Borrelia burgdorferi infection induces long-term memory-like responses in macrophages with tissue-wide consequences in the heart

Lyme carditis is an extracutaneous manifestation of Lyme disease characterized by episodes of atrioventricular block of varying degrees and additional, less reported cardiomyopathies. The molecular changes associated with the response to Borrelia burgdorferi over the course of infection are poorly understood. Here, we identify broad transcriptomic and proteomic changes in the heart during infection that reveal a profound down-regulation of mitochondrial components. We also describe the long-term functional modulation of macrophages exposed to live bacteria, characterized by an augmented glycolytic output, increased spirochetal binding and internalization, and reduced inflammatory responses. In vitro, glycolysis inhibition reduces the production of tumor necrosis factor (TNF) by memory macrophages, whereas in vivo, it produces the reversion of the memory phenotype, the recovery of tissue mitochondrial components, and decreased inflammation and spirochetal burdens. These results show that B. burgdorferi induces long-term, memory-like responses in macrophages with tissue-wide consequences that are amenable to be manipulated in vivo.

Lyme carditis is a manifestation of Lyme disease characterized by episodes of atrioventricular block and additional cardiomyopathies. This study describes the proteomic and transcriptomic changes in the heart upon infection with Borrelia burgdorferi, and identifies innate immune memory hallmarks specific to the response to the spirochete that are amenable to therapeutic manipulation.

Severity and properties of cardiac damage caused by Streptococcus pneumoniae are strain dependent

Streptococcus pneumoniae is an opportunistic Gram-positive pathogen that can cause invasive disease. Recent studies have shown that S. pneumoniae is able to invade the myocardium and kill cardiomyocytes, with one-in-five adults hospitalized for pneumococcal pneumonia having a pneumonia-associated adverse cardiac event. Furthermore, clinical reports have shown up to a 10-year increased risk of adverse cardiac events in patients formerly hospitalized for pneumococcal bacteremia. In this study, we investigated the ability of nine S. pneumoniae clinical isolates, representing eight unique serotypes, to cause cardiac damage in a mouse model of invasive disease. Following intraperitoneal challenge of C57BL/6 mice, four of these strains (D39, WU2, TIGR4, and 6A-10) caused high-grade bacteremia, while CDC7F:2617-97 and AMQ16 caused mid- and low-grade bacteremia, respectively. Three strains did not cause any discernible disease. Of note, only the strains capable of high-grade bacteremia caused cardiac damage, as inferred by serum levels of cardiac troponin-I. This link between bacteremia and heart damage was further corroborated by Hematoxylin & Eosin and Trichrome staining which showed cardiac cytotoxicity only in D39, WU2, TIGR4, and 6A-10 infected mice. Finally, hearts infected with these strains showed varying histopathological characteristics, such as differential lesion formation and myocytolysis, suggesting that the mechanism of heart damage varied between strains.

Endocytosis‒Mediated Invasion and Pathogenicity of Streptococcus agalactiae in Rat Cardiomyocyte (H9C2)

Streptococcus agalactiae infection causes high mortality in cardiovascular disease (CVD) patients, especially in case of setting prosthetic valve during cardiac surgery. However, the pathogenesis mechanism of S. agalactiae associate with CVD has not been well studied. Here, we have demonstrated the pathogenicity of S. agalactiae in rat cardiomyocytes (H9C2). Interestingly, both live and dead cells of S. agalactiae were uptaken by H9C2 cells. To further dissect the process of S. agalactiae internalization, we chemically inhibited discrete parts of cellular uptake system in H9C2 cells using genistein, chlorpromazine, nocodazole and cytochalasin B. Chemical inhibition of microtubule and actin formation by nocodazole and cytochalasin B impaired S. agalactiae internalization into H9C2 cells. Consistently, reverse‒ transcription PCR (RT‒PCR) and quantitative real time‒PCR (RT-qPCR) analyses also detected higher levels of transcripts for cytoskeleton forming genes, Acta1 and Tubb5 in S. agalactiae‒infected H9C2 cells, suggesting the requirement of functional cytoskeleton in pathogenesis. Host survival assay demonstrated that S. agalactiae internalization induced cytotoxicity in H9C2 cells. S. agalactiae cells grown with benzyl penicillin reduced its ability to internalize and induce cytotoxicity in H9C2 cells, which could be attributed with the removal of surface lipoteichoic acid (LTA) from S. agalactiae. Further, the LTA extracted from S. agalactiae also exhibited dose‒dependent cytotoxicity in H9C2 cells. Taken together, our data suggest that S. agalactiae cells internalized H9C2 cells through energy‒dependent endocytic processes and the LTA of S. agalactiae play major role in host cell internalization and cytotoxicity induction.

Identification and characterization of a dysfunctional cardiac myocyte phenotype: role of bacteria, Toll-like receptors, and endothelin

Cardiac myocyte dysfunction is clearly identified as underlying the acute heart failure associated with bacterial infection, as well as the chronic syndrome following cardiac damage, but the mechanisms leading to dysfunction in each case are not fully established. It is thought that local hormones such as endothelin 1 (ET-1) can increase the risk of heart failure in acute or chronic conditions. In the current study, we characterize myocytes as populations and identify a novel phenotype of the ventricular cardiac myocyte that does not contract appropriately on electrical stimulation. The noncontractile cardiac myocytes were viable and had normal calcium transients. The proportion of noncontractile cardiac myocytes was increased by bacteria (gram-positive Staphylococcus aureus or gram-negative Escherichia coli). Using selective ligands or myocytes from genetically modified mice, we established that the effects of S. aureus were mediated by Toll-like receptor 2/6 and of E. coli by Toll-like receptor 4. The transition to the noncontractile phenotype was strongly inhibited by ETA antagonism but unaffected by inhibition of NOS, suggesting that ET-1 and not NO mediates this phenomenon. These results are the first to describe the characteristics of this noncontractile phenotype and the mechanisms of its induction by bacteria. Description of the myocyte population, instead of effects only on individual cells, will be more relevant to the prediction of the depression of cardiac function.

Persistent Chlamydia pneumoniae infection of cardiomyocytes is correlated with fatal myocardial infarction

Acute myocardial infarction (AMI) associated with unfavorable prognosis is likely to be the consequence of a diffuse active chronic inflammatory process that destabilizes the whole coronary tree and myocardium, suggesting a possible common causal agent underlying both conditions. The main objective of this study was to investigate whether Chlamydia pneumoniae (CP) infection occurred beyond the coronary plaques, namely in the myocardium of individuals who died of AMI. The presence of CP cell wall antigen (OMP-2) and CP-HSP60 was investigated in the myocardium and coronary plaques of 10 AMI and 10 age-matched control patients by immunohistochemistry, electron microscopy, and molecular biology. OMP-2 antigens were found in the unaffected myocardium of 9 of 10 AMI patients. Conversely, only 1 of 10 control patients exhibited a positive staining for CP. Moreover, OMP-2 and CP-HSP60 were detected in the whole coronary tree. CP presence was strongly associated with a T-cell inflammatory infiltrate. Our results suggest that CP may underlie both coronary and myocardial vulnerabilities in patients who died of AMI and corroborate the notion that CP may act by reducing cardiac reserves, thus worsening the ischemic burden of myocardium.

Role of mitogen-activated protein kinase kinase in Porphyromonas gingivalis-induced myocardial cell hypertrophy and apoptosis

Secreted factors present in the medium following growth of the periodontal pathogen Porphyromonas gingivalis cause increased cardiomyocyte hypertrophy and apoptosis, whereas secreted factors from Actinobacillus actinomycetemcomitans and Prevotella intermedia have no such effects. The purpose of this study was to clarify the role of mitogen-activated protein kinase (MAPK)/extracellular-regulated protein kinase (ERK) pathways in P. gingivalis medium-induced H9c2 myocardial cell hypertrophy and apoptosis. Cellular morphology, DNA fragmentation, nuclear condensation, total mitogen-activated protein kinase/extracellular-regulated protein kinase-1 (ERK-1), total ERK-1 protein, and phosphorylated ERK-1 protein products in cultured H9c2 myocardial cells were measured by actin immunofluorescence, agarose gel electrophoresis, nuclear condensation, and western blotting following stimulation with P. gingivalis spent growth medium or pre-administration of U0126, a potent MEK-1/2 inhibitor. Components of P. gingivalis spent culture medium not only resulted in increased total MEK-1 and ERK-1 protein products, but also caused increased cellular size, DNA fragmentation, and nuclear condensation in H9c2 cells. These three parameters, and the phosphorylated ERK-1 protein products of H9c2 cells treated with P. gingivalis medium, were all significantly reduced after pre-administration of U0126. The results suggest that P. gingivalis-secreted factors may initiate MEK/ERK signal pathways and lead to myocardial cell hypertrophy and apoptosis.

Porphyromonas gingivalis-induced cellular hypertrophy and MMP-9 activity via different signaling pathways in H9c2 cardiomyoblast cells

BACKGROUND

Little is known about the pathogenesis of cardiomyocyte hypertrophy caused by periodontitis pathogens. The purpose of this study was to determine the effect of the periodontal pathogen Porphyromonas gingivalis on cardiomyocyte hypertrophy.

METHODS

Matrix metalloproteinase (MMP)-2 and MMP-9 activities and cellular morphology were measured by gelatin zymography and immunofluorescence after P. gingivalis-medium treatment with or without SB203580 (p38 mitogen-activated protein kinase cascade [p38] inhibitor), U0126 (mitogen-activated protein kinase kinase [MAPKK] inhibitor), LY294002 (phosphoinositide 3-kinase [PI3K] inhibitor), cyclosporin A (CsA; calcineurin inhibitor), SP600125 (c-Jun N-terminal kinase [JNK] inhibitor), proinflammatory interleukin (IL)-1, or anti-inflammatory IL-10 in cultured cardiomyoblast H9c2 cells.

RESULTS

P. gingivalis medium increased MMP-9 activities and cellular sizes (+87%) of H9c2 cells, whereas Actinobacillus actinomycetemcomitans medium and Prevotella intermedia medium had no effects. The increased activity of MMP-9 treated with P. gingivalis medium was not mediated through p38, extracellular-regulated kinase (ERK), PI3K, calcineurin, and JNK signaling pathways and was not inhibited by IL-10. However, the hypertrophy of H9c2 cells induced with P. gingivalis medium was reduced by administration of SB203580 (-37%), U0126 (-35%), LY294002 (-49%), CsA (-49%), and SP600125 (-24%).

CONCLUSIONS

Our findings suggest that P. gingivalis medium elevated MMP-9 activity and induced cardiomyoblast hypertrophy. However, P. gingivalis-induced H9c2 cell hypertrophy was mediated through p38, ERK, PI3K, calcineurin, and JNK signaling pathways, which are in a totally different regulatory pathway from P. gingivalis-elevated MMP-9 activity. These findings provide evidence that P. gingivalis infection activated multiple factors via different pathways to induce the development of hypertrophy of H9c2 cardiomyoblast cells.

Role of calcineurin in Porphyromonas gingivalis-induced myocardial cell hypertrophy and apoptosis

BACKGROUND AND OBJECTIVE

Periodontal pathogen Porphyromonas gingivalis (P. gingivalis) increased cardiomyocyte hypertrophy and apoptosis whereas Actinobaeillus actinomycetemcomitans and Prevotella intermedia had no effects. The purpose of this study is to clarify the role of calcineurin signaling pathway in P. gingivalis-induced H9c2 myocardial cell hypertrophy and apoptosis.

METHODS

DNA fragmentation, nuclear condensation, cellular morphology, calcineurin protein, Bcl2-associated death promoter (Bad) and nuclear factor of activated T cell (NFAT)-3 protein products in cultured H9c2 myocardial cell were measured by agarose gel electrophoresis, DAPI, immunofluorescence, and Western blotting following P. gingivalis and/or pre-administration of CsA (calcineurin inhibitors cyclosporin A).

RESULTS

P. gingivalis not only increased calcineurin protein, NFAT-3 protein products and cellular hypertrophy, but also increased DNA fragmentation, nuclear condensation and Bad protein products in H9c2 cells. The increased cellular sizes, DNA fragmentation, nuclear condensation, and Bad of H9c2 cells treated with P. gingivalis were all significantly reduced after pre-administration of CsA.

CONCLUSION

Our findings suggest that the activity of calcineurin signal pathway may be initiated by P. gingivalis and further lead to cell hypertrophy and death in culture H9c2 myocardial cells.

Cardiac apoptosis in severe relapsing fever borreliosis

Previous studies revealed that the heart suffers significant injury during experimental Lyme and relapsing fever borreliosis when the immune response is impaired (D. Cadavid, Y. Bai, E. Hodzic, K. Narayan, S. W. Barthold, and A. R. Pachner, Lab. Investig. 84:1439-1450, 2004; D. Cadavid, T. O'Neill, H. Schaefer, and A. R. Pachner, Lab. Investig. 80:1043-1054, 2000; and D. Cadavid, D. D. Thomas, R. Crawley, and A. G. Barbour, J. Exp. Med. 179:631-642, 1994). To investigate cardiac injury in borrelia carditis, we used antibody-deficient mice persistently infected with isogenic serotypes of the relapsing fever agent Borrelia turicatae. We studied infection in hearts 1 to 2 months after inoculation by TaqMan reverse transcription-PCR and immunohistochemistry (IHC) and inflammation by hematoxylin and eosin and trichrome staining, IHC, and in situ hybridization (ISH). We studied apoptosis by terminal transferase-mediated DNA nick end labeling assay and measured expression of apoptotic molecules by RNase protection assay, immunofluorescence, and immunoblot. All antibody-deficient mice, but none of the immunocompetent controls, developed persistent infection of the heart. Antibody-deficient mice infected with serotype 2 had more severe cardiac infection and injury than serotype 1-infected mice. The injury was more severe around the base of the heart and pericardium, corresponding to sites of marked infiltration by activated macrophages and upregulation of interleukin-6 (IL-6). Infected hearts showed evidence of apoptosis of macrophages and cardiomyocytes as well as significant upregulation of caspases, most notably caspase-1. We conclude that persistent infection with relapsing fever borrelias causes significant loss of cardiomyocytes associated with prominent infiltration by activated macrophages, upregulation of IL-6, induction of caspase-1, and apoptosis.

Histologic and molecular diagnosis of tularemia: a potential bioterrorism agent endemic to North America

Francisella tularensis (FT), a zoonotic bacterium that causes tularemia, has received attention as a possible bioterrorism threat. We developed a PCR assay for use in fixed, processed tissues, which are safer to handle and allow archival testing. PCR analysis for a 211-bp fragment of the FT lipoprotein gene was performed on tissues from 16 cases of tularemia. In all, 14/15 cases with intact DNA (93%) were positive for FT by PCR. Frequent histologic findings in PCR-positive tissues included irregular microabscesses and granulomas in liver, spleen, kidney, and lymph nodes, and necrotizing pneumonia. Unusual cases featuring suppurative leptomeningitis and gastrointestinal ulcers were also seen. As this disease is endemic in North America, and has been identified as a potential bioterroristic threat, awareness of the clinicopathologic spectrum of disease and available detection methods is increasingly important. This PCR assay, the first designed for use in processed tissues, is an excellent method for diagnosis of tularemia.

A comparative study between catalase gene therapy and the cardioprotector monohydroxyethylrutoside (MonoHER) in protecting against doxorubicin-induced cardiotoxicity in vitro

Cardiotoxicity is the main dose-limiting side effect of doxorubicin in the clinic. Being a free radical producer, doxorubicin affects the heart specifically because of its low antioxidant capacity. Among those antioxidants, catalase is present in very low levels in the heart compared to other organs. Since catalase is an essential enzyme in detoxifying hydrogen peroxide, the aim of the present study was to investigate the protective effect of catalase as delivered by an adenovirus vector against doxorubicin-induced cardiotoxicity in cultured neonatal rat cardiac myocytes (NeRCaMs). 7-Monohydroxyethylrutoside (MonoHER), a potent cardioprotector currently under clinical investigations, was included in the study as a reference. Neonatal rat cardiac myocytes were infected with different multiplicity of infections (MOIs) of adenovirus encoding catalase (AdCat). A control infection with an adenovirus vector encoding a nonrelated protein was included. The activity and content of catalase in infected cells were determined during 3 days postinfection. One group of NeRCaMs was infected with AdCat before treatment with doxorubicin (0–50 μM). The second and third group were treated with doxorubicin (0–50 μM) with and without 1 mM monohydroxyethylrutoside (monoHER), respectively. The LDH release and viability of treated cells were measured 24 and 48 h after doxorubicin treatment. The beating rate was followed in three other groups of cells receiving the same treatments within 3 days after doxorubicin (0–100 μM) treatment. Catalase activity increased in AdCat-infected cells, with different MOIs, starting from the second day after infection as compared to the mock-infected cells (P<0.03). At the third day of infection, an MOI of more than 50 caused cytopathic effects, which hampered the use of higher viral titres. With an MOI of 50, catalase activity increased 3.5-fold in AdCat-infected cells 3 days postinfection (P=0.021) compared to mock-infected cells. The beating rate and survival of NeRCaMs decreased in a concentration and time-dependent manner after doxorubicin treatment (P<0.0005). This cytotoxicity was associated with an increase in the LDH release from the treated cells (P<0.0005). The cells stopped beating 24 h after treatment with >50 μM doxorubicin. A 3.5-fold increase in the activity of catalase did not protect NeRCaMs against any of the cytotoxic effects of doxorubicin on NeRCaMs. In contrast, monoHER (1 mM) significantly protected NeRCaMs against the lethal effects of doxorubicin on the survival, LDH release and the beating rate of NeRCaMs (P<0.004) during 48 h after doxorubicin treatment. This protection resulted in a prolongation of the beating of doxorubicin-treated cells after the end of the experiment (i.e. >72 h). The present study (1) illustrates that the cytotoxicity of high MOI of AdCat (>50) limited the possibility to increase catalase activity more than 3.5-fold, which was not enough to protect infected NeRCaMs against doxorubicin-induced cardiotoxicity and (2) confirms the efficacy of monoHER as a cardioprotector. Thus, the use of monoHER proves more suitable for the prevention of doxorubicin-induced cardiotoxicity than catalase gene transfer employing adenovirus vectors.

Altering tissue tropism of Listeria monocytogenes by ectopically expressing human E-cadherin in transgenic mice

The Gram-positive bacterium Listeria monocytogenes invades a variety of cells in vitro and in vivo. Here, we show that L. monocytogenes is able to enter muscle cells if provided with the appropriate host receptor. Using a cardiac-specific promoter, human E-cadherin was misexpressed in the heart of transgenic mice. First, we demonstrate that L. monocytogenes is capable of infecting the E-cadherin-expressing, but not the N-cadherin-expressing cardiomyocytes in vitro. Second, we show that L. monocytogenes infects the heart of transgenic animals after administering the bacteria intravenously. This unique system may prove useful for understanding basic aspects of L. monocytogenes cell biology by comparing infection of muscle versus epithelial cells.

Infection of myocytes with chlamydiae

Chlamydial infection has been associated with myocarditis in animals and humans. However, the mechanism resulting in myocarditis following infection is not known. Here, evidence is presented that both Chlamydia trachomatis and Chlamydia pneumoniae can infect and replicate in myocytes isolated from neonate rats. The infected myocytes contained chlamydial inclusions, indicative of chlamydial growth, and infectious particles were recovered from the infected myocytes. It was also found that chlamydial infection at a late stage induced significant damage to the infected myocytes, as evidenced by an increased lactate dehydrogenase release, reactive oxygen species production and a reduced ATP level. However, no nuclear apoptosis was detected in the infected myocytes. Collectively, these observations have demonstrated that Chlamydia spp. are able to both infect and damage myocytes, suggesting a potential role of chlamydial infection in myocarditis.