase release relative to neutrophil numbers in bleomycin-injured Mmp7(-/-) and Sdc1(-/-) mice. Furthermore, we determined that soluble syndecan-1 directly stimulated neutrophil activation in the absence of cellular damage. These data indicate that MMP7 shedding of syndecan-1/CXCL1 complexes functions as a checkpoint that restricts neutrophil activation at sites of epithelial injury.

Immunization with outer membrane proteins (OprF and OprI) and flagellin B protects mice from pulmonary infection with mucoid and nonmucoid Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterium, which considered as a common cause of nosocomial infection and life-threatening complications in immunocompromized and cystic fibrosis patients. Here, we evaluate the protective effect of recombinant vaccines composed of outer membrane proteins OprF and OprI alone or in combination with flagellin B against mucoid and nonmucoid pseudomonas infection.

METHODS

BALB/C mice were immunized subcutaneous using OprF and OprI with or without flagellin B and antibody titers were determined. Serum bactericidal and opsonophagocytosis activities of immunized and control sera were estimated against mucoid and nonmucoid pseudomonas strains. Lung tissue sections from immunized and nonimmunized mice were analyzed and the levels of peripheral neutrophils infiltration into the lung and tissue inflammation were scored.

RESULTS

Subcutaneous immunization using OprF and OprI with or without flagellin B elicited higher antibody titers against OprF, OprI, and flagellin B. The produced antibodies successfully opsonized both mucoid and nonmucoid strains with subsequent activation of the terminal pathway of complement that enhances killing of nonmucoid strains via complement-mediated lysis. Furthermore, opsonized mucoid and nonmucoid strains showed enhanced opsonophagocytosis via human peripheral neutrophils, a mechanism that kills P. aeruginosa when complement mediated lysis is not effective especially with mucoid strains. Immunized mice also showed a significant prolonged survival time, lower bacteremia, and reduced lung damage when compared with control nonimmunized mice.

CONCLUSION

Our data showed that mice immunized with OprF/OprI or OprF/OprI and flagellin B are significantly protected from infection caused by mucoid and nonmucoid strains of P. aeruginosa.

Defensins Potentiate a Neutralizing Antibody Response to Enteric Viral Infection

α-defensins are abundant antimicrobial peptides with broad, potent antibacterial, antifungal, and antiviral activities in vitro. Although their contribution to host defense against bacteria in vivo has been demonstrated, comparable studies of their antiviral activity in vivo are lacking. Using a mouse model deficient in activated α-defensins in the small intestine, we show that Paneth cell α-defensins protect mice from oral infection by a pathogenic virus, mouse adenovirus 1 (MAdV-1). Survival differences between mouse genotypes are lost upon parenteral MAdV-1 infection, strongly implicating a role for intestinal defenses in attenuating pathogenesis. Although differences in α-defensin expression impact the composition of the ileal commensal bacterial population, depletion studies using broad-spectrum antibiotics revealed no effect of the microbiota on α-defensin-dependent viral pathogenesis. Moreover, despite the sensitivity of MAdV-1 infection to α-defensin neutralization in cell culture, we observed no barrier effect due to Paneth cell α-defensin activation on the kinetics and magnitude of MAdV-1 dissemination to the brain. Rather, a protective neutralizing antibody response was delayed in the absence of α-defensins. This effect was specific to oral viral infection, because antibody responses to parenteral or mucosal ovalbumin exposure were not affected by α-defensin deficiency. Thus, α-defensins play an important role as adjuvants in antiviral immunity in vivo that is distinct from their direct antiviral activity observed in cell culture.

A Toll-Like Receptor 5 Agonist Improves the Efficacy of Antibiotics in Treatment of Primary and Influenza Virus-Associated Pneumococcal Mouse Infections

Prophylactic intranasal administration of the Toll-like receptor 5 (TLR5) agonist flagellin protects mice against respiratory pathogenic bacteria. We hypothesized that TLR5-mediated stimulation of lung immunity might improve the therapeutic index of antibiotics for the treatment of Streptococcus pneumoniae respiratory infections in mice. Intranasal administration of flagellin was combined with either oral administration of amoxicillin or intraperitoneal injection of trimethoprim-sulfamethoxazole to treat S. pneumoniae-infected animals. Compared with standalone treatments, the combination of antibiotic and flagellin resulted in a lower bacterial load in the lungs and greater protection against S. pneumoniae dissemination and was associated with an early increase in neutrophil infiltration in the airways. The antibiotic-flagellin combination treatment was, however, not associated with any exacerbation of inflammation. Moreover, combination treatment was more efficacious than standalone antibiotic treatments in the context of post-influenza virus pneumococcal infection. Lastly, TLR5 signaling was shown to be mandatory for the efficacy of the combined antibacterial therapy. This report is the first to show that combining antibiotic treatment with the stimulation of mucosal innate immunity is a potent antibacterial strategy against pneumonia.

Osteopontin Exacerbates Pulmonary Damage in Influenza-Induced Lung Injury

The level of osteopontin (OPN) increases during bacterial lung infection. However, the OPN level in virus-induced lung injury is unclear, and the relationship between the hyer-production of OPN and lung injury remains to be thoroughly understood. Therefore, we sought to determine whether a relationship exists between OPN and pulmonary damage. Particularly, pulmonary edema and the destruction of pulmonary tissue. In this study, we found that the OPN level was significantly elevated in patients with pulmonary damage, and there was a positive correlation between the OPN serum level and disease severity in influenza lung injury. The epithelial sodium channel (ENaC) is the main mechanism of clearance of pulmonary edema fluid, and matrix metalloproteinase 7 (MMP7) can degrade the extracellular matrix. In lung epithelial cells, OPN markedly decreased the mRNA expression of the α-subunit of ENaC through integrin β3 and CD44 (OPN receptors); however, the expression of MMP7 was promoted by OPN interaction with integrin β1 and CD44. In addition, OPN increased the levels of tumor necrosis factor-α and interleukin-6. These findings suggested that OPN might increase influenza virus-induced lung injury by augmenting lung epithelial cell apoptosis and impairing ENaC and extracellular matrix destruction.

Plasticity of airway epithelial cell transcriptome in response to flagellin

Airway epithelial cells (AEC) are critical components of the inflammatory and immune response during exposure to pathogens. AECs in monolayer culture and differentiated epithelial cells in air-liquid interface (ALI) represent two distinct and commonly used in vitro models, yet differences in their response to pathogens have not been investigated. In this study, we compared the transcriptional effects of flagellin on AECs in monolayer culture versus ALI culture using whole-genome microarrays and RNA sequencing. We exposed monolayer and ALI AEC cultures to flagellin in vitro and analyzed the transcriptional response by microarray and RNA-sequencing. ELISA and RT-PCR were used to validate changes in select candidates. We found that AECs cultured in monolayer and ALI have strikingly different transcriptional states at baseline. When challenged with flagellin, monolayer AEC cultures greatly increased transcription of numerous genes mapping to wounding response, immunity and inflammatory response. In contrast, AECs in ALI culture had an unexpectedly muted response to flagellin, both in number of genes expressed and relative enrichment of inflammatory and immune pathways. We conclude that in vitro culturing methods have a dramatic effect on the transcriptional profile of AECs at baseline and after stimulation with flagellin. These differences suggest that epithelial responses to pathogen challenges are distinctly different in culture models of intact and injured epithelium.

Matrix metalloproteinases in pneumonia

Pneumonia is a worldwide infectious disease that is associated with significant morbidity and mortality and is the most common fatal infection acquired in hospitals. Despite advances in preventive strategies, such as antibiotic therapies and intensive care, the mortality rate still requires substantial improvement. Matrix metalloproteinases (MMPs) are a large family of zinc-dependent endopeptidases, which are known as the major enzymes responsible for the proteolytic degradation of proteinaceous components of the extracellular matrix (ECM). Although the main function of MMPs is the removal of the ECM during tissue resorption and progression of various diseases, MMPs also interact with multiple cytokines, participating in the pathology of infection and inflammation. This review presents a schematic overview of the different MMPs expressed in pneumonia. MMPs are key factors in the pathogenesis of various types of pneumonia, such as community-acquired pneumonia, hospital-acquired pneumonia, and ventilator-associated pneumonia. Here, we review the pathological roles of various MMPs in pneumonia.

Helicobacter pylori and gastritis: the role of extracellular matrix metalloproteases, their inhibitors, and the disintegrins and metalloproteases--a systematic literature review

Helicobacter pylori (H. pylori) is the etiologic agent of gastritis; it has been estimated that 50 % of the world's population could be infected by this bacteria. Gastritis may progress to chronic atrophic gastritis, a condition associated with the development of gastric cancer (GC). Several matrix metalloproteases (MMP) and tissue inhibitors of MMPs (TIMP) as well as disintegrins and metalloproteases (ADAM) have been reported as being involved in gastritis. Among other processes, these protein families participate in remodeling the extracellular matrix, cell signaling, immune response, angiogenesis, inflammation and epithelial mesenchymal transition. This systematic review analyzes the scientific evidence surrounding the relationship between members of the MMP, TIMP and ADAM families and infection by H. pylori in gastritis, considering both in vitro and in vivo studies. Given the potential clinical value of certain members of the MMP, TIMP and ADAM families as molecular markers in gastritis and the association of gastritis with GC, the need for further study is highlighted.

Comparison of localized versus systemic levels of Matrix metalloproteinases (MMPs), its tissue inhibitors (TIMPs) and cytokines in tuberculous and non-tuberculous pleuritis patients

The interaction of Matrix metalloproteinases (MMPs), its tissue inhibitors (TIMPs) and pro-inflammatory cytokines in response to Mycobacterium tuberculosis (MTB) infection is important to understand the immune response at the site of infection. We compared the levels of MMPs, TIMPs and cytokines in plasma (BL) and pleural fluid (PF) of tuberculosis (TB) and non tuberculosis (NTB) patients. Comparison between BL and PF showed significantly higher levels of MMP-1, TIMP-1 and -3 in TB PF; of MMP-7, -8, -9 in BL of both groups. Also, levels of MMP-1,-8,-9 and TIMP-3 were significantly higher in TB PF compared to NTB. Cytokines INF-γ, TNF-α, and IL-6 significantly increased in PF of both groups. A positive correlation of MMPs with TIMPs in TB, MMP-1 and -9 with IL-6 in TB PF and MMP-9 with IFN-γ in NTB PF was observed. This study implicates the possible usage of MMPs as bio-markers aiding diagnosis in TB pleuritis.

Activation of MMP-9 by human lung epithelial cells in response to the cystic fibrosis-associated pathogen Burkholderia cenocepacia reduced wound healing in vitro

Burkholderia cepacia complex is a group of bacterial pathogens that cause opportunistic infections in cystic fibrosis (CF). The most virulent of these is Burkholderia cenocepacia. Matrix metalloproteinases (MMPs) are upregulated in CF patients. The aim of this work was to examine the role of MMPs in the pathogenesis of B. cepacia complex, which has not been explored to date. Real-time PCR analysis showed that B. cenocepacia infection upregulated MMP-2 and MMP-9 genes in the CF lung cell line CFBE41o- within 1 h, whereas MMP-2, -7, and -9 genes were upregulated in the non-CF lung cell line 16HBE14o-. Conditioned media from both cell lines showed increased MMP-9 activation following B. cenocepacia infection. Conditioned media from B. cenocepacia-infected cells significantly reduced the rate of wound healing in confluent lung epithelia (P < 0.05), in contrast to conditioned media from Pseudomonas aeruginosa-infected cells, which showed predominant MMP-2 activation. Treatment of control conditioned media from both cell lines with the MMP activator 4-aminophenylmercuric acetate (APMA) also resulted in clear activation of MMP-9 and to a much lesser extent MMP-2. APMA treatment of control media also delayed the repair of wound healing in confluent epithelial cells. Furthermore, specific inhibition of MMP-9 in medium from cells exposed to B. cenocepacia completely reversed the delay in wound repair. These data suggest that MMP-9 plays a role in the reduced epithelial repair observed in response to B. cenocepacia infection and that its activation following B. cenocepacia infection contributes to the pathogenesis of this virulent pathogen.

Role of meprins to protect ileal mucosa of Crohn's disease patients from colonization by adherent-invasive E. coli

Ileal lesions in Crohn's disease (CD) patients are colonized by pathogenic adherent-invasive Escherichia coli (AIEC) able to adhere to and invade intestinal epithelial cells (IEC), and to survive within macrophages. The interaction of AIEC with IEC depends on bacterial factors mainly type 1 pili, flagella, and outer membrane proteins. In humans, proteases can act as host defence mechanisms to counteract bacterial colonization. The protease meprin, composed of multimeric complexes of the two subunits alpha and beta, is abundantly expressed in IECs. Decreased levels of this protease correlate with the severity of the inflammation in patients with inflammatory bowel disease. The aim of the present study was to analyze the ability of meprin to modulate the interaction of AIEC with IECs. In patients with ileal CD we observed decreased levels of meprins, in particular that of meprin β. Dose-dependent inhibition of the abilities of AIEC strain LF82 to adhere to and invade intestinal epithelial T84 cells was observed when bacteria were pre-treated with both exogenous meprin α and meprin β. Dose-dependent proteolytic degradation of type 1 pili was observed in the presence of active meprins, but not with heat-inactivated meprins, and pretreatment of AIEC bacteria with meprins impaired their ability to bind mannosylated host receptors and led to decreased secretion of the pro-inflammatory cytokine IL-8 by infected T84 cells. Thus, decreased levels of protective meprins as observed in CD patients may contribute to increased AIEC colonization.

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.

IL-13 and TH2 cytokine exposure triggers matrix metalloproteinase 7-mediated Fas ligand cleavage from bronchial epithelial cells

BACKGROUND

Bronchial epithelial damage and activation likely contribute to the inflammatory and airway-remodeling events characteristic of severe asthma. Interaction of Fas receptor (CD95) with its ligand (FasL; CD95L) is an important mechanism of cell-mediated apoptosis. Bronchial epithelial FasL expression provides immune barrier protection from immune cell-mediated damage.

OBJECTIVES

Membrane FasL (mFasL) is a cleavage target of matrix metalloproteinases (MMPs). We investigated whether the asthmatic T(H)2 environment might influence disease processes by increasing airway epithelial MMP-mediated cleavage of mFasL into proinflammatory soluble FasL.

METHODS

We used human airway epithelial cell lines and primary cells to model the human airway epithelium in vitro. Airway tissue from healthy subjects and patients with severe asthma was used to investigate MMP expression patterns in diseased airways.

RESULTS

We demonstrate that active MMP-7 is present in the ciliated epithelial cells of normal human airways. In patients with severe asthma, MMP-7 levels are increased in basal epithelial cells. Airway epithelial cell lines (1HAEo(-) and 16HBE14o(-)) in vitro express constitutively high levels of MMP-2 and MMP-9 but relatively low levels of MMP-7. T(H)2 cytokine (IL-4, IL-9, and IL-13) treatment of 1HAEo(-) cells increased MMP-7 mRNA and activity, triggered colocalization of intracellular MMP-7 with FasL, and caused mFasL cleavage with soluble FasL release. Small interfering RNA knockdown shows that cytokine-induced mFasL cleavage is dependent on MMP-7 activity.

CONCLUSIONS

MMPs serve multiple beneficial roles in the lung. However, chronic disordered epithelial expression of MMP-7 in patients with asthma might increase mFasL cleavage and contribute to airway epithelial damage and inflammation.

Matrix metalloproteinases as drug targets in infections caused by gram-negative bacteria and in septic shock

The mammalian immune system is optimized to cope effectively with the constant threat of pathogens. However, when the immune system overreacts, sepsis, severe sepsis, or septic shock can develop. Despite extensive research, these conditions remain the leading cause of death in intensive care units. The matrix metalloproteinases (MMPs) constitute a family of proteases that are expressed in developmental, physiological, and pathological processes and also in response to infections. Studies using MMP inhibitors and MMP knockout mice indicate that MMPs play essential roles in infection and in the host defense against infection. This review provides a brief introduction to some basic concepts of infections caused by gram-negative bacteria and reviews reports describing MMP expression and inhibition, as well as studies with MMP-deficient mice in models of infection caused by gram-negative bacteria and of septic shock. We discuss whether MMPs should be considered novel drug targets in infection and septic shock.

Epilysin (MMP-28) restrains early macrophage recruitment in Pseudomonas aeruginosa pneumonia

Several members of the matrix metalloproteinase (MMP) family function in various processes of innate immunity, particularly in controlling leukocyte influx. Epilysin (MMP-28) is expressed in numerous tissues and, in adult mice, it has the highest expression in lung, where it is detected in bronchial epithelial cells (Clara cells). Epilysin is also expressed by bone marrow-derived macrophages, but not by alveolar macrophages, suggesting that its expression by macrophages is dependent on localization and differentiation. To assess the role of this MMP, we generated epilysin-null (Mmp28(-/-)) mice. Although epilysin is constitutively expressed in normal tissues, Mmp28(-/-) mice have no overt phenotype. However, using a murine model of Pseudomonas aeruginosa pneumonia, we found that Mmp28(-/-) mice had an early increase in macrophage recruitment into the lungs, as well as enhanced bacterial clearance and reduced pulmonary neutrophilia, which we predicted were due to accelerated macrophage influx. Macrophage depletion in WT and Mmp28(-/-) mice confirmed a role for macrophages in clearing P. aeruginosa and regulating neutrophil recruitment. Furthermore, we observed that macrophages derived from Mmp28(-/-) mice migrated faster than did wild-type cells to bronchoalveolar lavage fluid from P. aeruginosa-treated mice of either genotype. These observations indicate that epilysin functions as an intrinsic negative regulator of macrophage recruitment by retarding the chemotaxis of these cells.

Pathogen recognition in the innate immune response

Immunity against microbial pathogens primarily depends on the recognition of pathogen components by innate receptors expressed on immune and non-immune cells. Innate receptors are evolutionarily conserved germ-line-encoded proteins and include TLRs (Toll-like receptors), RLRs [RIG-I (retinoic acid-inducible gene-I)-like receptors] and NLRs (Nod-like receptors). These receptors recognize pathogens or pathogen-derived products in different cellular compartments, such as the plasma membrane, the endosomes or the cytoplasm, and induce the expression of cytokines, chemokines and co-stimulatory molecules to eliminate pathogens and instruct pathogen-specific adaptive immune responses. In the present review, we will discuss the recent progress in the study of pathogen recognition by TLRs, RLRs and NLRs and their signalling pathways.

Differential Processing of {alpha}- and {beta}-Defensin Precursors by Matrix Metalloproteinase-7 (MMP-7)

Proteolytic processing of defensins is a critical mode of posttranslational regulation of peptide activity. Because mouse alpha-defensin precursors are cleaved and activated by matrix metalloproteinase-7 (MMP-7), we determined if additional defensin molecules, namely human neutrophil defensin pro-HNP-1 and beta-defensins, are targets for MMP-7. We found that MMP-7 cleaves within the pro-domain of the HNP-1 precursor, a reaction that does not generate the mature peptide but produces a 59-amino acid intermediate. This intermediate, which retains the carboxyl-terminal end of the pro-domain, had antimicrobial activity, indicating that the residues important for masking defensin activity reside in the amino terminus of this domain. Mature HNP-1 was resistant to processing by MMP-7 unless the peptide was reduced and alkylated, demonstrating that only the pro-domain of alpha-defensins is normally accessible for cleavage by this enzyme. From the 47-residue HBD-1 precursor, MMP-7 catalyzed removal of 6 amino acids from the amino terminus. Neither a 39-residue intermediate form of HBD-1 nor the mature 36-residue form of HBD-1 was cleaved by MMP-7. In addition, both pro-HBD-2, with its shorter amino-terminal extension, and pro-HBD-3 were resistant to MMP-7. However, human and mouse beta-defensin precursors that lack disulfide bonding contain a cryptic MMP-7-sensitive site within the mature peptide moiety. These findings support and extend accumulating evidence that the native three-dimensional structure of both alpha- and beta-defensins protects the mature peptides against proteolytic processing by MMP-7. We also conclude that sites for MMP-7 cleavage are more common at the amino termini of alpha-defensin rather than beta-defensin precursors, and that catalysis at these sites in alpha-defensin pro-domains results in acquisition of defensin activity.

Lessons from nature: "Pathogen-Mimetic" systems for mucosal nano-medicines

Mucosal surfaces establish an interface with external environments that provide a protective barrier with the capacity to selectively absorb and secrete materials important for homeostasis of the organism. In man, mucosal surfaces such as those in the gastrointestinal tract, respiratory tree and genitourinary system also represent significant barrier to the successful administration of certain pharmaceutical agents and the delivery of newly designed nano-scale therapeutic systems. This review examines morphological, physiological and biochemical aspects of these mucosal barriers and presents currently understood mechanisms used by a variety of virulence factors used by pathogenic bacteria to overcome various aspects of these mucosal barriers. Such information emphasizes the impediments that biologically active materials must overcome for absorption across these mucosal surfaces and provides a template for strategies to overcome these barriers for the successful delivery of nano-scale bioactive materials, also known as nano-medicines.

Burkholderia cepacia complex: epithelial cell–pathogen confrontations and potential for therapeutic intervention

Burkholderia cepaciacomplex (Bcc) is an important and virulent pathogen in cystic fibrosis patients. The interactions between this pathogen and the host lung epithelium are being widely investigated but remain to be elucidated. The complex is very versatile and its interactions with the lung epithelial cells are many and varied. The first steps in the interaction are penetration of the mucosal blanket and subsequent adherence to the epithelial cell surface. A range of epithelial receptors have been reported to bind to Bcc. The next step in pathogenesis is the invasion of the lung epithelial cell and also translocation across the epithelium to the serosal side. Furthermore, pathogenesis is mediated by a range of virulence factors that elicit their effects on the epithelial cells. This review outlines these interactions and examines the therapeutic implications of understanding the mechanisms of pathogenesis of this difficult, antibiotic-resistant, opportunistic pathogen.

Human leukocyte elastase counteracts matrix metalloproteinase-7 induced apoptosis resistance of tumor cells

Matrix metalloproteinase-7 (MMP-7/Matrilysin) is a component of the tumor microenvironment associated with malignant progression. Its expression in tumors protects tumor cells from CD95-mediated apoptosis and the cytotoxic activity of tumor specific CD8(+) T cells. In the present study, we show that human leukocyte elastase (HLE) secreted by polymorphonuclear leukocytes cleaves MMP-7 resulting in loss of enzymatic activity. The anti-apoptotic effect of MMP-7 is reduced in the presence of HLE for CD95-, doxorubicin- and CTL-mediated apoptosis. Our data indicates that HLE may be a natural inactivator of MMP-7 which can counteract MMP-7-induced apoptosis resistance.

Matrix metalloproteinase-7 (matrilysin) controls neutrophil egress by generating chemokine gradients

Matrilysin [matrix metalloproteinase 7 (MMP7)] is induced by mucosal injury of many tissues. To assess function of this proteinase, we subjected wild-type and Mmp7(-/-) mice to acute colon injury. When matrilysin expression was increasing, 73% of wild-type mice died, whereas only 32% of Mmp7(-/-) mice succumbed. Although re-epithelialization was delayed in Mmp7(-/-) mice, overall injury did not differ markedly between genotypes. We hypothesized that differences in acute inflammation caused increased mortality in wild-type mice. Indeed, whereas overall neutrophil influx into tissue was similar in wild-type and Mmp7(-/-) mice, their location and extent of migration differed between genotypes. Neutrophils were dispersed throughout the mucosa and within the lumen of wild-type mice, but these leukocytes were largely confined to the submucosa in Mmp7(-/-) mice. The levels of neutrophil chemokines, keratinocyte-derived chemokine and MIP-2, increased in the colon tissue of both genotypes, but these factors were detected only in lumenal lavages of wild-type mice. Our findings indicate that matrilysin mediates beneficial and deleterious effects in response to injury. On one hand, it promotes re-epithelialization, but it also controls the transepithelial influx of neutrophils, which if excessive, can lead to tissue damage.

Neutrophil elastase, proteinase 3 and cathepsin G: physicochemical properties, activity and physiopathological functions

Polymorphonuclear neutrophils form a primary line of defense against bacterial infections using complementary oxidative and non-oxidative pathways to destroy phagocytized pathogens. The three serine proteases elastase, proteinase 3 and cathepsin G, are major components of the neutrophil primary granules that participate in the non-oxidative pathway of intracellular pathogen destruction. Neutrophil activation and degranulation results in the release of these proteases into the extracellular medium as proteolytically active enzymes, part of them remaining exposed at the cell surface. Extracellular neutrophil serine proteases also help kill bacteria and are involved in the degradation of extracellular matrix components during acute and chronic inflammation. But they are also important as specific regulators of the immune response, controlling cellular signaling through the processing of chemokines, modulating the cytokine network, and activating specific cell surface receptors. Neutrophil serine proteases are also involved in the pathogenicity of a variety of human diseases. This review focuses on the structural and functional properties of these proteases that may explain their specific biological roles, and facilitate their use as molecular targets for new therapeutic strategies.

Individual matrix metalloproteinases control distinct transcriptional responses in airway epithelial cells infected with Pseudomonas aeruginosa

Airway epithelium is the initial point of host-pathogen interaction in Pseudomonas aeruginosa infection, an important pathogen in cystic fibrosis and nosocomial pneumonia. We used global gene expression analysis to determine airway epithelial transcriptional responses dependent on matrilysin (matrix metalloproteinase 7 [MMP-7]) and stromelysin-2 (MMP-10), two MMPs induced by acute P. aeruginosa pulmonary infection. Extraction of differential gene expression (EDGE) analysis of gene expression changes in P. aeruginosa-infected organotypic tracheal epithelial cell cultures from wild-type, Mmp7-/-, and Mmp10-/- mice identified 2,091 matrilysin-dependent and 1,628 stromelysin-2-dependent genes that were differentially expressed. Key node network analysis showed that these MMPs controlled distinct gene expression programs involved in proliferation, cell death, immune responses, and signal transduction, among other host defense processes. Our results demonstrate discrete roles for these MMPs in regulating epithelial responses to Pseudomonas infection and show that a global genomics strategy can be used to assess MMP function.

Synergistic up-regulation of epithelial cell matrix metalloproteinase-9 secretion in tuberculosis

Mycobacterium tuberculosis (MTb) kills approximately 2 million people each year. MTb must drive host tissue destruction to disseminate and also to cause pulmonary cavitation. Matrix metalloproteinase-9 (MMP-9, gelatinase B) is implicated in this Tb-related immunopathology. We demonstrate that conditioned media from MTb-infected monocytes (CoMTb), but not direct infection with MTb, up-regulates MMP-9 gene expression and secretion from primary human bronchial epithelial cells (NHBE). MMP-9 secretion was increased 8.7-fold by CoMTb (P < 0.05) as assayed by gelatin zymography. A549 and 16HBE14o epithelial cell MMP secretion was significantly less than primary NHBE secretion. MMP-9 secretion was decreased 53.2% by inhibition of the p38 mitogen-activated protein kinase (MAPK) by SB203580 (P < 0.01) and 48.3% by inhibition of extracellular signal-regulated kinase with PD98059 (P < 0.05). MMP-9 secretion was prostaglandin independent. TNF-alpha was necessary but not sufficient for MMP-9 up-regulation by the monocyte-epithelial cell network. Soluble factors derived from Tb culture synergized with TNF-alpha to increase MMP-9 secretion by NHBE 6-fold (P < 0.01 compared with either stimulus alone). Together, these data reveal a new mechanism by which host- and pathogen-derived factors act together in MTb infection to drive MAPK-dependent MMP-9 secretion from respiratory epithelial cells.

Molecular and cellular basis of microflora-host interactions

Mucosal surfaces represent the main sites in which environmental microorganisms and antigens interact with the host. In particular the intestinal mucosal surfaces are in continuous contact with a heterogeneous population of microorganisms of the endogenous flora and are exposed to food and microbes. As a result, the immune system of the host has to discriminate between pathogenic and commensal microorganisms. This article reviews the types of sentinel cells that continuously sense the environment and coordinate immune defenses as well as the mechanisms of the innate and adaptive immune systems that are activated by bacterial and viral molecular patterns leading to inflammatory, allergic, or regulatory immune response with special emphasis on probiotic bacteria.

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.

Mucosal interplay among commensal and pathogenic bacteria: lessons from flagellin and Toll-like receptor 5

Toll-like receptors (TLR) detect pathogen-associated molecular patterns (PAMP) and play a crucial role in triggering immunity. Due to their large surfaces in direct contact with the environment, mucosal tissues are the major sites of PAMP-TLR signalling. How innate and adaptive immunity are triggered through flagellin-TLR5 interaction is the main focus of the review. In view of recent reports on genetic polymorphism, we will summarize the impact of TLR5 on the susceptibility to mucosal infections and on various immuno-pathologies. Finally, the contribution of TLRs in the induction and maintenance of mucosal homeostasis and commensal discrimination is discussed.

Role of matrix metalloproteinase-7 in the modulation of a Chlamydia trachomatis infection

To determine the role of matrix metalloproteinase-7 (MMP-7) in the pathogenesis of chlamydial infection, C57BL/6 wild-type (WT) and MMP-7 knockout (KO) mice were infected intravaginally with Chlamydia trachomatis mouse pneumonitis (MoPn). Over a period of 6 weeks postinfection, various organs were cultured for C. trachomatis. Other infected animals were mated to assess their fertility status. No significant differences were observed between WT and KO mice in the number of animals with positive vaginal cultures, length of time of C. trachomatis shedding, or the number of C. trachomatis inclusion-forming units (IFU) recovered from their genital tracts. Likewise, the number of animals with hydrosalpinx, and the fertility rates and the number of embryos per mouse, were similar in WT and KO mice. Cultures from the spleen, lungs, kidneys and large intestine yielded similar numbers of IFU from WT and KO mice. However, the number of C. trachomatis IFU recovered from the small intestine of KO mice was significantly higher than that recovered from the small intestine of WT mice at 2 weeks postinfection. Because MMP-7 KO mice are deficient in active intestinal alpha-defensins, the results suggest that these components play a role in regulating colonization of the gastrointestinal tract by Chlamydia. By contrast, MMP-7 is dispensable in the progression and resolution of the genital tract infection.

Innate immune responses of human tracheal epithelium toPseudomonas aeruginosaflagellin, TNF-α, and IL-1β

We measured innate immune responses by primary human tracheal epithelial (HTE) cells grown as confluent, pseudostratified layers during exposure to inflammatory activators on apical vs. basolateral surfaces. Apical Pseudomonas aeruginosa strain PAK (but not flagellin mutant PAK·fliC), flagellin, and flagellin + PAK·fliC activated NF-κB and IL-8 expression and secretion. In contrast, HTE cells were insensitive to LPS compared to flagellin. Flagellin activated NF-κB in columnar but not basal cells. IL-1β + TNF-α elicited responses similar to those of flagellin. Basolateral flagellin or IL-1β + TNF-α caused 1.5- to 4-fold larger responses, consistent with the fact that NF-κB activation occurred in both columnar and basal cells. MyD88 (toll receptor-associated adapter), IL-1 receptor (IL1R)1, and TNF-α receptor (TNFR)1 were expressed in columnar and basal cells. ZO-1 was localized to tight junctions of columnar cells but not to basal cells. We infer the following. 1) Flagellin is necessary and sufficient to trigger inflammatory responses in columnar cells during accumulation of P. aeruginosa in the airway surface liquid (ASL); columnar cells express toll-like receptor 5 and MyD88, often associated with flagellin-activated cell signaling. 2) IL-1β + TNF-α in the ASL also activate columnar cells, and these cells also express IL1R1 and TNFR1. 3) Apical flagellin, IL-1β, and TNF-α do not activate basal cells because tight junctions between columnar cells prevent access from the apical surface to the basal cells. 4) Exposure of basolateral surfaces to inflammatory activators elicits larger responses because both columnar and basal cells are activated, likely because both cell types express receptors for flagellin, IL-1β, and TNF-α.

Flagellar activation of epithelial signaling

Mucosal epithelial cells are an important component of the innate immune system forming a physical and immunologic barrier to inhaled bacteria. As polarized cells with tight junctions, the immunologic signaling functions of airway epithelial cells differ from those of professional immune cells. While many bacterial gene products activate airway mucosal cells, flagella are especially immunostimulatory. The motility function provided by flagella is essential for the initial stages of respiratory infection associated with opportunists such as Pseudomonas aeruginosa. Apically presented toll-like receptor 5 responds specifically to bacterial flagellin transducing a number of epithelial proinflammatory signaling cascades, including the induction of Ca2+ fluxes; activation of NF-kappaB, IL-8, and matrilysin; and mucin expression. The complexities of flagella and flagellin structures, how these bacterial components initiate host signaling and their potential as a vaccine target are reviewed.

Bordetella bronchiseptica flagellin is a proinflammatory determinant for airway epithelial cells

Motility is an important virulence phenotype for many bacteria, and flagellin, the monomeric component of flagella, is a potent proinflammatory factor. Of the three Bordetella species, Bordetella pertussis and Bordetella parapertussis are nonmotile human pathogens, while Bordetella bronchiseptica expresses flagellin and causes disease in animals and immunocompromised human hosts. The BvgAS two-component signal transduction system regulates phenotypic-phase transition (Bvg+, Bvg-, and Bvg(i)) in bordetellae. The Bvg- phase of B. bronchiseptica is characterized by the expression of flagellin and the repression of adhesins and toxins necessary for the colonization of the respiratory tract. B. bronchiseptica naturally infects a variety of animal hosts and constitutes an excellent model to study Bordetella pathogenesis. Using in vitro coculture models of bacteria and human lung epithelial cells, we studied the effects of B. bronchiseptica flagellin on host defense responses. Our results show that B. bronchiseptica flagellin is a potent proinflammatory factor that induces chemokine, cytokine, and host defense gene expression. Furthermore, we investigated receptor specificity in the response to B. bronchiseptica flagellin. Our results show that B. bronchiseptica flagellin is able to signal effectively through both human and mouse Toll-like receptor 5.

Salmonella flagellin, a microbial target of the innate and adaptive immune system

Bacterial flagellins are important components of the motility apparatus used by many microbial pathogens. These proteins are also targets of the innate and adaptive immune response of the host during infection and autoimmune disease. Flagellin interacts with TLR-5 and leads to the generation of a pro-inflammatory response and activation of host dendritic cells in vivo. Furthermore, flagellin is recognized by antibody and CD4 T cells responses during Salmonella infection. Here, we review recent developments in the understanding of flagellin interactions with the host immune system.

Insulin-like growth factor binding protein-5 is a target of matrix metalloproteinase-7: implications for epithelial-mesenchymal signaling

Matrix metalloproteinase-7 (MMP-7) is localized to epithelial cells and is up-regulated in many cancers and in inflammation. We now report that MMP-7 targets a key mesenchymal cell type, the myofibroblast. Recombinant MMP-7 stimulated the proliferation and migration of human colonic myofibroblasts. These responses were partly attributable to activation of other MMPs, notably MMP-3 and MMP-8, and to stimulation of the mitogen-activated protein kinase and phosphatidylinositol 3-kinase signaling pathways. Using a proteomic approach, we identified insulin-like growth factor binding protein-5 (IGFBP-5) as a previously unsuspected target of MMP-7 produced by colonic myofibroblasts. We present evidence that the MMP-7 cleavage of IGFBP-5 liberates IGF-II that functions as an autocrine myofibroblast growth factor. Thus, MMP-7 may act as a signal from epithelial cells for local recruitment of myofibroblasts and stimulation of their proliferation. Similar effects of MMP-7 produced in epithelial tumors might account for the expansion of stroma through activation of myofibroblasts.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

The paradox of matrix metalloproteinases in infectious disease

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that perform multiple roles in the normal immune response to infection. MMPs facilitate leucocyte recruitment, cytokine and chemokine processing, defensin activation and matrix remodelling. However, excess MMP activity following infection may lead to immunopathology that causes host morbidity or mortality and favours pathogen dissemination or persistence. Here, we review the normal functions of MMPs in immunity and then discuss viral and bacterial infections where excess MMP activity has been implicated in pathology, specifically examining HIV, HTLV-1, hepatitis B, endotoxin shock, Helicobacter pylori and Mycobacterium tuberculosis. Tissue destruction may be exacerbated further by bacterial-derived enzymes which activate the host pro-MMPs. Finally, the potential for therapeutic targeting of excess MMP activity in infection is considered.

Modulation of lung epithelial functions by Pseudomonas aeruginosa

Microorganisms gain access to the airways and respiratory epithelial surface during normal breathing. Most inhaled microbes are trapped on the mucous layer coating the nasal epithelium and upper respiratory tract, and are cleared by ciliary motion. Microorganisms reaching the alveolar spaces are deposited on the pulmonary epithelium. This contact initiates complex offensive and defensive strategies by both parties. Here, we briefly outline how the pulmonary pathogen Pseudomonas aeruginosa uses multi-pronged strategies that include cell surface appendages, and secreted and injected virulence determinants to switch from an unobtrusive soil bacterium to a pathogen for lung epithelium colonization. Understanding the complex interactions between the lung epithelium and P. aeruginosa might enable more effective therapeutic strategies against infection in cystic fibrosis and immuno-compromised individuals.

Expression of matrix metalloprotease-2, -7 and -9 on human colon, liver and bile duct cell lines by enteric and gastricHelicobacterspecies

Gastric and enteric Helicobacter species have been associated with malignant and inflammatory diseases of the stomach, liver, gall bladder and intestine. Matrix metalloproteinases (MMPs) participate in degradation of extracellular matrix, which allows bacteria to come in contact with and interact with the cells. Enhanced level of MMPs facilitates metastasis and cell invasion of tumor cells by removal of physical barriers, as well as modulation of biologic activities of the proteins residing in the extracellular matrix. The aim of this study was to evaluate the effect of gastric and enteric Helicobacter on induction of MMPs in hepatocytes and epithelial cells of gall bladder and colon. Human hepatocytes HepG2, gall bladder epithelial cells TFK-1, and colon epithelial cells HT29 were infected with strains of H. pylori cagA+, cagE+, H. pylori cagA-, cagE-, H. pullorum, H. cholecystus, H. bilis and H. hepaticus. Protein levels of MMPs were analyzed by enzyme-linked immunosorbent assay and immunohistochemistry. Reverse transcription-quantitative polymerase chain reaction was used to study mRNA levels. Increased expression of MMP-2 and MMP-9 was observed on HepG2, TFK-1 and HT29 infected with H. pylori cagA+, cagE+ and H. cholecystus strains. H. pylori cagA+, cagE+, H. cholecystus, H. pullorum, H. bilis and H. hepaticus strains increased expression of MMP-7 on HT29, compared to uninfected control cells. The effect of MMP upregulation on HepG2, TFK-1 and HT29 was bacterial dose dependent. H. pylori cagA-, cagE- strain did not increase expression of MMPs. Inducible MMPs on colon and bile duct epithelial cells as well as hepatocytes may play an important role in facilitating invasion and progression of cancer by Helicobacter species colonizing the hepatobiliary and gastrointestinal tract.

Therapeutic inhibition of matrix metalloproteinases for the treatment of chronic obstructive pulmonary disease (COPD)

BACKGROUND

The incidence of chronic obstructive pulmonary disease (COPD) is increasing worldwide and is ranked as the fourth most common cause of death in the United States. COPD is caused by long-term exposure to cigarette smoke, toxic gases, and particulate matter, leading to airway flow limitation and pulmonary failure. The disease is characterized by an excess of extracellular matrix deposition, increased thickness of airway walls, and destruction of alveolar septae, resulting in reduced functional lung parenchyma and reduced elastic tethering forces to maintain airway patency. Matrix metalloproteinases (MMPs) have been suggested as the major proteolytic enzymes involved in the pathogeneses of COPD because these proteins are a unique family of metalloenzymes that, once activated, can destroy connective tissue. Although several MMP inhibitors have been developed, in vivo specificity and selectivity have slowed the progress.

SCOPE

This review discusses the structural features of MMPs, their pulmonary cellular sources during the course of the disease, past anti-MMP therapies, and future approaches to inhibiting these proteins for treating COPD patients. Literature searches of PubMed, BioMed, and Medline formed the basis of this analysis and our current understanding of pulmonary changes associated with COPD and the capacity of MMPs to induce a variety of these changes of current biomedical and clinical interest.

Pathogen-host interactions in Pseudomonas aeruginosa pneumonia

Pseudomonas aeruginosa is an important pathogen causing a wide range of acute and chronic infections. P. aeruginosa rarely causes infection in the normal host, but is an efficient opportunistic pathogen causing serious infections in patients who are mechanically ventilated, individuals who are immunocompromised, and patients with malignancies or HIV infection. Among these risk groups, the most vulnerable hosts are neutropenic and patients who are mechanically ventilated. In addition, P. aeruginosa is the most prevalent chronic infection contributing to the pathogenesis of cystic fibrosis. Because of the ubiquitous nature of P. aeruginosa and its ability to develop resistance to antibiotics, it continues to be problematic from a treatment perspective. The pathogenicity of P. aeruginosa is largely caused by multiple bacterial virulence factors and genetic flexibility enabling it to survive in varied environments. Lung injury associated with P. aeruginosa infection results from both the direct destructive effects of the organism on the lung parenchyma and exuberant host immune responses. This article focuses on the major bacterial virulence factors and important aspects of the host immunity that are involved in the pathogenesis of serious P. aeruginosa infection. In addition to antibiotic therapy, strategies directed toward enhancing host defense and/or limiting excessive inflammation could be important to improve outcome in P. aeruginosa lung infections.

Metalloproteinase-7 contributes to joint destruction in Staphylococcus aureus induced arthritis

Septic arthritis induced by Staphylococcus aureus causes a rapid destruction of joint cartilage and periarticular bone. The mechanisms behind this phenomenon are not fully understood. Earlier studies have shown that cytokines and metalloproteinases are of importance in bone metabolism. Matrix metalloproteinase-7 (MMP-7) has pleiotropic function including facilitating migration of both macrophages and neutrophils. The aim of this study has been to investigate the significance of MMP-7 expression in septic arthritis. MMP-7 deficient mice and congeneic controls were intravenously inoculated with an arthritogenic dose of S. aureus LS-1. This study shows that MMP-7 deficient mice exposed to S. aureus developed significantly less severe arthritis both clinically and histologically. Despite this finding, bacterial growth in the deficient animals was significantly increased. In vitro responses to staphylococcal antigens and superantigens did not differ between MMP-7(+/+) and MMP-7(-/-) mice with respect to cytokine production and if anything increased the production of certain chemokines. In addition MMP-7(-/-) mice exhibited decreased numbers of peripheral blood mononuclear cells before and one day after bacterial inoculation, but increased numbers of peripheral granulocytes on day 1. In conclusion, MMP-7 contributes to the development of a destructive course of septic arthritis despite decreased bacterial load. In addition, expression of MMP-7 is of importance for the distribution of peripheral leukocytes.

Gangliosides inhibit flagellin signaling in the absence of an effect on flagellin binding to toll-like receptor 5

A recent study (Ogushi, K., Wada, A., Niidome, T., Okuda, T., Llanes, R., Nakayama, M., Nishi, Y., Kurazono, H., Smith, K. D., Aderem, A., Moss, J., and Hirayama, T. (2004) J. Biol. Chem. 279, 12213-12219) concluded that gangliosides serve as co-receptors for flagellin signaling via toll-like receptor 5 (TLR5). In view of several findings in this study that were inconsistent with a role for gangliosides as co-receptors, we re-examined this important issue. Using TLR5-negative RAW 264.7 cells and a TLR5-enhanced yellow fluorescent protein chimera, we established an assay for specific binding of flagellin to cells. Inhibition of clatherin-mediated internalization of flagellin.TLR5-enhanced yellow fluorescent protein complexes did not impair flagellin activation of IRAK-1. Thus flagellin signal occurs at the cell surface and not intracellularly. Exogenous addition of mixed gangliosides (GM1, GD1a, and GT1b) as well as GD1a itself inhibited flagellin-induced interleukin-1 receptor-associated kinase activation as well as tumor necrosis factor alpha production in HeNC2, THP-1, and RAW 264.7 cells. Gangliosides inhibited flagellin signaling in the absence of an effect on flagellin binding to TLR5. Depletion of gangliosides in RAW 264.7 cells did not alter the concentration dependence or magnitude of flagellin signaling as measured by interleukin-1 receptor-associated kinase activation or tumor necrosis factor alpha production. Our findings are consistent with the conclusions that gangliosides are not essential co-receptors for flagellin and that the inhibitory effect of gangliosides is mediated by at least one mechanism that is distinct from any effect on the binding of flagellin to TLR5.

Matrilysin (MMP-7) expression in renal tubular damage: association with Wnt4

BACKGROUND

Matrilysin, a secreted matrix metalloproteinase and target gene of Wnt signaling, functions in epithelial repair and host defense, but no role in renal injury has been described.

METHODS

Matrilysin expression was assessed in human kidney specimens by immunohistochemistry, and in experimental renal injury in mice by immunohistochemistry, Northern blotting, and RNase protection assays (RPA). A relationship to Wnt4, which is also induced in renal injury, was determined by RPA and in situ hybridization.

RESULTS

Matrilysin was not detected in the normal human renal tubular epithelium by immunohistochemistry. However, prominent staining was detected in sections from autosomal-dominant polycystic kidney disease in the cyst lining epithelium, atrophic tubules, and cyst micropolyps, and from hydronephrosis in dilated and atrophic tubules. Matrilysin expression was also induced by acute folic acid nephropathy and unilateral ureteral obstruction (UUO) in the mouse, and expression increased as acute injury progressed to tubulointerstitial fibrosis. Matrilysin staining was primarily localized to epithelium of distal tubule/collecting duct origin in both human and murine renal disease. Wnt signaling can induce matrilysin expression, and we found that the pattern of matrilysin expression during progression of renal fibrosis in the mouse after UUO or folic acid nephropathy, and in the jck model of murine polycystic kidney disease, closely paralleled that of Wnt4.

CONCLUSION

These observations suggest that matrilysin may have a role in renal tubular injury and progression of tubulointerstitial fibrosis, and that Wnt4 may regulate matrilysin expression in the kidney.

How the Gut Links Innate and Adaptive Immunity

Mucosal surfaces represent the main sites in which environmental microorganisms and antigens interact with the host. Sentinel cells, including epithelial cells, lumenal macrophages, and intraepithelial dendritic cells, continuously sense the environment and coordinate defenses for the protection of mucosal tissues. The mucosal epithelial cells are crucial actors in coordinating defenses. They sense the outside world and respond to environmental signals by releasing chemokines and cytokines that recruit inflammatory and immune cells to control potential infectious agents and to attract cells able to trigger immune responses. Among immune cells, dendritic cells (DC) play a key role in controlling adaptive immune responses, due to their capacity to internalize foreign materials and to present antigens to naive T and B lymphocytes, locally or in draining organized lymphoid tissues. Immune cells recruited in epithelial tissues can, in turn, act upon the epithelial cells and change their phenotype in a process referred to as epithelial metaplasia.

Pseudomonas aeruginosaFlagellin and Alginate Elicit Very Distinct Gene Expression Patterns in Airway Epithelial Cells: Implications for Cystic Fibrosis Disease

Infection with the opportunistic pathogen Pseudomonas aeruginosa remains a major health concern. Two P. aeruginosa phenotypes relevant in human disease include motility and mucoidy. Motility is characterized by the presence of flagella and is essential in the establishment of acute infections, while mucoidy, defined by the production of the exopolysaccharide alginate, is critical in the development of chronic infections, such as the infections seen in cystic fibrosis patients. Indeed, chronic infection of the lung by mucoid P. aeruginosa is a major cause of morbidity and mortality in cystic fibrosis patients. We have used Calu-3 human airway epithelial cells to investigate global responses to infection with motile and mucoid P. aeruginosa. The response of airway epithelial cells to exposure to P. aeruginosa motile strains is characterized by a specific increase in gene expression in pathways controlling inflammation and host defense. By contrast, the response of airway epithelia to the stimuli presented by mucoid P. aeruginosa is not proinflammatory and, hence, may not be conducive to the effective elimination of the pathogen. The pattern of gene expression directed by flagellin, but not alginate, includes innate host defense genes, proinflammatory cytokines, and chemokines. By contrast, infection with alginate-producing P. aeruginosa results in an overall attenuation of host responses and an antiapoptotic effect.

Microbial DNA induces a host defense reaction of human respiratory epithelial cells

Epithelial cells represent the initial site of bacterial colonization in the respiratory tract. TLR9 has been identified in B cells and CD 123(+) dendritic cells and found to be involved in the recognition of microbial DNA. It was the aim of the study to investigate the role of TLR9 in the host defense reactions of the respiratory epithelium. Respiratory epithelial cell lines (IHAEo(-), Calu-3) or fully differentiated primary human cells as air-liquid interface cultures were stimulated with bacterial DNA or synthetic oligonucleotides containing CpG motifs (CpG oligodeoxynucleotides). Expression of TLR9, cytokines, and human beta-defensin 2 was determined by quantitative RT-PCR or by ELISA. We found that TLR9 is expressed by respiratory epithelial cell lines and fully differentiated primary epithelial cells at low levels. Stimulation of the above-mentioned cells with bacterial DNA or CpG oligodeoxynucleotide resulted in an inflammatory reaction characterized by a dose-dependent up-regulation of cytokines (IL-6, IL-8) and human beta-defensin 2. Up-regulation of NF-kappaB in epithelial cells in response to the CpG motif containing DNA was inhibited by overexpression of a dominant negative form of MyD88. These results provide clear evidence that the human respiratory epithelium is capable of detecting microbial DNA by TLR9. The respiratory epithelium has an important function in triggering innate immune responses and therefore represents an interesting target for anti-inflammatory therapy.