Genome-wide identification of genetic requirements of Pseudomonas aeruginosa PAO1 for rat cardiomyocyte (H9C2) infection by insertion sequencing.

Pseudomonas aeruginosa is a major infectious agent among Gram-negative bacteria, which causes both acute and chronic infections. Infections due to P. aeruginosa are hard to treat, as it entails various strategies like virulence factors synthesis, drug efflux systems & resistance and protein secretion systems during pathogenesis. Despite extensive research in Pseudomonas pathogenesis, novel drug targets and potential therapeutic strategies are urgently needed. In this study, we investigated the genetic requirements of P. aeruginosa PAO1 for rat cardiomyocyte (H9C2) infection by insertion sequencing (INSeq). A mutant library comprising ~70,000 mutants of PAO1 was generated and the differentiated form of H9C2 cells (d-H9C2) was infected with the library. The infected d-H9C2 cells were maintained with antibiotic-protection and without any antibiotics in the growth media for 24 h. Subsequently, DNA library for INSeq was prepared, sequenced and fitness analysis was performed. One hundred and thirteen mutants were negatively selected in the infection condition with antibiotic-protection, whereas 143 mutants were negatively selected in antibiotic-free condition. Surprisingly, a higher number of mutants showed enriched fitness than the mutants of reduced fitness during the infection. We demonstrated that the genes associated with flagella and T3SS are important for adhesion and invasion of cardiomyocytes, while pili and proteases are conditionally essential during host cell lysis. Hence, our findings highlight the essential genes for cardiomyocyte infection, particularly during the intracellular phase. The aerotaxis receptor Aer, plays a critical role during intracellular life. Genes such as flgE, flgF, flhA, flhB, fliA, fliC, fliF, motA, aotJ, aer, wbpJ, ponA, fleQ, PA5205, hmgA, trkH and pslH are essential for infection.

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.

LncRNA RMRP accelerates hypoxia-induced injury by targeting miR-214-5p in H9c2 cells.

OBJECTIVE: To elucidate the function of lncRNA RMRP in hypoxia-induced acute myocardial infarction (AMI) in vitro and explore its underlying mechanism. METHODS: Hypoxic injury was confirmed by measurement of cell viability, LDH release, migration, invasion, and apoptosis in H9c2 cells. The interactions between RMRP and miR-214-5p as well as miR-214-5p and p53 were also investigated. RESULTS: Hypoxia treatment significantly induced cell damage in H9c2 cells, accompanied with the up-regulation of RMRP expressions. Transfection of RMRP siRNA remarkably attenuated hypoxia-induced injury by enhancing cell viability, migration and invasion, and reducing cell apoptosis and LDH release; whereas, enforced expression of RMRP aggravated hypoxia-induced injury. Furthermore, RMRP served as an endogenous sponge for miR-214-5p, and its expression was negatively regulated by RMRP. The effects of RMRP knockdown on hypoxia-induced injury were further enhanced with miR-214-5p overexpression, but significantly abrogated with miR-214-5p silence. Moreover, p53 was verified as a direct target of miR-214-5p, and functional investigation revealed that RMRP regulated hypoxia-induced injury via modulating p53 signaling pathway, which was partially mediated by miR-214-5p. CONCLUSION: Our findings demonstrated the novel molecular mechanism of RMRP/miR-214-5p/p53 axis on the regulation of hypoxia-induced myocardial injury in H9c2 cells, which might provide potential therapeutic targets for AMI treatment.

Activation of CaMKII via ER-stress mediates coxsackievirus B3-induced cardiomyocyte apoptosis.

Cardiomyocyte apoptosis contributes to the development of coxsackievirus B3 (CVB3)-induced myocarditis, but the mechanism for the apoptosis by CVB3 infection remains unclear. Here, we showed that CVB3-induced endoplasmic reticulum (ER) stress response and apoptosis in cultured H9c2 cardiomyocytes. We found that Ca2+ -calmodulin-dependent kinase II (CaMKII) was activated by ER stress-dependent intracellular Ca2+ overload in the CVB3-infected H9c2 cardiomyocytes. Treatment with an inhibitor of ER stress, 4-phenylbutyric acid (4-PBA), attenuated intracellular Ca2+ accumulation indirectly and reduced CaMKII activity. Inhibition of CaMKII with pharmacological inhibitor (KN-93) or short hairpin RNA reduced CVB3-induced H9c2 apoptosis and repressed cytochrome c release from mitochondria to cytoplasm; whereas overexpression of the activated mutant of CaMKII (CaMKII-T287D) enhanced CVB3-induced H9c2 apoptosis and mitochondrial cytochrome c release, which could be alleviated by blocking of mitochondrial Ca2+ uniporter or mitochondrial permeability transition pore. Further in vivo investigation revealed that blocking of CaMKII with KN-93 prevented cardiomyocytes apoptosis and improved cardiac contractile function in CVB3-infected mouse heart. Collectively, these findings provide a novel evidence that CaMKII plays a vital role in the promotion of CVB3-induced cardiomyocyte apoptosis, which links ER stress and mitochondrial Ca2+ uptake.

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.

Generation of clinical-grade functional cardiomyocytes from human embryonic stem cells in chemically defined conditions.

A highly efficient cardiac differentiation from human pluripotent stem cells (hPSCs) is achievable using existing methods, especially with the standard B27 induction system. However, bovine serum albumin (BSA), one of the essential ingredients in B27, may pose significant complications for clinical studies owing to its animal origin and potential risks of virus contamination. Furthermore, the high cost of the B27 induction system also limits the applications of hPSCs-derived cardiomyocytes. Here, a BSA-free and chemically defined medium has been developed for differentiating hPSCs to clinical-grade cardiomyocytes, which generated over 80% cardiac troponin T (cTNT)-positive cardiomyocytes with high yield. When engrafting the cardiomyocytes into the hearts of myocardial infarction model rats, the rats survived with significantly improved heart functions in Δ ejection fraction and Δ fractional shortening. Importantly, the human embryonic stem cell (hESC) line (Q-CTS-hESC-2) chosen for differentiation was of a clinical-grade maintained in defined xeno-free conditions. Compliant with the biological safety requirements, the Q-CTS-hESC-2-derived cardiomyocytes have passed the sterility and pathogen criteria tests for clinical applications. This study reports, for the first time, the generation of clinical-grade and functional cardiomyocytes from hPSCs where BSA-free and chemically defined conditions were maintained throughout the whole process. This provides the possibility of future therapeutic use of clinical-grade hPSCs-derived cardiomyocytes in treating heart diseases. Copyright © 2016 John Wiley & Sons, Ltd.

SOX2-mediated inhibition of miR-223 contributes to STIM1 activation in phenylephrine-induced hypertrophic cardiomyocytes.

Stromal interaction molecule 1 (STIM1) is the key molecule responsible for store-operated Ca2+ entry (SOCE). Numerous studies have demonstrated that STIM1 levels appeared to be enhanced during cardiac hypertrophy. However, the mechanism underlining this process remains to be clarified. In this study, phenylephrine (PE) was employed to establish a model of hypertrophic neonatal rat cardiomyocytes (HNRCs) in vitro, and low expression of primary and mature miR-223 was detected in PE-induced HNRCs. Our results have revealed that downregulation of miR-223 by PE contributed to the increase of STIM1, which in turn induced cardiac hypertrophy. As expected, overexpression of miR-223 could prevent the increase in cell surface and reduce the mRNA levels of ANF and BNP in cardiomyocytes. To address the mechanism triggering downregulation of miR-223 under PE, we demonstrated that PE-induced inhibition of GSK-3ß activity led to the activation of ß-catenin, which initiates the transcription of SOX2. Increased expression of SOX2 occupied the promoter region of primary miR-223 and suppressed its transcription. Therefore, miR-223 appears to be a promising candidate for inhibiting cardiomyocyte hypertrophy, and miR-223/STIM1 axis might be one of interesting targets for the clinical treatment of hypertrophy.

Cell Invasion and Pyruvate Oxidase-Derived H2O2 Are Critical for Streptococcus pneumoniae-Mediated Cardiomyocyte Killing.

Streptococcus pneumoniae (the pneumococcus) is the leading cause of community-acquired pneumonia and is now recognized to be a direct contributor to adverse acute cardiac events. During invasive pneumococcal disease, S. pneumoniae can gain access to the myocardium, kill cardiomyocytes, and form bacterium-filled "microlesions" causing considerable acute and long-lasting cardiac damage. While the molecular mechanisms responsible for bacterial translocation into the heart have been elucidated, the initial interactions of heart-invaded S. pneumoniae with cardiomyocytes remain unclear. In this study, we used a model of low multiplicity of S. pneumoniae infection with HL-1 mouse cardiomyocytes to investigate these early events. Using adhesion/invasion assays and immunofluorescent and transmission electron microscopy, we showed that S. pneumoniae rapidly adhered to and invaded cardiomyocytes. What is more, pneumococci existed as intravacuolar bacteria or escaped into the cytoplasm. Pulse-chase assays with BrdU confirmed intracellular replication of pneumococci within HL-1 cells. Using endocytosis inhibitors, bacterial isogenic mutants, and neutralizing antibodies against host proteins recognized by S. pneumoniae adhesins, we showed that S. pneumoniae uptake by cardiomyocytes is not through the well-studied canonical interactions identified for vascular endothelial cells. Indeed, S. pneumoniae invasion of HL-1 cells occurred through clathrin-mediated endocytosis (CME) and independently of choline binding protein A (CbpA)/laminin receptor, CbpA/polymeric immunoglobulin receptor, or cell wall phosphorylcholine/platelet-activating factor receptor. Subsequently, we determined that pneumolysin and streptococcal pyruvate oxidase-derived H2O2 production were required for cardiomyocyte killing. Finally, we showed that this cytotoxicity could be abrogated using CME inhibitors or antioxidants, attesting to intracellular replication of S. pneumoniae as a key first step in pneumococcal pathogenesis within the heart.

A Periodontal pathogen Porphyromonas gingivalis deteriorates Isoproterenol-Induced myocardial remodeling in mice.

Heart failure is a serious disease induced by several conditions, including hypertrophic cardiomyopathy. Although many reports suggest that there is an association between periodontal disease and cardiovascular disease, the mechanisms have yet to be elucidated. The purpose of this study was to clarify the relationship between periodontal disease and heart disease, especially in cardiac hypertrophy. We used C57BL/6J mice and implanted two types of subcutaneous chambers. First, we subcutaneously implanted a coil-shaped chamber into the back of a mouse. Porphyromonas gingivalis (P.g.), a major periodontal pathogen, was injected into the chamber. Then, an osmotic pump was implanted to infuse isoproterenol. Four weeks after the ISO infusion, we performed echocardiography and harvested the heart and blood. We measured the serum level of anti-P.g.-IgG using ELISA. The mRNA levels of several factors were measured using PCR. We found stronger cardiomyocyte hypertrophy in the ISO(+)/P.g.(+) mice compared with the ISO(+)/P.g.(-) mice. The total square of randomly selected cardiomyocytes was 23% larger in the ISO(+)/P.g.(+) mice than in the ISO(+)/P.g.(-) mice. We detected a higher level of mRNA expression in Toll-like receptor 2 and NADPH oxidase 4 in the ISO(+)/P.g.(-) mice compared with the control group. We revealed that a periodontal pathogen affected ISO-induced cardiac hypertrophy via oxidative stress.

Heterologous expression of Streptococcus mutans Cnm in Lactococcus lactis promotes intracellular invasion, adhesion to human cardiac tissues and virulence.

In S. mutans, the expression of the surface glycoprotein Cnm mediates binding to extracellular matrix proteins, endothelial cell invasion and virulence in the Galleria mellonella invertebrate model. To further characterize Cnm as a virulence factor, the cnm gene from S. mutans strain OMZ175 was expressed in the non-pathogenic Lactococcus lactis NZ9800 using a nisin-inducible system. Despite the absence of the machinery necessary for Cnm glycosylation, Western blot and immunofluorescence microscopy analyses demonstrated that Cnm was effectively expressed and translocated to the cell wall of L. lactis. Similar to S. mutans, expression of Cnm in L. lactis enabled robust binding to collagen and laminin, invasion of human coronary artery endothelial cells and increased virulence in G. mellonella. Using an ex vivo human heart tissue colonization model, we showed that Cnm-positive strains of either S. mutans or L. lactis outcompete their Cnm-negative counterparts for tissue colonization. Finally, Cnm expression facilitated L. lactis adhesion and colonization in a rabbit model of infective endocarditis. Collectively, our results provide unequivocal evidence that binding to extracellular matrices mediated by Cnm is an important virulence attribute of S. mutans and confirm the usefulness of the L. lactis heterologous system for further characterization of bacterial virulence factors.

Complement Destabilizes Cardiomyocyte Function In Vivo after Polymicrobial Sepsis and In Vitro.

There is accumulating evidence during sepsis that cardiomyocyte (CM) homeostasis is compromised, resulting in cardiac dysfunction. An important role for complement in these outcomes is now demonstrated. Addition of C5a to electrically paced CMs caused prolonged elevations of intracellular Ca(2+) concentrations during diastole, together with the appearance of spontaneous Ca(2+) transients. In polymicrobial sepsis in mice, we found that three key homeostasis-regulating proteins in CMs were reduced: Na(+)/K(+)-ATPase, which is vital for effective action potentials in CMs, and two intracellular Ca(2+) concentration regulatory proteins, that is, sarcoplasmic/endoplasmic reticulum calcium ATPase 2 and the Na(+)/Ca(2+) exchanger. Sepsis caused reduced mRNA levels and reductions in protein concentrations in CMs for all three proteins. The absence of either C5a receptor mitigated sepsis-induced reductions in the three regulatory proteins. Absence of either C5a receptor (C5aR1 or C5aR2) diminished development of defective systolic and diastolic echocardiographic/Doppler parameters developing in the heart (cardiac output, left ventricular stroke volume, isovolumic relaxation, E' septal annulus, E/E' septal annulus, left ventricular diastolic volume). We also found in CMs from septic mice the presence of defective current densities for Ik1, l-type calcium channel, and Na(+)/Ca(2+) exchanger. These defects were accentuated in the copresence of C5a. These data suggest complement-related mechanisms responsible for development of cardiac dysfunction during sepsis.

Hydroxamic acid derivatives: a promising scaffold for rational compound optimization in Chagas disease.

This work describes the antitrypanocidal activity of two hydroxamic acid derivatives containing o-ethoxy (HAD1) and p-ethoxy (HAD2) as substituent in the aromatic ring linked to the isoxazoline ring. HAD1 and HAD2 induced a significant reduction in the number of intracellular parasites and consequently showed activity on the multiplication of the parasite. Treatment of cardiomyocytes and macrophages with the compounds revealed no significant loss in cell viability. Ultrastructural alterations after treatment of cardiomyocytes or macrophages infected by Trypanosoma cruzi with the IC50 value of HAD1 revealed alterations to amastigotes, showing initial damage seen as swelling of the kinetoplast. This gave a good indication of the ability of the drug to permeate through the host cell membrane as well as its selectivity to the parasite target. Both compounds HAD1 and 2 were able to reduce the cysteine peptidases and decrease the activity of metallopeptidases.

Coxsackievirus B3 Induces Autophagic Response in Cardiac Myocytes in vivo.

Viral myocarditis is a common disease that contributes to dilated cardiomyopathy or heart failure. Coxsackievirus B (CVB) is one of the major causative pathogens of viral myocarditis. Previous studies have shown that autophagy is exploited to promote CVB replication in cell lines. To study whether cardiac myocytes respond to CVB infection in a similar way, viral myocarditis was established by the inoculation of 3-week-old BALB/c mice with CVB3. Electron microscopic observation showed that autophagosome-like vesicles were induced in the cardiac myocytes of mice infected by CVB3 at 3, 5, and 7 days after viral infection. The lipidated microtubule-associated protein 1 light chain 3 (LC3), LC3-II, was also significantly increased in both myocardium and the cardiac myocytes extracted from the ventricles of mice infected with CVB3. The increased LC3-II coincided with high level of viral RNA and proteins in both myocardium and isolated cardiac myocytes. Moreover, viral protein synthesis was significantly decreased in primary cardiac myocytes by the treatment with 3-methyladenine, an inhibitor of autophagy. The expression and the phosphorylation of extracellular signal regulated kinase (ERK) were also increased in both myocardium and in the isolated cardiac myocytes of the virus-infected mice, while the interplay of ERK with autophagic response remains to be studied. This study demonstrated that cardiac myocytes respond to CVB3 infection by increased formation of autophagosomes in vivo, which might be exploited for viral replication.

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.

Cardiac dysfunction in StrepTSS: group A streptococcus disrupts the directional cardiomyocyte-to-macrophage crosstalk that maintains macrophage quiescence.

Myocardial dysfunction in group A streptococcal (GAS) toxic shock syndrome (StrepTSS) is characterized by severe biventricular dilatation and a striking reduction in ventricular performance; however, the mechanisms have not been fully elucidated. We have previously shown that pro-inflammatory cytokines are upregulated in the hearts of experimental animals with GAS bacteremia and that cardiomyocytes themselves as well as macrophages are the principal cytokine sources. Although macrophage-derived cytokines can clearly affect cardiac contractility, we questioned whether soluble cardiomyocyte-derived mediators might in turn affect macrophage function. Thus, we sought evidence of cardiomyocyte-to-macrophage directional cross-talk under resting versus GAS-stimulated conditions, using production of matrix metalloproteinase-9 (MMP-9) as an indicator of such signaling. Our results demonstrate that unstimulated cardiomyocytes produce a soluble inhibitor/s that maintains macrophage functional quiescence. Further, viable GAS induced production of cardiomyocyte-derived stimulator/s that overcomes quiescence and boosts macrophages production of MMP-9 and expression of pro-inflammatory cytokines (IL-1ß, IL-6) and cardiodepressant factors (iNOS). Understanding the role of these cardiomyocyte-derived effectors of macrophage function (herein termed "cardiokines") in sepsis-associated cardiomyopathy may suggest new targets for therapeutic intervention.

Displasia miocardial ventricular bilateral em um cão Shar-Pei / Bilateral ventricular myocardial dysplasia in a Shar-Pei dog

Um cão Shar-pei de cinco anos de idade foi encaminhado para exame de necropsia com histórico de morte súbita. Ao exame macroscópico foram observadas, no coração, áreas pálidas extensas envolvendo o miocárdio do ventrículo direito e esquerdo. Ao exame histológico foi observada infiltração intensa de células adiposas bem diferenciadas no miocárdio de ambos os ventrículos associada à moderada atrofia e degeneração de cardiomiócitos. Os achados microscópicos foram compatíveis com diagnóstico de displasia miocardial ventricular bilateral.

Do cardiomyocytes mount an immune response to Group A Streptococcus?

Some patients with Group A Streptococcal toxic shock syndrome (StrepTSS) develop a unique form of cardiomyopathy characterized by global hypokinesia and reduced cardiac index. Here we investigated the immune responses of cardiomyocytes to Group A Streptococcus both in vivo and in vitro. Our data demonstrate that cardiomyocyte-derived cytokines are produced following both direct GAS stimulation and after exposure to GAS-activated inflammatory cells. These locally produced, cardiomyocyte-derived cytokines may mediate cardiac contractile dysfunction observed in patients with StrepTSS-associated cardiomyopathy and may hold the key to our ability to attenuate this severe complication.

Fractalkine in human inflammatory cardiomyopathy.

BACKGROUND: Cardiac inflammation is important for the prognosis of patients with inflammatory cardiomyopathy (CMi), but the mechanisms leading to it are not fully elucidated. OBJECTIVE: To study the role of fractalkine (CX3CL1) in chemotactic and adhesive properties of peripheral blood mononuclear cells (PBMCs) in patients with CMi. METHODS AND RESULTS: Patients with enterovirus (EV)-positive CMi, patients with virus-negative CMi, patients with parvovirus B19 (B19) genomes with low intramyocardial inflammation and patients without cardiac inflammation and viral infection in the endomyocardial biopsy (EMB) were enrolled (n=10/group). The expression of CX3CL1 and monocyte chemoattractant protein (MCP-1) in EMBs was significantly increased in EV-positive and virus-negative patients with CMi in contrast to controls and B19-positive patients (EV+ vs controls: CX3CL1-area fraction (AF) % 0.078±0.012 vs 0.009±0.003 p<0.05; MCP-1-AF % 0.093±0.023 vs 0.011±0.009). The receptor (CX3CR1)-mediated chemotaxis was increased twofold in PBMCs in comparison with those of controls. The MCP-1 secretion was 3.1-fold higher in PBMCs from EV-positive patients compared with controls, and this elevation was further increased by CX3CL1 in EV-positive patients. No significant CX3CL1-mediated MCP-1 increase was seen in PBMCs from healthy controls. Moreover, spontaneously beating neonatal rat cardiomyocytes exposed to CX3CL1 exhibited an attenuated positive chronotropic response to ß-adrenergic stimulation with isoproterenol. CONCLUSION: The cardiac and plasma CX3CL1/CX3CR1 system is upregulated in CMi and this affects the functional potential of PBMCs. Moreover, a direct cardiodepressive effect of CX3CL1 in cardiac tissue was demonstrated since neonatal cardiomyocytes exhibited an attenuated positive chronotropic response to ß-adrenergic stimulation.

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.