Chlamydia pneumoniae affect surfactant trafficking and secretion due to changes of type II cell cytoskeleton

Stimulation of surfactant exocytosis in primary alveolar type II cells by A. fumigatus

Aspergillus fumigatus is an opportunistic fungal pathogen with small airborne spores (conidia) that may escape clearance by upper airways and directly impact the alveolar epithelium. Consequently, innate alveolar defense mechanisms are being activated, including professional phagocytosis by alveolar macrophages, recruitment of circulating neutrophils and probably enhanced secretion of pulmonary surfactant by the alveolar type II (AT II) cells. However, no data are available in support of the latter hypothesis. We therefore used a coculture model of GFP-Aspergillus conidia with primary rat AT II cells and studied fungal growth, cellular Ca2+ homeostasis, and pulmonary surfactant exocytosis by live cell video microscopy. We observed all stages of fungal development, including reversible attachment, binding and internalization of conidia as well as conidial swelling, formation of germ tubes and outgrowth of hyphae. In contrast to resting conidia, which did not provoke immediate cellular effects, metabolically active conidia, fungal cellular extracts (CE) and fungal culture filtrates (CF) prepared from swollen conidia caused a Ca2+-independent exocytosis. Ca2+ signals of greatly varying delays, durations and amplitudes were observed by applying CE or CF obtained from hyphae of A. fumigatus, suggesting compounds secreted by filamentous A. fumigatus that severely interfere with AT II cell Ca2+ homeostasis. The mechanisms underlying the stimulatory effects, with respect to exocytosis and Ca2+ signaling, are unclear and need to be identified.

Impact of micro-environmental changes on respiratory tract infections with intracellular bacteria

Community-acquired pneumonia is caused by intra- and extracellular bacteria, with some of these bacteria also being linked to the pathogenesis of chronic lung diseases, including asthma and chronic obstructive pulmonary disease. Chlamydia pneumoniae is an obligate intracellular pathogen that is highly sensitive to micro-environmental conditions controlling both pathogen growth and host immune responses. The availability of nutrients, as well as changes in oxygen, pH and interferon-γ levels, have been shown to directly influence the chlamydial life cycle and clearance. Although the lung has been traditionally regarded as a sterile environment, sequencing approaches have enabled the identification of a large number of bacteria in healthy and diseased lungs. The influence of the lung microbiota on respiratory infections has not been extensively studied so far and data on chlamydial infections are currently unavailable. In the present study, we speculate on how lung microbiota might interfere with acute and chronic infections by focusing exemplarily on the obligate intracellular C. pneumoniae. Furthermore, we consider changes in the gut microbiota as an additional player in the control of lung infections, especially in view the increasing evidence suggesting the involvement of the gut microbiota in various immunological processes throughout the human body.

ABC-cassette transporter 1 (ABCA1) expression in epithelial cells in Chlamydia pneumoniae infection

ATP-binding cassette transporter A1 (ABCA1) mediates reverse cholesterol transport and innate immunity response in different cell types. We have investigated the regulation of ABCA1 expression in response to intracellular Chlamydia pneumoniae infection in A549 epithelial lung carcinoma cells. C. pneumoniae infection decreased ABCA1 expression in A549 cells, and the activity of the ABCA1 promoter was decreased. The decreased promoter activity was dependent on its E-box and GnT-box elements of the promoter. Chlamydial growth was decreased in ABCA1-silenced epithelial lung carcinoma cells. These data indicate an important role for ABCA1 in intracellular bacterial infection.

Eukaryotic protein recruitment into the Chlamydia inclusion: implications for survival and growth

Chlamydia trachomatis (Ct) is an obligate intracellular human pathogen that multiplies within a parasitophorous vacuole called an inclusion. We report that the location of several host-cell proteins present in the cytosol, the nucleus, and membranes was altered during Ct development. The acyl-CoA synthetase enzyme ACSL3 and the soluble acyl-CoA binding protein ACBD6 were mobilized from organelle membranes and the nucleus, respectively, into the lumen of the inclusion. The nuclear protein ZNF23, a pro-apoptosis factor, was also translocated into the inclusion lumen. ZNF23, among other proteins, might be targeted by Ct to inhibit host cell apoptosis, thereby enabling bacterial survival. In contrast, the acyl-CoA:lysophosphatidylcholine acyltransferase LPCAT1, an endoplasmic reticulum membrane protein, was recruited to the inclusion membrane. The coordinated action of ACBD6, ACSL3 and LPCAT1 likely supports remodeling and scavenging of host lipids into bacterial-specific moieties essential to Ct growth. To our knowledge, these are the first identified host proteins known to be intercepted and translocated into the inclusion.

Paclitaxel tumor-priming enhances siRNA delivery and transfection in 3-dimensional tumor cultures

The clinical development of siRNA cancer therapeutics is limited by the poor interstitial transport and inefficient transfection in solid tumors. We have shown that paclitaxel pretreatment, by inducing apoptosis, causes expansion of the interstitial space and thereby improves nanoparticle delivery and transport in tumor interstitium (referred to as paclitaxel tumor priming) and efficacy of nanomedicines in tumor-bearing animals. The present study evaluated whether paclitaxel tumor priming improves the delivery and transfection of siRNA in 2- and 3-dimensional cultures of human oropharyngeal carcinoma FaDu cells. We used the fluorescent siGLO and confocal microcopy to monitor transport, and used survivin siRNA and immunostaining and immunoblotting to monitor transfection. Survivin is a chemoresistance gene/protein, inducible by chemotherapy. siRNA was loaded in cationic liposomes. The results showed that pretreatment with 50-200 nM paclitaxel (24 or 48 h before siRNA) enhanced the total uptake of siGLO into monolayers (∼15%, p < 0.05), and the depth of penetration into 3-dimensional spheroids and tumor fragment histocultures (2.1- to 2.5-times greater area under the penetration-depth curve). In both monolayer cells and histocultures, paclitaxel pretreatment induced survivin upregulation (p < 0.05). Survivin siRNA alone decreased the survivin levels in a dose-dependent manner, and applying survivin siRNA after paclitaxel pretreatment completely abolished the paclitaxel-induced survivin increases. These findings indicate that paclitaxel tumor priming did not compromise the siRNA functionality. In summary, paclitaxel tumor priming improved the penetration, transfection and functionality of siRNA in tumors, thus offering a promising and practical means to develop chemo-siRNA cancer gene therapy.

Amantadine inhibits platelet-activating factor induced clathrin-mediated endocytosis in human neutrophils

Receptor signaling is integral for adhesion, emigration, phagocytosis, and reactive oxygen species production in polymorphonuclear neutrophils (PMNs). Priming is an important part of PMN emigration, but it can also lead to PMN-mediated organ injury in the host. Platelet-activating factor (PAF) primes PMNs through activation of a specific G protein-coupled receptor. We hypothesize that PAF priming of PMNs requires clathrin-mediated endocytosis (CME) of the PAF receptor (PAFr), and, therefore, amantadine, known to inhibit CME, significantly antagonizes PAF signaling. PMNs were isolated by standard techniques to >98% purity and tested for viability. Amantadine (1 mM) significantly inhibited the PAF-mediated changes in the cellular distribution of clathrin and the physical colocalization [fluorescence resonance energy transfer positive (FRET+)] of early endosome antigen-1 and Rab5a, known components of CME and similar to hypertonic saline, a known inhibitor of CME. Furthermore, amantadine had no effect on the PAF-induced cytosolic calcium flux; however, phosphorylation of p38 MAPK was significantly decreased. Amantadine inhibited PAF-mediated changes in PMN physiology, including priming of the NADPH oxidase and shape change with lesser inhibition of increases in CD11b surface expression and elastase release. Furthermore, rimantadine, an amantadine analog, was a more potent inhibitor of PAF priming of the N-formyl-methionyl-leucyl-phenylalanine-activated oxidase. PAF priming of PMNs requires clathrin-mediated endocytosis that is inhibited when PMNs are pretreated with either amantadine or rimantadine. Thus, amantadine and rimantadine have the potential to ameliorate PMN-mediated tissue damage in humans.

Perfluorocarbons decrease Chlamydophila pneumoniae-mediated inflammatory responses of rat type II pneumocytes in vitro

Chlamydophila pneumoniae alter the expression of Toll-like receptor (TLR) 4 in alveolar type II (ATII)-cells. Subsequently nuclear factor kappaB (NF-kappaB) is activated and tumor necrosis factor-alpha (TNF-alpha) and macrophage inflammatory protein 2 (MIP-2) are produced. Perfluorocarbons (PFC) are beneficial in animals with bacterial pneumonia and reduce production of TNF-alpha. Using isolated ATII-cells, it was studied whether PFC prevent C. pneumoniae-induced TNF-alpha and MIP-2 release and what the underlying pathway is. PF5080 preincubation prevented C. pneumoniae-induced secretion of TNF-alpha (43 +/- 10 versus 661 +/- 41 pg/mL) and MIP-2 (573 +/- 41 versus 4786 +/- 502 pg/mL). The C. pneumoniae-induced 2.2-fold increase of TNF-alpha Receptor 1 expression was reduced by PF5080. C. pneumoniae reduced cytoplasmatic IkappaBalpha (3.7 +/- 0.3 versus 14 +/- 1) and increased NF-kappaB p65 (31 +/- 7.5 versus 3.6 +/- 1.1) compared with control. PF5080 prevented NF-kappaB activation. TLR4 expression was 1.5-fold higher after C. pneumoniae incubation, but remained at control levels after PF5080 pretreatment. After 24 h of C. pneumoniae incubation, in 88 +/- 6% of cells bacteria were found in the perinuclear region and in 50% of these cells bacteria adhered to cellular surface. After PF5080 preincubation, C. pneumoniae were in 32 +/- 4% attached to and in 5 +/- 1% internalized in ATII-cells. Since PF5080 was found in ATII-cell membranes, PF5080 effect could be explained by an alteration of the cellular membrane, preventing activation of the inflammatory cascade.

Chlamydophila pneumoniae induces expression of toll-like receptor 4 and release of TNF-alpha and MIP-2 via an NF-kappaB pathway in rat type II pneumocytes

Background

The role of alveolar type II cells in the regulation of innate and adaptive immunity is unclear. Toll-like receptors (TLRs) have been implicated in host defense. The purpose of the present study was to investigate whether Chlamydophila pneumoniae (I) alters the expression of TLR2 and/orTLR4 in type II cells in a (II) Rho-GTPase- and (III) NF-κB-dependent pathway, subsequently (IV) leading to the production of (IV) pro-inflammatory TNF-α and MIP-2.

Methods

Isolated rat type II pneumocytes were incubated with C. pneumoniae after pre-treatment with calcium chelator BAPTA-AM, inhibitors of NF-κB (parthenolide, SN50) or with a specific inhibitor of the Rho-GTPase (mevastatin). TLR2 and TLR4 mRNA expressions were analyzed by PCR. Activation of TLR4, Rac1, RhoA protein and NF-κB was determined by Western blotting and confocal laser scan microscopy (CLSM) and TNF-α and MIP-2 release by ELISA.

Results

Type II cells constitutively expressed TLR4 and TLR2 mRNA. A prominent induction of TLR4 but not TLR2 mRNA was detected after 2 hours of incubation with C. pneumoniae. The TLR4 protein expression reached a peak at 30 min, began to decrease within 1–2 hours and peaked again at 3 hours. Incubation of cells with heat-inactivated bacteria (56°C for 30 min) significantly reduced the TLR4 expression. Treated bacteria with polymyxin B (2 μg/ml) did not alter TLR4 expression. C. pneumoniae-induced NF-κB activity was blocked by TLR4 blocking antibodies. TLR4 mRNA and protein expression were inhibited in the presence of BAPTA-AM, SN50 or parthenolide. TNF-α and MIP-2 release was increased in type II cells in response to C. pneumoniae, whereas BAPTA-AM, SN50 or parthenolide decreased the C. pneumoniae-induced TNF-α and MIP-2 release. Mevastatin inhibited C. pneumoniae-mediated Rac1, RhoA and TLR4 expression.

Conclusion

The TLR4 protein expression in rat type II cells is likely to be mediated by a heat-sensitive C. pneumoniae protein that induces a fast Ca²⁺-mediated NF-κB activity, necessary for maintenance of TLR4 expression and TNF-α and MIP-2 release through possibly Rac and Rho protein-dependent mechanism. These results indicate that type II pneumocytes play an important role in the innate pulmonary immune system and in inflammatory response mechanism of the alveolus.

Contact of Chlamydophila pneumoniae with type II cell triggers activation of calcium-mediated NF-κB pathway

Nuclear factor-kappa B (NF-kappa B) plays an important role in inflammation, proliferation and regulation of apoptosis. The purpose of the present study on type II cells was to investigate whether Chlamydophila pneumoniae contact induces (I) a Ca2+ release, that (II) disrupts F-actin/beta-tubulin cytoskeletal association with NF-kappa B/I kappa B alpha, leading to (III) a subsequent NF-kappa B activation. Incubation of rat type II pneumocytes with C. pneumoniae caused an intracellular calcium release within seconds. Confocal laser scanning microscopy (CLSM) revealed that bacterial contact with cell surface leads to a disappearance of the microvilli and disturbs the co-localization between F-actin and NF-kappa B (p65). Using semi-quantitative CLSM, we show that at 10-30 min I kappa B alpha was decreased and p65 or p50 was simultaneously translocated from cytoplasm to the nucleus, resulting in a 19-fold and 17-fold increase versus control cells. During this time no bacteria were internalized into type II cells. The pre-treatment of cells with BAPTA-AM inhibited C. pneumoniae-mediated calcium release. BAPTA-AM or SN50 prevented the C. pneumoniae-induced changes in F-actin cytoskeleton and inhibited NF-kappa B activation. Paclitaxel reduced C. pneumoniae-mediated changes of beta-tubulin cytoskeleton and activation of NF-kappa B. These results suggest that calcium-mediated cytoskeleton reorganization is involved in C. pneumoniae-induced NF-kappa B activation in type II cells.

Alveolar epithelial cells type II are major target cells for C. pneumoniae in chronic but not in acute respiratory infection

Pulmonary presence of Chlamydia pneumoniae is associated with acute and chronic infections. We show that unapparent chlamydial infection in four out of 31 chronic obstructive pulmonary disease (COPD) patients (12.9%) is characterized by a significant increase in infected alveolar epithelial cells type II (18.2 +/- 3.5% vs. 2.3 +/- 0.9; IHC/ISH) compared to a newly established model of acute chlamydial infection (ACIM) in vital lung specimens from pulmonary lobectomy. Expression of cHSP60 demonstrated pathogen viability and virulence in the ACIM. We conclude that target cells differ in acute and chronic chlamydial infection and suggest the ACIM as a novel tool to analyze the host-pathogen-interactions in acute respiratory infections.