Impact of heterogeneity within cultured cells on bacterial invasion: analysis of Pseudomonas aeruginosa and Salmonella enterica serovar typhi entry into MDCK cells by using a green fluorescent protein-labelled cystic fibrosis transmembrane conductance regulator receptor

Evidence for intracellular Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant cause of global morbidity and mortality. Although it is often regarded as an extracellular pathogen toward human cells, numerous investigations report its ability to survive and replicate within host cells, and additional studies demonstrate specific mechanisms enabling it to adopt an intracellular lifestyle. This ability of P. aeruginosa remains less well-investigated than that of other intracellular bacteria, although it is currently gaining attention. If intracellular bacteria are not killed after entering host cells, they may instead receive protection from immune recognition and experience reduced exposure to antibiotic therapy, among additional potential advantages shared with other facultative intracellular pathogens. For this review, we compiled studies that observe intracellular P. aeruginosa across strains, cell types, and experimental systems in vitro, as well as contextualize these findings with the few studies that report similar observations in vivo. We also seek to address key findings that drove the perception that P. aeruginosa remains extracellular in order to reconcile what is currently understood about intracellular pathogenesis and highlight open questions regarding its contribution to disease.

Effects of Hydrosalpinx on Endometrial Implantation Failures: Evaluating Salpingectomy in Women Undergoing in vitro fertilization

Hydrosalpinx is a disease characterized by the obstruction of the salpinx, with progressive accumulation in the shape of a fluid-filled sac at the distal part of the tuba uterina, and closed to the ovary. Women with hydrosalpinges have lower implantation and pregnancy rates due to a combination of mechanical and chemical factors thought to disrupt the endometrial environment. Evidence suggests that the presence of hydrosalpinx reduces the rate of pregnancy with assisted reproductive technology. The main aim of the present is review to make an overview of the possible effects of hydrosalpinx on in vitro fertilization (IVF). We conducted a literature search on the PubMed, Ovid MEDLINE, and Google Scholar data bases regarding hydrosalpinx and IVF outcomes. Hydrosalpinx probably has a direct toxic effect on sperm motility and on the embryos. In addition, the increasing liquid inside the salpinges could alter the mechanisms of endometrial receptivity. The window of endometrial receptivity is essential in the implantation of blastocysts, and it triggers multiple reactions arising from the endometrium as well as the blastocysts. Hydrosalpinx could influence the expression of homeobox A10 (HOXA10) gene, which plays an essential role in directing embryonic development and implantation. Salpingectomy restores the endometrial expression of HOXA10; therefore, it may be one mechanism by which tubal removal could result in improved implantation rates in IVF. In addition, salpingectomy does not affect the ovarian response, nor reduces the antral follicle count. Further studies are needed to establish the therapeutic value of fluid aspiration under ultrasonographic guidance, during or after oocyte retrieval, in terms of pregnancy rate and ongoing pregnancy.

Polycystins and intercellular mechanotransduction: A precise dosage of polycystin 2 is necessary for alpha-actinin reinforcement of junctions upon mechanical stimulation

Polycystins 1 and 2, which are mutated in Autosomal Polycystic Kidney Disease, are involved in mechanotransduction through various mechanisms. In renal cells, polycystins not only have an important mechanotransductive role in primary cilia but are also present in intercellular contacts but their role there remains unclear. Here, we address the hypothesis that polycystins are involved in mechanotransduction via intercellular junctions, which would be expected to have consequences on tissue organization. We focused on the role of polycystin 2, which could be involved in mechanical organization at junctions either by its channel activity or by the direct recruitment of cytoskeleton components such as the F-actin cross-linker α-actinin. After mechanical stimulation of intercellular junctions in MDCK renal epithelial cells, α-actinin is rapidly recruited but this is inhibited upon overexpression of PC2 or the D509V mutant that lacks channel activity, and is also decreased upon PC2 silencing. This suggests that a precise dosage of PC2 is necessary for an adequate mechanosensitive α-actinin recruitment at junctions. At the multicellular level, a change in PC2 expression was associated with changes in velocity in confluent epithelia and during wound healing together with a loss of orientation. This study suggests that the mechanosensitive regulation of cytoskeleton by polycystins in intercellular contacts may be important in the context of ADPKD.

Measuring activity of endocytosis-regulating factors in T-lymphocytes by flow cytometry

Elucidation of the mechanisms regulating membrane traffic of lymphocyte receptors is of great interest to manipulate the immune response, as well as for accurately delivering drugs and nanoprobes to cells. Aiming to detect and characterize regulators of endocytosis and intracellular traffic, we have modified the FACS-based endocytosis assay to measure and quantify the activity of putative endocytic regulators as EGFP chimeras. To study the activity of putative endocytosis regulators, we transfected Jurkat T-lymphocytes with EGFP-tagged constructs of the regulators to be tested. Cells were then incubated with a αCD3(APC) antibody, and were allowed to internalize the label. After acid-washing the cells, APC fluorescence was measured by flow cytometry in cells gated for EGFP(+), as well as in their EGFP(-) (transfection-resistant) counterparts that were taken as internal controls. This approach facilitated intra- and inter-assay normalization of endocytic rates/loads by comparison with the internal control. We have used this assay to test the regulatory activity of polarity kinase EMK1, and here we substantiate a role for EMK1 in the control of receptor internalization in T-lymphocytes. The method here presented gives quantitative measures of internalization, and will facilitate the development of tools to modulate endocytic rates or the intracellular fate of internalized materials.

Pseudomonas aeruginosa pili and flagella mediate distinct binding and signaling events at the apical and basolateral surface of airway epithelium

Pseudomonas aeruginosa, an important opportunistic pathogen of man, exploits numerous factors for initial attachment to the host, an event required to establish bacterial infection. In this paper, we rigorously explore the role of two major bacterial adhesins, type IV pili (Tfp) and flagella, in bacterial adherence to distinct host receptors at the apical (AP) and basolateral (BL) surfaces of polarized lung epithelial cells and induction of subsequent host signaling and pathogenic events. Using an isogenic mutant of P. aeruginosa that lacks flagella or utilizing beads coated with purified Tfp, we establish that Tfp are necessary and sufficient for maximal binding to host N-glycans at the AP surface of polarized epithelium. In contrast, experiments utilizing a P. aeruginosa isogenic mutant that lacks Tfp or using beads coated with purified flagella demonstrate that flagella are necessary and sufficient for maximal binding to heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPGs) at the BL surface of polarized epithelium. Using two different cell-free systems, we demonstrate that Tfp-coated beads show highest binding affinity to complex N-glycan chains coated onto plastic plates and preferentially aggregate with beads coated with N-glycans, but not with single sugars or HS. In contrast, flagella-coated beads bind to or aggregate preferentially with HS or HSPGs, but demonstrate little binding to N-glycans. We further show that Tfp-mediated binding to host N-glycans results in activation of phosphatidylinositol 3-kinase (PI3K)/Akt pathway and bacterial entry at the AP surface. At the BL surface, flagella-mediated binding to HS activates the epidermal growth factor receptor (EGFR), adaptor protein Shc, and PI3K/Akt, and induces bacterial entry. Remarkably, flagella-coated beads alone can activate EGFR and Shc. Together, this work provides new insights into the intricate interactions between P. aeruginosa and lung epithelium that may be potentially useful in the development of novel treatments for P. aeruginosa infections.

Pseudomonas aeruginosa-mediated damage requires distinct receptors at the apical and basolateral surfaces of the polarized epithelium

Pseudomonas aeruginosa, an important opportunistic pathogen of humans, exploits epithelial damage to establish infection. We have rigorously explored the role of N-glycoproteins and heparan sulfate proteoglycans (HSPGs) in P. aeruginosa-mediated attachment and subsequent downstream events at the apical (AP) and basolateral (BL) surfaces of polarized epithelium. We demonstrate that the N-glycan chains at the AP surface are necessary and sufficient for binding, invasion, and cytotoxicity to kidney (MDCK) and airway (Calu-3) cells grown at various states of polarization on Transwell filters. Upregulation of N-glycosylation enhanced binding, whereas pharmacologic inhibition of N-glycosylation or infection of MDCK cells defective in N-glycosylation resulted in decreased binding. In contrast, at the BL surface, the HS moiety of HSPGs mediated P. aeruginosa binding, cytotoxicity, and invasion. In incompletely polarized epithelium, HSPG abundance was increased at the AP surface, explaining its increased susceptibility to P. aeruginosa colonization and damage. Using MDCK cells grown as three-dimensional cysts as a model for epithelial organs, we show that P. aeruginosa specifically colocalized with HS-rich areas at the BL membrane but with complex N-glycans at the AP surface. Finally, P. aeruginosa bound to HS chains and N-glycans coated on plastic surfaces, showing the highest binding affinity toward isolated HS chains. Together, these findings demonstrate that P. aeruginosa recognizes distinct receptors on the AP and BL surfaces of polarized epithelium. Changes in the composition of N-glycan chains and/or in the distribution of HSPGs may explain the enhanced susceptibility of damaged epithelium to P. aeruginosa.

Cystic fibrosis transmembrane conductance regulator and caveolin-1 regulate epithelial cell internalization of Pseudomonas aeruginosa

Patients with cystic fibrosis (CF) exhibit defective innate immunity and are susceptible to chronic lung infection with Pseudomonas aeruginosa. To investigate the molecular bases for the hypersusceptibility of CF patients to P. aeruginosa, we used the IB3-1 cell line with two defective CF transmembrane conductance regulator (CFTR) genes (DeltaF508/W1282X) to generate isogenic stable, clonal lung epithelial cells expressing wild-type (WT)-CFTR with an NH(2)-terminal green fluorescent protein (GFP) tag. GFP-CFTR exhibited posttranslational modification, subcellular localization, and anion transport function typical of WT-CFTR. P. aeruginosa internalization, a component of effective innate immunity, required functional CFTR and caveolin-1, as shown by: 1) direct correlation between GFP-CFTR expression levels and P. aeruginosa internalization; 2) enhanced P. aeruginosa internalization by aminoglycoside-induced read through of the CFTR W1282X allele in IB3-1 cells; 3) decreased P. aeruginosa internalization following siRNA knockdown of GFP-CFTR or caveolin-1; and 4) spatial association of P. aeruginosa with GFP-CFTR and caveolin-1 at the cell surface. P. aeruginosa internalization also required free lateral diffusion of GFP-CFTR, allowing for bacterial coclustering with GFP-CFTR and caveolin-1 at the plasma membrane. Thus efficient initiation of innate immunity to P. aeruginosa requires formation of an epithelial "internalization platform" involving both caveolin-1 and functional, laterally mobile CFTR.

Pseudomonas aeruginosa lipopolysaccharide: a major virulence factor, initiator of inflammation and target for effective immunity

Pseudomonas aeruginosa is one of the most important bacterial pathogens encountered by immunocompromised hosts and patients with cystic fibrosis (CF), and the lipopolysaccharide (LPS) elaborated by this organism is a key factor in virulence as well as both innate and acquired host responses to infection. The molecule has a fair degree of heterogeneity in its lipid A and O-antigen structure, and elaborates two different outer-core glycoforms, of which only one is ligated to the O-antigen. A close relatedness between the chemical structures and genes encoding biosynthetic enzymes has been established, with 11 major O-antigen groups identified. The lipid A can be variably penta-, hexa- or hepta-acylated, and these isoforms have differing potencies when activating host innate immunity via binding to Toll-like receptor 4 (TLR4). The O-antigen is a major target for protective immunity as evidenced by numerous animal studies, but attempts, to date, to produce a human vaccine targeting these epitopes have not been successful. Newer strategies employing live attenuated P. aeruginosa, or heterologous attenuated bacteria expressing P. aeruginosa O-antigens are potential means to solve some of the existing problems related to making a P. aeruginosa LPS-specific vaccine. Overall, there is now a large amount of information available about the genes and enzymes needed to produce the P. aeruginosa LPS, detailed chemical structures have been determined for the major O-antigens, and significant biologic and immunologic studies have been conducted to define the role of this molecule in virulence and immunity to P. aeruginosa infection.

Influence of cystic fibrosis transmembrane conductance regulator on gene expression in response to Pseudomonas aeruginosa infection of human bronchial epithelial cells

Chronic lung infection by Pseudomonas aeruginosa causes significant morbidity in cystic fibrosis patients initiated by the failure of innate immune responses. We used microarray analysis and real-time PCR to detect transcriptional changes associated with cytokine production in isogenic bronchial epithelial cell lines with either wild-type (WT) or mutant cystic fibrosis transmembrane conductance regulator (CFTR) in response to P. aeruginosa infection. The transcription of four NF-kappaB-regulated cytokine genes was maximal in the presence of WT CFTR: the interleukin-8 (IL-8), IL-6, CXCL1, and intracellular adhesion molecule 1 (ICAM-1) genes. Analysis of protein expression in two cell lines paired for wild-type and mutant CFTR with three P. aeruginosa strains showed IL-6 and IL-8 expressions were consistently enhanced by the presence of WT CFTR in both cell lines with all three strains of P. aeruginosa, although some strains gave small IL-8 increases in cells with mutant CFTR. CXCL1 production showed consistent enhancement in cells with WT CFTR using all three bacterial strains in one cell line, whereas in the other cell line, CXCL1 showed a significant increase in cells with either WT or mutant CFTR. ICAM-1 was unchanged at the protein level in one of the cell lines but did show mild enhancement with WT CFTR in the other cell pair. Inhibitions of NF-kappaB prior to infection indicated differing degrees of dependence on NF-kappaB for production of the cytokines, contingent on the cell line. Cytokine effectors of innate immunity to P. aeruginosa were found to be positively influenced by the presence of WT CFTR, indicating a role in resistance to P. aeruginosa infection.

Novel adenoviral vectors coding for GFP-tagged wtCFTR and deltaF508-CFTR: characterization of expression and electrophysiological properties in A549 cells

E1/E3-deleted adenoviral vectors expressing an N-terminal green fluorescent protein (GFP) reporter gene fused to either wtCFTR (H5.040CMVEGFP-wtCFTR) or deltaF508-CFTR (H5.040CMVEGFP-deltaF508CFTR) were generated. To characterize the expression and activity, A549 cells were infected with vectors expressing GFP-tagged and non-tagged forms of CFTR and deltaF508CFTR. CFTR activity was assayed in cell-attached and excised patches. For H5.040CMVEGFP-wtCFTR, forskolin-dependent outward current was observed in cell-attached patches from 56 of 67 GFP-positive cells. Single-channel conductances, open probability, mean open and mean closed time values for GFP-CFTR and CFTR were not significantly different. After excision, GFP-CFTR activity required ATP and exhibited a linear I-V relationship. For H5.040CMVEGFP-deltaF508CFTR, media were supplemented with 5 mM butyrate 16 h after infection. Forskolin-dependent outward current was observed in cell-attached patches from 21 of 30 butyrate-treated GFP-positive cells and 0 of 8 GFP-positive cells without butyrate. Single-channel conductances, open probability, mean open and mean closed time values for GFP-deltaF508CFTR and deltaF508CFTR were not significantly different. However, the increase in open probability with genistein was significantly smaller for GFP-deltaF508CFTR than for deltaF508CFTR. In excised patches, GFP-deltaF508CFTR activity required ATP and exhibited a linear I-V relationship. Despite the consistent detection of GFP-CFTR and GFP-deltaF508CFTR channels in the plasma membrane by patch clamping, GFP fluorescence was observed only in intracellular regions and was not altered by butyrate. The data show that high levels of functional GFP-tagged CFTR channels can be expressed with these adenoviral vector constructs.

Characterization of an ExoS Type III translocation-resistant cell line

Pseudomonas aeruginosa ExoS is a type III-secreted type III-secreted, bifunctional protein that causes diverse effects on eukaryotic cell function. The coculture of P. aeruginosa strains expressing ExoS with HL-60 myeloid cells revealed the cell line to be resistant to the toxic effects of ExoS. Differentiation of HL-60 cells with phorbol 12-myristate 13-acetate (TPA) rendered the cell line sensitive to ExoS. To understand the cellular basis for the alteration in sensitivity, undifferentiated and TPA-differentiated HL-60 cells were compared for differences in bacterial adherence, type III secretion induction, and ExoS translocation. These comparisons found that ExoS was translocated more efficiently in TPA-differentiated HL-60 cells than in undifferentiated cells. The studies support the ability of eukaryotic cells to influence P. aeruginosa TTS at the level of membrane translocation.

Airway epithelial cell-pathogen interactions

Cystic fibrosis (CF) airway becomes colonized with only a limited number of bacterial pathogens. It is of paramount importance to establish in vitro and in vivo models to better understand bacterial-host interactions under CF-like conditions. In this article, in vitro methods suitable to study Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) adherence to and uptake by airway epithelial cells are described. Acute and chronic respiratory infection models, which have been used in CF transgenic mice and mimic human CF lung pathology, are also taken into consideration.

Role of the cystic fibrosis transmembrane conductance regulator in internalization of Pseudomonas aeruginosa by polarized respiratory epithelial cells

Pseudomonas aeruginosa is an important human pathogen, producing lung infection in individuals with cystic fibrosis (CF), patients who are ventilated and those who are neutropenic. The respiratory epithelium provides the initial barrier to infection. Pseudomonas aeruginosa can enter epithelial cells, although the mechanism of entry and the role of intracellular organisms in its life cycle are unclear. We devised a model of infection of polarized human respiratory epithelial cells with P. aeruginosa and investigated the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in adherence, uptake and IL-8 production by human respiratory epithelial cells. We found that a number of P. aeruginosa strains could invade and replicate within cells derived from a patient with CF. Intracellular bacteria did not produce host cell cytotoxicity over a period of 24 h. When these cells were transfected with wild-type CFTR, uptake of bacteria was significantly reduced and release of IL-8 following infection enhanced. We propose that internalized P. aeruginosa may play an important role in the pathogenesis of infection and that, by allowing greater internalization into epithelial cells, mutant CFTR results in an increased susceptibility of bronchial infection with this microbe.

GFP-tagged CFTR transgene is functional in the G551D cystic fibrosis mouse colon

Trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) is central to its function, with the most common mutation, deltaF508, resulting in abnormal processing and trafficking. Therefore, there is a significant need to develop tools, which enable the trafficking of CFTR to be studied in vitro and in vivo. In previous studies it has been demonstrated that fusion of the green fluorescent protein (GFP) to the N-terminus of CFTR does lead to functional expression of CFTR chloride channels in epithelial cell lines. The aim of the present study was to examine whether it is possible to express GFP-tagged CFTR as a transgene in colonic and airway epithelial cells of cystic fibrosis (CF) mice and to correct the CF defect. Using the epithelial-specific human cytokeratin promoter K18, we generated bitransgenic mice cftr(G551D/G551) K18-GFP-CFTR(+/-), designated GFP mice. Transcripts for GFP-CFTR could be detected in bitransgenic mice by use of RT-PCR techniques. Expression of GFP-CFTR protein was detected specifically in the colonic epithelium by both direct GFP fluorescence and the use of an anti-GFP antibody. Ussing chamber studies showed that the ion transport defect in colon and airways observed in cftr(G551D/G551D) mice was partially corrected in the bitransgenic animals. Thus, K18-GFP-CFTR is functionally expressed in transgenic mice, which will be a valuable tool in studies on CFTR synthesis, processing and ion transport in native epithelial tissues.

Salmonella enterica serovar typhi modulates cell surface expression of its receptor, the cystic fibrosis transmembrane conductance regulator, on the intestinal epithelium

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is an epithelial receptor mediating the translocation of Salmonella enterica serovar Typhi to the gastric submucosa. Since the level of cell surface CFTR is directly related to the efficiency of serovar Typhi translocation, the goal of this study was to measure CFTR expression by the intestinal epithelium during infection. CFTR protein initially present in the epithelial cell cytoplasm was rapidly trafficked to the plasma membrane following exposure to live serovar Typhi or bacterial extracts. CFTR-dependent bacterial uptake by epithelial cells increased (>100-fold) following CFTR redistribution. The bacterial factor which triggers CFTR redistribution is heat and protease sensitive. These data suggest that serovar Typhi induces intestinal epithelial cells to increase membrane CFTR levels, leading to enhanced bacterial ingestion and submucosal translocation. This could be a key, early step in the infectious process leading to typhoid fever.

Interaction of bacterial pathogens with polarized epithelium

Many pathogens must surmount an epithelial cell barrier in order to establish an infection. While much has been learned about the interaction of bacterial pathogens with cultured epithelial cells, the influence of cell polarity on these events has only recently been appreciated. This review outlines bacterial-host epithelial cell interactions in the context of the distinct apical and basolateral surfaces of the polarized epithelium that lines the lumens of our organs.

Transgenic cystic fibrosis mice exhibit reduced early clearance of Pseudomonas aeruginosa from the respiratory tract

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) has been proposed to be an epithelial cell receptor for Pseudomonas aeruginosa involved in bacterial internalization and clearance from the lung. We evaluated the role of CFTR in clearing P. aeruginosa from the respiratory tract using transgenic CF mice that carried either the DeltaF508 Cftr allele or an allele with a Cftr stop codon (S489X). Intranasal application achieved P. aeruginosa lung infection in inbred C57BL/6 DeltaF508 Cftr mice, whereas DeltaF508 Cftr and S489X Cftr outbred mice required tracheal application of the inoculum to establish lung infection. CF mice showed significantly less ingestion of LPS-smooth P. aeruginosa by lung cells and significantly greater bacterial lung burdens 4.5 h postinfection than C57BL/6 wild-type mice. Microscopy of infected mouse and rhesus monkey tracheas clearly demonstrated ingestion of P. aeruginosa by epithelial cells in wild-type animals, mostly around injured areas of the epithelium. Desquamating cells loaded with P. aeruginosa could also be seen in these tissues. No difference was found between CF and wild-type mice challenged with an LPS-rough mucoid isolate of P. aeruginosa lacking the CFTR ligand. Thus, transgenic CF mice exhibit decreased clearance of P. aeruginosa and increased bacterial burdens in the lung, substantiating a key role for CFTR-mediated bacterial ingestion in lung clearance of P. aeruginosa.

The role of the CFTR in susceptibility to Pseudomonas aeruginosa infections in cystic fibrosis

Recent molecular and cellular studies have shed new light on the basis for the susceptibility of cystic fibrosis (CF) patients to Pseudomonas aeruginosa infection. Changes in airway liquid composition and/or viscosity, enhanced bacterial binding to mucin and epithelial cell receptors, increased innate inflammation owing to disruptions in lipid metabolism and a role for the CFTR protein in bacterial ingestion and clearance have all been postulated. The high P. aeruginosa infection rate in CF patients can potentially be explained by the specificity of the interaction between the CFTR and P. aeruginosa.

Role of the cystic fibrosis transmembrane conductance regulator in innate immunity to Pseudomonas aeruginosa infections

Chronic Pseudomonas aeruginosa infection occurs in 75-90% of patients with cystic fibrosis (CF). It is the foremost factor in pulmonary function decline and early mortality. A connection has been made between mutant or missing CF transmembrane conductance regulator (CFTR) in lung epithelial cell membranes and a failure in innate immunity leading to initiation of P. aeruginosa infection. Epithelial cells use CFTR as a receptor for internalization of P. aeruginosa via endocytosis and subsequent removal of bacteria from the airway. In the absence of functional CFTR, this interaction does not occur, allowing for increased bacterial loads in the lungs. Binding occurs between the outer core of the bacterial lipopolysaccharide and amino acids 108-117 in the first predicted extracellular domain of CFTR. In experimentally infected mice, inhibiting CFTR-mediated endocytosis of P. aeruginosa by inclusion in the bacterial inoculum of either free bacterial lipopolysaccharide or CFTR peptide 108-117 resulted in increased bacterial counts in the lungs. CFTR is also a receptor on gastrointestinal epithelial cells for Salmonella enterica serovar Typhi, the etiologic agent of typhoid fever. There was a significant decrease in translocation of this organism to the gastrointestinal submucosa in transgenic mice that are heterozygous carriers of a mutant DeltaF508 CFTR allele, suggesting heterozygous CFTR carriers may have increased resistance to typhoid fever. The identification of CFTR as a receptor for bacterial pathogens could underlie the biology of CF lung disease and be the basis for the heterozygote advantage for carriers of mutant alleles of CFTR.