Chlamydia pneumoniae infection promotes a proliferative phenotype in the vasculature through Egr-1 activation in vitro and in vivo

Early Growth Response-1: Friend or Foe in the Heart?

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Early growth response-1 (Egr-1) plays a critical regulatory role in a range of experimental models of cardiovascular diseases. Egr-1 is an immediate-early gene and is upregulated by various stimuli including shear stress, oxygen deprivation, oxidative stress and nutrient deprivation. However, recent research suggests a new, underexplored cardioprotective side of Egr-1. The main purpose of this review is to explore and summarise the dual nature of Egr-1 in cardiovascular pathobiology.

Hijacking and Use of Host Kinases by Chlamydiae

Chlamydia species are causative agents of sexually transmitted infections, blinding trachoma, and animal infections with zoonotic potential. Being an obligate intracellular pathogen, Chlamydia relies on the host cell for its survival and development, subverting various host cell processes throughout the infection cycle. A key subset of host proteins utilized by Chlamydia include an assortment of host kinase signaling networks which are vital for many chlamydial processes including entry, nutrient acquisition, and suppression of host cell apoptosis. In this review, we summarize the recent advancements in our understanding of host kinase subversion by Chlamydia.

Bioresponsive Nanoparticles Targeted to Infectious Microenvironments for Sepsis Management

Sepsis is a life-threatening disease resulted from a dysregulated host immune response to bacterial infections, continuing to cause high morbidity and mortality worldwide. Despite discoveries of many potential therapeutic targets, effective treatments of sepsis are lacking. Here, a strategy is reported to target infectious microenvironments (IMEs) via bioresponsive nanoparticles that simultaneously eliminate bacteria and alleviate the host inflammation response, thus managing sepsis in mice. The nanoparticle is made of copolymers sensitive to pH and bacterial enzymes to self-assemble into a micelle loaded with both an antibiotic (ciprofloxacin) and an anti-inflammatory agent ((2-[(aminocarbonyl)amino]-5-(4-fluorophenyl)-3-thiophenecarboxamide). In addition, the nanoparticle is conjugated with intercellular adhesion molecule-1 antibodies to target IMEs. Nanoparticle targeting to IMEs and local cues as triggers to deliver therapeutics in on-demand manners is demonstrated using an acute lung bacterial infection mouse model. In the sepsis mouse model induced by peritonitis at a lethal dose of bacterial invasion, it is shown that concurrently targeting pathogens and excessive inflammation pathways is valuable to manage the sepsis. The study illustrates not only the development of a new delivery system but also the mechanism-based therapy of nanomedicine for infectious diseases.

The Host Cell Transcription Factor EGR1 Is Induced by Bacteria through the EGFR-ERK1/2 Pathway

The essential first step in bacterial colonization is adhesion to the host epithelial cells. The early host-responses post-bacterial adhesions are still poorly understood. Early growth response 1 (EGR1) is an early response transcriptional regulator that can be rapidly induced by various environmental stimuli. Several bacteria can induce EGR1 expression in host cells, but the involved bacterial characteristics and the underlying molecular mechanisms of this response are largely unknown. Here, we show that EGR1 can be induced in host epithelial cells by different species of bacteria independent of the adherence level, Gram-staining type and pathogenicity. However, bacterial viability and contact with host cells is necessary, indicating that an active interaction between bacteria and the host is important. Furthermore, the strongest response is observed in cells originating from the natural site of the infection, suggesting that the EGR1 induction is cell type specific. Finally, we show that EGFR–ERK1/2 and β1-integrin signaling are the main pathways used for bacteria-mediated EGR1 upregulation. In conclusion, the increase of EGR1 expression in epithelial cells is a common stress induced, cell type specific response upon host-bacteria interaction that is mediated by EGFR–ERK1/2 and β1-integrin signaling.

Construction of a highly flexible and comprehensive gene collection representing the ORFeome of the human pathogen Chlamydia pneumoniae

Background

The Gram-negative bacterium Chlamydia pneumoniae (Cpn) is the leading intracellular human pathogen responsible for respiratory infections such as pneumonia and bronchitis. Basic and applied research in pathogen biology, especially the elaboration of new mechanism-based anti-pathogen strategies, target discovery and drug development, rely heavily on the availability of the entire set of pathogen open reading frames, the ORFeome. The ORFeome of Cpn will enable genome- and proteome-wide systematic analysis of Cpn, which will improve our understanding of the molecular networks and mechanisms underlying and governing its pathogenesis.

Results

Here we report the construction of a comprehensive gene collection covering 98.5% of the 1052 predicted and verified ORFs of Cpn (Chlamydia pneumoniae strain CWL029) in Gateway® ‘entry’ vectors. Based on genomic DNA isolated from the vascular chlamydial strain CV-6, we constructed an ORFeome library that contains 869 unique Gateway® entry clones (83% coverage) and an additional 168 PCR-verified ‘pooled’ entry clones, reaching an overall coverage of ~98.5% of the predicted CWL029 ORFs. The high quality of the ORFeome library was verified by PCR-gel electrophoresis and DNA sequencing, and its functionality was demonstrated by expressing panels of recombinant proteins in Escherichia coli and by genome-wide protein interaction analysis for a test set of three Cpn virulence factors in a yeast 2-hybrid system. The ORFeome is available in different configurations of resource stocks, PCR-products, purified plasmid DNA, and living cultures of E. coli harboring the desired entry clone or pooled entry clones. All resources are available in 96-well microtiterplates.

Conclusion

This first ORFeome library for Cpn provides an essential new tool for this important pathogen. The high coverage of entry clones will enable a systems biology approach for Cpn or host–pathogen analysis. The high yield of recombinant proteins and the promising interactors for Cpn virulence factors described here demonstrate the possibilities for proteome-wide studies.

Lysophosphatidic acid induces early growth response-1 (Egr-1) protein expression via protein kinase Cδ-regulated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activation in vascular smooth muscle cells

Lysophosphatidic acid (LPA) modulates vascular cell function in vitro and in vivo via regulating the expression of specific genes. Previously, we reported that a transcriptional mechanism controls LPA-induced expression of Egr-1 in vascular smooth muscle cells. Egr-1 is a master transcription factor mediating the expression of various genes that have been implied to modulate a broad spectrum of vascular pathologies. In this study, we determined the essential intracellular signaling pathway leading to LPA-induced Egr-1 expression. Our data demonstrate that activation of ERK1/2 and JNK, but not p38 MAPK, is required for LPA-induced Egr-1 expression in smooth muscle cells. We provide the first evidence that MEK-mediated JNK activation leads to LPA-induced gene expression. JNK2 is required for Egr-1 induction. Examining the upstream kinases that mediate ERK and JNK activation, leading to Egr-1 expression, we found that LPA-induced activation of MAPKs and expression of Egr-1 are dependent on PKC activation. We observed that LPA rapidly activates PKCδ and PKCθ. Overexpression of dominant-negative PKCδ, but not dominant-negative PKCθ, diminished activation of ERK and JNK and blocked LPA-induced expression of Egr-1 mRNA and protein. We also evaluated LPA receptor involvement. Our data reveal an intracellular regulatory mechanism: LPA induction of Egr-1 expression is via LPA cognate receptor (LPA receptor 1)-dependent and PKCδ-mediated ERK and JNK activation. This study provides the first evidence that PKCδ mediates ERK and JNK activation in the LPA signaling pathway and that this pathway is required for LPA-induced gene regulation as evidenced by Egr-1 expression.

Oxidized LDL promotes the mitogenic actions of Chlamydia pneumoniae in vascular smooth muscle cells

AIMS

The atherogenic actions of Chlamydia pneumoniae (C. pneumoniae), a common respiratory pathogen, are dependent upon a high-cholesterol environment in vivo. It is possible that oxidized low-density lipoprotein (oxLDL) is responsible for promoting the atherogenic effects of C. pneumoniae through a stimulation of cell proliferation. This study determined whether oxLDL can enhance the mitogenic action of C. pneumoniae in vascular smooth muscle cells (VSMCs) and the involvement of mitogen-activated protein kinase (MAPK) pathways and heat shock protein 60 (HSP60) in these mechanisms.

METHODS AND RESULTS

Primary rabbit VSMCs were treated with live C. pneumoniae, heat-inactivated C. pneumoniae or infection medium, and subsequently incubated for up to 48 h in the presence or absence of oxLDL. Chlamydia pneumoniae infection alone stimulated cell proliferation and the addition of oxLDL significantly amplified this proliferative effect. This proliferation was accompanied by extracellular signal-regulated kinase-1 and -2 (ERK1/2) activation and an up-regulation of HSP60 expression. Changes in proliferation and HSP60 expression were attenuated by the inhibition of ERK1/2.

CONCLUSION

These results indicate a novel role for oxLDL in promoting the mitogenic actions of C. pneumoniae in the vasculature. ERK1/2 is an important factor in the stress-mediated response and HSP60 up-regulation in VSMC. These data provide mechanistic evidence that C. pneumoniae may stimulate atherogenesis.

Impact of a low-oxygen environment on the efficacy of antimicrobials against intracellular Chlamydia trachomatis

Emergence of chronic inflammation in the urogenital tract induced by Chlamydia trachomatis infection in females is a long-standing concern. To avoid the severe sequelae of C. trachomatis infection, such as pelvic inflammatory diseases (PID), ectopic pregnancies, and tubal infertility, antibiotic strategies aim to eradicate the pathogen even in asymptomatic and uncomplicated infections. Although first-line antimicrobials have proven successful for the treatment of C. trachomatis infection, treatment failures have been observed in a notable number of cases. Due to the obligate intracellular growth of C. trachomatis, reliable antimicrobial susceptibility assays have to consider environmental conditions and host cell-specific factors. Oxygen concentrations in the female urogenital tract are physiologically low and decrease further during an inflammatory process. We compared MIC testing and time-kill curves (TKC) for doxycycline, azithromycin, rifampin, and moxifloxacin under hypoxia (2% O2) and normoxia (20% O2). While low oxygen availability only moderately decreased the antichlamydial activity of azithromycin in conventional MIC testing (0.08 μg/ml versus 0.04 μg/ml; P<0.05), TKC analyses revealed profound divergences for antibiotic efficacies between the two conditions. Thus, C. trachomatis was significantly less rapidly killed by doxycycline and azithromycin under hypoxia, whereas the efficacies of moxifloxacin and rifampin remained unaffected using concentrations at therapeutic serum levels. Chemical inhibition of multidrug resistance protein 1 (MDR-1), but not multidrug resistance-associated protein 1 (MRP-1), restored doxycycline activity against intracellular C. trachomatis under hypoxia. We suggest careful consideration of tissue-specific characteristics, including oxygen availability, when testing antimicrobial activities of antibiotics against intracellular bacteria.

Possibilities for therapeutic interventions in disrupting Chlamydophila pneumoniae involvement in atherosclerosis

Strong sero-epidemiologic, pathologic, and experimental evidence suggests that Chlamydophila pneumoniae (Cpn) infection may play a causative role in the development of atherosclerosis. Cpn is an obligate intracellular gram-negative bacterium that is responsible for 10% of cases of community-acquired pneumonia. In addition to its presence in the respiratory tract, live Cpn has been found within atherosclerotic plaques. Experimental findings have established Cpn's ability to infect vascular cells and elicit important atherogenic responses. Furthermore, Cpn infection can promote atherosclerotic development in different animal models. To date however, large-scale antibiotic clinical trials have not been effective in preventing major cardiovascular events. It is becoming apparent that Cpn undergoes a persistent state of infection, which is refractory to current chlamydial antibiotics. New treatment strategies that are effective toward acute and persistent forms of Cpn infection are needed in order to effectively eradicate the bacterium within the vascular wall. Possible therapeutics targets include Cpn-specific proteins and machinery directly involved in their survival, replication and maintenance. Alternatively, selectively targeting host cell pathways and machinery required for Cpn's actions in vascular cells also represent potential treatment strategies for atherosclerosis.

Hypoxia abrogates antichlamydial properties of IFN-γ in human fallopian tube cells in vitro and ex vivo

IFN-γ has an important role in the adaptive immune response against intracellular pathogens. In urogenital tract (UGT) infections with the obligate intracellular pathogen Chlamydia trachomatis, IFN-γ-mediated control of chlamydial growth implies the JAK-STAT signaling cascades and subsequent induction of the indoleamine 2,3-dioxygenase (IDO). As oxygen concentrations in the UGT are low under physiological conditions (O(2) < 5%) and further decrease during an inflammatory process, we wondered whether antibacterial properties of IFN-γ are maintained under hypoxic conditions. Using primary cells that were isolated from human fallopian tubes and an ex vivo human fallopian tube model (HFTM), we found that even high IFN-γ concentrations (200 units/mL) were not sufficient to limit growth of C. trachomatis under hypoxia. Reduced antibacterial activity of IFN-γ under hypoxia was restricted to the urogenital serovars D and L(2), but was not observed with the ocular serovar A. Impaired effectiveness of IFN-γ on chlamydial growth under hypoxia was accompanied by reduced phosphorylation of Stat-1 on Tyr701 and diminished IDO activity. This study shows that IFN-γ effector functions on intracellular C. trachomatis depend on the environmental oxygen supply, which could explain inadequate bacterial clearance and subsequent chronic infections eventually occurring in the UGT of women.

Monocyte 15-lipoxygenase gene expression requires ERK1/2 MAPK activity

IL-13 induces profound expression of 15-lipoxygenase (15-LO) in primary human monocytes. Our studies have defined the functional IL-13R complex, association of Jaks with the receptor components, and the tyrosine phosphorylation of several Stat molecules in response to IL-13. Furthermore, we identified both p38MAPK and protein kinase Cδ as critical regulators of 15-LO expression. In this study, we report an ERK1/2-dependent signaling cascade that regulates IL-13-mediated 15-LO gene expression. We show the rapid phosphorylation/activation of ERK1/2 upon IL-13 exposure. Our results indicate that Tyk2 kinase is required for the activation of ERK1/2, which is independent of the Jak2, p38MAPK, and protein kinase Cδ pathways, suggesting bifurcating parallel regulatory pathways downstream of the receptor. To investigate the signaling mechanisms associated with the ERK1/2-dependent expression of 15-LO, we explored the involvement of transcription factors, with predicted binding sites in the 15-LO promoter, in this process including Elk1, early growth response-1 (Egr-1), and CREB. Our findings indicate that IL-13 induces Egr-1 nuclear accumulation and CREB serine phosphorylation and that both are markedly attenuated by inhibition of ERK1/2 activity. We further show that ERK1/2 activity is required for both Egr-1 and CREB DNA binding to their cognate sequences identified within the 15-LO promoter. Furthermore, by transfecting monocytes with the decoy oligodeoxyribonucleotides specific for Egr-1 and CREB, we discovered that Egr-1 and CREB are directly involved in regulating 15-LO gene expression. These studies characterize an important regulatory role for ERK1/2 in mediating IL-13-induced monocyte 15-LO expression via the transcription factors Egr-1 and CREB.

Early growth response-1 is involved in foam cell formation and is upregulated by the TLR9-MyD88-ERK1/2 pathway

Early growth response-1 (Egr-1), a zinc finger transcription factor, plays a key regulatory role in pathological cardiovascular processes including atherosclerosis. Here, we investigate whether Egr-1 expression and foam cell formation require toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88). CpG DNA and its related synthetic CpG oligodeoxynucleotides (CpG ODN) play an important role in immunity and inflammation. CpG ODN increased expression of Egr-1 and formation of foam cells in Raw264.7 cells or bone marrow-derived macrophages. Egr-1 siRNA decreased foam cell formation by CpG ODN compared to that of control siRNA. In addition, when TLR9 or MyD88 was knocked down, CpG ODN-induced Egr-1 expression was also attenuated. CpG ODN increased ERK1/2 phosphorylation. U0126, a MEK pathway inhibitor, suppressed activation of Egr-1 expression by CpG ODN. CpG ODN-induced expression of tissue factor (TF) and NGFI-A binding protein 2 (Nab2), and the expression of both genes is blocked by knockdown of TLR9 or MyD88 siRNA or MEK inhibition. These results suggest that CpG ODN activates the TLR9-MyD88-ERK1/2 pathway causing expression of Egr-1 and its target genes such as TF and Nab2, thus inducing foam cell formation.

Molecular pathogenesis of chronic Chlamydia pneumoniae infection: a brief overview

Owing to its unique host cell-dependent development cycle, Chlamydia pneumoniae occupies an intracellular niche that enables the bacterium to survive and to multiply, secluded from both the extracellular and the cytoplasmic environments. Within its separate chlamydial inclusion, it is able to genetically switch between a replicative and a persisting non-replicative state, linking the pathogen to acute as well as chronic diseases. Although its role in acute respiratory infection has been established, a potential link between chronic vascular infection with C. pneumoniae and the development of atherosclerosis remains enigmatic, in particular because chronic chlamydial infection cannot be eradicated by antibiotics. C. pneumoniae has developed numerous mechanisms to establish an adequate growth milieu involving the type III secretion-mediated release of chlamydial effector proteins that interact with cellular structures and reprogram host cell regulatory pathways. This brief overview of these pathomechanisms focuses on chronic vascular infection.

Chlamydia pneumoniae hides inside apoptotic neutrophils to silently infect and propagate in macrophages

BACKGROUND

Intracellular pathogens have developed elaborate strategies for silent infection of preferred host cells. Chlamydia pneumoniae is a common pathogen in acute infections of the respiratory tract (e.g. pneumonia) and associated with chronic lung sequelae in adults and children. Within the lung, alveolar macrophages and polymorph nuclear neutrophils (PMN) are the first line of defense against bacteria, but also preferred host phagocytes of chlamydiae.

METHODOLOGY/PRINCIPAL FINDINGS

We could show that C. pneumoniae easily infect and hide inside neutrophil granulocytes until these cells become apoptotic and are subsequently taken up by macrophages. C. pneumoniae infection of macrophages via apoptotic PMN results in enhanced replicative activity of chlamydiae when compared to direct infection of macrophages, which results in persistence of the pathogen. Inhibition of the apoptotic recognition of C. pneumoniae infected PMN using PS- masking Annexin A5 significantly lowered the transmission of chlamydial infection to macrophages. Transfer of apoptotic C. pneumoniae infected PMN to macrophages resulted in an increased TGF-ss production, whereas direct infection of macrophages with chlamydiae was characterized by an enhanced TNF-alpha response.

CONCLUSIONS/SIGNIFICANCE

Taken together, our data suggest that C. pneumoniae uses neutrophil granulocytes to be silently taken up by long-lived macrophages, which allows for efficient propagation and immune protection within the human host.

Pitavastatin suppresses mitogen activated protein kinase-mediated Erg-1 induction in human vascular smooth muscle cells

Statins have been demonstrated to elicit a broad range of cellular events resulting in an attenuation of the inflammatory response and enhanced protection to the components of the vessel wall. The present study was designed to examine the effect of pitavastatin on pathways associated with the proinflammatory gene, early growth response (Egr)-1, in human vascular smooth muscle cells. Pretreatment with pitavastatin resulted in a dose-dependent reduction in Egr-1 protein and suppressed Egr-1 mRNA expression in response to phorbol 12-myristate 13-acetate (PMA). A reduction in Egr-1 expression reduced the activation of NGFI-A binding protein (NAB)-2, an Egr-1-dependent gene. Furthermore, these events appeared to be dependent on the ability of pitavastatin to attenuate signaling cascades associated with extracellular regulated kinase (ERK) 1/2, but not p38 and c-Jun N-terminal kinase (JNK).

Chlamydia pneumoniae aggravates vein graft intimal hyperplasia in a rat model

Background

Along with angioplasty, autologus vein grafts are commonly used for artery bypass grafting in patients with advanced arterial stenosis and drug-resistant angina pectoris. Although initially a successful procedure, long-term functionality is limited due to proliferation and migration of smooth muscle cells. Like in atherosclerosis, common chronic infections caused by viruses and bacteria may contribute to this process of vein graft failure. Here we investigated the possible role of Chlamydia pneumoniae (Cpn) in the pathogenesis of venous graft failure in an experimental animal model. In 2 groups (n = 10 rats/group), an epigastric vein-to-common femoral artery interposition graft was placed. Immediately thereafter, rats were infected with Cpn (5*10⁸ IFU) or injected with control solutions. Rats were sacrificed three weeks after surgery and the grafts were harvested for morphometrical and immunohistochemical analysis.

Results

Cpn administration immediately after vein grafting resulted in a significant increase in medial cross-sectional area, wall thickness and total wall area. There were no significant differences in T-cell or macrophage influx. Likewise, although positive immunostaining for both HSP60 and CRP could be detected, no differences were found between groups. Based on the observation that the number of cells/μm² was also not altered, we conclude that Cpn infection stimulates smooth muscle cell proliferation by hereunto unknown molecular mechanisms, resulting in a significant increase in intimal hyperplasia.

Conclusion

In conclusion, in a well defined animal model we present here for the first time evidence for a role of Chlamydia pneumoniae in the process of venous graft failure.

Endothelial cells are protected against phagocyte-transmitted Chlamydophila pneumoniae infections by laminar shear stress Gueinzius: Shear stress protects from C. pneumoniae infection

The respiratory pathogen Chlamydophila pneumoniae can be detected in atherosclerotic vessels, but the mechanism of dissemination from lung to vasculature remains unknown. Disturbance of vascular shear stress is a risk factor for atherosclerosis. We investigated whether polymorphonuclear neutrophils (PMN) might serve as carriers, transmitting C. pneumoniae to endothelial cells and how this is affected by shear stress. PMN were prepared from blood and incubated with C. pneumoniae. Real-time PCR and Pathfinder staining showed that after 1h, 20% of C. pneumoniae were ingested and started to form inclusions. When infected PMN were co-incubated with HUVEC for 96h, 10% of PMN-ingested C. pneumoniae were transmitted to HUVEC as shown by PCR and confocal microscopy. Infection of HEp-2 cells with C. pneumoniae harvested from HUVEC resulted in C. pneumoniae replication and confirmed that the bacteria remained infective. Exposure to laminar shear stress in a rotating cone-and-plate apparatus did not affect the transmission of C. pneumoniae from PMN to HUVEC, but led to a 75% reduction of inclusion formation. This can explain the focal distribution of C. pneumoniae in the vasculature and links two risk factors of atherosclerosis, i.e. the lack of laminar flow and infection.

Suppression of growth factor expression and human vascular smooth muscle cell growth by small interfering RNA targeting EGR-1

Smooth muscle cell (SMC) proliferation and migration are key processes that occur in the reparative response to injury after percutaneous coronary intervention and in failed bypass grafts for the treatment of atherosclerosis. In the present study, we generated novel synthetic small interfering RNA (siRNA) molecules targeting the coding region of human early growth response-1 (EGR-1) mRNA that attenuate the expression of EGR-1 and that of fibroblast growth factor-2 (FGF-2) and granulocyte-colony stimulating factor (G-CSF). These agents suppressed SMC proliferation in a dose-dependent and non-toxic manner and blocked SMC regrowth from the wound edge following mechanical injury in vitro. In contrast, the scrambled counterpart did not inhibit SMC proliferation, EGR-1 protein expression or SMC regrowth after injury. These findings demonstrate that EGR-1 siRNA can serve as inhibitors of SMC proliferation and wound repair suggesting that these agents may potentially be useful in the control of vascular proliferative disorders.

Histone deacetylase inhibitor trichostatin a potentiates doxorubicin-induced apoptosis by up-regulating PTEN expression

BACKGROUND

The tumor suppressor gene PTEN is a major negative regulator of the PI3K/Akt cellular survival pathway. Overexpression of PTEN by adenoviral transfection increases doxorubicin-induced apoptosis. Whereas doxorubicin-induced apoptosis can be potentiated by the histone deacetylase (HDAC) inhibitor Trichostatin A (TSA), the mechanisms underlying this process remain unclear. The aim of this work was to investigate whether changes in PTEN expression are involved in TSA/doxorubicin-induced apoptosis.

METHODS

We treated 293 T cells with TSA and doxorubicin, detected apoptosis by using Hoechst 33342 staining, and examined changes of PTEN and Egr-1 expression by quantitative real-time polymerase chain reaction (PCR). Luciferase reporter assay was used to evaluate the promoter activity of PTEN and Western blot and enzyme-linked immunosorbent assay (ELISA) were used to confirm changes in the expression of PTEN. The chromatin immunoprecipitation (ChIP) assay was performed to estimate the acetylation level of PTEN promoter.

RESULTS

Doxorubicin-induced apoptosis was enhanced by TSA, whereas small interfering RNA (siRNA) targeting PTEN inhibited TSA/doxorubicin-induced apoptosis. Also, TSA promoted Egr-1 expression, which is the main transcription factor of PTEN, and this resulted in up-regulation of PTEN expression, which consequently potentiated apoptosis. Moreover, histone acetyltransferase p300 was able to synergistically activate PTEN transcription with Egr-1, implicating the role of histone acetylation in the regulation of PTEN expression.

CONCLUSIONS

TSA promoted doxorubicin-induced apoptosis through a mechanism that involved the stimulation of Egr-1 expression, acetylation of core histones at the PTEN promoter, and consequently induction of PTEN transcription. These findings provide a theoretical basis for the therapeutic application of combined treatment of TSA/doxorubicin for cancer.

Host cell responses to Chlamydia pneumoniae in gamma interferon-induced persistence overlap those of productive infection and are linked to genes involved in apoptosis, cell cycle, and metabolism

The respiratory pathogen Chlamydia (Chlamydophila) pneumoniae is associated with chronic diseases, including atherosclerosis and giant-cell arteritis, which are accompanied by the occurrence of these obligate intracellular bacteria in blood vessels. There, C. pneumoniae seems to be present in a persistent state. Persistence is characterized by modified bacterial metabolism and morphology, as well as a reversible arrest of chlamydial development. In cell culture, this persistent state can be induced by gamma interferon (IFN-gamma). To elucidate this long-term interaction between chlamydiae and their host cells, microarray screening on epithelial HeLa cells was performed. Transcription of persistently (and productively) infected cells was compared with that of mock-infected cells. Sixty-six host cell genes were regulated at 24 h and/or 96 h of IFN-gamma-induced persistence. Subsequently, a set of 17 human host cell genes related to apoptosis, cell cycle, or metabolism was identified as permanently up- or down-regulated by real-time PCR. Some of these chlamydia-dependent host cell responses were diminished or even absent in the presence of rifampin. However, other expression patterns were not altered by the inhibition of bacterial RNA polymerase, suggesting two different modes of host cell activation. Thus, in the IFN-gamma model, the persisting bacteria cause long-lasting changes in the expression of genes coding for functionally important proteins. They might be potential drug targets for the treatment of persistent C. pneumoniae infections.

Chlamydia pneumoniae stimulates the proliferation of HUVEC through the induction of VEGF by THP-1

Chlamydia pneumoniae, a gram-negative bacterium, is an important human intracellular pathogen; studies of C. pneumoniae pathogenesis have shown that the organism can infect many cell types associated with both respiratory and vascular sites, including arterial smooth muscle cells, macrophages and vascular endothelium. Recently, the recognition of atherosclerosis as an inflammatory disease in its genesis, progression and ultimate clinical manifestations has created an interesting area of vascular research. We assessed the hypothesis that growth factors from THP-1 macrophages infected with C. pneumoniae are involved in the regulation of cell proliferation in HUVEC. The induction of these factors were dependent on time of infection, as medium harvested 48 h after infection had a greater activity than media harvested at 12 or 24 h after infection. Heat-killed C. pneumoniae produced similar results to those of live bacteria. In addition, conditioned medium filtered sterile from infected macrophages induced the proliferation of HUVEC, thus demonstrating its angiogenic potential. Moreover, pretreatment of macrophages with cytochalasin D, a phagocytosis inhibitor, yielded almost comparable results, suggesting that bacterium cell-attachment is sufficient for VEGF, IL-1beta and IL-8 induction. Further studies are necessary to elucidate the biological role of chlamydial involvement in the complex and mutifactored processes of angiogenesis and possibly contribute to the development of therapeutic strategies.

Chlamydia trachomatis infection induces cleavage of the mitotic cyclin B1

The obligate intracellular pathogen Chlamydia trachomatis interferes with a number of host cell processes, including cytoskeletal organization, vesicular trafficking, and apoptosis. In this study we report that C. trachomatis-infected cells proliferate more slowly than uninfected cells, suggesting that C. trachomatis may also manipulate the eukaryotic cell cycle. We further demonstrate that C. trachomatis infection destabilizes specific cell cycle proteins involved in the G2/M transition. C. trachomatis-infected cells, compared to uninfected cells, have lower levels of cyclin-dependent kinase 1. Additionally, C. trachomatis infection induces an N-terminal truncation of the mitotic cyclin B1. Manipulation of the host cell cycle may represent a strategy used by C. trachomatis to ensure a stable environment conducive to bacterial growth and replication.

Association between seroprevalence of anti-chlamydial antibodies and long-term cardiovascular mortality in chronic hemodialysis patients

Chlamydial infection has been suspected in the pathogenesis of ischemic heart disease. However, it remains undetermined if persistent chlamydial infection is related to cardiovascular mortality in regular hemodialysis (HD) patients. We measured Chlamydia pneumoniae (Cp) antibody seropositivity in 154 HD subjects (age 59 +/- 11 years, time on HD 13 +/- 7 years, male/female = 101/53), and prospectively examined an association between Cp antibody status and cardiovascular death for 56 months of follow-up. Seropositivity for Cp IgA and IgG antibodies at the entry of the study was 50.6 and 60.8%, respectively. There was no significant difference in age, time on HD, serum albumin, C-reactive protein (CRP) and interleukin-6 (IL-6) between those positive and negative for IgA antibodies. During follow-up over 56 months, 31 patients (20.1%) expired, 16 (55.2%) of them of cardiovascular causes. Serological IgA and IgG antibody positivity did not influence mortality, while multiple Cox proportional hazards analysis revealed that diabetes, ischemic changes on electrocardiogram, log-transformed CRP and intact parathyroid hormone were independent determinants of cardiovascular death. These observations suggest that serological Cp antibody status does not affect long-term cardiovascular mortality in chronic HD patients.

Mycoplasma fermentans and TNF-beta interact to amplify immune-modulating cytokines in human lung fibroblasts

Mycoplasma can establish latent infections and are associated with arthritis, leukemia, and chronic lung disease. We developed an experimental model in which lung cells are deliberately infected with Mycoplasma fermentans. Human lung fibroblasts (HLF) were exposed to live M. fermentans and immune-modulating cytokine release was assessed with and without known inducers of cytokine production. M. fermentans increased IL-6, IL-8/CXCL8, MCP-1/CCL2, and Gro-alpha/CXCL1 production. M. fermentans interacted with TNF-beta to release more IL-6, CXCL8, and CXCL1 than predicted by the responses to either stimulus alone. The effects of live infection were recapitulated by exposure to M. fermentans-derived macrophage-activating lipopeptide-2 (MALP-2), a Toll-like receptor-2- and receptor-6-specific ligand. The synergistic effect of combined stimuli was more pronounced with prolonged incubations. Preexposure to TNF-beta sensitized the cells to subsequent MALP-2 challenge, but preexposure to MALP-2 did not alter the IL-6 response to TNF-beta. Exposure to M. fermentans or MALP-2 did not enhance nuclear localization, DNA binding, or transcriptional activity of NF-kappaB and did not modulate early NF-kappaB activation in response to TNF-beta. Application of specific inhibitors of various MAPKs suggested that p38 and JNK/stress-activated protein kinase were involved in early IL-6 release after exposure to TNF-beta and M. fermentans, respectively. The combined response to M. fermentans and TNF-beta, however, was uniquely sensitive to delayed application of SP-600125, suggesting that JNK/stress-activated protein kinase contributes to the amplification of IL-6 release. Thus M. fermentans interacts with stimuli such as TNF-beta to amplify lung cell production of immune-modulating cytokines. The mechanisms accounting for this interaction can now be dissected with the use of this in vitro model.

Chronic perivascular inoculation with Chlamydophila pneumoniae results in plaque formation in vivo

Hypercholesterolemic and normocholesterolemic rabbit models of chronic arterial Chlamydophila (Chlamydia) pneumoniae (CPN) inoculation were established and the role of both viable and inactivated bacteria was investigated in atherogenesis. A total of 29 rabbits were randomized to four groups. Groups A and B were fed a cholesterol-enriched diet, and groups C and D were fed a normal diet. Arterial segments of group A and C animals were inoculated in vivo using viable CPN chronically using repeated perivascular applications. Contralateral arteries were treated using heat-inactivated CPN. Group B and D animals were treated with repeated perivascular injections of bacterial lipopolysaccharide (LPS) and saline (control). Additional hypercholesterolemic rabbits were treated by repeated injections using viable and inactivated CPN, each controlled by saline injections. To compare the effects of this chronic inoculation model, additional animals received single injections of either viable CPN, inactivated CPN, LPS, or saline. Vascular tissues (n=162 treated arteries of 29 rabbits) were analyzed using morphometry at histology. CPN was detected by fluorescence-immunohistochemistry and nested polymerase chain reaction. Only in hypercholesterolemic, but not in normocholesterolemic rabbits, chronic perivascular infection of all bacterial components, viable and heat-inactivated CPN, as well as LPS resulted in a significant increase in atheromatous lesion formation (lesion area index: 0.23+/-0.08, 0.25+/-0.09, and 0.15+/-0.05) when compared to controls (lesion area index 0.01+/-0.01, P=0.002). CPN persisted in atheromatous lesions and vascular tissues. Single perivascular infection using CPN or inactivated CPN was not able to induce lesion formation (lesion area index: 0.03+/-0.03, 0.03+/-0.02 vs 0.03+/-0.02 after single saline inoculation, P=0.965). In conclusion, chronic vascular infection with CPN or CPN components acts as a cofactor requiring other major atherogenic stimuli, rather than as a causative agent.

Early growth response-1 in cardiovascular pathobiology

The immediate-early gene product and zinc finger transcription factor early growth response (Egr)-1 plays a key master regulatory role in multiple cardiovascular pathological processes. This article reviews the amazing recent evidence implicating Egr-1 in atherosclerosis, intimal thickening after acute vascular injury, ischemic pathology, angiogenesis, allograft rejection, and cardiac hypertrophy.