Pseudomonas aeruginosaInfection Destroys the Barrier Function of Lung Epithelium and Enhances Polyplex-Mediated Transfection

Molecular detection of multidrug-resistant Pseudomonas aeruginosa of different avian sources with pathogenicity testing and in vitro evaluation of antibacterial efficacy of silver nanoparticles against multidrug-resistant P. aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a serious zoonotic pathogen threaten the poultry industry causing severe economic losses therefor, this study aimed to isolation, phenotypic, molecular identification of P. aeruginosa from different avian sources (chickens, turkey, pigeons, table eggs, and dead in shell chicken embryos), from different Egyptian governorates (Giza, Qalubia, Beheira, El-Minya, and Al-Sharqia) with applying of antibiotic sensitivity test on all P. aeruginosa isolates. Highly resistant isolates (n = 49) were subjected to molecular identification of P. aeruginosa with detection of resistant genes including carbapenemase-encoding genes blaKPC, blaOXA-48, and blaNDM. On the base of molecular results, a highly resistant P. aeruginosa strain was tested for its pathogenicity on day old specific pathogen free (SPF) chicks. Also, in vitro experiment was adopted to evaluate the efficacy of silver nanoparticles (Ag-NPs) against highly antibiotic-resistant P. aeruginosa strains. The overall isolation percentage was from all examined samples were 36.2% (571/1,576) representing 45.2% (532/1,176) from different birds' tissues and 39/400 (9.7%) from total egg samples. Some of isolated strains showed multidrug resistance (MDR) against kanamycin, amoxicillin, amoxicillin-clavulanic acid, neomycin, chloramphenicol, vancomycin, cefotaxime clavulanic acid, lincomycin-spectinomycin, co-trimoxazole, cefoxitin, gentamycin, and doxycycline. These MDR strains were also molecularly positive for ESBL and carbapenemase-encoding genes. MDR strain showed high pathogenicity with histopathological alterations in different organs in challenged birds. Main histopathological lesions were necrosis of hepatocytes, renal tubular epithelium, and heart muscle bundles. The MDR strain showed in vitro sensitivity to Ag-NPs. In conclusion, MDR P. aeruginosa is a serious pathogen causing high morbidity, mortality, and pathological tissue alterations. Ag NPs revealed a promising in vitro antimicrobial sensitivity against MDR P. aeruginosa and further in vivo studies were recommended.

Evaluating Bacterial Pathogenesis Using a Model of Human Airway Organoids Infected with Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is one of the leading invasive agents of human pulmonary infection, especially in patients with compromised immunity. Prior studies have used various in vitro models to establish P. aeruginosa infection and to analyze transcriptomic profiles of either the host or pathogen, and yet how much those works are relevant to the genuine human airway still raises doubts. In this study, we cultured and differentiated human airway organoids (HAOs) that recapitulate, to a large extent, the histological and physiological features of the native human mucociliary epithelium. HAOs were then employed as a host model to monitor P. aeruginosa biofilm development. Through dual-species transcriptome sequencing (RNA-seq) analyses, we found that quorum sensing (QS) and several associated protein secretion systems were significantly upregulated in HAO-associated bacteria. Cocultures of HAOs and QS-defective mutants further validated the role of QS in the maintenance of a robust biofilm and disruption of host tissue. Simultaneously, the expression magnitude of multiple inflammation-associated signaling pathways was higher in the QS mutant-infected HAOs, suggesting that QS promotes immune evasion at the transcriptional level. Altogether, modeling infection of HAOs by P. aeruginosa captured several crucial facets in host responses and bacterial pathogenesis, with QS being the most dominant virulence pathway showing profound effects on both bacterial biofilm and host immune responses. Our results revealed that HAOs are an optimal model for studying the interaction between the airway epithelium and bacterial pathogens. IMPORTANCE Human airway organoids (HAOs) are an organotypic model of human airway mucociliary epithelium. The HAOs can closely resemble their origin organ in terms of epithelium architecture and physiological function. Accumulating studies have revealed the great values of the HAO cultures in host-pathogen interaction research. In this study, HAOs were used as a host model to grow Pseudomonas aeruginosa biofilm, which is one of the most common pathogens found in pulmonary infection cases. Dual transcriptome sequencing (RNA-seq) analyses showed that the cocultures have changed the gene expression pattern of both sides significantly and simultaneously. Bacterial quorum sensing (QS), the most upregulated pathway, contributed greatly to biofilm formation, disruption of barrier function, and subversion of host immune responses. Our study therefore provides a global insight into the transcriptomic responses of both P. aeruginosa and human airway epithelium.

Airway Epithelial Cell Junctions as Targets for Pathogens and Antimicrobial Therapy

Intercellular contacts between epithelial cells are established and maintained by the apical junctional complexes (AJCs). AJCs conserve cell polarity and build epithelial barriers to pathogens, inhaled allergens, and environmental particles in the respiratory tract. AJCs consist of tight junctions (TJs) and adherens junctions (AJs), which play a key role in maintaining the integrity of the airway barrier. Emerging evidence has shown that different microorganisms cause airway barrier dysfunction by targeting TJ and AJ proteins. This review discusses the pathophysiologic mechanisms by which several microorganisms (bacteria and viruses) lead to the disruption of AJCs in airway epithelial cells. We present recent progress in understanding signaling pathways involved in the formation and regulation of cell junctions. We also summarize the potential chemical inhibitors and pharmacological approaches to restore the integrity of the airway epithelial barrier. Understanding the AJCs-pathogen interactions and mechanisms by which microorganisms target the AJC and impair barrier function may further help design therapeutic innovations to treat these infections.

Pathophysiology of Lung Disease and Wound Repair in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive, life-threatening condition affecting many organs and tissues, the lung disease being the chief cause of morbidity and mortality. Mutations affecting the CF Transmembrane Conductance Regulator (CFTR) gene determine the expression of a dysfunctional protein that, in turn, triggers a pathophysiological cascade, leading to airway epithelium injury and remodeling. In vitro and in vivo studies point to a dysregulated regeneration and wound repair in CF airways, to be traced back to epithelial CFTR lack/dysfunction. Subsequent altered ion/fluid fluxes and/or signaling result in reduced cell migration and proliferation. Furthermore, the epithelial-mesenchymal transition appears to be partially triggered in CF, contributing to wound closure alteration. Finally, we pose our attention to diverse approaches to tackle this defect, discussing the therapeutic role of protease inhibitors, CFTR modulators and mesenchymal stem cells. Although the pathophysiology of wound repair in CF has been disclosed in some mechanisms, further studies are warranted to understand the cellular and molecular events in more details and to better address therapeutic interventions.

Investigation and Functional Enrichment Analysis of the Human Host Interaction Network with Common Gram-Negative Respiratory Pathogens Predicts Possible Association with Lung Adenocarcinoma

Haemophilus influenzae (Hi), Moraxella catarrhalis (MorCa) and Pseudomonas aeruginosa (Psa) are three of the most common gram-negative bacteria responsible for human respiratory diseases. In this study, we aimed to identify, using the functional enrichment analysis (FEA), the human gene interaction network with the aforementioned bacteria in order to elucidate the full spectrum of induced pathogenicity. The Human Pathogen Interaction Database (HPIDB 3.0) was used to identify the human proteins that interact with the three pathogens. FEA was performed via the ToppFun tool of the ToppGene Suite and the GeneCodis database so as to identify enriched gene ontologies (GO) of biological processes (BP), cellular components (CC) and diseases. In total, 11 human proteins were found to interact with the bacterial pathogens. FEA of BP GOs revealed associations with mitochondrial membrane permeability relative to apoptotic pathways. FEA of CC GOs revealed associations with focal adhesion, cell junctions and exosomes. The most significantly enriched annotations in diseases and pathways were lung adenocarcinoma and cell cycle, respectively. Our results suggest that the Hi, MorCa and Psa pathogens could be related to the pathogenesis and/or progression of lung adenocarcinoma via the targeting of the epithelial cellular junctions and the subsequent deregulation of the cell adhesion and apoptotic pathways. These hypotheses should be experimentally validated.

Optimized Pre-Clinical Grade Production of Two Novel Lentiviral Vector Pseudotypes for Lung Gene Delivery

Lung gene therapy requires efficient transduction of slow-replicating epithelia and stable expression of delivered transgenes in the respiratory tract. Lentiviral (LV) vectors have the ideal coding, expression, and transducing capacity required for gene therapy. A modified envelope glycoprotein from the Jaagsiekte Sheep Retrovirus, termed Jenv, is well suited for LV-mediated lung gene therapy due to its inherent lung tropism. Here, two novel Jenv-pseudotyped LVs that effectively transduce lung tissue and yield titers similar to the gold standard, vesicular stomatitis virus glycoprotein (VSVg)-pseudotyped LVs, were generated. As the concentration efficiency of LVs was found to depend on envelope pseudotype, a large-scale production method tailored for Jenv-pseudotyped LVs was developed and the most appropriate method of concentration was determined. In contrast to VSVg and Ebola virus glycoprotein-pseudotyped LVs, ultracentrifugation through a sucrose cushion drastically reduced the yield of Jenv LVs, whereas polyethylene glycol precipitation and tangential flow filtration (TFF) proved to be more suitable methods for concentrating Jenv LVs. Importantly, pressure during TFF was found to be crucial for increasing LV recovery. Finally, a unique mouse model was developed to test the suitability of these novel Jenv-pseudotyped LVs for use in lung gene therapy applications.

Impaired Airway Epithelial Barrier Integrity in Response to Stenotrophomonas maltophilia Proteases, Novel Insights Using Cystic Fibrosis Bronchial Epithelial Cell Secretomics

Stenotrophomonas maltophilia is a Gram-negative opportunistic pathogen that can chronically colonize the lungs of people with cystic fibrosis (CF) and is associated with lethal pulmonary hemorrhage in immunocompromised patients. Its secreted virulence factors include the extracellular serine proteases StmPR1, StmPR2, and StmPR3. To explore the impact of secreted virulence determinants on pulmonary mucosal defenses in CF, we examined the secretome of human CFBE41o- bronchial epithelial cells in response to treatment with S. maltophilia K279a cell culture supernatant (CS) using a liquid-chromatography-tandem mass spectrometry (LC-MS/MS) based label-free quantitative (LFQ) shotgun proteomics approach for global profiling of the cell secretome. Secretome analysis identified upregulated pathways mainly relating to biological adhesion and epithelial cell signaling in infection, whereas no specific pathways relating to the immune response were enriched. Further exploration of the potentially harmful effects of K279a CS on CF bronchial epithelial cells, demonstrated that K279a CS caused CFBE41o- cell condensation and detachment, reversible by the serine protease inhibitor PMSF. K279a CS also decreased trans-epithelial electrical resistance in CFBE41o- cell monolayers suggestive of disruption of tight junction complexes (TJC). This finding was corroborated by an observed increase in fluorescein isothiocyanate (FITC) dextran permeability and by demonstrating PMSF-sensitive degradation of the tight junction proteins ZO-1 and occludin, but not JAM-A or claudin-1. These observations demonstrating destruction of the CFBE41o- TJC provide a novel insight regarding the virulence of S. maltophilia and may explain the possible injurious effects of this bacterium on the CF bronchial epithelium and the pathogenic mechanism leading to lethal pulmonary hemorrhage.

Lung infection caused by Pseudomonas aeruginosa in a CD26/DPP4 deficient F344 rat model

Background

Pseudomonas aeruginosa (PA) is the most important opportunistic pathogen in causing nosocomial infections and, furthermore, poses a permanent threat for severe chronic infections in patients with cystic fibrosis or COPD. The transmembrane protein CD26 with dipeptidyl peptidase-4 (DPP4) activity shows an increased expression in inflamed tissue. We tested whether CD26/DPP4 deficiency leads to reduced inflammation and decreased structural damage when infected with PA.

Methods

CD26/DPP4⁺ and CD26/DPP4⁻ rats were instilled intratracheally with NaCl (controls) or with PA. Six hours later, bacterial distribution was detected with the in vivo imaging system 200 (IVIS). Lungs were then processed for molecular biology, light and electron microscopy and analyzed qualitatively, quantitatively and stereologically. Bacterial numbers were determined in homogenized lungs.

Results

Compared to saline treated controls, in both infected groups (1) the acinar airspace was significantly increased, (2) the volume density of the alveolar epithelium was significantly decreased, (3) the septal thickness was significantly reduced, (4) more than 40% of the alveolar epithelial surface was damaged, and up to 36% of the epithelial surface was covered with edema. In infected CD26⁻ rats, the increase in lung weight was significantly less pronounced, the portion of edematous alveolar airspace was significantly lower and the part of edema interspersed with PA was decreased significantly.

Conclusions

CD26/DPP4 deficiency resulted in reduced pulmonary edema under sublethal PA infection, implicating a role for CD26 in infection progression. The partly pronounced structural damage may mask further possible influences of CD26 on the inflammatory response.

Bacterial and Viral Identification Rate in Acute Exacerbation of Chronic Obstructive Pulmonary Disease in Korea

PURPOSE

The most common cause of acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is respiratory infection. Most studies of bacterial or viral cause in AECOPD have been conducted in Western countries. We investigated bacterial and viral identification rates in AECOPD in Korea.

MATERIALS AND METHODS

We reviewed and analyzed medical records of 736 cases of AECOPD at the Korea University Guro Hospital. We analyzed bacterial and viral identification rates and classified infections according to epidemiological factors, such as Global Initiative for Chronic Obstructive Lung Disease stage, mortality, and seasonal variation.

RESULTS

The numbers of AECOPD events involving only bacterial identification, only viral identification, bacterial-viral co-identification, and no identification were 200 (27.2%), 159 (21.6%), 107 (14.5%), and 270 (36.7%), respectively. The most common infectious bacteria identified were Pseudomonas aeruginosa (13.0%), Streptococcus pneumoniae (11.4%), and Haemophilus influenzae (5.3%); the most common viruses identified were influenza virus (12.4%), rhinovirus (9.4%), parainfluenza virus (5.2%), and metapneumovirus (4.9%). The bacterial identification rate tended to be higher at more advanced stages of chronic obstructive pulmonary disease (p=0.020 overall, p=0.011 for P. aeruginosa, p=0.048 for S. pneumoniae). Staphylococcus aureus and Klebsiella pneumoniae were identified more in mortality group (p=0.003 for S. aureus, p=0.009 for K. pneumoniae). All viruses were seasonal (i.e., greater prevalence in a particular season; p<0.050). Influenza virus and rhinovirus were mainly identified in the winter, parainfluenza virus in the summer, and metapneumovirus in the spring.

CONCLUSION

This information on the epidemiology of respiratory infections in AECOPD will improve the management of AECOPD using antibiotics and other treatments in Korea.

Metformin attenuates the effect of Staphylococcus aureus on airway tight junctions by increasing PKCζ-mediated phosphorylation of occludin

Airway epithelial tight junction (TJ) proteins form a resistive barrier to the external environment, however, during respiratory bacterial infection TJs become disrupted compromising barrier function. This promotes glucose flux/accumulation into the lumen which acts as a nutrient source for bacterial growth. Metformin used for the treatment of diabetes increases transepithelial resistance (TEER) and partially prevents the effect of bacteria but the mechanisms of action are unclear. We investigated the effect of metformin and Staphylococcus aureus on TJ proteins, zonula occludins (ZO)-1 and occludin in human airway epithelial cells (H441). We also explored the role of AMP-activated protein kinase (AMPK) and PKCζ in metformin-induced effects. Pretreatment with metformin prevented the S. aureus-induced changes in ZO-1 and occludin. Metformin also promoted increased abundance of full length over smaller cleaved occludin proteins. The nonspecific PKC inhibitor staurosporine reduced TEER but did not prevent the effect of metformin indicating that the pathway may involve atypical PKC isoforms. Investigation of TJ reassembly after calcium depletion showed that metformin increased TEER more rapidly and promoted the abundance and localization of occludin at the TJ. These effects were inhibited by the AMPK inhibitor, compound C and the PKCζ pseudosubstrate inhibitor (PSI). Metformin increased phosphorylation of occludin and acetyl-coA-carboxylase but only the former was prevented by PSI. This study demonstrates that metformin improves TJ barrier function by promoting the abundance and assembly of full length occludin at the TJ and that this process involves phosphorylation of the protein via an AMPK-PKCζ pathway.

CFTR rescue with VX-809 and VX-770 favors the repair of primary airway epithelial cell cultures from patients with class II mutations in the presence of Pseudomonas aeruginosa exoproducts

BACKGROUND

Progressive airway damage due to bacterial infections, especially with Pseudomonas aeruginosa remains the first cause of morbidity and mortality in CF patients. Our previous work revealed a repair delay in CF airway epithelia compared to non-CF. This delay was partially prevented after CFTR correction (with VRT-325) in the absence of infection. Our goals were now to evaluate the effect of the Orkambi combination (CFTR VX-809 corrector + VX-770 potentiator) on the repair of CF primary airway epithelia, in infectious conditions.

METHODS

Primary airway epithelial cell cultures from patients with class II mutations were mechanically injured and wound healing rates and transepithelial resistances were monitored after CFTR rescue, in the absence and presence of P. aeruginosa exoproducts.

RESULTS

Our data revealed that combined treatment with VX-809 and VX-770 elicited a greater beneficial impact on airway epithelial repair than VX-809 alone, in the absence of infection. The treatment with Orkambi was effective not only in airway epithelial cell cultures from patients homozygous for the F508del mutation but also from heterozygous patients carrying F508del and another class II mutation (N1303 K, I507del). The stimulatory effect of the Orkambi treatment was prevented by CFTR inhibition with GlyH101. Finally, Orkambi combination elicited a slight but significant improvement in airway epithelial repair and transepithelial resistance, despite the presence of P. aeruginosa exoproducts.

CONCLUSIONS

Our findings indicate that Orkambi may favor airway epithelial integrity in CF patients with class II mutations. Complementary approaches would however be needed to further improve CFTR rescue and airway epithelial repair.

Quorum Sensing Down-Regulation Counteracts the Negative Impact of Pseudomonas aeruginosa on CFTR Channel Expression, Function and Rescue in Human Airway Epithelial Cells

The function of cystic fibrosis transmembrane conductance regulator (CFTR) channels is crucial in human airways. However unfortunately, chronic Pseudomonas aeruginosa infection has been shown to impair CFTR proteins in non-CF airway epithelial cells (AEC) and to alter the efficiency of new treatments with CFTR modulators designed to correct the basic CFTR default in AEC from cystic fibrosis (CF) patients carrying the F508del mutation. Our aim was first to compare the effect of laboratory strains, clinical isolates, engineered and natural mutants to determine the role of the LasR quorum sensing system in CFTR impairment, and second, to test the efficiency of a quorum sensing inhibitor to counteract the deleterious impact of P. aeruginosa both on wt-CFTR and on the rescue of F508del-CFTR by correctors. We first report that exoproducts from either the laboratory PAO1 strain or a clinical ≪Early≫ isolate (from an early stage of infection) altered CFTR expression, localization and function in AEC expressing wt-CFTR. Genetic inactivation of the quorum-sensing LasR in PAO1 (PAO1ΔlasR) or in a natural clinical mutant (≪Late≫ CF-adapted clinical isolate) abolished wt-CFTR impairment. PAO1 exoproducts also dampened F508del-CFTR rescue by VRT-325 or Vx-809 correctors in CF cells, whereas PAO1ΔlasR had no impact. Importantly, treatment of P. aeruginosa cultures with a quorum sensing inhibitor (HDMF) prevented the negative effect of P. aeruginosa exoproducts on wt-CFTR and preserved CFTR rescue by correctors in CF AEC. These findings indicate that LasR-interfering strategies could be of benefits to counteract the deleterious effect of P. aeruginosa in infected patients.

Staphylococcus Aureus V8 protease disrupts the integrity of the airway epithelial barrier and impairs IL-6 production in vitro

OBJECTIVE

Staphylococcus aureus (S. aureus) infection is known to contribute to the severity and recalcitrance of chronic rhinosinusitis (CRS), and its secreted products have been shown to alter the airway barrier. Extracellular proteases secreted by S. aureus are thought to be important in epithelial infection and immune evasion; however, their effect on airway mucosal barrier function is not known.

METHODS

To investigate the impact of extracellular proteases on airway epithelial integrity, the purified S. aureus proteases V8 protease, Staphopain A, Staphopain B, Exfoliative toxin A, and serine protease-like A-F were applied to human nasal epithelial cell air-liquid interface (HNEC-ALI) cultures. Transepithelial electrical resistance (TEER), permeability (Papp) measurements, and immuno-localization of the tight junction proteins claudin-1 and ZO-1 were used to assess barrier integrity. Effects of the proteases on inflammation and cell viability were measured using interleukin-6 (IL-6) ELISA and a lactate dehydrogenase assay.

RESULTS

Application of V8 protease to HNEC-ALI cultures caused a significant concentration and time-dependent decrease in TEER (22.67%, P < 0.0001), a reciprocal Papp increase (20.14-fold, P < 0.05), and a discontinuous ZO-1 immuno-localization compared to control. IL-6 production was significantly reduced in V8 protease-treated cells (153.5 pg/mL, P = 0.0069) compared to control (548.3 pg/mL), whereas no difference in cell viability was observed.

CONCLUSION

S. aureus V8 protease causes dysfunction of mucosal barrier structure and function indicative of a leaky barrier. A reduction in IL-6 levels suggests that the mucosal immunity is impaired by this protease and thus has the potential to contribute to CRS recalcitrance.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E8-E15, 2018.

Rhamnolipids Enhance in Vivo Oral Bioavailability of Poorly Absorbed Molecules

PURPOSE

This report describes the effect of rhamnolipids (RLs) on the tight junctions (TJ) of the intestinal epithelium using the rat in-situ closed loop model.

METHODS

We investigated the transport of 5 (6)-carboxyfluorescein (CF) and fluorescein isothiocyanate-labeled dextrans with average molecular weights of 4.4 and 10 kDa (FD-4 and FD-10) when co-administered with different concentrations of RLs. Lactate dehydrogenase (LDH) leakage assay and histopathological examination of treated intestinal loops were used to assess potential toxicity of RLs. Further, the effect of kaempferol on accelerating the resealing of the tight junctions in vivo was also investigated RESULTS: Data shows that administration of different RLs concentrations (1.0-5.0% v/v) increased CF absorption through rat intestine by 2.84- and 15.82-folds with RLs concentrations of 1.0% and 5.0% v/v, respectively. RLs exhibited size-dependent increase on FD-4 and FD-10 absorption. Dosing RLs at 1.0% v/v didn't cause a significant LDH leakage or histopathological changes to intestinal mucosa compared to higher concentrations, which showed a progressive damaging effect. Using kaempferol, a natural flavonoid that stimulates the assembly of the TJs, proved to enhance the recovery of barrier properties of the intestinal mucosa treated with high concentrations of RLs (2.5% and 5% v/v).

CONCLUSIONS

These results collectively illustrate the ability of RLs to enhance oral bioavailability of different molecules across the intestinal epithelial membrane in a concentration- and time-dependent fashion.

Quorum-sensing inhibition abrogates the deleterious impact of Pseudomonas aeruginosa on airway epithelial repair

Chronic Pseudomonas aeruginosa lung infections are associated with progressive epithelial damage and lung function decline. In addition to its role in tissue injury, the persistent presence of P. aeruginosa-secreted products may also affect epithelial repair ability, raising the need for new antivirulence therapies. The purpose of our study was to better understand the outcomes of P. aeruginosa exoproducts exposure on airway epithelial repair processes to identify a strategy to counteract their deleterious effect. We found that P. aeruginosa exoproducts significantly decreased wound healing, migration, and proliferation rates, and impaired the ability of directional migration of primary non-cystic fibrosis (CF) human airway epithelial cells. Impact of exoproducts was inhibited after mutations in P. aeruginosa genes that encoded for the quorum-sensing (QS) transcriptional regulator, LasR, and the elastase, LasB, whereas impact was restored by LasB induction in ΔlasR mutants. P. aeruginosa purified elastase also induced a significant decrease in non-CF epithelial repair, whereas protease inhibition with phosphoramidon prevented the effect of P. aeruginosa exoproducts. Furthermore, treatment of P. aeruginosa cultures with 4-hydroxy-2,5-dimethyl-3(2H)-furanone, a QS inhibitor, abrogated the negative impact of P. aeruginosa exoproducts on airway epithelial repair. Finally, we confirmed our findings in human airway epithelial cells from patients with CF, a disease featuring P. aeruginosa chronic respiratory infection. These data demonstrate that secreted proteases under the control of the LasR QS system impair airway epithelial repair and that QS inhibitors could be of benefit to counteract the deleterious effect of P. aeruginosa in infected patients.-Ruffin, M., Bilodeau, C., Maillé, É., LaFayette, S. L., McKay, G. A., Trinh, N. T. N., Beaudoin, T., Desrosiers, M.-Y., Rousseau, S., Nguyen, D., Brochiero, E. Quorum-sensing inhibition abrogates the deleterious impact of Pseudomonas aeruginosa on airway epithelial repair.

Possible mechanisms of Pseudomonas aeruginosa-associated lung disease

Pseudomonas aeruginosa is an opportunistic bacterium causing lung injury in immunocompromised patients correlated with high morbidity and mortality. Many bacteria, including P. aeruginosa, use extracellular signals to synchronize group behaviors, a process known as quorum sensing (QS). In the P. aeruginosa complex QS system controls expression of over 300 genes, including many involved in host colonization and disease. P. aeruginosa infection elicits a complex immune response due to a large number of immunogenic factors present in the bacteria or released during infection. Here, we focused on the mechanisms by which P. aeruginosa triggers lung injury and inflammation, debating the possible ways that P. aeruginosa evades the host immune system, which leads to immune suppression and resistance.

Mimicking the host and its microenvironment in vitro for studying mucosal infections by Pseudomonas aeruginosa

Why is a healthy person protected from Pseudomonas aeruginosa infections, while individuals with cystic fibrosis or damaged epithelium are particularly susceptible to this opportunistic pathogen? To address this question, it is essential to thoroughly understand the dynamic interplay between the host microenvironment and P. aeruginosa. Therefore, using model systems that represent key aspects of human mucosal tissues in health and disease allows recreating in vivo host-pathogen interactions in a physiologically relevant manner. In this review, we discuss how factors of mucosal tissues, such as apical-basolateral polarity, junctional complexes, extracellular matrix proteins, mucus, multicellular complexity (including indigenous microbiota), and other physicochemical factors affect P. aeruginosa pathogenesis and are thus important to mimic in vitro. We highlight in vitro cell and tissue culture model systems of increasing complexity that have been used over the past 35 years to study the infectious disease process of P. aeruginosa, mainly focusing on lung models, and their respective advantages and limitations. Continued improvements of in vitro models based on our expanding knowledge of host microenvironmental factors that participate in P. aeruginosa pathogenesis will help advance fundamental understanding of pathogenic mechanisms and increase the translational potential of research findings from bench to the patient's bedside.

Mechanism of fibroblast inflammatory responses to Pseudomonas aeruginosa elastase

Receptor tyrosine kinases, including the epidermal growth factor receptors (EGFR), are able to activate the mitogen-activated protein kinases (MAPK) via several adaptor proteins and protein kinases such as Raf. EGFR can be activated by a variety of extracellular stimuli including neutrophil elastase, but we are aware of no report as to whether Pseudomonas aeruginosa produced elastase (PE) could elicit such signalling through EGFR activation. We sought to test the inference that PE modulates inflammatory responses in human lung fibroblasts and that the process occurs by activation of the EGFR/MAPK pathways. We utilized IL-8 cytokine expression as a pathway-specific end point measure of the fibroblast inflammatory response to PE. Western blot analysis was performed to detect phosphorylation of EGFR and signal transduction intermediates. Northern blot, real-time PCR, and ELISA methods were utilized to determine cytokine gene expression levels. We found that PE induces phosphorylation of the EGFR and the extracellular signal-regulated proteins (ERK1/2) of the MAPK pathway, and nuclear translocation of NF-κB. Furthermore, enzymically active PE enhances IL-8 mRNA and protein secretion. Pretreatment of the cells with specific inhibitors of EGFR, MAPK kinase and NF-κB markedly attenuated the PE-induced signal proteins phosphorylation and IL-8 gene expression and protein secretion. Collectively, the data show that PE produced by Pseudomonas aeruginosa can modulate lung inflammation by exploiting the EGFR/ERK signalling cascades and enhancing IL-8 production in the lungs via NF-κB activation.

NAD-independent L-lactate dehydrogenase is required for L-lactate utilization in Pseudomonas stutzeri SDM

BACKGROUND

Various Pseudomonas strains can use L-lactate as their sole carbon source for growth. However, the L-lactate-utilizing enzymes in Pseudomonas have never been identified and further studied.

METHODOLOGY/PRINCIPAL FINDINGS

An NAD-independent L-lactate dehydrogenase (L-iLDH) was purified from the membrane fraction of Pseudomonas stutzeri SDM. The enzyme catalyzes the oxidation of L-lactate to pyruvate by using FMN as cofactor. After cloning its encoding gene (lldD), L-iLDH was successfully expressed, purified from a recombinant Escherichia coli strain, and characterized. An lldD mutant of P. stutzeri SDM was constructed by gene knockout technology. This mutant was unable to grow on L-lactate, but retained the ability to grow on pyruvate.

CONCLUSIONS/SIGNIFICANCE

It is proposed that L-iLDH plays an indispensable function in Pseudomonas L-lactate utilization by catalyzing the conversion of L-lactate into pyruvate.

Inhibition of protein kinase C attenuates Pseudomonas aeruginosa elastase-induced epithelial barrier disruption

Pseudomonas aeruginosa pulmonary infection compromises the human airway epithelium, and can be especially devastating to immunocompromised or debilitated individuals. We have reported earlier that P. aeruginosa elastase (PE) increases paracellular permeability in epithelial cell monolayers by mechanisms involving tight junction (TJ) disruption and cytoskeletal reorganization, leading to destruction of epithelial barrier function. The aim of this study was to investigate putative TJ targets and potential mechanisms by which PE induces barrier disruption. We found that PE decreased localization of TJ proteins, occludin and zonula occludens (ZO)-1, in membrane fractions, and induced reorganization of F-actin within 1 hour. Although inhibition of protein kinase (PK) C α/β signaling modestly altered the extent of cytoskeletal disruption and ZO-1 translocation, we found PKC signaling to play a significant role in decreased occludin functionality during PE exposure. Furthermore, elevated PKC levels correlated with decreased levels of TJ proteins in membrane fractions, and increased paracellular permeability in a time-dependent manner. Therefore, we conclude that PKC signaling is involved during PE-induced epithelial barrier disruption via TJ translocation and cytoskeletal reorganization. Specifically, occludin, as well as associated ZO-1 and F-actin, may be early targets of PE pathogenesis occurring via a PKC-dependent pathway.

Claudins in lung diseases

Tight junctions are the most apically localized part of the epithelial junctional complex. They regulate the permeability and polarity of cell layers and create compartments in cell membranes. Claudins are structural molecules of tight junctions. There are 27 claudins known, and expression of different claudins is responsible for changes in the electrolyte and solute permeability in cells layers. Studies have shown that claudins and tight junctions also protect multicellular organisms from infections and that some infectious agents may use claudins as targets to invade and weaken the host's defense. In neoplastic diseases, claudin expression may be up- or downregulated. Since their expression is associated with specific tumor types or with specific locations of tumors to a certain degree, they can, in a restricted sense, also be used as tumor markers. However, the regulation of claudin expression is complex involving growth factors and integrins, protein kinases, proto-oncogens and transcription factors. In this review, the significance of claudins is discussed in lung disease and development.

Contribution of lethal toxin and edema toxin to the pathogenesis of anthrax meningitis

Bacillus anthracis is a Gram-positive spore-forming bacterium that causes anthrax disease in humans and animals. Systemic infection is characterized by septicemia, toxemia, and meningitis, the main neurological complication associated with high mortality. We have shown previously that B. anthracis Sterne is capable of blood-brain barrier (BBB) penetration, establishing the classic signs of meningitis, and that infection is dependent on the expression of both major anthrax toxins, lethal toxin (LT) and edema toxin (ET). Here we further investigate the contribution of the individual toxins to BBB disruption using isogenic toxin mutants deficient in lethal factor, ΔLF, and edema factor, ΔEF. Acute infection with B. anthracis Sterne and the ΔLF mutant resulted in disruption of human brain microvascular endothelial cell (hBMEC) monolayer integrity and tight junction protein zona occludens-1, while the result for cells infected with the ΔEF mutant was similar to that for the noninfected control. A significant decrease in bacterial invasion of BBB endothelium in vitro was observed during infection with the ΔLF strain, suggesting a prominent role for LT in promoting BBB interaction. Further, treatment of hBMECs with purified LT or chemicals that mimic LT action on host signaling pathways rescued the hypoinvasive phenotype of the ΔLF mutant and resulted in increased bacterial uptake. We also observed that toxin expression reduced bacterial intracellular survival by inducing the bulk degradative autophagy pathway in host cells. Finally, in a murine model of anthrax meningitis, mice infected with the ΔLF mutant exhibited no mortality, brain bacterial load, or evidence of meningitis compared to mice infected with the parental or ΔEF strains.

Magnetically guided lentiviral-mediated transduction of airway epithelial cells

BACKGROUND

Lentiviral (LV) vectors are able to only slowly and inefficiently transduce nondividing cells such as those of the airway epithelium. To address this issue, we have exploited the magnetofection technique in in vitro models of airway epithelium.

METHODS

Magnetofectins were formed by noncovalent interaction between LV particles and polycation-coated iron oxide nanoparticles. Efficiency of LV-mediated transduction (as evaluated through green fluorescent protein (GFP) expression by cytofluorimetric analysis) was measured in bronchial epithelial cells in the presence or absence of a magnetic field. Cytotoxicity was evaluated by lactate dehydrogenase (LDH) release; cell monolayer integrity by measurement of transepithelial resistance (TER) and evaluation of correct zonula occludens-1 (ZO-1) localization at tight junctions (TJs) by immunofluorescence and confocal microscopy.

RESULTS

In nonpolarized cells, magnetofectins enhanced LV-mediated transduction at multiplicity of infection (MOI) of 50 up to 3.9-fold upon a 24-h incubation, to levels that approached those achieved at MOI of 200 for LV alone, in the presence or absence of the magnetic field. Magnetofection significantly increased the percentage of transduced cells up to 186-fold already after 15 min of incubation. In polarized cells, magnetofection increased GFP+ cells up to 24-fold compared to LV alone. Magnetofection did not enhance LDH release and slightly altered TER but not ZO-1 localization at the TJs.

CONCLUSIONS

We conclude that magnetofection can facilitate in vitro LV-mediated transduction of airway epithelial cells, in the absence of overt cytotoxicity and maintaining epithelial integrity, by lowering the necessary vector dose and reducing the incubation time required to achieve efficient transduction.

A VSV-G Pseudotyped Last Generation Lentiviral Vector Mediates High Level and Persistent Gene Transfer in Models of Airway Epithelium In Vitro and In Vivo

The aim of this work was to evaluate the efficiency and duration of gene expression mediated by a VSV-G pseudotyped last generation lentiviral (LV) vector. We studied LV efficiency in ex-vivo models of respiratory epithelial cells, obtained from bronchial biopsies and nasal polyps, by GFP epifluorescence and cytofluorimetry. In vivo efficiency and persistence of gene expression was investigated by GFP immunohistochemistry and luciferase activity in lung cryosections and homogenates, respectively, upon intranasal and intratracheal administration protocols in C57Bl/6 mice. Both primary bronchial and nasal epithelial cells were transduced up to 70–80% 72 hr after the LV infection. In vivo nasal luciferase expression was increased by lysophosphatidylcholine pre-treatment of the nose. Conversely, the bronchial epithelium was transduced in the absence of any pre-conditioning treatment and luciferase expression lasted for at least 6 months without any decline. We conclude that a last generation LV vector is a promising gene transfer agent in the target organ of genetic and acquired lung diseases, as in the case of cystic fibrosis.

Impact of lentiviral vector-mediated transduction on the tightness of a polarized model of airway epithelium and effect of cationic polymer polyethylenimine

Lentiviral (LV) vectors are promising agents for efficient and long-lasting gene transfer into the lung and for gene therapy of genetically determined pulmonary diseases, such as cystic fibrosis, however, they have not been evaluated for cytotoxicity and impact on the tightness of the airway epithelium. In this study, we evaluated the transduction efficiency of a last-generation LV vector bearing Green Fluorescent Protein (GFP) gene as well as cytotoxicity and tight junction (TJ) integrity in a polarized model of airway epithelial cells. High multiplicities of infection (MOI) showed to be cytotoxic, as assessed by increase in propidium iodide staining and decrease in cell viability, and harmful for the epithelial tightness, as demonstrated by the decrease of transepithelial resistance (TER) and delocalization of occludin from the TJs. To increase LV efficiency at low LV:cell ratio, we employed noncovalent association with the polycation branched 25 kDa polyethylenimine (PEI). Transduction of cells with PEI/LV particles resulted in 2.5–3.6-fold increase of percentage of GFP-positive cells only at the highest PEI:LV ratios (1×10⁷ PEI molecules/transducing units with 50 MOI LV) as compared to plain LV. At this dose PEI/LV transduction resulted in 6.5 ± 2.4% of propidium iodide-positive cells. On the other hand, PEI/LV particles did not determine any alteration of TER and occludin localization. We conclude that PEI may be useful for improving the efficiency of gene transfer mediated by LV vectors in airway epithelial cells, in the absence of high acute cytotoxicity and alteration in epithelial tightness.

Impact of chronic pulmonary infection with Pseudomonas aeruginosa on transfection mediated by viral and nonviral vectors

Pseudomonas aeruginosa plays a crucial role in the lung pathology of cystic fibrosis (CF). We showed that acute infection with P. aeruginosa has a substantial impact on gene transfer into lung epithelial cells mediated by polyplexes. As an extension of those studies we report here on the effect of chronic pulmonary infection with P. aeruginosa on transfection of lung epithelial cells by viral and nonviral vectors. As an in vivo model of the persistent chronic infection in patients with CF we used C57BL/6 mice intratracheally infected with P. aeruginosa encapsulated in agar beads. Two weeks after infection the presence of viable bacteria in the lungs was confirmed, mostly in the bronchial lumen. In lung tissue sections stained with hematoxylin and eosin, extensive inflammatory infiltrations were found. At that time point the mice received an intratracheal dose of luciferase gene complexed with either Lipofectamine (Lf), a GL67 lipid mixture (GL67), or polyethylenimine (PEI) or with lentivirus (LV) as a carrier system. Luciferase activity was determined by a luminescence assay in supernatants of lung homogenates. The transfection level induced by PEI/DNA polyplexes complexed with serum albumin was decreased in infected mice. Lf-mediated transfection was almost completely blocked in infected mice. Transfection levels in mice treated with LV or plain PEI/DNA polyplexes were unchanged in infected animals as compared with control mice. The only carrier that displayed a clearly increased transfection level in infected mice was the GL67 lipid mixture, which is tentatively ascribed to the presence of polyethylene glycol in this carrier.

Lentiviral vectors and cystic fibrosis gene therapy

Cystic fibrosis (CF) is a chronic autosomic recessive syndrome, caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene, a chloride channel expressed on the apical side of the airway epithelial cells. The lack of CFTR activity brings a dysregulated exchange of ions and water through the airway epithelium, one of the main aspects of CF lung disease pathophysiology. Lentiviral (LV) vectors, of the Retroviridae family, show interesting properties for CF gene therapy, since they integrate into the host genome and allow long-lasting gene expression. Proof-of-principle that LV vectors can transduce the airway epithelium and correct the basic electrophysiological defect in CF mice has been given. Initial data also demonstrate that LV vectors can be repeatedly administered to the lung and do not give rise to a gross inflammatory process, although they can elicit a T cell-mediated response to the transgene. Future studies will clarify the efficacy and safety profile of LV vectors in new complex animal models with CF, such as ferrets and pigs.

Structure and function of Pseudomonas aeruginosa protein PA1324 (21-170)

Pseudomonas aeruginosa is the prototypical biofilm-forming gram-negative opportunistic human pathogen. P. aeruginosa is causatively associated with nosocomial infections and with cystic fibrosis. Antibiotic resistance in some strains adds to the inherent difficulties that result from biofilm formation when treating P. aeruginosa infections. Transcriptional profiling studies suggest widespread changes in the proteome during quorum sensing and biofilm development. Many of the proteins found to be upregulated during these processes are poorly characterized from a functional standpoint. Here, we report the solution NMR structure of PA1324, a protein of unknown function identified in these studies, and provide a putative biological functional assignment based on the observed prealbumin-like fold and FAST-NMR ligand screening studies. PA1324 is postulated to be involved in the binding and transport of sugars or polysaccharides associated with the peptidoglycan matrix during biofilm formation.

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.

Alternative estimation of human exposure of single-walled carbon nanotubes using three-dimensional tissue-engineered human lung

Recent discoveries of various forms of carbon nanostructure have stimulated research on their applications and hold promise for applications in medicine and other related engineering areas. Although carbon nanotubes (CNTs) are already being produced on a massive scale, few studies have been performed which test the potential harmful effects of this new technology. The authors used a three-dimensional in vitro model of the human airway using a coculture of normal human bronchial epithelial cells and normal human fibroblasts for the health risk assessment of CNTs on the human respiratory systems. The authors used aqueous single-walled carbon nanotube (SWCNT) solution. The average length and diameter of nanotube ropes were about 500 nm and less than 10 nm, respectively. The authors measured the production of nitric oxide (NO) as an inflammatory marker and mitochondrial activity using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay as a cytotoxic response of the cell layers following exposure of different concentration of aqueous SWCNT solution. The results indicated that NO production was dramatically increased and cell viability was decreased following exposure of different concentrations of SWCNTs. Transepithelial electrical resistance (TER) across the coculture layers was measured to observe the changes in airway physiological function following exposure of different concentrations of SWCNTs. TER value was dramatically decreased following exposure of 20% SWCNT (8 microg/ml). In this study, the authors presented viable alternatives to in vivo tests to evaluate the toxicity of engineered SWCNTs. Cytotoxic/inflammatory responses and barrier function of the human lung layers following exposure of SWCNTs were observed using in vitro coculture system of airway.

Engraftment of bone marrow-derived stem cells to the lung in a model of acute respiratory infection by Pseudomonas aeruginosa

Stem cell therapy presents an attractive approach to cure cystic fibrosis (CF) lung disease. We set out to investigate the effect of epithelial damage caused by Pseudomonas aeruginosa, a pathogenic bacterium widely occurring in CF, on the engraftment of bone marrow cells in airway epithelium. Intravenous or intratracheal administration of unfractionated green fluorescent protein (GFP(+)) bone marrow cells in P. aeruginosa-infected mice resulted in none or very few GFP(+) cells detected in the lungs of the recipient mice, respectively. Only when GFP(+) bone marrow cells were purified to obtain a cell suspension enriched in progenitor cells and injected intratracheally, significant numbers of GFP(+) cells were detected. Localization of the donor cells at the level of airway epithelium was confirmed by Y-chromosome fluorescence in situ hybridization (FISH) analysis. All donor-derived Y-chromosome(+) cells were found to express cytokeratin (CK). The fractions of GFP(+) cells expressing CK were 0.34 and 0.76% for the 10(5) and 10(6) colony forming units (cfu) bacterial inoculums, respectively. When scored by Y-chromosome positivity these numbers were 0.60 and 1.12%, respectively. Our results show for the first time that tissue damage inflicted by bacteria like P. aeruginosa facilitates the airway engraftment of heterologous bone marrow-derived stem cells and their epithelial transformation.

Azithromycin maintains airway epithelial integrity during Pseudomonas aeruginosa infection

Tight junctions (TJs) play a key role in maintaining bronchial epithelial integrity, including apical-basolateral polarity and paracellular trafficking. Patients with chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) often suffer from chronic infections by the opportunistic Gram-negative bacterium Pseudomonas aeruginosa, which produces multiple virulence factors, including rhamnolipids. The macrolide antibiotic azithromycin (azm) has been shown to improve lung function in patients with CF without reducing the bacterial count within the lung. However, the mechanism of this effect is still debated. It has previously been shown that azm increased transepithelial electrical resistance (TER) in a bronchial epithelial cell line. In this study we used an air-liquid interface model of human airway epithelia and measured TER, changes in TJ expression and architecture after exposure to live P. aeruginosa PAO1, and PAO1-Deltarhl which is a PAO1 mutant lacking rhlA and rhlB, which encode key enzymes for rhamnolipid production. In addition, the cells were challenged with bacterial culture medium conditioned by these strains, purified rhamnolipids, or synthetic 3O-C(12)-HSL. Virulence factors secreted by P. aeruginosa reduced TER and caused TJ rearrangement in the bronchial epithelium, exposing the epithelium to further bacterial infiltration. Pretreatment of the bronchial epithelium with azm attenuated this effect and facilitated epithelial recovery. These data suggest that azm protects the bronchial epithelium during P. aeruginosa infection independent of antimicrobial activity, and could explain in part the beneficial results seen in clinical trials of patients with CF.

Polyethylenimine-mediated gene delivery to the lung and therapeutic applications

Nonviral gene delivery is now considered a promising alternative to viral vectors. Among nonviral gene delivery agents, polyethylenimine (PEI) has emerged as a potent candidate for gene delivery to the lung. PEI has some advantages over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. However, intracellular (mainly the nuclear membrane) and extracellular obstacles still hamper its efficiency in vitro and in vivo, depending on the route of administration and the type of PEI. Nuclear delivery has been increased by adding nuclear localization signals. To overcome nonspecific interactions with biological fluids, extracellular matrix components and nontarget cells, strategies have been developed to protect polyplexes from these interactions and to increase target specificity and gene expression. When gene delivery into airway epithelial cells of the conducting airways is necessary, aerosolization of complexes seems to be better suited to guarantee higher transgene expression in the airway epithelial cells with lower toxicity than observed with either intratracheal or intravenous administration. Aerosolization, indeed, is useful to target the alveolar epithelium and pulmonary endothelium. Proof-of-principle that PEI-mediated gene delivery has therapeutic application to some genetic and acquired lung disease is presented, using as genetic material either plasmidic DNA or small-interfering RNA, although optimization of formulation and delivery protocols and limitation of toxicity need further studies.

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.

EGF and K+ channel activity control normal and cystic fibrosis bronchial epithelia repair

Severe lesions of airway epithelia are observed in cystic fibrosis (CF) patients. The regulatory mechanisms of cell migration and proliferation processes, involved in the repair of injured epithelia, then need to be better understood. A model of mechanical wounding of non-CF (NuLi) and CF (CuFi) bronchial monolayers was employed to study the repair mechanisms. We first observed that wound repair, under paracrine and autocrine EGF control, was slower (up to 33%) in CuFi than in NuLi. Furthermore, EGF receptor (EGFR) activation, following wounding, was lower in CuFi than in NuLi monolayers. Cell proliferation and migration assays indicated a similar rate of proliferation in both cell lines but with reduced (by 25%) CuFi cell migration. In addition, cell migration experiments performed in the presence of conditioned medium, collected from NuLi and CuFi wounded bronchial monolayers, suggested a defect in EGF/EGFR signaling in CF cells. We (49) recently demonstrated coupling between the EGF response and K(+) channel function, which is crucial for EGF-stimulated alveolar repair. In CuFi cells, lower EGF/EGFR signaling was accompanied by a 40-70% reduction in K(+) currents and KvLQT1, ATP-sensitive potassium (K(ATP)), and Ca(2+)-activated K(+) (KCa3.1) channel expression. In addition, EGF-stimulated bronchial wound healing, cell migration, and proliferation were severely decreased by K(+) channel inhibitors. Finally, acute CFTR inhibition failed to reduce wound healing, EGF secretion, and K(+) channel expression in NuLi. In summary, the delay in CuFi wound healing could be due to diminished EGFR signaling coupled with lower K(+) channel function, which play a crucial role in bronchial repair.

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.