Pseudomonas aeruginosa induction of apoptosis in respiratory epithelial cells: analysis of the effects of cystic fibrosis transmembrane conductance regulator dysfunction and bacterial virulence factors

Acquisition, co-option, and duplication of the rtx toxin system and the emergence of virulence in Kingella

The bacterial genus Kingella includes two pathogenic species, namely Kingella kingae and Kingella negevensis, as well as strictly commensal species. Both K. kingae and K. negevensis secrete a toxin called RtxA that is absent in the commensal species. Here we present a phylogenomic study of the genus Kingella, including new genomic sequences for 88 clinical isolates, genotyping of another 131 global isolates, and analysis of 52 available genomes. The phylogenetic evidence supports that the toxin-encoding operon rtxCA was acquired by a common ancestor of the pathogenic Kingella species, and that a preexisting type-I secretion system was co-opted for toxin export. Subsequent genomic reorganization distributed the toxin machinery across two loci, with 30-35% of K. kingae strains containing two copies of the rtxA toxin gene. The rtxA duplication is largely clonal and is associated with invasive disease. Assays with isogenic strains show that a single copy of rtxA is associated with reduced cytotoxicity in vitro. Thus, our study identifies key steps in the evolutionary transition from commensal to pathogen, including horizontal gene transfer, co-option of an existing secretion system, and gene duplication.

Imaging host-pathogen interactions using epithelial and bacterial cell infection models

The age-old saying, seeing is believing, could not be truer when we think about the value of imaging interactions between epithelial cells and bacterial pathogens. Imaging and culturing techniques have vastly improved over the years, and the breadth and depth of these methods is ever increasing. These technical advances have benefited researchers greatly; however, due to the large number of potential model systems and microscopy techniques to choose from, it can be overwhelming to select the most appropriate tools for your research question. This Review discusses a variety of available epithelial culturing methods and quality control experiments that can be performed, and outlines various options commonly used to fluorescently label bacterial and mammalian cell components. Both light- and electron-microscopy techniques are reviewed, with descriptions of both technical aspects and common applications. Several examples of imaging bacterial pathogens and their interactions with epithelial cells are discussed to provide researchers with an idea of the types of biological questions that can be successfully answered by using microscopy.

CHAC1 Is Differentially Expressed in Normal and Cystic Fibrosis Bronchial Epithelial Cells and Regulates the Inflammatory Response Induced by Pseudomonas aeruginosa

In cystic fibrosis (CF), Pseudomonas aeruginosa (Pa) colonizes the lungs, leading to chronic inflammation of the bronchial epithelium. ChaC glutathione-specific γ-glutamylcyclotransferase 1 (CHAC1) mRNA is differentially expressed in primary human airway epithelial cells from bronchi (hAECBs) from patients with CF and healthy patients at baseline and upon infection with Pa. CHAC1 degrades glutathione and is associated with ER stress and apoptosis pathways. In this study, we examined the roles of CHAC1 in the inflammatory response and apoptosis in lung epithelial cells. First, we confirmed by reverse transcription quantitative polymerase chain reaction that CHAC1 mRNA was overexpressed in hAECBs from patients without CF compared with the expression in hAECBs from patients with CF upon Pa (PAK strain) infection. Moreover, the Pa virulence factors LPS and flagellin were shown to induce CHAC1 expression in cells from patients without CF. Using NCI-H292 lung epithelial cells, we found that LPS-induced CHAC1 mRNA expression was PERK-independent and involved ATF4. Additionally, using CHAC1 small interfering RNA, we showed that reduced CHAC1 expression in the context of LPS and flagellin stimulation was associated with modulation of inflammatory markers and alteration of NF-κB signaling. Finally, we showed that Pa was not able to induce apoptosis in NCI-H292 cells. Our results suggest that CHAC1 is involved in the regulation of inflammation in bronchial cells during Pa infection and may explain the excessive inflammation present in the respiratory tracts of patients with CF.

Human Cellular Models for the Investigation of Lung Inflammation and Mucus Production in Cystic Fibrosis

Chronic inflammation, oxidative stress, mucus plugging, airway remodeling, and respiratory infections are the hallmarks of the cystic fibrosis (CF) lung disease. The airway epithelium is central in the innate immune responses to pathogens colonizing the airways, since it is involved in mucociliary clearance, senses the presence of pathogens, elicits an inflammatory response, orchestrates adaptive immunity, and activates mesenchymal cells. In this review, we focus on cellular models of the human CF airway epithelium that have been used for studying mucus production, inflammatory response, and airway remodeling, with particular reference to two- and three-dimensional cultures that better recapitulate the native airway epithelium. Cocultures of airway epithelial cells, macrophages, dendritic cells, and fibroblasts are instrumental in disease modeling, drug discovery, and identification of novel therapeutic targets. Nevertheless, they have to be implemented in the CF field yet. Finally, novel systems hijacking on tissue engineering, including three-dimensional cocultures, decellularized lungs, microfluidic devices, and lung organoids formed in bioreactors, will lead the generation of relevant human preclinical respiratory models a step forward.

Physiological study of pulmonary involvement in adults with cystic fibrosis through simulated modeling of different clinical scenarios

Cystic fibrosis is an inherited disorder of the cystic fibrosis transmembrane conductance regulator gene (CFTR) that affects the respiratory system. Current treatment is palliative, but there is a gene therapy under investigation which involves inserting a functional CFTR gene into affected cells. Given the clinical variety of the disease, it is necessary to characterize key indicators in its evolution (e.g., the number of functional alveolar sacs and its relationship with a healthy lung function), to anticipate its advancement. A dynamic model was used to evaluate the evolution of cystic fibrosis over time. We considered the application of conventional medical treatments and evaluated the benefits of the application of an experimental gene therapy that would reverse lung damage. Without treatment the life expectancy of the patient is low, but it is increased with the application of conventional treatments, being the progressive loss of the lung function inevitable. Simulating the application of a gene therapy, the life expectancy of patients would not be limited, given the recovery of all altered cellular processes. With this model we can make predictions that demonstrate the need for a curative treatment, in addition to presenting the evolution of pathology in a specific clinical setting. Graphical abstract Graphic representation of the analysis performed in the present work on simulation of different clinical situations regarding patients with cystic fibrosis of pulmonary involvement.

Newborn Cystic Fibrosis Pigs Have a Blunted Early Response to an Inflammatory Stimulus

RATIONALE

Studies suggest that inappropriate responses to proinflammatory stimuli might contribute to inflammation in cystic fibrosis (CF) lungs. However, technical challenges have made it difficult to distinguish whether altered responses in CF airways are an intrinsic defect or a secondary effect of chronic disease in their tissue of origin. The CF pig model provides an opportunity to study the inflammatory responses of CF airways at birth, before the onset of infection and inflammation.

OBJECTIVES

To test the hypothesis that acute inflammatory responses are perturbed in porcine CF airways.

METHODS

We investigated the inflammatory responses of newborn CF and non-CF pig airways following a 4-hour exposure to heat-killed Staphylococcus aureus, in vivo and in vitro.

MEASUREMENTS AND MAIN RESULTS

Following an in vivo S. aureus challenge, markers of inflammation were similar between CF and littermate control animals through evaluation of bronchoalveolar lavage and tissues. However, transcriptome analysis revealed genotype-dependent differences as CF pigs showed a diminished host defense response compared with their non-CF counterparts. Furthermore, CF pig airways exhibited an increase in apoptotic pathways and a suppression of ciliary and flagellar biosynthetic pathways. Similar differences were observed in cultured airway epithelia from CF and non-CF pigs exposed to the stimulus.

CONCLUSIONS

Transcriptome profiling suggests that acute inflammatory responses are dysregulated in the airways of newborn CF pigs.

Abnormal unsaturated fatty acid metabolism in cystic fibrosis: biochemical mechanisms and clinical implications

Cystic fibrosis is an inherited multi-organ disorder caused by mutations in the CFTR gene. Patients with this disease exhibit characteristic abnormalities in the levels of unsaturated fatty acids in blood and tissue. Recent studies have uncovered an underlying biochemical mechanism for some of these changes, namely increased expression and activity of fatty acid desaturases. Among other effects, this drives metabolism of linoeate to arachidonate. Increased desaturase expression appears to be linked to cystic fibrosis mutations via stimulation of the AMP-activated protein kinase in the absence of functional CFTR protein. There is evidence that these abnormalities may contribute to disease pathophysiology by increasing production of eicosanoids, such as prostaglandins and leukotrienes, of which arachidonate is a key substrate. Understanding these underlying mechanisms provides key insights that could potentially impact the diagnosis, clinical monitoring, nutrition, and therapy of patients suffering from this deadly disease.

Abnormal n-6 fatty acid metabolism in cystic fibrosis is caused by activation of AMP-activated protein kinase

Cystic fibrosis (CF) patients and model systems exhibit consistent abnormalities in PUFA metabolism, including increased metabolism of linoleate to arachidonate. Recent studies have connected these abnormalities to increased expression and activity of the Δ6- and Δ5-desaturase enzymes. However, the mechanism connecting these changes to the CF transmembrane conductance regulator (CFTR) mutations responsible for CF is unknown. This study tests the hypothesis that increased activity of AMP-activated protein kinase (AMPK), previously described in CF bronchial epithelial cells, causes these changes in fatty acid metabolism by driving desaturase expression. Using CF bronchial epithelial cell culture models, we confirm elevated activity of AMPK in CF cells and show that it is due to increased phosphorylation of AMPK by Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ). We also show that inhibition of AMPK or CaMKKβ reduces desaturase expression and reverses the metabolic alterations seen in CF cells. These results signify a novel AMPK-dependent mechanism linking the genetic defect in CF to alterations in PUFA metabolism.

Epithelial uptake of flagella initiates proinflammatory signaling

The airway epithelium serves multiple roles in the defense of the lung. Not only does it act as a physical barrier, it acts as a distal extension of the innate immune system. We investigated the role of the airway epithelium in the interaction with flagella, an important virulence factor of the pathogen Pseudomonas aeruginosa, a cause of ventilator associated pneumonia and significant morbidity and mortality in patients with cystic fibrosis. Flagella were required for transmigration across polarized airway epithelial cells and this was a direct consequence of motility, and not a signaling effect. Purified flagella did not alter the barrier properties of the epithelium but were observed to be rapidly endocytosed inside epithelial cells. Neither flagella nor intact P. aeruginosa stimulated epithelial inflammasome signaling. Flagella-dependent signaling required dynamin-based uptake as well as TLR5 and primarily led to the induction of proinflammatory (Tnf, Il6) as well as neutrophil (Cxcl1, Cxcl2, Ccl3) and macrophage (Ccl20) chemokines. Although flagella are important in invasion across the epithelial barrier their shedding in the airway lumen results in epithelial uptake and signaling that has a major role in the initial recruitment of immune cells in the lung.

Pharmacodynamic evaluation of the intracellular activity of antibiotics towards Pseudomonas aeruginosa PAO1 in a model of THP-1 human monocytes

Pseudomonas aeruginosa invades epithelial and phagocytic cells, which may play an important role in the persistence of infection. We have developed a 24-h model of THP-1 monocyte infection with P. aeruginosa PAO1 in which bacteria are seen multiplying in vacuoles by electron microscopy. The model has been used to quantitatively assess antibiotic activity against intracellular and extracellular bacteria by using a pharmacodynamic approach (concentration-dependent experiments over a wide range of extracellular concentrations to calculate bacteriostatic concentrations [Cs] and maximal relative efficacies [Emax]; Hill-Langmuir equation). Using 16 antipseudomonal antibiotics (three aminoglycosides, nine β-lactams, three fluoroquinolones, and colistin), dose-response curves were found to be undistinguishable for antibiotics of the same pharmacological class if data were expressed as a function of the corresponding MICs. Extracellularly, all of the antibiotics reached a bacteriostatic effect at their MIC, and their Emax exceeded the limit of detection (-4.5 log(10) CFU compared to the initial inoculum). Intracellularly, Cs values remained unchanged for β-lactams, fluoroquinolones, and colistin but were approximately 10 times higher for aminoglycosides, whereas Emax values were markedly reduced (less negative), reaching -3 log(10) CFU for fluoroquinolones and only -1 to -1.5 log(10) CFU for all other antibiotics. The decrease in intracellular aminoglycoside potency (higher Cs) can be ascribed to the acid pH to which bacteria are exposed in vacuoles. The decrease in the Emax may reflect a reversible alteration of bacterial responsiveness to antibiotics in the intracellular milieu. The model may prove useful for comparison of antipseudomonal antibiotics to reduce the risk of persistence or relapse of pseudomonal infections.

Interactions of linoleic and alpha-linolenic acids in the development of fatty acid alterations in cystic fibrosis

Patients with cystic fibrosis (CF) exhibit characteristic polyunsaturated fatty acid abnormalities, including low linoleic acid and high arachidonic acid levels that are thought to contribute to the pathophysiology of this disease. Recent studies indicate that changes in fatty acid metabolism are responsible for these abnormalities. This study examines the role of fatty acid substrate concentrations in the development of these alterations in a cultured cell model of CF. By incubating cells with varying concentrations of exogenous fatty acids, it shows that increasing the concentration of substrates from the parallel n-3 and n-6 polyunsaturated fatty acid pathways (linoleic acid and alpha-linolenic acid, respectively) not only increases formation of the products in that pathway, but also reduces metabolism in the parallel pathway. In particular, we demonstrate that high levels of linoleic acid and low levels of alpha-linolenic acid are required to observe the typical fatty acid alterations of cystic fibrosis. These results shed light on the mechanisms of fatty acid metabolic abnormalities in cystic fibrosis. They also have implications for the nutritional therapy of CF, highlighting the importance of specific fatty acid content, and in understanding the anti-inflammatory effects of n-3 fatty acids.

Non-apoptotic toxicity of Pseudomonas aeruginosa toward murine cells

Although P. aeruginosa is especially dangerous in cystic fibrosis (CF), there is no consensus as to how it kills representative cell types that are of key importance in the lung. This study concerns the acute toxicity of the sequenced strain, PAO1, toward a murine macrophage cell line (RAW 264.7). Toxicity requires brief contact with the target cell, but is then delayed for more than 12 h. None of the classical toxic effectors of this organism is required and cell death occurs without phagocytosis or acute perturbation of the actin cytoskeleton. Apoptosis is not required for toxicity toward either RAW 264.7 cells or for alveolar macrophages. Transcriptional profiling shows that encounter between PAO1 and RAW 264.7 cells elicits an early inflammatory response, followed by growth arrest. As an independent strategy to understand the mechanism of toxicity, we selected variant RAW 264.7 cells that resist PAO1. Upon exposure to P. aeruginosa, they are hyper-responsive with regard to classical inflammatory cytokine production and show transient downregulation of transcripts that are required for cell growth. They do not show obvious morphologic changes. Although they do not increase interferon transcripts, when exposed to PAO1 they dramatically upregulate a subset of the responses that are characteristic of exposure to g-interferon, including several guanylate-binding proteins. The present observations provide a novel foundation for learning how to equip cells with resistance to a complex challenge.

MudPIT analysis of released proteins in Pseudomonas aeruginosa laboratory and clinical strains in relation to pro-inflammatory effects

Pseudomonas aeruginosa (Pa) is the most common virulent pathogen contributing to the pathogenesis of cystic fibrosis (CF). During bacterial lung colonization, the products of its metabolism are released in the extracellular space contributing to the pathogenic events associated with its presence. To gain insights on the mechanisms involved in the Pa pathogenesis we focused our attention on proteins released by Pa using a MudPIT approach combined with cell biology assays. Conditioned medium (CM) collected under aerobic and microaerobic conditions from Pa clinical strains (in early and late colonization), unlike the laboratory strain, induced expression of IL-8 mRNA in CF airway epithelial cells. We have identified proteins released by clinically relevant Pa strains, focusing on the pro-inflammatory effects as metalloproteases (MMPs). In fact, their expression pattern was associated with the highest pro-inflammatory activity measured in the early clinically isolated strain. The relation was further supported by the result of the analysis of a larger and independent set of Pa isolates derived from sporadically and chronically infected CF patients: 76% of sporadic samples expressed protease activity (n = 44), while only 27% scored positive in the chronically infected individuals (n = 38, p < 0.0001, Fisher's exact test). Finally, looking for a possible mechanism of action of bacterial MMPs, we found that CM from early clinical isolates can cleave CXCR1 on the surface of human neutrophils, suggesting a potential role for the bacterially released MMPs in the protection of the pathogen from the host's response.

A novel host-responsive sensor mediates virulence and type III secretion during Pseudomonas aeruginosa-host cell interactions

Sensitive sensory mechanisms are instrumental in affording Pseudomonas aeruginosa the capacity to establish diverse yet severe human infections, which can manifest themselves in long-term untreatable disease. The ability of P. aeruginosa to tightly regulate gene expression and virulence factor production, in response to activation of these sensory components, enables the pathogen to sustain infection despite the host immune response and aggressive antibiotic treatment. Although a number of factors are recognized as playing a role in early infection, very little is known regarding the sensors involved in this process. In this study, we identified P. aeruginosa PA3191 as a novel host-responsive sensor that plays a key role during P. aeruginosa-host interactions and is required for optimum colonization and dissemination in a mouse model of infection. We demonstrated that PA3191 contributed to modulation of the type III secretion system (T3SS) in response to host cells and T3SS-inducing conditions in vitro. PA3191 (designated GtrS) acted in concert with the response regulator GltR to regulate the OprB transport system and subsequently carbon metabolism. Through this signal transduction pathway, T3SS activation was mediated via the RsmAYZ regulatory cascade and involved the global anaerobic response regulator Anr.

Corynebacterium diphtheriae 67-72p hemagglutinin, characterized as the protein DIP0733, contributes to invasion and induction of apoptosis in HEp-2 cells

Although Corynebacterium diphtheriae has been classically described as an exclusively extracellular pathogen, there is growing evidence that it may be internalized by epithelial cells. The aim of the present report was to investigate the nature and involvement of the surface-exposed non-fimbrial 67-72 kDa proteins (67-72p), previously characterized as adhesin/hemagglutinin, in C. diphtheriae internalization by HEp-2 cells. Transmission electron microscopy and bacterial internalization inhibition assays indicated the role of 67-72p as invasin for strains of varied sources. Cytoskeletal changes with accumulation of polymerized actin in HEp-2 cells beneath adherent 67-72p-adsorbed microspheres were observed by the Fluorescent actin staining test. Trypan blue staining method and Methylthiazole tetrazolium reduction assay showed a significant decrease in viability of HEp-2 cells treated with 67-72p. Morphological changes in HEp-2 cells observed after treatment with 67-72p included vacuolization, nuclear fragmentation and the formation of apoptotic bodies. Flow cytometry revealed an apoptotic volume decrease in HEp-2 cells treated with 67-72p. Moreover, a double-staining assay using Propidium Iodide/Annexin V gave information about the numbers of vital vs. early apoptotic cells and late apoptotic or secondary necrotic cells. The comparative analysis of MALDI-TOF MS experiments with the probes provided for 67-72p CDC-E8392 with an in silico proteome deduced from the complete genome sequence of C. diphtheriae identified with significant scores 67-72p as the protein DIP0733. In conclusion, DIP0733 (67-72p) may be directly implicated in bacterial invasion and apoptosis of epithelial cells in the early stages of diphtheria and C. diphtheriae invasive infection.

Apoptosis and the airway epithelium

The airway epithelium functions as a barrier and front line of host defense in the lung. Apoptosis or programmed cell death can be elicited in the epithelium as a response to viral infection, exposure to allergen or to environmental toxins, or to drugs. While apoptosis can be induced via activation of death receptors on the cell surface or by disruption of mitochondrial polarity, epithelial cells compared to inflammatory cells are more resistant to apoptotic stimuli. This paper focuses on the response of airway epithelium to apoptosis in the normal state, apoptosis as a potential regulator of the number and types of epithelial cells in the airway, and the contribution of epithelial cell apoptosis in important airways diseases.

DHA and EPA reverse cystic fibrosis-related FA abnormalities by suppressing FA desaturase expression and activity

Patients and models of cystic fibrosis (CF) exhibit consistent abnormalities of polyunsaturated fatty acid composition, including decreased linoleate (LA) and docosahexaenoate (DHA) and variably increased arachidonate (AA), related in part to increased expression and activity of fatty acid desaturases. These abnormalities and the consequent CF-related pathologic manifestations can be reversed in CF mouse models by dietary supplementation with DHA. However, the mechanism is unknown. This study investigates this mechanism by measuring the effect of exogenous DHA and eicosapentaenoate (EPA) supplementation on fatty acid composition and metabolism, as well as on metabolic enzyme expression, in a cell culture model of CF. We found that both DHA and EPA suppress the expression and activity of Δ5- and Δ6-desaturases, leading to decreased flux through the n-3 and n-6 PUFA metabolic pathways and decreased production of AA. The findings also uncover other metabolic abnormalities, including increased fatty acid uptake and markedly increased retroconversion of DHA to EPA, in CF cells. These results indicate that the fatty acid abnormalities of CF are related to intrinsic alterations of PUFA metabolism and that they may be reversed by supplementation with DHA and EPA.

In vivo fluorescence imaging of bacteriogenic cyanide in the lungs of live mice infected with cystic fibrosis pathogens

BACKGROUND

Pseudomonas aeruginosa (PA) and Burkholderia cepacia complex (Bcc), commonly found in the lungs of cystic fibrosis (CF) patients, often produce cyanide (CN), which inhibits cellular respiration. CN in sputa is a potential biomarker for lung infection by CF pathogens. However, its actual concentration in the infected lungs is unknown.

METHODS AND FINDINGS

This work reports observation of CN in the lungs of mice infected with cyanogenic PA or Bcc strains using a CN fluorescent chemosensor (4',5'-fluorescein dicarboxaldehyde) with a whole animal imaging system. When the CN chemosensor was injected into the lungs of mice intratracheally infected with either PA or B. cepacia strains embedded in agar beads, CN was detected in the millimolar range (1.8 to 4 mM) in the infected lungs. CN concentration in PA-infected lungs rapidly increased within 24 hours but gradually decreased over the following days, while CN concentration in B. cepacia-infected lungs slowly increased, reaching a maximum at 5 days. CN concentrations correlated with the bacterial loads in the lungs. In vivo efficacy of antimicrobial treatments was tested in live mice by monitoring bacteriogenic CN in the lungs.

CONCLUSIONS

The in vivo imaging method was also found suitable for minimally invasive testing the efficacy of antibiotic compounds as well as for aiding the understanding of bacterial cyanogenesis in CF lungs.

Increased elongase 6 and Δ9-desaturase activity are associated with n-7 and n-9 fatty acid changes in cystic fibrosis

Patients with cystic fibrosis, caused by mutations in CFTR, exhibit specific and consistent alterations in the levels of particular unsaturated fatty acids compared with healthy controls. Evidence suggests that these changes may play a role in the pathogenesis of this disease. Among these abnormalities are increases in the levels of n-7 and n-9 fatty acids, particularly palmitoleate (16:1n-7), oleate (18:1n-9), and eicosatrienoate or mead acid (20:3n-9). The underlying mechanisms of these particular changes are unknown, but similar changes in the n-3 and n-6 fatty acid families have been correlated with increased expression of fatty acid metabolic enzymes. This study demonstrated that cystic fibrosis cells in culture exhibit increased metabolism along the metabolic pathways leading to 16:1n-7, 18:1n-9, and 20:3n-9 compared with wild-type cells. Furthermore, these changes are accompanied by increased expression of the enzymes that produce these fatty acids, namely Δ5, Δ6, and Δ9 desaturases and elongases 5 and 6. Taken together, these findings suggest that fatty acid abnormalities of the n-7 and n-9 series in cystic fibrosis are as a result, at least in part, of increased expression and activity of these metabolic enzymes in CFTR-mutated cells.

Host DNA repair proteins in response to Pseudomonas aeruginosa in lung epithelial cells and in mice

Although DNA repair proteins in bacteria are critical for pathogens' genome stability and for subverting the host defense, the role of host DNA repair proteins in response to bacterial infection is poorly defined. Here, we demonstrate, for the first time, that infection with the Gram-negative bacterium Pseudomonas aeruginosa significantly altered the expression and enzymatic activity of 8-oxoguanine DNA glycosylase (OGG1) in lung epithelial cells. Downregulation of OGG1 by a small interfering RNA strategy resulted in severe DNA damage and cell death. In addition, acetylation of OGG1 is required for host responses to bacterial genotoxicity, as mutations of OGG1 acetylation sites increased Cockayne syndrome group B (CSB) protein expression. These results also indicate that CSB may be involved in DNA repair activity during infection. Furthermore, OGG1 knockout mice exhibited increased lung injury after infection with P. aeruginosa, as demonstrated by higher myeloperoxidase activity and lipid peroxidation. Together, our studies indicate that P. aeruginosa infection induces significant DNA damage in host cells and that DNA repair proteins play a critical role in the host response to P. aeruginosa infection, serving as promising targets for the treatment of this condition and perhaps more broadly Gram-negative bacterial infections.

Bacterial distribution in lung parenchyma early after pulmonary infection with Pseudomonas aeruginosa

Nosocomial infections often cause lethal pneumogenic sepsis. Information on early bacteria-host interaction in the lung is limited. In the present study, mice were sacrificed 60 min and 4 h after Pseudomonas aeruginosa (PA) infection to investigate lung morphology by using electron microscopy and light microscopy. After 1 h, bacteria were found in the alveoli partly in contact with surfactant. Alveolar macrophages were seen with up to 10 intracellular bacteria close to protrusions of alveolar epithelial type I cells and the gas/blood barrier. A rare but surprising finding was bacteria and even replicating bacteria in alveolar epithelial type II cells (AEII). No bacteria were seen in capillaries. Neither engulfment of bacteria by neutrophils nor structural damage of the pulmonary barrier was visible. After 4 h, many neutrophils were found within the capillaries, but also in the alveolar space. Thus, we hypothesize that, in early stages of infection, the uptake of PA even by single AEII can influence the course of the disease.

Proteolysis of Pseudomonas exotoxin A within hepatic endosomes by cathepsins B and D produces fragments displaying in vitro ADP-ribosylating and apoptotic effects

To assess Pseudomonas exotoxin A (ETA) compartmentalization, processing and cytotoxicity in vivo, we have studied the fate of internalized ETA with the use of the in vivo rodent liver model following toxin administration, cell-free hepatic endosomes, and pure in vitro protease assays. ETA taken up into rat liver in vivo was rapidly associated with plasma membranes (5-30 min), internalized within endosomes (15-60 min), and later translocated into the cytosolic compartment (30-90 min). Coincident with endocytosis of intact ETA, in vivo association of the catalytic ETA-A subunit and low molecular mass ETA-A fragments was observed in the endosomal apparatus. After an in vitro proteolytic assay with an endosomal lysate and pure proteases, the ETA-degrading activity was attributed to the luminal species of endosomal acidic cathepsins B and D, with the major cleavages generated in vitro occurring mainly within domain III of ETA-A. Cell-free endosomes preloaded in vivo with ETA intraluminally processed and extraluminally released intact ETA and ETA-A in vitro in a pH-dependent and ATP-dependent manner. Rat hepatic cells underwent in vivo intrinsic apoptosis at a late stage of ETA infection, as assessed by the mitochondrial release of cytochrome c, caspase-9 and caspase-3 activation, and DNA fragmentation. In an in vitro assay, intact ETA induced ADP-ribosylation of EF-2 and mitochondrial release of cytochrome c, with the former effect being efficiently increased by a cathepsin B/cathepsin D pretreatment. The data show a novel processing pathway for internalized ETA, involving cathepsins B and D, resulting in the production of ETA fragments that may participate in cytotoxicity and mitochondrial dysfunction.

Linoleic acid supplementation results in increased arachidonic acid and eicosanoid production in CF airway cells and in cftr-/- transgenic mice

Cystic fibrosis (CF) patients display a fatty acid imbalance characterized by low linoleic acid levels and variable changes in arachidonic acid. This led to the recommendation that CF patients consume a high-fat diet containing >6% linoleic acid. We hypothesized that increased conversion of linoleic acid to arachidonic acid in CF leads to increased levels of arachidonate-derived proinflammatory metabolites and that this process is exacerbated by increasing linoleic acid levels in the diet. To test this hypothesis, we determined the effect of linoleic acid supplementation on downstream proinflammatory biomarkers in two CF models: 1) in vitro cell culture model using 16HBE14o(-) sense [wild-type (WT)] and antisense (CF) human airway epithelial cells; and 2) in an in vivo model using cftr(-/-) transgenic mice. Fatty acids were analyzed by gas chromatography-mass spectrometry (GC/MS), and IL-8 and eicosanoids were measured by ELISA. Neutrophils were quantified in bronchoalveolar lavage fluid from knockout mice following linoleic acid supplementation and exposure to aerosolized Pseudomonas LPS. Linoleic acid supplementation increased arachidonic acid levels in CF but not WT cells. IL-8, PGE(2), and PGF(2α) secretion were increased in CF compared with WT cells, with a further increase following linoleic acid supplementation. cftr(-/-) Mice supplemented with 100 mg of linoleic acid had increased arachidonic acid levels in lung tissue associated with increased neutrophil infiltration into the airway compared with control mice. These findings support the hypothesis that increasing linoleic acid levels in the setting of loss of cystic fibrosis transmembrane conductance regulator (CFTR) function leads to increased arachidonic acid levels and proinflammatory mediators.

Pseudomonas aeruginosa and the host pulmonary immune response

Pseudomonas aeruginosa is a highly adaptable, opportunistic pathogen that is commonly found in the environment. It can infect a number of sites in the body and disseminate. It can cause both acute and chronic pulmonary infection and the acuity of infection and accompanying inflammatory phenotype is determined, for the most part, by the host. Although P. aeruginosa has been a successful opportunist in the context of a number of different disease states, it has been best studied in the context of cystic fibrosis (CF). The adaptability of P. aeruginosa has enabled it to adjust quickly to the CF airway, transitioning from initial colonization to chronic infection. The organism quickly expresses virulence factors that allow it to circumvent some elements of the host immune response and, even more importantly, quickly develops antimicrobial resistance. In the case of CF, chronic infection resulting in progressive lung damage, coupled with antimicrobial resistance, becomes an increasingly important issue as individuals with CF live longer. It is for these reasons that both organism- and host-targeted immunotherapies are being increasingly explored.

Proinflammatory phenotype and increased caveolin-1 in alveolar macrophages with silenced CFTR mRNA

The inflammatory milieu in the respiratory tract in cystic fibrosis (CF) has been linked to the defective expression of the cystic transmembrane regulator (CFTR) in epithelial cells. Alveolar macrophages (AM), important contibutors to inflammatory responses in the lung, also express CFTR. The present study analyzes the phenotype of human AM with silenced CFTR. Expression of CFTR mRNA and the immature form of the CFTR protein decreased 100-fold and 5.2-fold, respectively, in AM transfected with a CFTR specific siRNA (CFTR-siRNA) compared to controls. Reduction of CFTR expression in AM resulted in increased secretion of IL-8, increased phosphorylation of NF-κB, a positive regulator of IL-8 expression, and decreased expression of IκB-α, the inhibitory protein of NF-κB activation. AM with silenced CFTR expression also showed increased apoptosis. We hypothesized that caveolin-1 (Cav1), a membrane protein that is co-localized with CFTR in lipid rafts and that is related to inflammation and apoptosis in macrophages, may be affected by decreased CFTR expression. Messenger RNA and protein levels of Cav1 were increased in AM with silenced CFTR. Expression and transcriptional activity of sterol regulatory element binding protein (SREBP), a negative transcriptional regulator of Cav1, was decreased in AM with silenced CFTR, but total and free cholesterol mass did not change. These findings indicate that silencing of CFTR in human AM results in an inflammatory phenotype and apoptosis, which is associated to SREBP-mediated regulation of Cav1.

Multiple drug resistance and strength of attachment to surfaces in Pseudomonas aeruginosa isolates

AIMS

To investigate the presence of a relationship between the strength of attachment of Pseudomonas aeruginosa to stainless steel surfaces and their observed multiple drug resistance.

METHODS AND RESULTS

Multiple drug resistance of clinical and environmental isolates of Ps. aeruginosa was evaluated using disc diffusion method. The blot succession technique was used to quantify the strength of attachment of Ps. aeruginosa isolates. Different multiple drug-resistant Ps. aeruginosa isolates exhibited variable attachment strength. Although the highest multiple drug-resistant clinical isolate was shown to have the least attachment strength among clinical isolates, a weak correlation was found between attachment strength and multiple resistance among our investigated Ps. aeruginosa isolates.

CONCLUSIONS

There is a weak correlation between multiple drug resistance and strength of attachment to stainless steel surfaces.

SIGNIFICANCE AND IMPACT OF THE STUDY

Even low-resistant Ps. aeruginosa could have the potential of attaching firmly to surfaces and forming biofilm.

Ubiquitin B: an essential mediator of trichostatin A-induced tumor-selective killing in human cancer cells

Although histone deacetylase inhibitors (HDACis) are emerging as a new class of anticancer agents, the mechanism of tumor-selective killing by HDACi is not well understood. We used suppression of mortality by antisense rescue technique (SMART) to screen the key genes responsible for the tumor-selective killing by trichostatin A (TSA). Twenty-four genes were identified, the most significant of which was ubiquitin B (UbB). The expression of UbB was selectively upregulated by TSA in tumor cells, but not non-malignant cells. Further observation indicated that TSA induced a substantial dissipation of mitochondrial transmembrane potential, release of cytochrome c into the cytosol, and proteolytic cleavage of caspases-3/9 in HeLa cells, which was apparently mediated by ubiquitylation and the subsequent degradation of mitochondrial membrane proteins including BCL-2 and MCL-1. In contrast, knockdown of UbB expression inhibited the TSA-induced apoptotic cascade by abolishing TSA-induced ubiquitylation and the subsequent degradation of mitochondrial membrane proteins. Furthermore, apicidine, another HDACi, exhibited activity similar to that of TSA. Interestingly, TSA induced UbB-dependent proteasomal degradation of BCR-ABL fusion protein in K562 leukemic cells. Thus, our findings highlight the essential role of UbB and UbB-dependent proteasomal protein degradation in HDACi-induced tumor selectivity. The mechanism provides a novel starting point for dissecting the molecular mechanism underlying the tumor selectivity of HDACi.

Identification of LIV1, a putative zinc transporter gene responsible for HDACi-induced apoptosis, using a functional gene screen approach

Histone deacetylase inhibitors (HDACi) show promise as a novel class of antitumoral agents and have shown the ability to induce apoptosis of tumor cells. To gain a better understanding of the action of HDACi, we conducted a functional gene screen approach named suppression of mortality by antisense rescue technique to identify the key genes responsible for the tumor-selective killing trichostatin A. Over 20 genes associated with HDACi-induced mortality were identified. One of the confirmed positive hits is LIV1, a putative zinc transporter. LIV1 is significantly induced by treatment with HDACi in a number of tumor cells, but not in normal cells. Knockdown of LIV1 suppressed apoptosis induced by HDACi in tumor cells. Although HDACi induced a slight increase in the free intracellular zinc concentration, knockdown of LIV1 significantly enhanced the intracellular zinc level, which was associated with resistance to apoptosis. On the other hand, pretreatment of the cells with a specific zinc chelator TPEN reversed the apoptosis resistance conferred by knockdown of LIV1. However, the biological effects of TPEN were abolished by addition of physiologic concentrations of zinc. Taken together, the present study identifies LIV1 as a critical mediator responsible for HDACi-induced apoptosis. The effect of LIV1 is, at least in part, mediated by affecting intracellular zinc homeostasis, which may be related to alteration of the catalytic activity of the Caspase 3 and expression of some BCL-2 family genes. As such, these findings highlight a novel mechanism underlying the action of HDACi that could be potentially useful in the clinical setting.

The triterpenoid CDDO limits inflammation in preclinical models of cystic fibrosis lung disease

Excessive inflammation in cystic fibrosis (CF) lung disease is a contributor to progressive pulmonary decline. Effective and well-tolerated anti-inflammatory therapy may preserve lung function, thereby improving quality and length of life. In this paper, we assess the anti-inflammatory effects of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) in preclinical models of CF airway inflammation. In our experiments, mice carrying the R117H Cftr mutation have significantly reduced airway inflammatory responses to both LPS and flagellin when treated with CDDO before inflammatory challenge. Anti-inflammatory effects observed include reduced airway neutrophilia, reduced concentrations of proinflammatory cytokines and chemokines, and reduced weight loss. Our findings with the synthetic triterpenoids in multiple cell culture models of CF human airway epithelia agree with effects previously described in other disease models (e.g., neoplastic cells). These include the ability to reduce NF-kappaB activation while increasing nuclear factor erythroid-related factor 2 (Nrf2) activity. As these two signaling pathways appear to be pivotal in regulating the net inflammatory response in the CF airway, these compounds are a promising potential anti-inflammatory therapy for CF lung disease.

Staphylococcus aureus activates type I IFN signaling in mice and humans through the Xr repeated sequences of protein A

The activation of type I IFN signaling is a major component of host defense against viral infection, but it is not typically associated with immune responses to extracellular bacterial pathogens. Using mouse and human airway epithelial cells, we have demonstrated that Staphylococcus aureus activates type I IFN signaling, which contributes to its virulence as a respiratory pathogen. This response was dependent on the expression of protein A and, more specifically, the Xr domain, a short sequence-repeat region encoded by DNA that consists of repeated 24-bp sequences that are the basis of an internationally used epidemiological typing scheme. Protein A was endocytosed by airway epithelial cells and subsequently induced IFN-beta expression, JAK-STAT signaling, and IL-6 production. Mice lacking IFN-alpha/beta receptor 1 (IFNAR-deficient mice), which are incapable of responding to type I IFNs, were substantially protected against lethal S. aureus pneumonia compared with wild-type control mice. The profound immunological consequences of IFN-beta signaling, particularly in the lung, may help to explain the conservation of multiple copies of the Xr domain of protein A in S. aureus strains and the importance of protein A as a virulence factor in the pathogenesis of staphylococcal pneumonia.

Impaired interleukin-8 chemokine secretion by staphylococcus aureus-activated epithelium and T-cell chemotaxis in cystic fibrosis

Staphylococcus aureus is frequently isolated from lungs of patients with cystic fibrosis (CF). Upon lung infection with S. aureus, airway epithelial cells (AEC) produce high levels of chemokines that enhance T-cell chemotaxis. Although the number of lymphocytes is increased in the airways and bronchoalveolar lavage fluid of patients with CF, the mechanisms responsible for their accumulation and the role of S. aureus in this process are largely unknown. This study investigated early S. aureus impact on chemokine secretion by CF epithelial cells and chemotaxis of CF T cells. CF and non-CF AEC were grown in a cell culture model and apically stimulated with S. aureus. Supernatants were quantified for chemokine secretions and assayed for T-cell chemotaxis. CF AEC secreted constitutively larger amounts of IL-8, GROalpha, MIG, MIP-3beta, and MCP-1 than non-CF epithelial cells. S. aureus interaction with epithelial cells increased chemokine production by non-CF cells but had no effect on CF cells. Chemotaxis of T cells derived from patients with CF was greater than that of T cells from subjects without CF. Moreover, there were more CF T cells expressing CXCR1 as compared with non-CF T cells. Under our experimental conditions, inhibition of IL-8 or its receptor CXCR1 resulted in a considerable decrease in T-cell chemotaxis (up to 80%). These data suggest that IL-8 and its receptor CXCR1 are key players in the chemotaxis of CF T cells and could be used as targets to develop therapies for CF.

Involvement of glycosaminoglycans in vesicular stomatitis virus G glycoprotein pseudotyped lentiviral vector-mediated gene transfer into airway epithelial cells

BACKGROUND

The involvement of surface molecules in HIV-1-derived lentivirus (LV)-mediated transduction of airway epithelial cells has not been studied so far. The present study aimed to evaluate the role of glycosaminoglycans (GAGs) in gene transfer mediated by a third generation vesicular stomatitis virus G glycoprotein (VSV-G) pseudotyped LV vector in an in vitro model of polarized airway epithelial cells.

METHODS

Human bronchial (16HBE-S1) and tracheal (CFT1-C2) epithelial cells were grown either on plastic or on filters and transduced with the LV vector polypurine tract (PPT)-green fluoresecent protein (GFP). Zonula Occludens (ZO)-1, a marker of tight junction, and GAG localization were assessed by cytofluorimetry and confocal microscopy. Soluble GAGs and removal of cell surface GAGs were used to affect LV-mediated transduction.

RESULTS

Extensive optimization of experimental parameters (presence of polybrene during the infection, the incubation time in the presence of LV particles, period of time intercurring between infection and gene expression analysis) was carried out in plastic-adherent cells. Polybrene resulted to be cytotoxic and was not further used. In CFT1-C2 polarized cells, EGTA treatment determined a 20% decrease in transepithelial resistance, a diminished ZO-1 localization at the tight junction location and a 31% increase in GFP positive cells. Heparane sulfate was distributed evenly on the cell surface. Heparin and soluble chondroitin sulfate A and B inhibited LV-mediated transduction in a dose-dependent fashion. These results were confirmed upon enzymatic removal of GAGs from the cell surface.

CONCLUSIONS

Taken together, these results show that GAGs are involved in VSV-G LV transduction of airway epithelial cells.

Mechanical induction of an epithelial cell chymase associated with wound edge migration

Chymase is a chymotrypsin-like serine protease predominantly produced by mast cells. In this study, human cutaneous and gingival keratinocytes, ovary surface epithelia, and a porcine epithelial cell line were assayed by homology-based cloning, and the amplified DNA fragment was identified as a chymase. In vitro, chymase could not be induced by serum or cytokine treatment alone. Chymase was activated 3-fold within 60 min in basal media by scratch wounding cultured monolayers and further potentiated over 10-fold at 18 h by additional serum and cytokine treatment. Chymase activity was cell-associated and found to peak within 24 h of wounding and then steadily decreased as cultures healed, reaching baseline levels before confluence was reestablished. Affinity column purified enzyme effectively degraded fibronectin and was found by Western blot analysis using a human chymase antibody to be of about 30 kDa. Immunostaining revealed chymase activation at the wound edge colocalizing with reactive oxygen species generation. Specifically, chymase activation was attenuated by inhibition of nitric oxide, superoxide, and peroxynitrite. Exogenous peroxynitrite but not hydrogen peroxide also resulted in chymase activation in unwounded monolayers. Disruption of cytoskeletal stress fibers by cytochalasin D attenuated both wound-activated chymase and reactive oxygen species generation. Chymase inhibitor chymostatin reduced the loss of cell-cell contacts and the onset of porcine and human skin epithelial cell migration at the wound edge. This shows that an epithelial chymase is rapidly activated by a ligand-independent mechanism following mechanical stress via cytoskeletal and reactive oxygen species signaling and is associated with the onset of epithelial cell migration.

LXA4 stimulates ZO-1 expression and transepithelial electrical resistance in human airway epithelial (16HBE14o-) cells

Lipoxin A(4) (LXA(4)) is a biologically active eicosanoid produced in human airways that displays anti-inflammatory properties. In cystic fibrosis and severe asthma, LXA(4) production has been reported to be decreased, and, in such diseases, one of the consequences of airway inflammation is disruption of the tight junctions. In the present study, we investigated the possible role of LXA(4) on tight junction formation, using transepithelial electrical resistance (TER) measurements, Western blotting, and immunofluorescence. We observed that exposure to LXA(4) (100 nM) for 2 days significantly increased zonula occludens-1 (ZO-1), claudin-1, and occludin expression at the plasma membrane of confluent human bronchial epithelial 16HBE14o- cells. LXA(4) (100 nM) stimulated the daily increase of the 16HBE14o- cell monolayer TER, and this effect was inhibited by boc-2 (LXA(4) receptor antagonist). LXA(4) also had a rapid effect on ZO-1 immunofluorescence at the plasma membrane and increased TER within 10 min. In conclusion, our experiments provide evidence that LXA(4) plays certainly a new role for the regulation of tight junction formation and stimulation of the localization and expression of ZO-1 at the plasma membrane through a mechanism involving the LXA(4) receptor.

Tumor Necrosis Factor-α in Airway Secretions from Cystic Fibrosis Patients Upregulate Endothelial Adhesion Molecules and Induce Airway Epithelial Cell Apoptosis: Implications for Cystic Fibrosis Lung Disease

Airway inflammation plays a crucial role in lung damage in cystic fibrosis (CF) and is characterized by a persistent influx of neutrophils into the airways. We hypothesized that the high levels of inflammatory products that accumulate in the microenvironment of the CF lung contribute to induce the persistent neutrophil recruitment and the airway epithelial damage. Thus, we evaluated the in vitro effect of sputum sol phase (SSP) from CF patients on a) adhesion molecule expression by human microvascular endothelial cells (HMECs) and b) apoptosis of human bronchial epithelial cells (HBECs), both wild-type and CFTR-defective. SSP was obtained from 7 clinically stable adult CF patients and 8 patients with an acute exacerbation. HMECs and HBECs were cultured in the absence or presence of SSP. Cell adhesion molecule expression was assessed by flow cytometry and cell death by the detection of histone-associated DNA fragments, caspase activation, and cytochrome c release. SSP obtained from CF patients, especially at the time of an acute exacerbation, induced a) an upregulation of endothelial adhesion molecules on cultured HMECs that was associated with an increase of neutrophil adhesion to these cells, and was mediated at least in part by TNF-α and IL-1 and b) apoptosis of airway epithelial cells, mainly activated by TNF-α pathway. These results suggest that the high concentrations of inflammatory mediators in CF airways contribute both to the chronic neutrophil influx and the airway damage, and support the crucial role of early anti-inflammatory treatment in the disease.

Peroxisome proliferator-activated receptor-gamma in cystic fibrosis lung epithelium

The pathophysiology of cystic fibrosis (CF) inflammatory lung disease is not well understood. CF airway epithelial cells respond to inflammatory stimuli with increased production of proinflammatory cytokines as a result of increased NF-kappaB activation. Peroxisome proliferator-activated receptor-gamma (PPARgamma) inhibits NF-kappaB activity and is reported to be reduced in CF. If PPARgamma participates in regulatory dysfunction in the CF lung, perhaps PPARgamma ligands might be useful therapeutically. Cell models of CF airway epithelium were used to evaluate PPARgamma expression and binding to NF-kappaB at basal and under conditions of inflammatory stimulation by Pseudomonas aeruginosa or TNFalpha/IL-1beta. An animal model of CF was used to evaluate the potential of PPARgamma agonists as therapeutic agents in vivo. In vitro, PPARgamma agonists reduced IL-8 and MMP-9 release from airway epithelial cells in response to PAO1 or TNFalpha/IL-1beta stimulation. Less NF-kappaB bound to PPARgamma in CF than normal cells, in two different assays; PPARgamma agonists abrogated this reduction. PPARgamma bound less to its target DNA sequence in CF cells. To test the importance of the reported PPARgamma inactivation by phosphorylation, we observed that inhibitors of ERK, but not JNK, were synergistic with PPARgamma agonists in reducing IL-8 secretion. In vivo, administration of PPARgamma agonists reduced airway inflammation in response to acute infection with P. aeruginosa in CF, but not wild-type, mice. In summary, PPARgamma inhibits the inflammatory response in CF, at least in part by interaction with NF-kappaB in airway epithelial cells. PPARgamma agonists may be therapeutic in CF.

A mechanism accounting for the low cellular level of linoleic acid in cystic fibrosis and its reversal by DHA

Specific fatty acid alterations have been described in the blood and tissues of cystic fibrosis (CF) patients. The principal alterations include decreased levels of linoleic acid (LA) and docosahexaenoic acid (DHA). We investigated the potential mechanisms of these alterations by studying the cellular uptake of LA and DHA, their distribution among lipid classes, and the metabolism of LA in a human bronchial epithelial cell model of CF. CF (antisense) cells demonstrated decreased levels of LA and DHA compared with wild type (WT, sense) cells expressing normal CFTR. Cellular uptake of LA and DHA was higher in CF cells compared with WT cells at 1 h and 4 h. Subsequent incorporation of LA and DHA into most lipid classes and individual phospholipids was also increased in CF cells. The metabolic conversion of LA to n-6 metabolites, including 18:3n-6 and arachidonic acid, was upregulated in CF cells, indicating increased flux through the n-6 pathway. Supplementing CF cells with DHA inhibited the production of LA metabolites and corrected the n-6 fatty acid defect. In conclusion, the evidence suggests that low LA level in cultured CF cells is due to its increased metabolism, and this increased LA metabolism is corrected by DHA supplementation.

Cell culture models demonstrate that CFTR dysfunction leads to defective fatty acid composition and metabolism

Cystic fibrosis (CF) is associated with fatty acid alterations characterized by low linoleic and docosahexaenoic acid. It is not clear whether these fatty acid alterations are directly linked to cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction or result from nutrient malabsorption. We hypothesized that if fatty acid alterations are a result of CFTR dysfunction, those alterations should be demonstrable in CF cell culture models. Two CF airway epithelial cell lines were used: 16HBE, sense and antisense CFTR cells, and C38/IB3-1 cells. Wild-type (WT) and CF cells were cultured in 10% fetal bovine serum (FBS) or 10% horse serum. Fatty acid levels were analyzed by GC-MS. Culture of both WT and CF cells in FBS resulted in very low linoleic acid levels. When cells were cultured in horse serum containing concentrations of linoleic acid matching those found in human plasma, physiological levels of linoleic acid were obtained and fatty acid alterations characteristic of CF tissues were then evident in CF compared with WT cells. Kinetic studies with radiolabeled linoleic acid demonstrated in CF cells increased conversion to longer and more-desaturated fatty acids such as arachidonic acid. In conclusion, these data demonstrate that CFTR dysfunction is associated with altered fatty acid metabolism in cultured airway epithelial cells.

Chromosomalgfplabelling ofPseudomonas aeruginosausing a mini-Tn7transposon: application for studies of bacteria–host interactions

Analysis of bacterial interactions with host cells using multiple techniques is essential for studies on microbial pathogenesis and for the development of new antimicrobial therapies. Pseudomonas aeruginosa is an important opportunistic pathogen that can cause severe, often life-threatening pulmonary infections in individuals with impaired host defense mechanisms. Using a mini-Tn7 transposon delivery system, we have chromosomally labelled the strain P. aeruginosa PAK with a green fluorescent protein gene (gfp) and tested PAKgfp as a research tool for studies of bacteria–host interactions. We were able to reliably and rapidly measure the interactions of PAKgfp with A549 human lung epithelial cells by using flow cytometry, a fluorometric microplate reader-based assay, and fluorescence microscopy. With these analytical tools, we have demonstrated the adhesion of PAKgfp to the extracellular matrix protein fibronectin and the involvement of fibronectin in PAKgfp–A549 cell interactions. PAKgfp can be successfully used to explore the effects of various pharmacological compounds on P. aeruginosa – host cell interactions in both in vitro and in vivo systems, with potentially important medical applications.

The type III toxins of Pseudomonas aeruginosa disrupt epithelial barrier function

The type III secreted toxins of Pseudomonas aeruginosa are important virulence factors associated with clinically important infection. However, their effects on bacterial invasion across mucosal surfaces have not been well characterized. One of the most commonly expressed toxins, ExoS, has two domains that are predicted to affect cytoskeletal integrity, including a GTPase-activating protein (GAP) domain, which targets Rho, a major regulator of actin polymerization; and an ADP-ribosylating domain that affects the ERM proteins, which link the plasma membrane to the actin cytoskeleton. The activities of these toxins, and ExoS specifically, on the permeability properties of polarized airway epithelial cells with intact tight junctions were examined. Strains expressing type III toxins altered the distribution of the tight junction proteins ZO-1 and occludin and were able to transmigrate across polarized airway epithelial monolayers, in contrast to DeltaSTY mutants. These effects on epithelial permeability were associated with the ADP-ribosylating domain of ExoS, as bacteria expressing plasmids lacking expression of the ExoS GAP activity nonetheless increased the permeation of fluorescent dextrans, as well as bacteria, across polarized airway epithelial cells. Treatment of epithelial cells with cytochalasin D depolymerized actin filaments and increased permeation across the monolayers but did not eliminate the differential effects of wild-type and toxin-negative mutants on the epithelial cells, suggesting that additional epithelial targets are involved. Confocal imaging studies demonstrated that ZO-1, occludin, and ezrin undergo substantial redistribution in human airway cells intoxicated by ExoS, -T, and -Y. These studies support the hypothesis that type III toxins enhance P. aeruginosa's invasive capabilities by interacting with multiple eukaryotic cytoskeletal components.

Elevated furin levels in human cystic fibrosis cells result in hypersusceptibility to exotoxin A-induced cytotoxicity

Progressive pulmonary disease and infections with Pseudomonas aeruginosa remain an intractable problem in cystic fibrosis (CF). At the cellular level, CF is characterized by organellar hyperacidification, which results in altered protein and lipid glycosylation. Altered pH of the trans-Golgi network (TGN) may further disrupt the protein processing and packaging that occurs in this organelle. Here we measured activity of the major TGN endoprotease furin and demonstrated a marked upregulation in human CF cells. Increased furin activity was linked to elevated production in CF of the immunosuppressive and tissue remodeling cytokine TGF-beta and its downstream effects, including macrophage deactivation and augmented collagen secretion by epithelial cells. As furin is responsible for the proteolytic processing of a range of endogenous and exogenous substrates including growth factors and bacterial toxins, we determined that elevated furin-dependent activation of exotoxin A caused increased cell death in CF respiratory epithelial cells compared with genetically matched CF transmembrane conductance regulator-corrected cells. Thus elevated furin levels in CF respiratory epithelial cells contributes to bacterial toxin-induced cell death, fibrosis, and local immunosuppression. These data suggest that the use of furin inhibitors may represent a strategy for pharmacotherapy in CF.