Barbara Bayer

Absence of NF-κB subunit p50 improves heart failure after myocardial infarction

Background: NF kappa B (NF‐κB) is a ubiquitous transcription factor activated by various stimuli implicated in heart failure progression including reactive oxygen species (ROS), hypoxia, and inflammatory cytokines. Although NF‐κB is involved in ischemic preconditioning, unstable angina pectoris, and atherogenesis, its role in heart failure has not been determined. Therefore, we investigated left ventricular remodeling in mice with a targeted deletion of the NF‐κB subunit p50/NF‐κB1 after myocardial infarction. Methods and results: p50 knockout (KO) and wild‐type (WT) animals underwent coronary artery ligation. Transthoracic echocardiography was performed at days 0, 21, and 56 at midpapillary levels. Early mortality was significantly lower in KO than in WT animals. Moreover, p50 KOs exhibited significantly reduced ventricular dilatation over 8 wk compared to WT controls (end‐systolic diameters by transthoracic echocardiography, WT vs. KO, 0.55±0.04 vs. 0.34±0.03 cm) and preserved left ventricular contractility. Collagen content and matrixmetalloproteinase (MMP) ‐9 expression were significantly lower in KO mice after myocardial infarction and may account for improved left ventricular remodeling. Conclusions: Absence of the NF‐κB subunit p50 improves early survival and reduces left ventricular dilatation after myocardial infarction. NF‐κB might therefore be an attractive target to treat heart failure.—Frantz, S., Hu, K., Bayer, B., Gerondakis, S., Strotmann, J., Adamek, A., Ertl, G., Bauersachs, J. Absence of NF‐κB subunit p50 improves heart failure after myocardial infarction. FASEB J. 20, E1309–E1314 (2006)

Increased Mortality and Aggravation of Heart Failure in Estrogen Receptor-β Knockout Mice After Myocardial Infarction

Background—Lower mortality rates among women with chronic heart failure than among men may depend in part on the action of female sex hormones, especially estrogens. The biological effects of estrogens are mediated by 2 distinct estrogen receptor (ER) subtypes (ER&agr; and ER&bgr;). The present study was undertaken to determine the role of ER&bgr; in the development of chronic heart failure after experimental myocardial infarction (MI). Methods and Results—Female ER&bgr; null mice (BERKOChapel Hill) and wild-type littermates (WT) were ovariectomized, given 17&bgr;-estradiol, and subjected to chronic anterior MI (MI; BERKO n=31, WT n=30) or sham operation (sham; BERKO n=14, WT n=14). At 8 weeks after MI, both genotypes revealed left ventricular remodeling and impaired contractile function at similar average infarct size (BERKO-MI 32.9±5% versus WT-MI 33.0±4%); however, BERKO mice showed increased mortality (BERKO-MI 42% versus WT-MI 23%), increased body weight and fluid retention (P<0.01), higher ventricular pro-ANP expression (BERKO-MI 27.9-fold versus sham, WT-MI 5.2-fold versus sham; BERKO-MI versus WT-MI P<0.001), higher atrial natriuretic peptide serum levels, and increased phospholamban expression (P<0.05) compared with WT mice. Conclusions—Systemic deletion of ER&bgr; in female mice increases mortality, aggravates clinical and biochemical markers of heart failure, and contributes to impaired expression of Ca2+-handling proteins in chronic heart failure after MI. Further studies are required to delineate the relative importance of cardiac and vascular effects of ER&bgr; and the role of ER&agr; in the development of heart failure.

Monocytes/macrophages prevent healing defects and left ventricular thrombus formation after myocardial infarction

Myocardial infarction (MI) leads to rapid necrosis of cardiac myocytes. To achieve tissue integrity and function, inflammatory cells are activated, including monocytes/macrophages. However, the effect of monocyte/macrophage recruitment after MI remains poorly defined. After experimental MI, monocytes and macrophages were depleted through serial injections of clodronate‐containing liposomes. Monocyte/macrophage infiltration was reduced in the myocardium after MI by active treatment. Mortality was increased due to thromboembolic events in monocyte‐ and macrophage‐depleted animals (92 vs. 33%; P<0.01). Left ventricular thrombi were detectable as early as 24 h after MI; this was reproduced in a genetic model of monocyte/macrophage ablation. A general prothrombotic state, increased infarct expansion, and deficient neovascularization were not observed. Severely compromised extracellular matrix remodeling (collagen I, placebo liposome vs. clodronate liposome, 2.4±0.2 vs. 0.8±0.2 arbitrary units; P<0.001) and locally lost integrity of the endocardium after MI are potential mechanisms. Patients with a left ventricular thrombus had a relative decrease of CD14+CD16+ monocyte/macrophage subsets in the peripheral blood after MI (no thrombus vs. thrombus, 14.2±0.9 vs. 7.80±0.4%; P<0.05). In summary, monocytes/macrophages are of central importance for healing after MI. Impaired monocyte/macrophage function appears to be an unrecognized new pathophysiological mechanism for left ventricular thrombus development after MI.—Frantz, S., Hofmann, U., Fraccarollo, D., Schäfer, A., Kranepuhl, S., Hagedorn, I., Nieswandt, B., Nahrendorf, M., Wagner, H., Bayer, B., Pachel, C., Schön, M.P., Kneitz, S., Bobinger, T., Weidemann, F., Ertl, G., Bauersachs, J. Monocytes/macrophages prevent healing defects and left ventricular thrombus formation after myocardial infarction. FASEB J. 27, 871–881 (2013). www.fasebj.org

Peroxisome proliferator activated‐receptor agonism and left ventricular remodeling in mice with chronic myocardial infarction

Peroxisome proliferator activated receptor γ (PPARγ) has been implicated in several cellular pathways assumed to beneficially affect heart failure progression. In contrast, population‐based studies demonstrate an increased incidence of heart failure in patients treated with PPARγ agonists. Therefore, we examined the effect of pioglitazone, a PPARγ agonist, on chronic left ventricular remodeling after experimental myocardial infarction (MI) in mice. Mice were treated with placebo or pioglitazone (20 mg kg−1 by gavage) from week 1 to week 6 after ligation of the left anterior descending artery. Serial transthoracic echocardiography was performed at weeks 1, 3, and 6. Over 6 weeks, there was no difference in mortality (placebo 12%, pioglitazone 10%). Echocardiography showed significant left ventricular dilatation in animals with MI (week 6, end‐systolic area, placebo sham 9.6±1.3 vs placebo MI 14.4±2.5 mm2). However, there was no difference between the placebo and pioglitazone groups (week 6, end‐systolic area, pioglitazone MI 14.8±2.9 mm2, P=NS vs placebo). Moreover, there were no changes in metabolic parameters, inflammation, and collagen deposition. Endothelial function in the aorta was not changed by PPARγ activation. In conclusion, PPARγ activation did not adversely affect left ventricular remodeling and survival in mice with chronic MI. However, we were also not able to identify a protective effect of pioglitazone.

Stress-dependent dilated cardiomyopathy in mice with cardiomyocyte-restricted inactivation of cyclic GMP-dependent protein kinase I

Aims Cardiac hypertrophy is a common and often lethal complication of arterial hypertension. Elevation of myocyte cyclic GMP levels by local actions of endogenous atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) or by pharmacological inhibition of phosphodiesterase-5 was shown to counter-regulate pathological hypertrophy. It was suggested that cGMP-dependent protein kinase I (cGKI) mediates this protective effect, although the role in vivo is under debate. Here, we investigated whether cGKI modulates myocyte growth and/or function in the intact organism. Methods and results To circumvent the systemic phenotype associated with germline ablation of cGKI, we inactivated the murine cGKI gene selectively in cardiomyocytes by Cre/loxP-mediated recombination. Mice with cardiomyocyte-restricted cGKI deletion exhibited unaltered cardiac morphology and function under resting conditions. Also, cardiac hypertrophic and contractile responses to β-adrenoreceptor stimulation by isoprenaline (at 40 mg/kg/day during 1 week) were unaltered. However, angiotensin II (Ang II, at 1000 ng/kg/min for 2 weeks) or transverse aortic constriction (for 3 weeks) provoked dilated cardiomyopathy with marked deterioration of cardiac function. This was accompanied by diminished expression of the [Ca2+]i-regulating proteins SERCA2a and phospholamban (PLB) and a reduction in PLB phosphorylation at Ser16, the specific target site for cGKI, resulting in altered myocyte Ca2+i homeostasis. In isolated adult myocytes, CNP, but not ANP, stimulated PLB phosphorylation, Ca2+i-handling, and contractility via cGKI. Conclusion These results indicate that the loss of cGKI in cardiac myocytes compromises the hypertrophic program to pathological stimulation, rendering the heart more susceptible to dysfunction. In particular, cGKI mediates stimulatory effects of CNP on myocyte Ca2+i handling and contractility.

Mena/VASP and αII-Spectrin complexes regulate cytoplasmic actin networks in cardiomyocytes and protect from conduction abnormalities and dilated cardiomyopathy

BackgroundIn the heart, cytoplasmic actin networks are thought to have important roles in mechanical support, myofibrillogenesis, and ion channel function. However, subcellular localization of cytoplasmic actin isoforms and proteins involved in the modulation of the cytoplasmic actin networks are elusive. Mena and VASP are important regulators of actin dynamics. Due to the lethal phenotype of mice with combined deficiency in Mena and VASP, however, distinct cardiac roles of the proteins remain speculative. In the present study, we analyzed the physiological functions of Mena and VASP in the heart and also investigated the role of the proteins in the organization of cytoplasmic actin networks.ResultsWe generated a mouse model, which simultaneously lacks Mena and VASP in the heart. Mena/VASP double-deficiency induced dilated cardiomyopathy and conduction abnormalities. In wild-type mice, Mena and VASP specifically interacted with a distinct αII-Spectrin splice variant (SH3i), which is in cardiomyocytes exclusively localized at Z- and intercalated discs. At Z- and intercalated discs, Mena and β-actin localized to the edges of the sarcomeres, where the thin filaments are anchored. In Mena/VASP double-deficient mice, β-actin networks were disrupted and the integrity of Z- and intercalated discs was markedly impaired.ConclusionsTogether, our data suggest that Mena, VASP, and αII-Spectrin assemble cardiac multi-protein complexes, which regulate cytoplasmic actin networks. Conversely, Mena/VASP deficiency results in disrupted β-actin assembly, Z- and intercalated disc malformation, and induces dilated cardiomyopathy and conduction abnormalities.

5-Lipoxygenase facilitates healing after myocardial infarction

Early healing after myocardial infarction (MI) is characterized by a strong inflammatory reaction. Most leukotrienes are pro-inflammatory and are therefore potential mediators of healing and remodeling after myocardial ischemia. The enzyme 5-lipoxygenase (5-LOX) has a key role in the transformation of arachidonic acid in leukotrienes. Thus, we tested the effect of 5-LOX on healing after MI. After chronic coronary artery ligation, early mortality was significantly increased in 5-LOX−/− when compared to matching wildtype (WT) mice due to left ventricular rupture. This effect could be reproduced in mice treated with the 5-LOX inhibitor Zileuton. A perfusion mismatch due to the vasoactive potential of leukotrienes is not responsible for left ventricular rupture since local blood flow assessed by magnetic resonance perfusion measurements was not different. However, after MI, there was an accentuation of the inflammatory reaction with an increase of pro-inflammatory macrophages. Yet, mortality was not changed in chimeric mice (WT vs. 5-LOX−/− bone marrow in 5-LOX−/− animals), indicating that an altered function of 5-LOX−/− inflammatory cells is not responsible for the phenotype. Collagen production and accumulation of fibroblasts were significantly reduced in 5-LOX−/− mice in vivo after MI. This might be due to an impaired migration of 5-LOX−/− fibroblasts, as shown in vitro to serum. In conclusion, a lack or inhibition of 5-LOX increases mortality after MI because of healing defects. This is not mediated by a change in local blood flow, but through an altered inflammation and/or fibroblast function.

The Estrogen Receptor-α Is Required and Sufficient to Maintain Physiological Glucose Uptake in the Mouse Heart

Estrogens attenuate cardiac hypertrophy and increase cardiac contractility via their cognate estrogen receptors (ERs) ER&agr; and ER&bgr;. Because female sex hormones enhance global glucose use and because myocardial function and mass are tightly linked to cardiac glucose metabolism, we tested the hypothesis that expression and activation of the ER&agr; might be required and sufficient to maintain physiological cardiac glucose uptake in the murine heart. Cardiac glucose uptake quantified in vivo by 18F-fluorodeoxyglucose positron emission tomography was strongly impaired in ovariectomized compared with gonadal intact female C57BL/6JO mice. The selective ER&agr; agonist 16&agr;-LE2 and the nonselective ER&agr; and ER&bgr; agonist 17&bgr;-estradiol completely restored cardiac glucose uptake in ovariectomized mice. Cardiac 18F-fluorodeoxyglucose uptake was strongly decreased in female ER&agr; knockout mice compared with wild-type littermates. Analysis of cardiac mRNA accumulation by quantitative RT-PCR revealed an upregulation of genes involved in glycolisis and tricarboxylic acid cycle by ER&agr; treatment. In conclusion, systemic activation of ER&agr; is sufficient, and its expression is required to maintain physiological glucose uptake in the murine heart, which is likely to contribute to known cardioprotective estrogen effects.

High dose aspirin and left ventricular remodelingafter myocardial infarction

AbstractBackgroundProinflammatory proteins like inflammatory cytokines are implicated in myocardial depression and left ventricular remodeling after myocardial infarction. High-dose aspirin inhibits cytokine activation. Therefore, we tested the influence of high-dose aspirin treatment on left ventricular remodeling in mice after myocardial infarction.Methods and resultsMice were treated for 4 weeks with placebo or aspirin (120 mg/kg per day) by Alzet mini-osmotic pumps after ligation of the left anterior descending coronary artery. Serial transthoracic echocardiography was performed at days 1, 7, and 28. Over the 4 weeks, mortality was not different between the groups (placebo 30.8%, aspirin 30.8%). On echocardiography, animals after myocardial infarction exhibited left ventricular dilatation (week 4, end-systolic area, placebo sham 8.9 ± 1.7 vs. placebo MI 15.9 ± 2.5 mm2), which was not changed by aspirin treatment (week 4, end-systolic area, aspirin MI 14.5 ± 1.3 mm2, p= ns vs. placebo MI). The expression of the proinflammatory cytokines TNF and IL-1β were markedly upregulated in mice with myocardial infarction on placebo. Cytokine expression was significantly reduced by aspirin treatment while collagen deposition was not influenced.ConclusionContinuous aspirin treatment (120 mg/kg/d) reduces the expression of proinflammatory cytokines after myocardial infarction, but does not affect post-infarct cardiac remodeling and cardiac function.

Exogenous Administration of a Recombinant Variant of TWEAK Impairs Healing after Myocardial Infarction by Aggravation of Inflammation

Background Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are upregulated after myocardial infarction (MI) in both humans and mice. They modulate inflammation and the extracellular matrix, and could therefore be important for healing and remodeling after MI. However, the function of TWEAK after MI remains poorly defined. Methods and results Following ligation of the left coronary artery, mice were injected twice per week with a recombinant human serum albumin conjugated variant of TWEAK (HSA-Flag-TWEAK), mimicking the activity of soluble TWEAK. Treatment with HSA-Flag-TWEAK resulted in significantly increased mortality in comparison to the placebo group due to myocardial rupture. Infarct size, extracellular matrix remodeling, and apoptosis rates were not different after MI. However, HSA-Flag-TWEAK treatment increased infiltration of proinflammatory cells into the myocardium. Accordingly, depletion of neutrophils prevented cardiac ruptures without modulating all-cause mortality. Conclusion Treatment of mice with HSA-Flag-TWEAK induces myocardial healing defects after experimental MI. This is mediated by an exaggerated neutrophil infiltration into the myocardium.