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Aims: Heart failure with preserved ejection fraction (HFpEF) is frequently (30%) associated with right ventricular (RV) dysfunction, which increases morbidity and mortality in these patients. Yet cellular mechanisms of RV remodelling and RV dysfunction in HFpEF are not well understood. Here, we evaluated RV cardiomyocyte function in a rat model of metabolically induced HFpEF., Methods and Results: Heart failure with preserved ejection fraction-prone animals (ZSF-1 obese) and control rats (Wistar Kyoto) were fed a high-caloric diet for 13 weeks. Haemodynamic characterization by echocardiography and invasive catheterization was performed at 22 and 23 weeks of age, respectively. After sacrifice, organ morphometry, RV histology, isolated RV cardiomyocyte function, and calcium (Ca 2+ ) transients were assessed. ZSF-1 obese rats showed a HFpEF phenotype with left ventricular (LV) hypertrophy, LV diastolic dysfunction (including increased LV end-diastolic pressures and E/e' ratio), and preserved LV ejection fraction. ZSF-1 obese animals developed RV dilatation (50% increased end-diastolic area) and mildly impaired RV ejection fraction (42%) with evidence of RV hypertrophy. In isolated RV cardiomyocytes from ZSF-1 obese rats, cell shortening amplitude was preserved, but cytosolic Ca 2+ transient amplitude was reduced. In addition, augmentation of cytosolic Ca 2+ release with increased stimulation frequency was lost in ZSF-1 obese rats. Myofilament sensitivity was increased, while contractile kinetics were largely unaffected in intact isolated RV cardiomyocytes from ZSF-1 obese rats. Western blot analysis revealed significantly increased phosphorylation of cardiac myosin-binding protein C (Ser282 cMyBP-C) but no change in phosphorylation of troponin I (Ser23, 24 TnI) in RV myocardium from ZSF-1 obese rats., Conclusions: Right ventricular dysfunction in obese ZSF-1 rats with HFpEF is associated with intrinsic RV cardiomyocyte remodelling including reduced cytosolic Ca 2+ amplitudes, loss of frequency-dependent augmentation of Ca 2+ release, and increased myofilament Ca 2+ sensitivity., (© 2021 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology.)

Aims: Heart failure with preserved ejection fraction (HFpEF) is an increasingly prevalent disease. Physical exercise has been shown to alter disease progression in HFpEF. We examined cardiomyocyte Ca 2+ homeostasis and left ventricular function in a metabolic HFpEF model in sedentary and trained rats following 8 weeks of moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT)., Methods and Results: Left ventricular in vivo function (echocardiography) and cardiomyocyte Ca 2+ transients (CaTs) (Fluo-4, confocal) were compared in ZSF-1 obese (metabolic syndrome, HFpEF) and ZSF-1 lean (control) 21- and 28-week-old rats. At 21 weeks, cardiomyocytes from HFpEF rats showed prolonged Ca 2+ reuptake in cytosolic and nuclear CaTs and impaired Ca 2+ release kinetics in nuclear CaTs. At 28 weeks, HFpEF cardiomyocytes had depressed CaT amplitudes, decreased sarcoplasmic reticulum (SR) Ca 2+ content, increased SR Ca 2+ leak, and elevated diastolic [Ca 2+ ] following increased pacing rate (5 Hz). In trained HFpEF rats (HIIT or MICT), cardiomyocyte SR Ca 2+ leak was significantly reduced. While HIIT had no effects on the CaTs (1-5 Hz), MICT accelerated early Ca 2+ release, reduced the amplitude, and prolonged the CaT without increasing diastolic [Ca 2+ ] or cytosolic Ca 2+ load at basal or increased pacing rate (1-5 Hz). MICT lowered pro-arrhythmogenic Ca 2+ sparks and attenuated Ca 2+ -wave propagation in cardiomyocytes. MICT was associated with increased stroke volume in HFpEF., Conclusions: In this metabolic rat model of HFpEF at an advanced stage, Ca 2+ release was impaired under baseline conditions. HIIT and MICT differentially affected Ca 2+ homeostasis with positive effects of MICT on stroke volume, end-diastolic volume, and cellular arrhythmogenicity., (© 2021 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology.)

Background: Sodium-glucose linked transporter type 2 (SGLT-2) inhibition has been shown to reduce cardiovascular mortality in heart failure independently of glycemic control and prevents the onset of atrial arrhythmias, a common co-morbidity in heart failure with preserved ejection fraction (HFpEF). The mechanism behind these effects is not fully understood, and it remains unclear if they could be further enhanced by additional SGLT-1 inhibition. We investigated the effects of chronic treatment with the dual SGLT-1&2 inhibitor sotagliflozin on left atrial (LA) remodeling and cellular arrhythmogenesis (i.e. atrial cardiomyopathy) in a metabolic syndrome-related rat model of HFpEF., Methods: 17 week-old ZSF-1 obese rats, a metabolic syndrome-related model of HFpEF, and wild type rats (Wistar Kyoto), were fed 30 mg/kg/d sotagliflozin for 6 weeks. At 23 weeks, LA were imaged in-vivo by echocardiography. In-vitro, Ca 2+ transients (CaT; electrically stimulated, caffeine-induced) and spontaneous Ca 2+ release were recorded by ratiometric microscopy using Ca 2+ -sensitive fluorescent dyes (Fura-2) during various experimental protocols. Mitochondrial structure (dye: Mitotracker), Ca 2+ buffer capacity (dye: Rhod-2), mitochondrial depolarization (dye: TMRE) and production of reactive oxygen species (dye: H2DCF) were visualized by confocal microscopy. Statistical analysis was performed with 2-way analysis of variance followed by post-hoc Bonferroni and student's t-test, as applicable., Results: Sotagliflozin ameliorated LA enlargement in HFpEF in-vivo. In-vitro, LA cardiomyocytes in HFpEF showed an increased incidence and amplitude of arrhythmic spontaneous Ca 2+ release events (SCaEs). Sotagliflozin significantly reduced the magnitude of SCaEs, while their frequency was unaffected. Sotagliflozin lowered diastolic [Ca 2+ ] of CaT at baseline and in response to glucose influx, possibly related to a ~ 50% increase of sodium sodium-calcium exchanger (NCX) forward-mode activity. Sotagliflozin prevented mitochondrial swelling and enhanced mitochondrial Ca 2+ buffer capacity in HFpEF. Sotagliflozin improved mitochondrial fission and reactive oxygen species (ROS) production during glucose starvation and averted Ca 2+ accumulation upon glycolytic inhibition., Conclusion: The SGLT-1&2 inhibitor sotagliflozin ameliorated LA remodeling in metabolic HFpEF. It also improved distinct features of Ca 2+ -mediated cellular arrhythmogenesis in-vitro (i.e. magnitude of SCaEs, mitochondrial Ca 2+ buffer capacity, diastolic Ca 2+ accumulation, NCX activity). The safety and efficacy of combined SGLT-1&2 inhibition for the treatment and/or prevention of atrial cardiomyopathy associated arrhythmias should be further evaluated in clinical trials.

Heart failure (HF) with preserved ejection fraction (HFpEF) is present in about 50% of HF patients. Atrial remodeling is common in HFpEF and associated with increased mortality. We postulate that atrial remodeling is associated with atrial dysfunction in vivo related to alterations in cardiomyocyte Calcium (Ca) signaling and remodeling. We examined atrial function in vivo and Ca transients (CaT) (Fluo4-AM, field stim) in atrial cardiomyocytes of ZSF-1 rats without (Ln; lean hypertensive) and with metabolic syndrome (Ob; obese, hypertensive, diabetic) and HFpEF., Results: At 21weeks Ln showed an increased left ventricular (LV) mass and left ventricular end-diastolic pressure (LVEDP), but unchanged left atrial (LA) size and preserved atrial ejection fraction vs. wild-type (WT). CaT amplitude in atrial cardiomyocytes was increased in Ln (2.9±0.2 vs. 2.3±0.2F/F 0 in WT; n=22 cells/group; p<0.05). Studying subcellular Ca release in more detail, we found that local central cytosolic CaT amplitude was increased, while subsarcolemmal CaT amplitudes remained unchanged. Moreover, Sarcoplasmic reticulum (SR) Ca content (caffeine) was preserved while Ca spark frequency and tetracaine-dependent SR Ca leak were significantly increased in Ln. Ob mice developed a HFpEF phenotype in vivo, LA area was significantly increased and atrial in vivo function was impaired, despite increased atrial CaT amplitudes in vitro (2.8±0.2; p<0.05 vs. WT). Ob cells showed alterations of the tubular network possibly contributing to the observed phenotype. CaT kinetics as well as SR Ca in Ob were not significantly different from WT, but SR Ca leak remained increased. Angiotensin II (Ang II) reduced in vitro cytosolic CaT amplitudes and let to active nuclear Ca release in Ob but not in Ln or WT., Summary: In hypertensive ZSF-1 rats, a possibly compensatory increase of cytosolic CaT amplitude and increased SR Ca leak precede atrial remodeling and HFpEF. Atrial remodeling in ZSF-1 HFpEF is associated with an altered tubular network in-vitro and atrial contractile dysfunction in vivo, indicating insufficient compensation. Atrial cardiomyocyte dysfunction in vitro is induced by the addition of angiotensin II., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Aims: Heart failure with preserved ejection fraction (HFpEF) is increasingly common, but the underlying cellular mechanisms are not well understood. We investigated cardiomyocyte function and the role of SEA0400, an Na(+) /Ca(2+) exchanger (NCX) inhibitor in a rat model of chronic kidney disease (CKD) with HFpEF., Methods and Results: Male Wistar rats were subjected to subtotal nephrectomy (NXT) or sham operation (Sham). After 8 and 24 weeks, in vivo (haemodynamics, echocardiography) and in vitro function (LV cardiomyocyte cell shortening (CS), and Ca(2+) transients (CaT)) were determined without and with SEA0400. In a subgroup of rats, SEA0400 or vehicle was given p.o. (1 mg/kg b.w.) between week 8 and 24. NXT resulted in stable compensated CKD and HFpEF [hypertrophied left ventricle, prolonged LV isovolumetric relaxation constant TAU (IVRc TAU), elevated end diastolic pressure (EDP), increased lung weight (pulmonary congestion), and preserved LV systolic function (EF, dP/dt)]. In NXT cardiomyocytes, the amplitude of CS and CaT were unchanged but relaxation and CaT decay were progressively prolonged at 8 and 24 weeks vs. Sham, individually correlating with diastolic dysfunction in vivo. NCX forward mode activity (caffeine response) was progressively reduced, while NCX protein expression was up-regulated, suggesting increased NCX reverse mode activity in NXT. SEA0400 acutely improved relaxation in NXT in vivo and in cardiomyocytes and improved cardiac remodelling and diastolic function when given chronically., Conclusions: This model of renal HFpEF is associated with slowed relaxation of LV cardiomyocytes. Treatment with SEA0400 improved cardiomyocyte function, remodelling, and HFpEF., (© 2016 The Authors. European Journal of Heart Failure © 2016 European Society of Cardiology.)

Cardiac hypertrophy is commonly observed in conditions of increased hemodynamic or metabolic stress. This hypertrophy is not compensatory but rather reflects activation of maladaptive cellular processes that promote disease progression. Myocardial hypertrophy serves as a diagnostic and prognostic marker of cardiac remodeling, and underlying regulatory processes have provided effective therapeutic targets to slow disease progression and improve outcome. We review hypertrophic signaling pathways in cardiomyocytes and discuss established and novel targets for pharmacological intervention. New drugs in the pipeline include the third generation aldosterone antagonists (PF-03882845 and BAY94-8862) and biased angiotensin II receptor agonists. Furthermore, different approaches to stimulate cGMP-dependent protective signaling are currently evaluated in clinical trials, including the combination of the vasopeptidase neprilysin inhibitor and an angiotensin receptor blocker (ARNi). In an overview on cardiomyocyte hypertrophic signaling, we also highlight emerging experimental treatment concepts such as inhibition of Ca-mediated transcriptional regulation, adeno-associated viruses for sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA2a), PI3 kinase gene transfer and microRNA-based therapy. We conclude that antihypertrophic therapy extends beyond blocking the classical β-adrenergic and renin-angiotensin-aldosterone system-dependent signaling cascades, although new therapies require clinical validation regarding outcome.

Background: A hallmark of heart failure is impaired cytoplasmic Ca(2+) handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca(2+) handling via altered excitation-transcription coupling contribute to the development and progression of heart failure., Methods and Results: Using tissue and isolated cardiomyocytes from nonfailing and failing human hearts, as well as mouse and rabbit models of hypertrophy and heart failure, we provide compelling evidence for structural and functional changes of the nuclear envelope and nuclear Ca(2+) handling in cardiomyocytes as remodeling progresses. Increased nuclear size and less frequent intrusions of the nuclear envelope into the nuclear lumen indicated altered nuclear structure that could have functional consequences. In the (peri)nuclear compartment, there was also reduced expression of Ca(2+) pumps and ryanodine receptors, increased expression of inositol-1,4,5-trisphosphate receptors, and differential orientation among these Ca(2+) transporters. These changes were associated with altered nucleoplasmic Ca(2+) handling in cardiomyocytes from hypertrophied and failing hearts, reflected as increased diastolic Ca(2+) levels with diminished and prolonged nuclear Ca(2+) transients and slowed intranuclear Ca(2+) diffusion. Altered nucleoplasmic Ca(2+) levels were translated to higher activation of nuclear Ca(2+)/calmodulin-dependent protein kinase II and nuclear export of histone deacetylases. Importantly, the nuclear Ca(2+) alterations occurred early during hypertrophy and preceded the cytoplasmic Ca(2+) changes that are typical of heart failure., Conclusions: During cardiac remodeling, early changes of cardiomyocyte nuclei cause altered nuclear Ca(2+) signaling implicated in hypertrophic gene program activation. Normalization of nuclear Ca(2+) regulation may therefore be a novel therapeutic approach to prevent adverse cardiac remodeling., (© 2014 American Heart Association, Inc.)

Rationale: Synchronized release of Ca²⁺ into the cytosol during each cardiac cycle determines cardiomyocyte contraction., Objective: We investigated synchrony of cytosolic [Ca²⁺] decay during diastole and the impact of cardiac remodeling., Methods and Results: Local cytosolic [Ca²⁺] transients (1-µm intervals) were recorded in murine, porcine, and human ventricular single cardiomyocytes. We identified intracellular regions of slow (slowCaR) and fast (fastCaR) [Ca²⁺] decay based on the local time constants of decay (TAUlocal). The SD of TAUlocal as a measure of dyssynchrony was not related to the amplitude or the timing of local Ca²⁺ release. Stimulation of sarcoplasmic reticulum Ca²⁺ ATPase with forskolin or istaroxime accelerated and its inhibition with cyclopiazonic acid slowed TAUlocal significantly more in slowCaR, thus altering the relationship between SD of TAUlocal and global [Ca²⁺] decay (TAUglobal). Na⁺/Ca²⁺ exchanger inhibitor SEA0400 prolonged TAUlocal similarly in slowCaR and fastCaR. FastCaR were associated with increased mitochondrial density and were more sensitive to the mitochondrial Ca²⁺ uniporter blocker Ru360. Variation in TAUlocal was higher in pig and human cardiomyocytes and higher with increased stimulation frequency (2 Hz). TAUlocal correlated with local sarcomere relengthening. In mice with myocardial hypertrophy after transverse aortic constriction, in pigs with chronic myocardial ischemia, and in end-stage human heart failure, variation in TAUlocal was increased and related to cardiomyocyte hypertrophy and increased mitochondrial density., Conclusions: In cardiomyocytes, cytosolic [Ca²⁺] decay is regulated locally and related to local sarcomere relengthening. Dyssynchronous intracellular [Ca²⁺] decay in cardiac remodeling and end-stage heart failure suggests a novel mechanism of cellular contractile dysfunction.

BackgroundAlthough the angiotensin receptor-neprilysin inhibitor (ARNI) sacubitril/valsartan started a new era in heart failure (HF) treatment, less is known about the tissue-level effects of the drug on the atrial myocardial functional reserve and arrhythmogenesis.Methods and ResultsRight atrial (RA) biopsies were retrieved from patients (n = 42) undergoing open-heart surgery, and functional experiments were conducted in muscle strips (n = 101). B-type natriuretic peptide (BNP) did not modulate systolic developed force in human myocardium during β-adrenergic stimulation, but it significantly reduced diastolic tension (p < 0.01) and the probability of arrhythmias (p < 0.01). In addition, patient's plasma NTproBNP positively correlated with isoproterenol-induced contractile reserve in atrial tissue in vitro (r = 0.65; p < 0.01). Sacubitrilat+valsartan (Sac/Val) did not show positive inotropic effects on atrial trabeculae function but reduced arrhythmogeneity. Atrial and ventricular biopsies from patients with end-stage HF (n = 10) confirmed that neprilysin (NEP) is equally expressed in human atrial and ventricular myocardium. RA NEP expression correlates positively with RA ejection fraction (EF) (r = 0.806; p < 0.05) and left ventricle (LV) NEP correlates inversely with left atrial (LA) volume (r = −0.691; p < 0.05).ConclusionBNP ameliorates diastolic tension during adrenergic stress in human atrial myocardium and may have positive long-term effects on the inotropic reserve. BNP and Sac/Val reduce atrial arrhythmogeneity during adrenergic stress in vitro. Myocardial NEP expression is downregulated with declining myocardial function, suggesting a compensatory mechanism in HF.

Background: Heart failure with preserved ejection fraction (HFPEF) is increasingly common but the established heart failure (HF) drugs are not effective. The underlying cellular mechanisms are incompletely understood. Therefore we investigated cardiomyocyte function and intracellular Ca2+ homeostasis in a model of HFPEF.Methods: Young male Wistar rats were subjected to subtotal nephrectomy (NXT) or sham operation (SOP). Serial blood/urine samples, echocardiography and pressure-volume loops at 8 and 24 weeks were performed. After sacrifice, left ventricular (LV) hypertrophy and NCX function (Caffeine induced Ca2+ transient, TAU) and protein expression (Western blot) were determined. Cardiomyocyte function (Ca2+ transients, sarcoplasmic reticulum (SR) diastolic Ca2+ leak (Ca2+ sparks) and SR Ca2+ content; Fluo4-AM) were quantified in isolated LV cardiomyocytes without and with the NCX inhibitor SEA0400 (300nM).Results: NXT rats showed stable compensated renal impairment and significantly hypertrophied LV at 8 weeks with a further increase after 24 weeks. LV systolic function (EF, dP/dt) was preserved. End diastolic pressure (EDP) volume relationship was markedly shifted left- and upwards and lung weight were significantly increased, indicating HFPEF with pulmonary congestion. LV cardiomyocytes from NXT showed no significant differences in amplitudes of Ca2+ transients. However, time for early (50%) relaxation of the Ca2+ transients at 8 weeks were significantly prolonged with a further increase after 24 weeks (RT50 17.2±2.9 and 30.8±2.7 vs. 27.6±1.8 and 41.8±2.6 ms; n≥20; p< 0.05). TAU was significantly prolonged at 8 and 24 weeks indicating reduced NCX forward mode activity, while NCX protein expression was upregulated. At 8 weeks, Ca2+ spark frequency tended to be increased (p=0.07) while SR Ca2+ content was unchanged. SEA0400 accelerated Ca2+ transient decay but did not affect Ca2+ spark frequency. At 24 weeks, Ca2+ spark frequency was increased (4.3±0.7 vs. 11.5±1.8 sparks/s/μm3; n≥20; p<0.05) and SR Ca2+ content was decreased (p<0.05). SEA0400 significantly accelerated Ca2+ transient decay and reduced Ca2+ spark frequency.Conclusion: In this model of HFPEF, relaxation of cardiomyocytes was slower and cytosolic Ca2+ decay was prolonged. Diastolic Ca2+ leak increased significantly during diseases progression. Whereas NCX forward mode activity was already reduced early despite increased NCX protein expression. Acute treatment with NCX inhibitor SEA0400 normalized cytosolic Ca2+ transients in young NXT rats suggesting a role of reverse mode NCX activity and decreased Ca2+ leak at later time points. [ABSTRACT FROM PUBLISHER]