Ultrafiltration combined with size exclusion chromatography efficiently isolates extracellular vesicles from cell culture media for compositional and functional studies

Appropriate isolation methods are essential for unravelling the relative contribution of extracellular vesicles (EVs) and the EV-free secretome to homeostasis and disease. We hypothesized that ultrafiltration followed by size exclusion chromatography (UF-SEC) provides well-matched concentrates of EVs and free secreted molecules for proteomic and functional studies. Conditioned media of BEAS-2B bronchial epithelial cells were concentrated on 10 kDa centrifuge filters, followed by separation of EVs and free protein using sepharose CL-4B SEC. Alternatively, EVs were isolated by ultracentrifugation. EV recovery was estimated by bead-coupled flow cytometry and tuneable resistive pulse sensing. The proteomic composition of EV isolates and SEC protein fractions was characterized by nano LC-MS/MS. UF-SEC EVs tended to have a higher yield and EV-to-protein rate of purity than ultracentrifugation EVs. UF-SEC EVs and ultracentrifugation EVs showed similar fold-enrichments for biological pathways that were distinct from those of UF-SEC protein. Treatment of BEAS-2B cells with UF-SEC protein, but not with either type of EV isolate increased the IL-8 concentration in the media whereas EVs, but not protein induced monocyte adhesion to endothelial cells. Thus, UF-SEC is a useful alternative for ultracentrifugation and allows comparing the proteomic composition and functional effects of EVs and free secreted molecules.

Macrophage microRNA-155 promotes cardiac hypertrophy and failure

BACKGROUND

Cardiac hypertrophy and subsequent heart failure triggered by chronic hypertension represent major challenges for cardiovascular research. Beyond neurohormonal and myocyte signaling pathways, growing evidence suggests inflammatory signaling pathways as therapeutically targetable contributors to this process. We recently reported that microRNA-155 is a key mediator of cardiac inflammation and injury in infectious myocarditis. Here, we investigated the impact of microRNA-155 manipulation in hypertensive heart disease.

METHODS AND RESULTS

Genetic loss or pharmacological inhibition of the leukocyte-expressed microRNA-155 in mice markedly reduced cardiac inflammation, hypertrophy, and dysfunction on pressure overload. These alterations were macrophage dependent because in vivo cardiomyocyte-specific microRNA-155 manipulation did not affect cardiac hypertrophy or dysfunction, whereas bone marrow transplantation from wild-type mice into microRNA-155 knockout animals rescued the hypertrophic response of the cardiomyocytes and vice versa. In vitro, media from microRNA-155 knockout macrophages blocked the hypertrophic growth of stimulated cardiomyocytes, confirming that macrophages influence myocyte growth in a microRNA-155-dependent paracrine manner. These effects were at least partly mediated by the direct microRNA-155 target suppressor of cytokine signaling 1 (Socs1) because Socs1 knockdown in microRNA-155 knockout macrophages largely restored their hypertrophy-stimulating potency.

CONCLUSIONS

Our findings reveal that microRNA-155 expression in macrophages promotes cardiac inflammation, hypertrophy, and failure in response to pressure overload. These data support the causative significance of inflammatory signaling in hypertrophic heart disease and demonstrate the feasibility of therapeutic microRNA targeting of inflammation in heart failure.

MicroRNA profiling identifies microRNA-155 as an adverse mediator of cardiac injury and dysfunction during acute viral myocarditis

RATIONALE

Viral myocarditis results from an adverse immune response to cardiotropic viruses, which causes irreversible myocyte destruction and heart failure in previously healthy people. The involvement of microRNAs and their usefulness as therapeutic targets in this process are unknown.

OBJECTIVE

To identify microRNAs involved in viral myocarditis pathogenesis and susceptibility.

METHODS AND RESULTS

Cardiac microRNAs were profiled in both human myocarditis and in Coxsackievirus B3-injected mice, comparing myocarditis-susceptible with nonsusceptible mouse strains longitudinally. MicroRNA responses diverged depending on the susceptibility to myocarditis after viral infection in mice. MicroRNA-155, -146b, and -21 were consistently and strongly upregulated during acute myocarditis in both humans and susceptible mice. We found that microRNA-155 expression during myocarditis was localized primarily in infiltrating macrophages and T lymphocytes. Inhibition of microRNA-155 by a systemically delivered LNA-anti-miR attenuated cardiac infiltration by monocyte-macrophages, decreased T lymphocyte activation, and reduced myocardial damage during acute myocarditis in mice. These changes were accompanied by the derepression of the direct microRNA-155 target PU.1 in cardiac inflammatory cells. Beyond the acute phase, microRNA-155 inhibition reduced mortality and improved cardiac function during 7 weeks of follow-up.

CONCLUSIONS

Our data show that cardiac microRNA dysregulation is a characteristic of both human and mouse viral myocarditis. The inflammatory microRNA-155 is upregulated during acute myocarditis, contributes to the adverse inflammatory response to viral infection of the heart, and is a potential therapeutic target for viral myocarditis.

Serum C-reactive protein level is associated with abdominal aortic aneurysm size and may be produced by aneurysmal tissue

BACKGROUND

Abdominal aortic aneurysms (AAA) are characterized by extensive transmural inflammation and C-reactive protein (CRP) has emerged as an independent risk factor for the development of cardiovascular disease. Therefore, we evaluated a possible association between serum CRP and aneurysm dimension in patients with asymptomatic AAA. Furthermore, the possibility of CRP production by aneurysmal tissue has been examined.

METHODS AND RESULTS

Serum CRP was determined highly sensitive (hsCRP) and aneurysmal size was measured in 39 patients with AAA. The presence of CRP mRNA was assessed in the aneurysmal tissue of 16 patients. Mean (SD) hsCRP was 3.23 (2.96) mg/L. After log-transformation, hsCRP correlated significantly with aneurysmal size (r=0.477, P=0.002). When the patients were divided into 3 equally sized groups according to hsCRP level, aortic diameter increased from lowest to upper hsCRP-tertile (49 mm, 61 mm, and 67 mm, respectively; P<0.05 for 3rd versus 1st tertile). This association persisted after correction for risk factors. CRP mRNA was found in 25% of aneurysmal aortic tissues.

CONCLUSIONS

This is the first report showing that serum hsCRP is associated with aneurysmal size and that-in at least some patients-CRP may be produced by aneurysmal tissue. These data underscore the inflammatory nature of AAA formation, suggesting that serum hsCRP may serve as a marker of AAA disease and that CRP produced in vascular tissue might contribute to aneurysm formation.

C-reactive protein in peripheral arterial disease: Relation to severity of the disease and to future cardiovascular events

BACKGROUND

Serum C-reactive protein (CRP) has proven to be an independent marker of the extent of atherosclerosis in patients with coronary, cerebrovascular, and peripheral arterial disease. In this prospective observational study, we wanted to assess the relationship between serum CRP and extent of disease transversely and longitudinally in time, as well as future cardiovascular complications in patients with peripheral arterial disease (PAD). Hypothesizing that CRP not only is a marker of but also actively participates in atherogenesis, we explored the possibility of CRP production by femoral atherosclerotic plaques.

METHODS

Serum CRP was measured as highly sensitive (hsCRP) in 387 patients with PAD attending the vascular clinic of a university and 2 affiliated teaching hospitals. Serum hsCRP was related to the ankle-brachial pressure index (ABPI) as an indication of severity of disease at inclusion and at 12 months' follow-up and to future events (death and coronary, cerebral, and peripheral arterial events). In femoral plaques, the production of CRP was analyzed with reverse transcription-polymerase chain reaction, and CRP plaque localization was assessed with immunostaining on serial tissue sections with antibodies toward CRP, smooth muscle cells, T cells, and macrophages.

RESULTS

The hsCRP (average +/- SD) was 3.26 +/- 2.41 mg/L. Serum hsCRP showed a correlation with baseline and 12-month follow-up ABPI (Spearman rank correlation; P < .05 for both correlations). When the patients were divided into three equally sized groups according to baseline serum hsCRP, the ABPI at baseline and at 12 months decreased significantly from the low- to the high-hsCRP group (baseline ABPI: 0.70, 0.65, and 0.57, P < .01; 12-month follow-up ABPI: 0.78, 0.70, and 0.65, P < .01). These associations persisted after correction for conventional risk factors. Furthermore, serum hsCRP was related to the combined end point "death and/or any cardiovascular event" (log-rank test; P = .04) during a median 24-month follow-up period. Reverse transcription-polymerase chain reaction analysis showed CRP production in 4 of 14 femoral plaques. CRP was detected in all femoral plaques, but not in healthy brachial arteries. Immunoreactivity for CRP was observed in smooth muscle cells, macrophages, and T cells.

CONCLUSIONS

Serum hsCRP was related to the severity of PAD, showing a relation to future hemodynamic function and cardiovascular events in PAD patients. In addition to coronary plaques, aneurysmal aortas, and failed venous coronary bypasses, femoral plaques also produce CRP, thus illustrating that the production of CRP may represent a universal response to vascular injury and suggesting that vascular CRP may contribute to plaque development.

Human heat shock protein 60 stimulates vascular smooth muscle cell proliferation through Toll-like receptors 2 and 4

Heat shock proteins (HSPs) of endogenous and exogenous origin are suspected contributors to the initiation and aggravation of vascular pathologies like atherosclerosis and restenosis. Toll-like receptors (TLRs) 2 and 4 are well-known receptors for exogenous pathogen-associated molecular patterns and have recently been thought to play a role in HSP60-induced cellular activation. We hypothesized that human HSP60 directly stimulates venous smooth muscle cell (VSMC) proliferation through a TLR-dependent mechanism. Localization of HSP60, TLR2 and TLR4 was studied in failed venous grafts and normal venous tissue by double immunostaining. In vitro VSMCs were incubated for 48 h with recombinant human HSP60. In other experiments, VSMCs were pre-incubated for 30 min with specific anti-TLR2 and anti-TLR4 antibodies. VSMC proliferation was determined by Ki67 immunoreactivity, and mean values were compared between experimental and control groups. In addition, human embryonic kidney (HEK) cells transfected with human TLR2 or TLR4/MD-2 were exposed to HSP60 for 48 h, and proliferation was determined by using a hemocytometer. Co-localization of HSP60 and TLRs was detected in all neointimal lesions but was virtually absent in normal veins. Human HSP60 stimulated VSMC proliferation in a concentration-dependent fashion. In addition, TLR2 and TLR4 antibodies attenuated VSMC proliferation. The role of TLR-mediated stimulation of cell proliferation by HSP60 was supported by the significant increase in proliferation of transfected HEK cells. These findings provide supporting evidence for the role of HSP60 and TLR2 and TLR4 in vascular disease. Moreover, our data surpass the infection- and autoimmunity-based hypotheses of cardiovascular disease and suggest an additional HSP60-related autocrine process.

How to Count Our Microbes? The Effect of Different Quantitative Microbiome Profiling Approaches

Next-generation sequencing (NGS) has instigated the research on the role of the microbiome in health and disease. The compositional nature of such microbiome datasets makes it however challenging to identify those microbial taxa that are truly associated with an intervention or health outcome. Quantitative microbiome profiling overcomes the compositional structure of microbiome sequencing data by integrating absolute quantification of microbial abundances into the NGS data. Both cell-based methods (e.g., flow cytometry) and molecular methods (qPCR) have been used to determine the absolute microbial abundances, but to what extent different quantification methods generate similar quantitative microbiome profiles has so far not been explored. Here we compared relative microbiome profiling (without incorporation of microbial quantification) to three variations of quantitative microbiome profiling: (1) microbial cell counting using flow cytometry (QMP), (2) counting of microbial cells using flow cytometry combined with Propidium Monoazide pre-treatment of fecal samples before metagenomics DNA isolation in order to only profile the microbial composition of intact cells (QMP-PMA), and (3) molecular based quantification of the microbial load using qPCR targeting the 16S rRNA gene. Although qPCR and flow cytometry both resulted in accurate and strongly correlated results when quantifying the bacterial abundance of a mock community of bacterial cells, the two methods resulted in highly divergent quantitative microbial profiles when analyzing the microbial composition of fecal samples from 16 healthy volunteers. These differences could not be attributed to the presence of free extracellular prokaryotic DNA in the fecal samples as sample pre-treatment with Propidium Monoazide did not improve the concordance between qPCR-based and flow cytometry-based QMP. Also lack of precision of qPCR was ruled out as a major cause of the disconcordant findings, since quantification of the fecal microbial load by the highly sensitive digital droplet PCR correlated strongly with qPCR. In conclusion, quantitative microbiome profiling is an elegant approach to bypass the compositional nature of microbiome NGS data, however it is important to realize that technical sources of variability may introduce substantial additional bias depending on the quantification method being used.

Cigarette smoke extract induced exosome release is mediated by depletion of exofacial thiols and can be inhibited by thiol-antioxidants

INTRODUCTION

Airway epithelial cells have been described to release extracellular vesicles (EVs) with pathological properties when exposed to cigarette smoke extract (CSE). As CSE causes oxidative stress, we investigated whether its oxidative components are responsible for inducing EV release and whether this could be prevented using the thiol antioxidants N-acetyl-l-cysteine (NAC) or glutathione (GSH).

METHODS

BEAS-2B cells were exposed for 24h to CSE, H₂O₂, acrolein, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), bacitracin, rutin or the anti-protein disulfide isomerase (PDI) antibody clone RL90; with or without NAC or GSH. EVs in media were measured using CD63⁺CD81⁺ bead-coupled flow cytometry or tunable resistive pulse sensing (TRPS). For characterization by Western Blotting, cryo-transmission electron microscopy and TRPS, EVs were isolated using ultracentrifugation. Glutathione disulfide and GSH in cells were assessed by a GSH reductase cycling assay, and exofacial thiols using Flow cytometry.

RESULTS

CSE augmented the release of the EV subtype exosomes, which could be prevented by scavenging thiol-reactive components using NAC or GSH. Among thiol-reactive CSE components, H₂O₂ had no effect on exosome release, whereas acrolein imitated the NAC-reversible exosome induction. The exosome induction by CSE and acrolein was paralleled by depletion of cell surface thiols. Membrane impermeable thiol blocking agents, but not specific inhibitors of the exofacially located thiol-dependent enzyme PDI, stimulated exosome release.

SUMMARY/CONCLUSION

Thiol-reactive compounds like acrolein account for CSE-induced exosome release by reacting with cell surface thiols. As acrolein is produced endogenously during inflammation, it may influence exosome release not only in smokers, but also in ex-smokers with chronic obstructive pulmonary disease. NAC and GSH prevent acrolein- and CSE-induced exosome release, which may contribute to the clinical benefits of NAC treatment.

Redox-dependent thiol modifications: implications for the release of extracellular vesicles

Extracellular vesicles (EVs), including microvesicles and exosomes, are emerging as important regulators of homeostasis and pathophysiology. During pro-inflammatory and pro-oxidant conditions, EV release is induced. As EVs released under such conditions often exert pro-inflammatory and procoagulant effects, they may actively promote the pathogenesis of chronic diseases. There is evidence that thiol group-containing antioxidants can prevent EV induction by pro-inflammatory and oxidative stimuli, likely by protecting protein thiols of the EV-secreting cells from oxidation. As the redox state of protein thiols greatly impacts three-dimensional protein structure and, consequently, function, redox modifications of protein thiols may directly modulate EV release in response to changes in the cell's redox environment. In this review article, we discuss targets of redox-dependent thiol modifications that are known or expected to be involved in the regulation of EV release, namely redox-sensitive calcium channels, N-ethylmaleimide sensitive factor, protein disulfide isomerase, phospholipid flippases, actin filaments, calpains and cell surface-exposed thiols. Thiol protection is proposed as a strategy for preventing detrimental changes in EV signaling in response to inflammation and oxidative stress. Identification of the thiol-containing proteins that modulate EV release in pro-oxidant environments could provide a rationale for broad application of thiol group-containing antioxidants in chronic inflammatory diseases.

Cytomegalovirus infection aggravates atherogenesis in apoE knockout mice by both local and systemic immune activation

Since the 1970s, cytomegalovirus (CMV) infection has been associated with atherosclerotic disease. However, the exact contribution of the virus remains uncertain. In this article we describe both a direct and indirect immune-mediated effect of the virus on the disease process. Eight-week-old apolipoprotein E (apoE) knockout mice were infected with mouse CMV (MCMV) or mock injected, and they were sacrificed at 2 and 20 weeks post-injection (p.i.) to study atherosclerosis, vascular wall IFNgamma and TNFalpha expression and MCMV spread. To study plasma IFNgamma and TNFalpha levels, blood was collected at 1, 2, 4 and 6 days p.i. in addition to days of sacrifice. Plasma cytokine levels were increased after MCMV infection at early time points and decreased to mock levels at 2 and 20 weeks p.i. At 2 weeks p.i., more aortic arch samples showed local cytokine expression after MCMV infection. The number of early atherosclerotic lesions and the percentage of mice containing early lesions were increased at 2 weeks p.i., while at 20 weeks p.i., the MCMV-induced effect on atherogenesis was seen on the late lesions. In conclusion, MCMV infection induces a systemic immune response reflecting an indirect effect of MCMV infection on atherosclerosis in addition to a local aortic immune response reflecting a direct effect of the virus on the atherosclerotic process.

Impaired mitochondrial Ca2+ homeostasis in respiratory chain-deficient cells but efficient compensation of energetic disadvantage by enhanced anaerobic glycolysis due to low ATP steady state levels

Energy-producing pathways, adenine nucleotide levels, oxidative stress response and Ca(2+) homeostasis were investigated in cybrid cells incorporating two pathogenic mitochondrial DNA point mutations, 3243A>G and 3302A>G in tRNA(Leu(UUR)), as well as Rho(0) cells and compared to their parental 143B osteosarcoma cell line. All cells suffering from a severe respiratory chain deficiency were able to proliferate as fast as controls. The major defect in oxidative phosphorylation was efficiently compensated by a rise in anaerobic glycolysis, so that the total ATP production rate was preserved. This enhancement of glycolysis was enabled by a considerable decrease of cellular total adenine nucleotide pools and a concomitant shift in the AMP+ADP/ATP ratios, while the energy charge potential was still in the normal range. Further important consequences were an increased production of superoxide which, however, was neither escorted by major changes in the antioxidative defence systems nor was it leading to substantial oxidative damage. Most interestingly, the lowered mitochondrial membrane potential led to a disturbed intramitochondrial calcium homeostasis, which most likely is a major pathomechanism in mitochondrial diseases.

Serological markers of persistent C. trachomatis infections in women with tubal factor subfertility

BACKGROUND

Persistent C. trachomatis infections are assumed to increase the risk of tubal pathology. We studied whether serological markers, assumed to be associated with persistent C. trachomatis infections, could identify subfertile women at risk of tubal pathology.

METHODS

Sera of 313 subfertile women, who all underwent a laparoscopy with tubal testing to assess the grade of tubal pathology, were tested for the presence of immunoglobulin (Ig) G and IgA antibodies to C. trachomatis, IgG antibodies to chlamydia heat shock protein 60 (cHSP60) and C-reactive protein (CRP).

RESULTS

C. trachomatis IgA, cHSP60 IgG and CRP, all serological markers of persistent infections, were significantly more prevalent in women with tubal pathology as compared to those without tubal pathology. The predictive value of the currently used screening test for tubal pathology (IgG to C. trachomatis) could be significantly improved by adding the CRP test.

CONCLUSIONS

In subfertile women with tubal pathology, serological markers of persistent C. trachomatis infections are significantly more common as compared to women without tubal pathology. C. trachomatis IgG-positive subfertile women with slightly elevated (< 10 mg/l) CRP levels are at highest risk of persistent C. trachomatis infections and tubal pathology.

Gram-negative bacterial membrane vesicle release in response to the host-environment: different threats, same trick?

Bacteria are confronted with a multitude of stressors when occupying niches within the host. These stressors originate from host defense mechanisms, other bacteria during niche competition or result from physiological challenges such as nutrient limitation. To counteract these stressors, bacteria have developed a stress-induced network to mount the adaptations required for survival. These stress-induced adaptations include the release of membrane vesicles from the bacterial envelope. Membrane vesicles can provide bacteria with a plethora of immediate and ultimate benefits for coping with environmental stressors. This review addresses how membrane vesicles aid Gram-negative bacteria to cope with host-associated stress factors, focusing on vesicle biogenesis and the physiological functions. As many of the pathways, that drive vesicle biogenesis, confer we propose that shedding of membrane vesicles by Gram-negative bacteria entails an integrated part of general stress responses.

Extracellular vesicles released in response to respiratory exposures: implications for chronic disease

Extracellular vesicles (EV) are secreted signaling entities that enhance various pathological processes when released in response to cellular stresses. Respiratory exposures such as cigarette smoke and air pollution exert cellular stresses and are associated with an increased risk of several chronic diseases. The aim of this review was to examine the evidence that modifications in EV contribute to respiratory exposure-associated diseases. Publications were searched using PubMed and Google Scholar with the search terms (cigarette smoke OR tobacco smoke OR air pollution OR particulate matter) AND (extracellular vesicles OR exosomes OR microvesicles OR microparticles OR ectosomes). All original research articles were included and reviewed. Fifty articles were identified, most of which investigated the effect of respiratory exposures on EV release in vitro (25) and/or on circulating EV in human plasma (24). The majority of studies based their main observations on the relatively insensitive scatter-based flow cytometry of EV (29). EV induced by respiratory exposures were found to modulate inflammation (19), thrombosis (13), endothelial dysfunction (11), tissue remodeling (6), and angiogenesis (3). By influencing these processes, EV may play a key role in the development of cardiovascular diseases and chronic obstructive pulmonary disease and possibly lung cancer and allergic asthma. The current findings warrant additional research with improved methodologies to evaluate the contribution of respiratory exposure-induced EV to disease etiology, as well as their potential as biomarkers of exposure or risk and as novel targets for preventive or therapeutic strategies.

Viral-bacterial interactions in the respiratory tract

In the respiratory tract, viruses and bacteria can interact on multiple levels. It is well known that respiratory viruses, particularly influenza viruses, increase the susceptibility to secondary bacterial infections. Numerous mechanisms, including compromised physical and immunological barriers, and changes in the microenvironment have hereby been shown to contribute to the development of secondary bacterial infections. In contrast, our understanding of how bacteria shape a response to subsequent viral infection is still limited. There is emerging evidence that persistent infection (or colonization) of the lower respiratory tract (LRT) with potential pathogenic bacteria, as observed in diseases like chronic obstructive pulmonary disease or cystic fibrosis, modulates subsequent viral infections by increasing viral entry receptors and modulating the inflammatory response. Moreover, recent studies suggest that even healthy lungs are not, as had long been assumed, sterile. The composition of the lung microbiome may thus modulate responses to viral infections. Here we summarize the current knowledge on the co-pathogenesis between viruses and bacteria in LRT infections.

Chlamydophila pneumoniae (Chlamydia pneumoniae) accelerates the formation of complex atherosclerotic lesions in Apo E3-Leiden mice

OBJECTIVE

Atherosclerosis is an inflammatory process and is characterised by the presence of T-lymphocytes in the lesions. To study the role of Chlamydophila pneumoniae (C. pneumoniae) in this process and the effect of infection on T-cell influx, we infected Apo E3-Leiden mice with C. pneumoniae and investigated the effect on lesion development and T-cell influx in atherosclerotic lesions at different time points post infection (pi).

METHODS

Nine week old mice, fed an atherogenic diet, were either mock-infected or infected with C. pneumoniae and sacrificed at 1, 6 and 9 months pi. Longitudinal sections of the aortic arches of the mice were stained with hematoxylin-eosin for atherosclerotic lesion type and lesion area analysis, or with rabbit-anti-CD3(+) to detect the presence of T-cells in the atherosclerotic lesions. T-cell influx was expressed as number of T-lymphocytes/lesion area.

RESULTS

At 1 month pi, type 1, 2 and 3 lesions were present. At other time points pi, more complex lesion types 4, 5a and 5b were also present. Although infection did not influence the total lesion number or area, we observed an effect of C. pneumoniae infection on lesion type. Infection resulted in a significant shift in lesion formation from type 3 to type 4 (P=0.022) at 6 months pi, and from type 4 to type 5a (P=0.002) at 9 months pi. T-cells were observed at every time point pi. At 1 month pi, a significant increase in T-cell influx in the C. pneumoniae-infected atherosclerotic lesions was observed (P=0.0005).

CONCLUSION

This study shows that C. pneumoniae infection enhances the inflammatory process by increasing T-lymphocytes in the plaque and accelerates the formation of complex lesions.

An activator of protein kinase C (phorbol dibutyrate) attenuates atrial-natriuretic-factor-stimulated cyclic GMP accumulation in smooth-muscle cells

Rat thoracic aortic smooth-muscle cells (A-10; A.T.C.C. CRL 1476) displays a high density of vasopressin and atrial-natriuretic-factor (ANF) receptors and a low density of beta-adrenergic receptors. ANF stimulates cGMP (cyclic GMP) accumulation in a time- and dose-dependent fashion. Pretreatment of these cells with phorbol dibutyrate (PDBu), a known activator of protein kinase C, attenuated ANF-stimulated cGMP accumulation without affecting basal cGMP concentrations. This effect was concentration-dependent and was observed as early as 2 min after treatment. 4 alpha-Phorbol 12, 13-didecanoate (alpha PDD), which does not activate protein kinase C, did not inhibit the cGMP accumulation. PDBu pretreatment did not affect the density and affinity of ANF receptors. These data suggest that PDBu, presumably via activation of protein kinase C, might stimulate phosphorylation of a key regulatory protein in the ANF/cGMP pathway.

Chlamydia pneumoniae infection induces an unstable atherosclerotic plaque phenotype in LDL-receptor, ApoE double knockout mice

OBJECTIVES

To study whether Chlamydia pneumoniae (Cpn) infection affects atherosclerotic plaque morphology in atherogenic (LDLr/ApoE(-/-)) mice.

METHODS

In mice sacrificed 20 or 40 weeks after Cpn infection aortic arch sections were analysed for lesion and fibrous cap area and the presence of matrix metalloproteinases (MMP)-2 and -9.

RESULTS

All infected mice seroconverted, demonstrated Cpn DNA in their aortas on PCR and developed atherosclerotic plaques. Infection was not associated with changes in lesion area or type, but was associated with reduced the fibrous cap area and increased MMP-2 and -9 immunoreactivity.

CONCLUSION

These findings suggest that Cpn infection may predispose to plaque instability.

MCMV infection increases early T-lymphocyte influx in atherosclerotic lesions in apoE knockout mice

BACKGROUND

Multiple epidemiological studies have suggested that cytomegalovirus (CMV) infection is associated with atherosclerotic disease. However, conclusive proof that the virus is directly related to the progression of the disease is still lacking.

OBJECTIVES

The goal of this study was to investigate whether MCMV is able to exacerbate the atherosclerotic process in atherosclerosis-susceptible mice.

STUDY DESIGN

apoE knockout mice kept on a chow diet were sacrificed at both 2 and 20 weeks post infection (p.i.). C57Bl/6J mice fed an atherogenic diet were sacrificed at 2 weeks p.i. Lesion area, lesion composition (endothelial cells and smooth muscle cells) and inflammatory influx (T-lymphocytes and macrophages) in lesions were determined. The former one was determined by means of a microscope coupled to a computer-assisted morphometry system. The latter ones were scored after immunohistochemical staining.

RESULTS

In the chronic phase of the infection mean lesion size was significantly increased after MCMV infection in the apoE knockout mice. This increase could to a large extent be attributed to a significant increase in type V lesion area after MCMV infection. Also, a significant increase in T-lymphocyte influx was observed in the acute phase of the infection in lesions from apoE knockout mice after MCMV infection while this effect was absent in C57Bl/6J mice. After MCMV infection no increase was observed in macrophage, smooth muscle cell and endothelial cell number in lesions from both mice strains.

CONCLUSIONS

MCMV infection may exacerbate the atherosclerotic process in apoE knockout mice by means of an acute lymphocytic inflammatory response. In contrast to the MCMV induced effect in apoE knockout mice, MCMV infection did not increase the influx of T-lymphocytes in atherosclerotic lesions of C57Bl/6J mice.

Delivery of Chlamydia pneumoniae to the vessel wall aggravates atherosclerosis in LDLr-/- mice

OBJECTIVE

The role of Chlamydia pneumoniae in atherosclerosis is still debated. In this study a novel mouse model was applied to determine the direct impact of C. pneumoniae on the arterial wall and the development of atherosclerosis.

METHODS

Direct effects of C. pneumoniae on collar-induced atherosclerosis were studied after local delivery of C. pneumoniae to carotid arteries of LDL receptor-deficient (LDLr-/-) mice.

RESULTS

The presence of C. pneumoniae in the vessel wall was quantified by RT-PCR (6.2 x 10(4) copies/artery) and resulted in a 2.0-fold increase in intima/media ratios (p<0.05) and a 1.7-fold increase in stenosis (p<0.05). Immunostaining revealed a 2.98-fold (p<0.01) increased macrophage content and a tendency towards lower numbers of smooth muscle cells and collagen in lesions of infected carotid arteries. Direct delivery of another respiratory pathogen, Mycoplasma pneumoniae, to the carotids did not affect size or composition of the atherosclerotic lesions. Presence of C. pneumoniae in the carotid arteries resulted within 7 days in a marked upregulation of the expression of MCP-1 (p<0.01) and ICAM-1 as determined on mRNA and protein levels. These in vivo data were in line with data obtained with in vitro infections of macrophages and endothelial cells with C. pneumoniae.

CONCLUSIONS

We conclude that C. pneumoniae in carotid arteries leads to more pronounced atherosclerotic lesions with a more vulnerable morphology and that this model is suitable to monitor direct effects of C. pneumoniae on atherogenesis.

Murine cytomegalovirus infection directs macrophage differentiation into a pro-inflammatory immune phenotype: implications for atherogenesis

We have previously demonstrated that mouse cytomegalovirus (MCMV) aggravates atherosclerosis in apolipoprotein E knockout (apoE(-/-)) mice, most likely by enhancing both systemic and local (e.g. in the vascular wall) cytokine production. However, until now it was unclear which cell type is responsible for this enhanced pro-inflammatory cytokine production. In this study we focused on the macrophage (mPhi), which besides being an important source of such cytokines, is known to be an important player in both atherosclerosis and viral clearance. We investigated whether MCMV could induce a pro-inflammatory immune mPhi phenotype, which ultimately may contribute to the development of atherosclerosis. To this end, peritoneal exudate cells (PEC) were elicited in apoE(-/-) mice by either MCMV or thioglycolate injection, and mPhi were phenotyped at 1 week post-intraperitoneal injection. MCMV-induced peritoneal mPhi contained MCMV DNA but had limited MCMV mRNA expression, indicating latent infection. These mPhi showed increased production of interferon-gamma (IFNgamma), exclusive production of interleukin-18 (IL-18) and increased expression of major histocompatibility complex (MHC) class II, CD40, CD80 and CD86, when compared with thioglycolate-induced mPhi. From these results, we conclude that intraperitoneal injection of MCMV induces an immune-responsive exudate in which at 7 days post-infection, MCMV-infected mPhi express a pro-inflammatory immune phenotype. As such, the MCMV-induced mPhi may be an important player in aggravating atherosclerosis through systemic and/or local immune activation.

Inflammatory markers in depressed post-myocardial infarction patients

BACKGROUND

Depressive disorder in the post-myocardial infarction (MI) period has been associated with increased cardiac morbidity and mortality. Possible pathophysiological mechanisms behind this association are not clear. Major depression in physically healthy subjects has been related to immune abnormalities including increased plasma levels of interleukin-6 (IL-6), tumor necrosis factor alfa (TNF-alpha) and C-reactive protein (CRP). In patients with MI, increased inflammatory markers, such as CRP and TNF-alpha, have been associated with increased cardiovascular events. It was the aim of this study to test the hypothesis that depression in post-MI patients is associated with increased inflammation as compared to non-depressed post-MI patients.

METHODS

The cytokines IL-6 and TNF-alpha ; the soluble cytokine receptors sIL-6R, sTNF-RI and sTNF-RII; neopterin; and the inflammation-sensitive plasma proteins (ISPs) CRP and haptoglobin were assessed in a group of 57 patients with a diagnosis of depression post-MI and in a control group of 46 non-depressed post-MI patients, matched for age, gender and time elapsed since MI.

RESULTS

Cytokine, neopterin and ISP levels were not statistically different in the depressed post-MI group as compared to the non-depressed post-MI group. Several inflammatory markers were however elevated in both cohorts when compared with levels reported in healthy subjects, indicating persistent inflammation several months after MI.

CONCLUSIONS

There was no indication of increased inflammation in depressed post-MI patients as compared to non-depressed post-MI patients.

Characterization of Feces-Derived Bacterial Membrane Vesicles and the Impact of Their Origin on the Inflammatory Response

The human gastrointestinal tract harbors a diverse and complex microbiome, which interacts in a variety of ways with the host. There is compelling evidence that gut microbial dysbiosis, defined as an alteration of diversity and abundance in intestinal microbes, is an etiological factor in inflammatory bowel disease (IBD). Membrane vesicles (MVs), which are nano-sized particles released by bacteria, have been found to interact with the host and modulate the development and function of the immune system. As a result MVs have been suggested to play a critical role in both health and disease. In this study we developed a method to isolate, characterize and assess the immunoreactivity of heterogeneous populations of MVs from fecal samples (fMVs) of healthy volunteers. We successfully isolated 2*10⁹-2*10¹⁰ particles/ml from 0.5 gram of feces by using a combination of ultrafiltration and size exclusion chromatography (SEC) from 10 fecal samples. Bead-based flowcytometry in combination with tunable resistive pulse sensing (TRPS) provided a reliable method for (semi-)quantitative determination of fMVs originating from both Gram-positive and Gram-negative bacteria, while transmission electron microscopy confirmed the presence of fMVs. Real time 16s PCR on bacterial cell fractions or isolated fMVs DNA of the most common phyla (Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria) revealed differences in the relative abundance between bacteria and the fMVs. Moreover, fMVs evoke the release of TNF- by THP-1 cells in a dose-dependent matter. Also, a significant positive correlation was found between Actinobacteria/-Proteobacteria derived vesicles and the release of TNF-. It has become increasingly clear that fMVs could provide an additional layer to the definition of homeostasis or dysbiosis of the microbiota. The current study supports their potential involvement in the intestinal homeostasis or inflammatory disorders and provides putative interesting incentives for future research.

Chlamydia pneumoniae infection of brain cells: An in vitro study

Inspired by the suggested associations between neurological diseases and infections, we determined the susceptibility of brain cells to Chlamydia pneumoniae (Cpn). Murine astrocyte (C8D1A), neuronal (NB41A3) and microglial (BV-2) cell lines were inoculated with Cpn. Infection was established by immunofluorescence and real-time PCR at various time points. Productive infection was assessed by transferring medium of infected cells to a detection layer. Finally, apoptosis and necrosis post-infection was determined. Our data demonstrate that the neuronal cell line is highly sensitive to Cpn, produces viable progeny and is prone to die after infection by necrosis. Cpn tropism was similar in an astrocyte cell line, apart from the higher production of extracellular Cpn and less pronounced necrosis. In contrast, the microglial cell line is highly resistant to Cpn as the immunohistochemical signs almost completely disappeared after 24 h. Nevertheless, significant Cpn DNA amounts could be detected, suggesting Cpn persistence. Low viable progeny and hardly any necrotic microglial cells were observed. Further research is warranted to determine whether these cell types show the same sensitivity to Cpn in an in vivo setting.