Publications by authors named "Heiko Bugger"

56 Publications

Mass Spectrometry-Based Redox and Protein Profiling of Failing Human Hearts.

Int J Mol Sci 2021 Feb 11;22(4). Epub 2021 Feb 11.

Faculty of Technical Chemistry, Institute of Chemical Technologies and Analytics, Vienna University of Technology-TU Wien, Getreidemarkt 9/164, 1060 Vienna, Austria.

Oxidative stress contributes to detrimental functional decline of the myocardium, leading to the impairment of the antioxidative defense, dysregulation of redox signaling, and protein damage. In order to precisely dissect the changes of the myocardial redox state correlated with oxidative stress and heart failure, we subjected left-ventricular tissue specimens collected from control or failing human hearts to comprehensive mass spectrometry-based redox and quantitative proteomics, as well as glutathione status analyses. As a result, we report that failing hearts have lower glutathione to glutathione disulfide ratios and increased oxidation of a number of different proteins, including constituents of the contractile machinery as well as glycolytic enzymes. Furthermore, quantitative proteomics of failing hearts revealed a higher abundance of proteins responsible for extracellular matrix remodeling and reduced abundance of several ion transporters, corroborating contractile impairment. Similar effects were recapitulated by an in vitro cell culture model under a controlled oxygen atmosphere. Together, this study provides to our knowledge the most comprehensive report integrating analyses of protein abundance and global and peptide-level redox state in end-stage failing human hearts as well as oxygen-dependent redox and global proteome profiles of cultured human cardiomyocytes.
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http://dx.doi.org/10.3390/ijms22041787DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7916846PMC
February 2021

Complications and mortality of cardiovascular emergency admissions during COVID-19 associated restrictive measures.

PLoS One 2020 24;15(9):e0239801. Epub 2020 Sep 24.

Division of Cardiology, Medical University of Graz, Graz, Austria.

While hospital admissions for myocardial infarction (MI) and pulmonary embolism (PE) are decreased during the COVID-19 pandemic, controversy remains about respective complication and mortality rates. This study evaluated admission rates, complications, and intrahospital mortality for selected life-threatening cardiovascular emergencies (MI, PE, and acute aortic dissection (AAD)) during COVID-19-associated restrictive social measures (RM) in Styria, Austria. By screening a patient information system for International Statistical Classification of Diseases and Related Health Problems (ICD) diagnosis codes covering more than 85% of acute hospital admissions in the state of Styria (~1.24 million inhabitants), we retrospectively identified patients with admission diagnoses for MI (I21, I22), PE (I26), and AAD (I71). Rates of complications such as cardiogenic shock and cardiopulmonary resuscitation, treatment escalations (thrombolysis for PE), and mortality were analyzed by patient chart review during 6 weeks following onset of COVID-19 associated RM, and during respective time frames in the years 2016 to 2019. 1,668 patients were included. Cumulative admissions for MI, PE and AAD decreased (RR 0.77; p<0.001) during RM compared to previous years. In contrast, intrahospital mortality increased by 65% (RR 1.65; p = 0.041), mainly driven by mortality following MI (RR 1.80; p = 0.042). PE patients received more frequently thrombolysis treatment (RR 3.63; p = 0.006), while rates of cardiogenic shock and cardiopulmonary resuscitation remained unchanged. Of 226 patients hospitalized during RM, 81 patients with suspected COVID-19 disease were screened for SARS-CoV-2 infection with only 5 testing positive. Thus, cumulative hospital admissions for cardiovascular emergencies decreased during COVID-19 associated RM while intrahospital mortality increased.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239801PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7514100PMC
October 2020

Empagliflozin protects heart from inflammation and energy depletion via AMPK activation.

Pharmacol Res 2020 08 17;158:104870. Epub 2020 May 17.

Division of Cardiology, Medical University of Graz, Auenbruggerplatz 15, 8036 Graz, Austria. Electronic address:

Aims: Sodium-glucose co-transporter 2 (SGLT2) were originally developed as kidney-targeting anti-diabetic drugs. However, due to their beneficial cardiac off-target effects (as SGLT2 is not expressed in the heart), these antagonists currently receive intense clinical interest in the context of heart failure (HF) in patients with or without diabetes mellitus (DM). Since the mechanisms by which these beneficial effects are mediated are still unclear yet, inflammation that is present in DM and HF has been proposed as a potential pharmacological intervention strategy. Therefore, we tested the hypothesis that the SGLT2 inhibitor, empagliflozin, displays anti-inflammatory potential along with its glucose-lowering property.

Methods And Results: Lipopolysaccharide (LPS) was used to induce inflammation in vitro and in vivo. In cardiomyocytes and macrophages empagliflozin attenuated LPS-induced TNFα and iNOS expression. Analysis of intracellular signalling pathways suggested that empagliflozin activates AMP kinase (AMPK) in both cell types with or without LPS-treatment. Moreover, the SGLT2 inhibitor increased the expression of anti-inflammatory M2 marker proteins in LPS-treated macrophages. Additionally, empagliflozin-mediated AMPK activation prevented LPS-induced ATP/ADP depletion. In vivo administration of LPS in mice impaired cardiac contractility and aortic endothelial relaxation in response to acetylcholine, whereby co-administration of empagliflozin preserved cardiovascular function. These findings were accompanied by improved cardiac AMPK phosphorylation and ATP/ADP, reduced cardiac iNOS, plasma TNFα and creatine kinase MB levels.

Conclusion: Our data identify a novel cardio protective mechanism of SGLT2 inhibitor, empagliflozin, suggesting that AMPK activation-mediated energy repletion and reduced inflammation contribute to the observed cardiovascular benefits of the drug in HF.
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http://dx.doi.org/10.1016/j.phrs.2020.104870DOI Listing
August 2020

Mitochondrial ROS in myocardial ischemia reperfusion and remodeling.

Biochim Biophys Acta Mol Basis Dis 2020 07 12;1866(7):165768. Epub 2020 Mar 12.

Division of Cardiology, Medical University of Graz, Graz, Austria.

Despite major progress in interventional and medical treatments, myocardial infarction (MI) and subsequent development of heart failure (HF) are still associated with high mortality. Both during ischemia reperfusion (IR) in the acute setting of MI, as well as in the chronic remodeling process following MI, oxidative stress substantially contributes to cardiac damage. Reactive oxygen species (ROS) generated within mitochondria are particular drivers of mechanisms contributing to IR injury, including induction of mitochondrial permeability transition or oxidative damage of intramitochondrial structures and molecules. But even beyond the acute setting, mechanisms like inflammatory signaling, extracellular remodeling, or pro-apoptotic signaling that contribute to post-infarction remodeling are regulated by mitochondrial ROS. In the current review, we discuss both sources and consequences of mitochondrial ROS during IR and in the chronic setting following MI, thereby emphasizing the potential therapeutic value of attenuating mitochondrial ROS to improve outcome and prognosis for patients suffering MI.
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http://dx.doi.org/10.1016/j.bbadis.2020.165768DOI Listing
July 2020

Mitochondrial Mechanisms in Diabetic Cardiomyopathy.

Diabetes Metab J 2020 02;44(1):33-53

Division of Cardiology, Medical University of Graz, Graz, Austria.

Mitochondrial medicine is increasingly discussed as a promising therapeutic approach, given that mitochondrial defects are thought to contribute to many prevalent diseases and their complications. In individuals with diabetes mellitus (DM), defects in mitochondrial structure and function occur in many organs throughout the body, contributing both to the pathogenesis of DM and complications of DM. Diabetic cardiomyopathy (DbCM) is increasingly recognized as an underlying cause of increased heart failure in DM, and several mitochondrial mechanisms have been proposed to contribute to the development of DbCM. Well established mechanisms include myocardial energy depletion due to impaired adenosine triphosphate (ATP) synthesis and mitochondrial uncoupling, and increased mitochondrial oxidative stress. A variety of upstream mechanisms of impaired ATP regeneration and increased mitochondrial reactive oxygen species have been proposed, and recent studies now also suggest alterations in mitochondrial dynamics and autophagy, impaired mitochondrial Ca²⁺ uptake, decreased cardiac adiponectin action, increased O-GlcNAcylation, and impaired activity of sirtuins to contribute to mitochondrial defects in DbCM, among others. In the current review, we present and discuss the evidence that underlies both established and recently proposed mechanisms that are thought to contribute to mitochondrial dysfunction in DbCM.
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http://dx.doi.org/10.4093/dmj.2019.0185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7043970PMC
February 2020

Dysregulation of the Mitochondrial Proteome Occurs in Mice Lacking Adiponectin Receptor 1.

Front Endocrinol (Lausanne) 2019 13;10:872. Epub 2019 Dec 13.

Division of Cardiology and Angiology I, Heart Center Freiburg University, Freiburg, Germany.

Decreased serum adiponectin levels in type 2 diabetes has been linked to the onset of mitochondrial dysfunction in diabetic complications by impairing AMPK-SIRT1-PGC-1α signaling via impaired adiponectin receptor 1 (AdipoR1) signaling. Here, we aimed to characterize the previously undefined role of disrupted AdipoR1 signaling on the mitochondrial protein composition of cardiac, renal, and hepatic tissues as three organs principally associated with diabetic complications. Comparative proteomics were performed in mitochondria isolated from the heart, kidneys and liver of mice. A total of 790, 1,573, and 1,833 proteins were identified in cardiac, renal and hepatic mitochondria, respectively. While 121, 98, and 78 proteins were differentially regulated in cardiac, renal, and hepatic tissue of 1 mice, respectively; only 15 proteins were regulated in the same direction across all investigated tissues. Enrichment analysis of differentially expressed proteins revealed disproportionate representation of proteins involved in oxidative phosphorylation conserved across tissue types. Curated pathway analysis identified HNF4, NRF1, LONP, RICTOR, SURF1, insulin receptor, and PGC-1α as candidate upstream regulators. In high fat-fed non-transgenic mice with obesity and insulin resistance, AdipoR1 gene expression was markedly reduced in heart (-70%), kidney (-80%), and liver (-90%) (all < 0.05) as compared to low fat-fed mice. NRF1 was the only upstream regulator downregulated both in 1 mice and in high fat-fed mice, suggesting common mechanisms of regulation. Thus, AdipoR1 signaling regulates mitochondrial protein composition across all investigated tissues in a functionally conserved, yet molecularly distinct, manner. The biological significance and potential implications of impaired AdipoR1 signaling are discussed.
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http://dx.doi.org/10.3389/fendo.2019.00872DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6923683PMC
December 2019

HDAC inhibition improves cardiopulmonary function in a feline model of diastolic dysfunction.

Sci Transl Med 2020 01;12(525)

Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.

Heart failure with preserved ejection fraction (HFpEF) is a major health problem without effective therapies. This study assessed the effects of histone deacetylase (HDAC) inhibition on cardiopulmonary structure, function, and metabolism in a large mammalian model of pressure overload recapitulating features of diastolic dysfunction common to human HFpEF. Male domestic short-hair felines ( = 31, aged 2 months) underwent a sham procedure ( = 10) or loose aortic banding ( = 21), resulting in slow-progressive pressure overload. Two months after banding, animals were treated daily with suberoylanilide hydroxamic acid (b + SAHA, 10 mg/kg, = 8), a Food and Drug Administration-approved pan-HDAC inhibitor, or vehicle (b + veh, = 8) for 2 months. Echocardiography at 4 months after banding revealed that b + SAHA animals had significantly reduced left ventricular hypertrophy (LVH) ( < 0.0001) and left atrium size ( < 0.0001) versus b + veh animals. Left ventricular (LV) end-diastolic pressure and mean pulmonary arterial pressure were significantly reduced in b + SAHA ( < 0.01) versus b + veh. SAHA increased myofibril relaxation ex vivo, which correlated with in vivo improvements of LV relaxation. Furthermore, SAHA treatment preserved lung structure, compliance, blood oxygenation, and reduced perivascular fluid cuffs around extra-alveolar vessels, suggesting attenuated alveolar capillary stress failure. Acetylation proteomics revealed that SAHA altered lysine acetylation of mitochondrial metabolic enzymes. These results suggest that acetylation defects in hypertrophic stress can be reversed by HDAC inhibitors, with implications for improving cardiac structure and function in patients.
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http://dx.doi.org/10.1126/scitranslmed.aay7205DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065257PMC
January 2020

Visualization of Sirtuin 4 Distribution between Mitochondria and the Nucleus, Based on Bimolecular Fluorescence Self-Complementation.

Cells 2019 12 6;8(12). Epub 2019 Dec 6.

Gottfried Schatz Research Center, Chair of Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, 8010 Graz, Austria.

Mitochondrial sirtuins (Sirts) control important cellular processes related to stress. Despite their regulatory importance, however, the dynamics and subcellular distributions of Sirts remain debatable. Here, we investigate the subcellular localization of sirtuin 4 (Sirt4), a sirtuin variant with a mitochondrial targeting sequence (MTS), by expressing Sirt4 fused to the superfolder green fluorescent protein (Sirt4-sfGFP) in HeLa and pancreatic β-cells. Super resolution fluorescence microscopy revealed the trapping of Sirt4-sfGFP to the outer mitochondrial membrane (OMM), possibly due to slow mitochondrial import kinetics. In many cells, Sirt4-sfGFP was also present within the cytosol and nucleus. Moreover, the expression of Sirt4-sfGFP induced mitochondrial swelling in HeLa cells. In order to bypass these effects, we applied the self-complementing split fluorescent protein (FP) technology and developed mito-STAR (mitochondrial sirtuin 4 tripartite abundance reporter), a tripartite probe for the visualization of Sirt4 distribution between mitochondria and the nucleus in single cells. The application of mito-STAR proved the importation of Sirt4 into the mitochondrial matrix and demonstrated its localization in the nucleus under mitochondrial stress conditions. Moreover, our findings highlight that the self-complementation of split FP is a powerful technique to study protein import efficiency in distinct cellular organelles.
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http://dx.doi.org/10.3390/cells8121583DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6953047PMC
December 2019

Impaired SIRT3 activity mediates cardiac dysfunction in endotoxemia by calpain-dependent disruption of ATP synthesis.

J Mol Cell Cardiol 2019 08 13;133:138-147. Epub 2019 Jun 13.

Heart Center Freiburg University, Department of Cardiology and Angiology, Freiburg, Germany; Faculty of Medicine, University of Freiburg, Freiburg, Germany; Division of Cardiology, Medical University of Graz, Graz, Austria. Electronic address:

Background: Sepsis-induced cardiomyopathy contributes to the high mortality of septic shock in critically ill patients. Since the underlying mechanisms are incompletely understood, we hypothesized that sepsis-induced impairment of sirtuin 3 (SIRT3) activity contributes to the development of septic cardiomyopathy.

Methods And Results: Treatment of mice with lipopolysaccharide (LPS) for 6 h resulted in myocardial NAD depletion and increased mitochondrial protein acetylation, indicating impaired myocardial SIRT3 activity due to NAD depletion. LPS treatment also resulted in impaired cardiac output in isolated working hearts, indicating endotoxemia-induced cardiomyopathy. Maintaining normal myocardial NAD levels in LPS-treated mice by Poly(ADP-ribose)polymerase 1 (PARP1) deletion prevented cardiac dysfunction, whereas additional SIRT3 deficiency blunted this beneficial effect, indicating that impaired SIRT3 activity contributes to cardiac dysfunction in endotoxemia. Measurements of mitochondrial ATP synthesis suggest that LPS-induced contractile dysfunction may result from cardiac energy depletion due to impaired SIRT3 activity. Pharmacological inhibition of mitochondrial calpains using MDL28170 normalized LPS-induced cleavage of the ATP5A1 subunit of ATP synthase and normalized contractile dysfunction, suggesting that cardiac energy depletion may result from calpain-mediated cleavage of ATP5A1. These beneficial effects were completely blunted by SIRT3 deficiency. Finally, a gene set enrichment analysis of hearts of patients with septic, ischemic or dilated cardiomyopathy revealed a sepsis-specific suppression of SIRT3 deacetylation targets, including ATP5A1, indicating a functional relevance of SIRT3-dependent pathways in human sepsis.

Conclusions: Impaired SIRT3 activity may mediate cardiac dysfunction in endotoxemia by facilitating calpain-mediated disruption of ATP synthesis, suggesting SIRT3 activation as a potential therapeutic strategy to treat septic cardiomyopathy.
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http://dx.doi.org/10.1016/j.yjmcc.2019.06.008DOI Listing
August 2019

Established and Emerging Mechanisms of Diabetic Cardiomyopathy.

J Lipid Atheroscler 2019 May 13;8(1):26-47. Epub 2019 May 13.

Division of Cardiology, Medical University of Graz, Graz, Austria.

Diabetes mellitus increases the risk for the development of heart failure even in the absence of coronary artery disease and hypertension, a cardiac entity termed diabetic cardiomyopathy (DC). Clinically, DC is increasingly recognized and typically characterized by concentric cardiac hypertrophy and diastolic dysfunction, ultimately resulting in heart failure with preserved ejection fraction (HFpEF) and potentially even heart failure with reduced ejection fraction (HFrEF). Numerous molecular mechanisms have been proposed to underlie the alterations in myocardial structure and function in DC, many of which show similar alterations in the failing heart. Well investigated and established mechanisms of DC include increased myocardial fibrosis, enhanced apoptosis, oxidative stress, impaired intracellular calcium handling, substrate metabolic alterations, and inflammation, among others. In addition, a number of novel mechanisms that receive increasing attention have been identified in recent years, including autophagy, dysregulation of microRNAs, epigenetic mechanisms, and alterations in mitochondrial protein acetylation, dynamics and quality control. This review aims to provide an overview and update of established underlying mechanisms of DC, as well as a discussion of recently identified and emerging mechanisms that may also contribute to the structural and functional alterations in DC.
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http://dx.doi.org/10.12997/jla.2019.8.1.26DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7379081PMC
May 2019

Postpartum hormones oxytocin and prolactin cause pro-arrhythmic prolongation of cardiac repolarization in long QT syndrome type 2.

Europace 2019 Jul;21(7):1126-1138

Department of Cardiology and Angiology I, Heart Center University of Freiburg, Hugstetter Str. 55, Freiburg, Germany.

Aims: Women with long QT syndrome 2 (LQT2) have a particularly high postpartal risk for lethal arrhythmias. We aimed at investigating whether oxytocin and prolactin contribute to this risk by affecting repolarization.

Methods And Results: In female transgenic LQT2 rabbits (HERG-G628S, loss of IKr), hormone effects on QT/action potential duration (APD) were assessed (0.2-200 ng/L). Hormone effects (200 ng/L) on ion currents and cellular APD were determined in transfected cells and LQT2 cardiomyocytes. Hormone effects on ion channels were assessed with qPCR and western blot. Experimental data were incorporated into in silico models to determine the pro-arrhythmic potential. Oxytocin prolonged QTc and steepened QT/RR-slope in vivo and prolonged ex vivo APD75 in LQT2 hearts. Prolactin prolonged APD75 at high concentrations. As underlying mechanisms, we identified an oxytocin- and prolactin-induced acute reduction of IKs-tail and IKs-steady (-25.5%, oxytocin; -13.3%, prolactin, P < 0.05) in CHO-cells and LQT2-cardiomyocytes. IKr currents were not altered. This oxytocin-/prolactin-induced IKs reduction caused APD90 prolongation (+11.9%/+13%, P < 0.05) in the context of reduced/absent IKr in LQT2 cardiomyocytes. Hormones had no effect on IK1 and ICa,L in cardiomyocytes. Protein and mRNA levels of CACNA1C/Cav1.2 and RyR2 were enhanced by oxytocin and prolactin. Incorporating these hormone effects into computational models resulted in reduced repolarization reserve and increased propensity to pro-arrhythmic permanent depolarization, lack of capture and early afterdepolarizations formation.

Conclusions: Postpartum hormones oxytocin and prolactin prolong QT/APD in LQT2 by reducing IKs and by increasing Cav1.2 and RyR2 expression/transcription, thereby contributing to the increased postpartal arrhythmic risk in LQT2.
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http://dx.doi.org/10.1093/europace/euz037DOI Listing
July 2019

Platelet Serotonin Aggravates Myocardial Ischemia/Reperfusion Injury via Neutrophil Degranulation.

Circulation 2019 02;139(7):918-931

Faculty of Medicine (M.M., N.H., C.S., T.W., T.M., C.H., C.K., M.S., L.D., C.W., D.S., C.N., H.B., D.W., C.B., I.H., D.D.), University of Freiburg, Germany.

Background: Platelets store large amounts of serotonin that they release during thrombus formation or acute inflammation. This facilitates hemostasis and modulates the inflammatory response.

Methods: Infarct size, heart function, and inflammatory cell composition were analyzed in mouse models of myocardial reperfusion injury with genetic and pharmacological depletion of platelet serotonin. These studies were complemented by in vitro serotonin stimulation assays of platelets and leukocytes in mice and men, and by measuring plasma serotonin levels and leukocyte activation in patients with acute coronary syndrome.

Results: Platelet-derived serotonin induced neutrophil degranulation with release of myeloperoxidase and hydrogen peroxide (HO) and increased expression of membrane-bound leukocyte adhesion molecule CD11b, leading to enhanced inflammation in the infarct area and reduced myocardial salvage. In patients hospitalized with acute coronary syndrome, plasmatic serotonin levels correlated with CD11b expression on neutrophils and myeloperoxidase plasma levels. Long-term serotonin reuptake inhibition-reported to protect patients with depression from cardiovascular events-resulted in the depletion of platelet serotonin stores in mice. These mice displayed a reduction in neutrophil degranulation and preserved cardiac function. In line, patients with depression using serotonin reuptake inhibition, presented with suppressed levels of CD11b surface expression on neutrophils and lower myeloperoxidase levels in blood.

Conclusions: Taken together, we identify serotonin as a potent therapeutic target in neutrophil-dependent thromboinflammation during myocardial reperfusion injury.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.118.033942DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370531PMC
February 2019

Transgenic short-QT syndrome 1 rabbits mimic the human disease phenotype with QT/action potential duration shortening in the atria and ventricles and increased ventricular tachycardia/ventricular fibrillation inducibility.

Eur Heart J 2019 03;40(10):842-853

Department of Cardiology and Angiology I, Heart Center University of Freiburg, Hugstetter Str. 55, Freiburg, Germany.

Aims: Short-QT syndrome 1 (SQT1) is an inherited channelopathy with accelerated repolarization due to gain-of-function in HERG/IKr. Patients develop atrial fibrillation, ventricular tachycardia (VT), and sudden cardiac death with pronounced inter-individual variability in phenotype. We generated and characterized transgenic SQT1 rabbits and investigated electrical remodelling.

Methods And Results: Transgenic rabbits were generated by oocyte-microinjection of β-myosin-heavy-chain-promoter-KCNH2/HERG-N588K constructs. Short-QT syndrome 1 and wild type (WT) littermates were subjected to in vivo ECG, electrophysiological studies, magnetic resonance imaging, and ex vivo action potential (AP) measurements. Electrical remodelling was assessed using patch clamp, real-time PCR, and western blot. We generated three SQT1 founders. QT interval was shorter and QT/RR slope was shallower in SQT1 than in WT (QT, 147.8 ± 2 ms vs. 166.4 ± 3, P < 0.0001). Atrial and ventricular refractoriness and AP duration were shortened in SQT1 (vAPD90, 118.6 ± 5 ms vs. 154.4 ± 2, P < 0.0001). Ventricular tachycardia/fibrillation (VT/VF) inducibility was increased in SQT1. Systolic function was unaltered but diastolic relaxation was enhanced in SQT1. IKr-steady was increased with impaired inactivation in SQT1, while IKr-tail was reduced. Quinidine prolonged/normalized QT and action potential duration (APD) in SQT1 rabbits by reducing IKr. Diverse electrical remodelling was observed: in SQT1, IK1 was decreased-partially reversing the phenotype-while a small increase in IKs may partly contribute to an accentuation of the phenotype.

Conclusion: Short-QT syndrome 1 rabbits mimic the human disease phenotype on all levels with shortened QT/APD and increased VT/VF-inducibility and show similar beneficial responses to quinidine, indicating their value for elucidation of arrhythmogenic mechanisms and identification of novel anti-arrhythmic strategies.
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http://dx.doi.org/10.1093/eurheartj/ehy761DOI Listing
March 2019

Purinergic receptor Y (P2Y)- dependent VCAM-1 expression promotes immune cell infiltration in metabolic syndrome.

Basic Res Cardiol 2018 10 18;113(6):45. Epub 2018 Oct 18.

Department of Cardiology and Angiology I, University Heart Center Freiburg, Faculty of Medicine, University of Freiburg, Hugstetter Str. 55, 79106, Freiburg, Germany.

Sterile inflammation of visceral fat, provoked by dying adipocytes, links the metabolic syndrome to cardiovascular disease. Danger-associated molecular patterns, such as adenosine triphosphate (ATP), are released by activated or dying cells and orchestrate leukocyte infiltration and inflammation via the purinergic receptor P2Y. The gene expression of ATP receptor P2Y did not change in several tissues in the course of obesity, but was increased within epididymal fat. Adipose tissue from P2Y mice consuming high-fat diet (HFD) contained less crown-like structures with a reduced frequency of adipose tissue macrophages (ATMs). This was likely due to decreased leukocyte migration because of missing VCAM-1 exposition on P2Y deficient hypertrophic adipose tissue endothelial cells. Accordingly, P2Y mice showed blunted traits of the metabolic syndrome: they gained less weight compared to P2Y controls, while intake of food and movement behaviour remained unchanged. Liver and adipose tissue were smaller in P2Y animals. Insulin tolerance testing (ITT) performed in obese P2Y mice revealed a better insulin sensitivity as well as lower plasma C-peptide and cholesterol levels. We demonstrate that interfering with somatic P2Y signalling prevents excessive immune cell deposition in diet-induced obesity (DIO), both attenuating adipose tissue inflammation and ameliorating the metabolic phenotype. Thus, blocking the P2Y cascade may be a promising strategy to limit metabolic disease and its sequelae.
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http://dx.doi.org/10.1007/s00395-018-0702-1DOI Listing
October 2018

Electro-mechanical (dys-)function in long QT syndrome type 1.

Int J Cardiol 2019 Jan 9;274:144-151. Epub 2018 Jul 9.

Department of Cardiology and Angiology I, Heart Center, University of Freiburg, Freiburg, Germany; Faculty of Medicine, University of Freiburg, Freiburg, Germany. Electronic address:

Background: Prolonged repolarization is the hallmark of long QT syndrome (LQTS), which is associated with subclinical mechanical dysfunction. We aimed at elucidating mechanical cardiac function in LQTS type 1 (loss of I) and its modification upon further prolongation of the action potential (AP) by I-blockade (E-4031).

Methods: Transgenic LQT1 and wild type (WT) rabbits (n = 12/10) were subjected to tissue phase mapping MRI, ECG, and epicardial AP recording. Protein and mRNA levels of ion channels and Ca handling proteins (n = 4/4) were determined. In silico single cell AP and tension modeling was performed.

Results: At baseline, QT intervals were longer in LQT1 compared to WT rabbits, but baseline systolic and diastolic myocardial peak velocities were similar in LQT1 and WT. E-4031 prolonged QT more pronouncedly in LQT1. Additionally, E-4031 increased systolic and decreased diastolic peak velocities more markedly in LQT1 - unmasking systolic and diastolic LQT1-specific mechanical alterations. E-4031-induced alterations of diastolic peak velocities correlated with the extent of QT prolongation.

Conclusion: While baseline mechanical function is normal in LQT1 despite a distinct QT prolongation, further prolongation of repolarization by I-blocker E-4031 unmasks mechanical differences between LQT1 and WT with enhanced systolic and impaired diastolic function only in LQT1. These data indicate an importance of the extent of QT prolongation and the contribution of different impaired ion currents for conveying mechanical dysfunction.
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http://dx.doi.org/10.1016/j.ijcard.2018.07.050DOI Listing
January 2019

The effect of oxygen in Sirt3-mediated myocardial protection: a proof-of-concept study in cultured cardiomyoblasts.

J Thromb Thrombolysis 2018 Jul;46(1):102-112

Department of Cardiology, University Heart Center Zurich, University Hospital Zurich, Ramistr. 100, 8098, Zurich, Switzerland.

Sirtuin 3 is a nicotinamide adenine dinucleotide dependent mitochondrial deacetylase that governs mitochondrial metabolism and oxidative defense. The demise in myocardial function following myocardial ischemia has been associated with mitochondrial dysfunction. Sirt3 maintains myocardial contractile function and protects from cardiac hypertrophy. The role of Sirt3 in ischemia is controversial. Our objective was to understand, under what circumstances Sirt3 is protective in different facets of ischemia, using an in vitro proof-of-concept approach based on simulated ischemia in cultured cardiomyoblasts. Cultured H9c2 cardiomyoblasts were subjected to hypoxia and/or serum deprivation, the combination of which we refer to as simulated ischemia. Apoptosis, as assessed by Annexin V staining in life-cell imaging and propidium-iodide inclusion in flow cytometry, was enhanced following simulated ischemia. Interestingly, serum deprivation was a stronger trigger of apoptosis than hypoxia. Knockdown of Sirt3 further increased apoptosis upon serum deprivation, whereas no such effect occurred upon additional hypoxia. Similarly, only upon serum deprivation but not upon simulated ischemia, silencing of Sirt3 led to a deterioration of mitochondrial function in extracellular flux analysis. In the absence of oxygen these Sirt3-dependent effects were abolished. These data indicate, that Sirt3-mediated myocardial protection is oxygen-dependent. Thus, mitochondrial respiration takes center-stage in Sirt3-dependent prevention of stress-induced myocardial damage.
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http://dx.doi.org/10.1007/s11239-018-1677-3DOI Listing
July 2018

Gene expression analysis to identify mechanisms underlying heart failure susceptibility in mice and humans.

Basic Res Cardiol 2018 01 29;113(1). Epub 2017 Dec 29.

Cardiology and Angiology I, Heart Center, Freiburg University, Hugstetter Str. 55, 79106, Freiburg, Germany.

Genetic factors are known to modulate cardiac susceptibility to ventricular hypertrophy and failure. To determine how strain influences the transcriptional response to pressure overload-induced heart failure (HF) and which of these changes accurately reflect the human disease, we analyzed the myocardial transcriptional profile of mouse strains with high (C57BL/6J) and low (129S1/SvImJ) susceptibility for HF development, which we compared to that of human failing hearts. Following transverse aortic constriction (TAC), C57BL/6J mice developed overt HF while 129S1/SvImJ did not. Despite a milder aortic constriction, impairment of ejection fraction and ventricular remodeling (dilation, fibrosis) was more pronounced in C57BL/6J mice. Similarly, changes in myocardial gene expression were more robust in C57BL/6J (461 genes) compared to 129S1/SvImJ mice (71 genes). When comparing these patterns to human dilated cardiomyopathy (1344 genes), C57BL/6J mice tightly grouped to human hearts. Overlay and bioinformatic analysis of the transcriptional profiles of C57BL/6J mice and human failing hearts identified six co-regulated genes (POSTN, CTGF, FN1, LOX, NOX4, TGFB2) with established link to HF development. Pathway enrichment analysis identified angiotensin and IGF-1 signaling as most enriched putative upstream regulator and pathway, respectively, shared between TAC-induced HF in C57BL/6J mice and in human failing hearts. TAC-induced heart failure in C57BL/6J mice more closely reflects the gene expression pattern of human dilated cardiomyopathy compared to 129S1/SvImJ mice. Unbiased as well as targeted gene expression and pathway analyses identified periostin, angiotensin signaling, and IGF-1 signaling as potential causes of increased HF susceptibility in C57BL/6J mice and as potentially useful drug targets for HF treatment.
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http://dx.doi.org/10.1007/s00395-017-0666-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5764079PMC
January 2018

Mitochondrial Reactive Oxygen Species in Lipotoxic Hearts Induce Post-Translational Modifications of AKAP121, DRP1, and OPA1 That Promote Mitochondrial Fission.

Circ Res 2018 01 1;122(1):58-73. Epub 2017 Nov 1.

From the Division of Endocrinology and Metabolism, Fraternal Order of Eagles Diabetes Research Center, Roy J. and Lucille A. Carver College of Medicine (K.T., J.S., G.A.J., A.R.T., R.M., H.C.K., Y.Z., R.S., R.O.P., E.D.A.) and Department of Health and Human Physiology (V.A.L.), University of Iowa, Iowa City; Division of Endocrinology, Metabolism, and Diabetes and Program in Molecular Medicine (K.T., H.B., A.R.W., J.S., X.X.H., C.L.S., E.D.A.), Nora Eccles Harrison Cardiovascular Research and Training Institute (K.W.S.), and Department of Biochemistry (O.K.), University of Utah School of Medicine, Salt Lake City; Cardiology and Angiology I (H.B.) and Institute for Experimental Cardiovascular Medicine (E.A.R.-Z., P.K.), Heart Center Freiburg University, and Faculty of Medicine (H.B., E.A.R.-Z., P.K.), University of Freiburg, Germany; Division of Molecular and Cellular Pathology, Department of Pathology, University of Alabama at Birmingham (A.R.W.); Department of Radiology (T.L.S., K.I.S.) and Diabetic Cardiovascular Disease Center, Cardiovascular Division (J.E.S.), Washington University School of Medicine, St. Louis, MO; Division of Cardiology, Department of Medicine, University of Colorado Anschutz Medical Center, Aurora (G.C.S.); and Department of Biochemistry and Nebraska Redox Biology Center, University of Nebraska, Lincoln (O.K.).

Rationale: Cardiac lipotoxicity, characterized by increased uptake, oxidation, and accumulation of lipid intermediates, contributes to cardiac dysfunction in obesity and diabetes mellitus. However, mechanisms linking lipid overload and mitochondrial dysfunction are incompletely understood.

Objective: To elucidate the mechanisms for mitochondrial adaptations to lipid overload in postnatal hearts in vivo.

Methods And Results: Using a transgenic mouse model of cardiac lipotoxicity overexpressing ACSL1 (long-chain acyl-CoA synthetase 1) in cardiomyocytes, we show that modestly increased myocardial fatty acid uptake leads to mitochondrial structural remodeling with significant reduction in minimum diameter. This is associated with increased palmitoyl-carnitine oxidation and increased reactive oxygen species (ROS) generation in isolated mitochondria. Mitochondrial morphological changes and elevated ROS generation are also observed in palmitate-treated neonatal rat ventricular cardiomyocytes. Palmitate exposure to neonatal rat ventricular cardiomyocytes initially activates mitochondrial respiration, coupled with increased mitochondrial polarization and ATP synthesis. However, long-term exposure to palmitate (>8 hours) enhances ROS generation, which is accompanied by loss of the mitochondrial reticulum and a pattern suggesting increased mitochondrial fission. Mechanistically, lipid-induced changes in mitochondrial redox status increased mitochondrial fission by increased ubiquitination of AKAP121 (A-kinase anchor protein 121) leading to reduced phosphorylation of DRP1 (dynamin-related protein 1) at Ser637 and altered proteolytic processing of OPA1 (optic atrophy 1). Scavenging mitochondrial ROS restored mitochondrial morphology in vivo and in vitro.

Conclusions: Our results reveal a molecular mechanism by which lipid overload-induced mitochondrial ROS generation causes mitochondrial dysfunction by inducing post-translational modifications of mitochondrial proteins that regulate mitochondrial dynamics. These findings provide a novel mechanism for mitochondrial dysfunction in lipotoxic cardiomyopathy.
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http://dx.doi.org/10.1161/CIRCRESAHA.117.311307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5756120PMC
January 2018

Interregional electro-mechanical heterogeneity in the rabbit myocardium.

Prog Biophys Mol Biol 2017 11 24;130(Pt B):344-355. Epub 2017 Jun 24.

Department of Cardiology and Angiology I, Heart Center University of Freiburg, Hugstetter Strasse 55, 79106 Freiburg, Germany; Faculty of Medicine, University of Freiburg, Breisacher Strasse 153, 79110 Freiburg, Germany; Institute for Experimental Cardiovascular Medicine, Heart Center University of Freiburg, Medical Center - University of Freiburg, Elsaesserstrasse 2q, 79110 Freiburg, Germany. Electronic address:

Background: Increased electrical heterogeneity has been causatively linked to arrhythmic disorders, yet the knowledge about physiological heterogeneity remains incomplete. This study investigates regional electro-mechanical heterogeneities in rabbits, one of the key animal models for arrhythmic disorders.

Methods And Findings: 7 wild-type rabbits were examined by phase-contrast magnetic resonance imaging in vivo to assess cardiac wall movement velocities. Using a novel data-processing algorithm regional contraction-like profiles were calculated. Contraction started earlier and was longer in left ventricular (LV) apex than base. Patch clamp recordings showed longer action potentials (AP) in LV apex compared to the base of LV, septum, and right ventricle. Western blots of cardiac ion channels and calcium handling proteins showed lower expression of Cav1.2, KvLQT1, Kv1.4, NCX and Phospholamban in LV apex vs. base. A single-cell in silico model integrating the quantitative regional differences in ion channels reproduced a longer contraction and longer AP in apex vs. base.

Conclusions: Apico-basal electro-mechanical heterogeneity is physiologically present in the healthy rabbit heart. An apico-basal electro-mechanical gradient exists with longer APD and contraction duration in the apex and associated regionally heterogeneous expression of five key proteins. This pattern of apical mechanical dominance probably serves to increase pumping efficiency.
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http://dx.doi.org/10.1016/j.pbiomolbio.2017.06.016DOI Listing
November 2017

Phase-contrast magnet resonance imaging reveals regional, transmural, and base-to-apex dispersion of mechanical dysfunction in patients with long QT syndrome.

Heart Rhythm 2017 09 4;14(9):1388-1397. Epub 2017 May 4.

Department of Cardiology and Angiology I, Heart Center, University of Freiburg, Freiburg, Germany; Faculty of Medicine, University of Freiburg, Freiburg, Germany; Institute for Experimental Cardiovascular Medicine, Heart Center, University of Freiburg, Freiburg, Germany. Electronic address:

Background: Regional dispersion of prolonged repolarization is a hallmark of long QT syndrome (LQTS). We have also revealed regional heterogeneities in mechanical dysfunction in transgenic rabbit models of LQTS.

Objective: In this clinical pilot study, we investigated whether patients with LQTS exhibit dispersion of mechanical/diastolic dysfunction.

Methods: Nine pediatric patients with genotyped LQTS (12.2 ± 3.3 years) and 9 age- and sex-matched healthy controls (10.6 ± 1.5 years) were subjected to phase-contrast magnetic resonance imaging to analyze radial (Vr) and longitudinal (Vz) myocardial velocities during systole and diastole in the left ventricle (LV) base, mid, and apex. Twelve-lead electrocardiograms were recorded to assess the heart rate-corrected QT (QTc) interval.

Results: The QTc interval was longer in patients with LQTS than in controls (469.1 ± 39.4 ms vs 417.8 ± 24.4 ms; P < .01). Patients with LQTS demonstrated prolonged radial and longitudinal time-to-diastolic peak velocities (TTP), a marker for prolonged contraction duration, in the LV base, mid, and apex. The longer QTc interval positively correlated with longer time-to-diastolic peak velocities (correlation coefficient 0.63; P < .01). Peak diastolic velocities were reduced in LQTS in the LV mid and apex, indicating impaired diastolic relaxation. In patients with LQTS, regional (TTPmax-min) and transmural (TTPVz-Vr) dispersion of contraction duration was increased in the LV apex (TTPVz_max-min: 38.9 ± 25.5 ms vs 20.2 ± 14.7 ms; P = .07; TTPVz-Vr: -21.7 ± 14.5 ms vs -8.7 ± 11.3 ms; P < .05). The base-to-apex longitudinal relaxation sequence was reversed in patients with LQTS compared with controls (TTPVz_base-apex: 14.4 ± 14.9 ms vs -10.1 ± 12.7 ms; P < .01).

Conclusion: Patients with LQTS exhibit diastolic dysfunction with reduced diastolic velocities and prolonged contraction duration. Mechanical dispersion is increased in LQTS with an increased regional and transmural dispersion of contraction duration and altered apicobasal longitudinal relaxation sequence. LQTS is an electromechanical disorder, and phase-contrast magnetic resonance imaging Heterogeneity in mechanical dysfunction enables a detailed assessment of mechanical consequences of LQTS.
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http://dx.doi.org/10.1016/j.hrthm.2017.04.045DOI Listing
September 2017

Diabetic Cardiomyopathy: Does the Type of Diabetes Matter?

Int J Mol Sci 2016 Dec 18;17(12). Epub 2016 Dec 18.

Cardiology and Angiology I, University Heart Center Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany.

In recent years, type 2 diabetes mellitus has evolved as a rapidly increasing epidemic that parallels the increased prevalence of obesity and which markedly increases the risk of cardiovascular disease across the globe. While ischemic heart disease represents the major cause of death in diabetic subjects, diabetic cardiomyopathy (DC) summarizes adverse effects of diabetes mellitus on the heart that are independent of coronary artery disease (CAD) and hypertension. DC increases the risk of heart failure (HF) and may lead to both heart failure with preserved ejection fraction (HFpEF) and reduced ejection fraction (HFrEF). Numerous molecular mechanisms have been proposed to underlie DC that partially overlap with mechanisms believed to contribute to heart failure. Nevertheless, the existence of DC remains a topic of controversy, although the clinical relevance of DC is increasingly recognized by scientists and clinicians. In addition, relatively little attention has been attributed to the fact that both underlying mechanisms and clinical features of DC may be partially distinct in type 1 versus type 2 diabetes. In the following review, we will discuss clinical and preclinical literature on the existence of human DC in the context of the two different types of diabetes mellitus.
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http://dx.doi.org/10.3390/ijms17122136DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5187936PMC
December 2016

SIRT3 in Cardiac Physiology and Disease.

Front Cardiovasc Med 2016 13;3:38. Epub 2016 Oct 13.

Division of Cardiology and Angiology I, Heart Center Freiburg University , Freiburg , Germany.

Functional defects in mitochondrial biology causally contribute to various human diseases, including cardiovascular disease. Impairment in oxidative phosphorylation, mitochondrial oxidative stress, and increased opening of the mitochondrial permeability transition pore add to the underlying mechanisms of heart failure or myocardial ischemia-reperfusion (IR) injury. Recent evidence demonstrated that the mitochondrial NAD-dependent deacetylase sirtuin 3 (SIRT3) may regulate these mitochondrial functions by reversible protein lysine deacetylation. Loss of function studies demonstrated a role of impaired SIRT3 activity in the pathogenesis of myocardial IR injury as well as in the development of cardiac hypertrophy and the transition into heart failure. Gain of function studies and treatment approaches increasing mitochondrial NAD availability that ameliorate these cardiac pathologies have led to the proposal that activation of SIRT3 may represent a promising therapeutic strategy to improve mitochondrial derangements in various cardiac pathologies. In the current review, we will present and discuss the available literature on the role of SIRT3 in cardiac physiology and disease.
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http://dx.doi.org/10.3389/fcvm.2016.00038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5061741PMC
October 2016

Mitochondrial sirtuins in the heart.

Heart Fail Rev 2016 09;21(5):519-28

Department of Cardiology and Angiology I, Heart Center Freiburg University, Hugstetter Str. 55, 79106, Freiburg, Germany.

Sirtuins (SIRTs) are NAD(+)-dependent enzymes that catalyze deacylation of protein lysine residues. In mammals, seven sirtuins have been identified, SIRT1-7. SIRT3-5 are mainly or exclusively localized within mitochondria and mainly participate in the regulation of energy metabolic pathways. Since mitochondrial ATP regeneration is inevitably linked to the maintenance of cardiac pump function, it is not surprising that recent studies revealed a role for mitochondrial sirtuins in the regulation of myocardial energetics and function. In addition, mitochondrial sirtuins modulate the extent of myocardial ischemia reperfusion injury and the development of cardiac hypertrophy and failure. Thus, targeting mitochondrial sirtuins has been proposed as a novel approach to improve myocardial mitochondrial energetics, which is frequently impaired in cardiac disease and considered an important underlying cause contributing to several cardiac pathologies, including myocardial ischemia reperfusion injury and heart failure. In the current review, we present and discuss the available literature on mitochondrial sirtuins and their potential roles in cardiac physiology and disease.
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http://dx.doi.org/10.1007/s10741-016-9570-7DOI Listing
September 2016

Mechanisms of acquired long QT syndrome in patients with propionic academia.

Heart Rhythm 2016 06 27;13(6):1335-45. Epub 2016 Feb 27.

Department of Cardiology and Angiology I, Heart Center University of Freiburg, Freiburg, Germany. Electronic address:

Background: Propionic acidemia (PROP) is a rare metabolic disorder caused by deficiency of propionyl-CoA carboxylase. PROP patients demonstrate QT prolongations associated with ventricular tachycardia and syncopes. Mechanisms responsible for this acquired long QT syndrome (acqLQTS) are unknown.

Objective: The aim of the study was to investigate acute and chronic effects of metabolites accumulating in PROP patients on major repolarizing potassium currents (IKs and IKr) and their channel subunits.

Methods: Voltage clamp studies were performed in CHO-KCNQ1/KCNE1 or HEK-KCNH2 cells to determine effects of propionic acid (PA; 1-10 mM), propionylcarnitine (PC; 25 µM-10 mM), methylcitrate (MC; 25 µM-10 mM), 0.2 M phosphate buffer (PB), or patient serum on IKs and IKr currents. Metabolite effects on action potentials were recorded in current clamp mode in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM). Protein expression of α- and β-subunits of IKs (KCNQ1/KCNE1) and IKr (KCNH2) was evaluated with Western blots.

Results: Acute application of PA, PC, MC, and patient serum had no direct effect on net IKr densities (and KCNH2 expression), although it changed IKr gating kinetics. In contrast, PA, PC, MC, and patient serum all reduced IKs-tail (-67% ± 4.2%, -27% ± 6.7%, -16% ± 6.3%, -42.8% ± 5.15; P < .001) and IKs-end pulse currents. PA significantly prolonged action potential duration (APD) in hiPSC-CM and QT interval in wild-type but not in LQT1 rabbits lacking IKs. Moreover, PC and MC (1 mM) decreased KCNQ1 protein expression (relative density: 0.58 ± 0.08 and 0.16 ± 0.05; P < .01). Chronic exposure to 10 mM PA, in contrast, increased KCNQ1 5.4-fold (P < .001) owing to decreased protein degradation.

Conclusion: Acute reduction of IKs by PROP metabolites may be responsible for APD prolongation and acqLQTS observed in PROP patients.
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http://dx.doi.org/10.1016/j.hrthm.2016.02.003DOI Listing
June 2016

Preserved recovery of cardiac function following ischemia-reperfusion in mice lacking SIRT3.

Can J Physiol Pharmacol 2016 Jan 19;94(1):72-80. Epub 2015 Jul 19.

a Division of Cardiology and Angiology I, Heart Center Freiburg University, Freiburg, Germany.

Lack of the mitochondrial deacetylase sirtuin 3 (SIRT3) impairs mitochondrial function and increases the susceptibility to induction of the mitochondrial permeability transition pore. Because these alterations contribute to myocardial ischemia-reperfusion (IR) injury, we hypothesized that SIRT3 deficiency may increase cardiac injury following myocardial IR. Hearts of 10-week-old mice were perfused in the isolated working mode and subjected to 17.5 min of global no-flow ischemia, followed by 30 min of reperfusion. Measurements before ischemia revealed a decrease in cardiac power (-20%) and rate pressure product (-15%) in SIRT3(-/-) mice. Mitochondrial state 3 respiration (-15%), ATP synthesis (-39%), and ATP/O ratios (-29%) were decreased in hearts of SIRT3(-/-) mice. However, percent recovery of cardiac power (WT 94% ± 9%; SIRT3(-/-) 89% ± 9%) and rate pressure product (WT 89% ± 16%; SIRT3(-/-) 96% ± 3%) following IR was similar in both groups. Myocardial infarct size was not increased in SIRT3(-/-) mice following permanent ligation of the left anterior descending coronary artery (LAD). Left ventricular pressure and dP/dtmax, and mitochondrial respiration and ATP synthesis were not different between groups following LAD ligation. Thus, despite pre-existing defects in cardiac function and mitochondrial respiratory capacity in SIRT3(-/-) mice, SIRT3 deficiency does not additionally impair cardiac function following IR or following myocardial infarction.
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http://dx.doi.org/10.1139/cjpp-2015-0152DOI Listing
January 2016

Mitochondrial Mechanisms in Septic Cardiomyopathy.

Int J Mol Sci 2015 Aug 3;16(8):17763-78. Epub 2015 Aug 3.

Department of Cardiology and Angiology, Heart Center Freiburg University, Hugstetter Str. 55, 79106 Freiburg, Germany.

Sepsis is the manifestation of the immune and inflammatory response to infection that may ultimately result in multi organ failure. Despite the therapeutic strategies that have been used up to now, sepsis and septic shock remain a leading cause of death in critically ill patients. Myocardial dysfunction is a well-described complication of severe sepsis, also referred to as septic cardiomyopathy, which may progress to right and left ventricular pump failure. Many substances and mechanisms seem to be involved in myocardial dysfunction in sepsis, including toxins, cytokines, nitric oxide, complement activation, apoptosis and energy metabolic derangements. Nevertheless, the precise underlying molecular mechanisms as well as their significance in the pathogenesis of septic cardiomyopathy remain incompletely understood. A well-investigated abnormality in septic cardiomyopathy is mitochondrial dysfunction, which likely contributes to cardiac dysfunction by causing myocardial energy depletion. A number of mechanisms have been proposed to cause mitochondrial dysfunction in septic cardiomyopathy, although it remains controversially discussed whether some mechanisms impair mitochondrial function or serve to restore mitochondrial function. The purpose of this review is to discuss mitochondrial mechanisms that may causally contribute to mitochondrial dysfunction and/or may represent adaptive responses to mitochondrial dysfunction in septic cardiomyopathy.
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http://dx.doi.org/10.3390/ijms160817763DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4581220PMC
August 2015

Adrenergic Repression of the Epigenetic Reader MeCP2 Facilitates Cardiac Adaptation in Chronic Heart Failure.

Circ Res 2015 Sep 20;117(7):622-33. Epub 2015 Jul 20.

From the Institute of Experimental and Clinical Pharmacology and Toxicology (S.C.M., R.G., S.P., E.B.M.O., T.S., N.B., A.L., C.R., H.I., J.O., K.A., L.H.), Hermann-Staudinger-Graduiertenschule (S.P.), University Heart Center Freiburg-Bad Krozingen (T.S., A.L., H.B., C.H., F.B., C.B., B.S.), Department of Medicine IV, Nephrology and Primary Care, Medical Center (J.W.), Institute of Anatomy and Cell Biology (O.K.), Renal Division, University Clinic Freiburg (O.K.), Medical Physics (D.E.), and BIOSS Centre for Biological Signalling Studies (L.H.), University of Freiburg, Freiburg, Germany; Department of Molecular Biology, UT Southwestern Medical Center at Dallas, TX (N.B.); Department of Genetic Epidemiology, Institute of Human Genetics, University of Münster, Münster, Germany (F.R., M.S.); Department of Cardiothoracic Surgery, Jena University Hospital, Friedrich Schiller University of Jena, Jena, Germany (A.S., M.S., T.D.); Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany (U.B.); Institute of Molecular and Translational Therapeutic Strategies (IMTTS), IFB-Tx (S.K.G., T.T.) and REBIRTH Excellence Cluster (T.T.), Hannover Medical School, Hannover, Germany; Max-Planck-Institut für Herz- und Lungenforschung, Bad Nauheim, Germany (M.K.); and National Heart and Lung Institute, Imperial College, London, United Kingdom (T.T.).

Rationale: In chronic heart failure, increased adrenergic activation contributes to structural remodeling and altered gene expression. Although adrenergic signaling alters histone modifications, it is unknown, whether it also affects other epigenetic processes, including DNA methylation and its recognition.

Objective: The aim of this study was to identify the mechanism of regulation of the methyl-CpG-binding protein 2 (MeCP2) and its functional significance during cardiac pressure overload and unloading.

Methods And Results: MeCP2 was identified as a reversibly repressed gene in mouse hearts after transverse aortic constriction and was normalized after removal of the constriction. Similarly, MeCP2 repression in human failing hearts resolved after unloading by a left ventricular assist device. The cluster miR-212/132 was upregulated after transverse aortic constriction or on activation of α1- and β1-adrenoceptors and miR-212/132 led to repression of MeCP2. Prevention of MeCP2 repression by a cardiomyocyte-specific, doxycycline-regulatable transgenic mouse model aggravated cardiac hypertrophy, fibrosis, and contractile dysfunction after transverse aortic constriction. Ablation of MeCP2 in cardiomyocytes facilitated recovery of failing hearts after reversible transverse aortic constriction. Genome-wide expression analysis, chromatin immunoprecipitation experiments, and DNA methylation analysis identified mitochondrial genes and their transcriptional regulators as MeCP2 target genes. Coincident with its repression, MeCP2 was removed from its target genes, whereas DNA methylation of MeCP2 target genes remained stable during pressure overload.

Conclusions: These data connect adrenergic activation with a microRNA-MeCP2 epigenetic pathway that is important for cardiac adaptation during the development and recovery from heart failure.
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http://dx.doi.org/10.1161/CIRCRESAHA.115.306721DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4568894PMC
September 2015

Antioxidant treatment normalizes mitochondrial energetics and myocardial insulin sensitivity independently of changes in systemic metabolic homeostasis in a mouse model of the metabolic syndrome.

J Mol Cell Cardiol 2015 Aug 22;85:104-16. Epub 2015 May 22.

Division of Endocrinology, Metabolism, and Diabetes, Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, UT 84112, USA; Fraternal Order of Eagles Diabetes Research Center, Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA. Electronic address:

Cardiac dysfunction in obesity is associated with mitochondrial dysfunction, oxidative stress and altered insulin sensitivity. Whether oxidative stress directly contributes to myocardial insulin resistance remains to be determined. This study tested the hypothesis that ROS scavenging will improve mitochondrial function and insulin sensitivity in the hearts of rodent models with varying degrees of insulin resistance and hyperglycemia. The catalytic antioxidant MnTBAP was administered to the uncoupling protein-diphtheria toxin A (UCP-DTA) mouse model of insulin resistance (IR) and obesity, at early and late time points in the evolution of IR, and to db/db mice with severe obesity and type-two diabetes. Mitochondrial function was measured in saponin-permeabilized cardiac fibers. Aconitase activity and hydrogen peroxide emission were measured in isolated mitochondria. Insulin-stimulated glucose oxidation, glycolysis and fatty acid oxidation rates were measured in isolated working hearts, and 2-deoxyglucose uptake was measured in isolated cardiomyocytes. Four weeks of MnTBAP attenuated glucose intolerance in 13-week-old UCP-DTA mice but was without effect in 24-week-old UCP-DTA mice and in db/db mice. Despite the absence of improvement in the systemic metabolic milieu, MnTBAP reversed cardiac mitochondrial oxidative stress and improved mitochondrial bioenergetics by increasing ATP generation and reducing mitochondrial uncoupling in all models. MnTBAP also improved myocardial insulin mediated glucose metabolism in 13 and 24-week-old UCP-DTA mice. Pharmacological ROS scavenging improves myocardial energy metabolism and insulin responsiveness in obesity and type 2 diabetes via direct effects that might be independent of changes in systemic metabolism.
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http://dx.doi.org/10.1016/j.yjmcc.2015.05.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4530070PMC
August 2015