Effects of different exercise modalities on cardiac dysfunction in heart failure with preserved ejection fraction.

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 Ca2+ 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 Ca2+ 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 Ca2+ reuptake in cytosolic and nuclear CaTs and impaired Ca2+ release kinetics in nuclear CaTs. At 28 weeks, HFpEF cardiomyocytes had depressed CaT amplitudes, decreased sarcoplasmic reticulum (SR) Ca2+ content, increased SR Ca2+ leak, and elevated diastolic [Ca2+ ] following increased pacing rate (5 Hz). In trained HFpEF rats (HIIT or MICT), cardiomyocyte SR Ca2+ leak was significantly reduced. While HIIT had no effects on the CaTs (1-5 Hz), MICT accelerated early Ca2+ release, reduced the amplitude, and prolonged the CaT without increasing diastolic [Ca2+ ] or cytosolic Ca2+ load at basal or increased pacing rate (1-5 Hz). MICT lowered pro-arrhythmogenic Ca2+ sparks and attenuated Ca2+ -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, Ca2+ release was impaired under baseline conditions. HIIT and MICT differentially affected Ca2+ homeostasis with positive effects of MICT on stroke volume, end-diastolic volume, and cellular arrhythmogenicity.

Effects of Endurance Training on Detrimental Structural, Cellular, and Functional Alterations in Skeletal Muscles of Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Heart failure with preserved ejection fraction (HFpEF) is underpinned by detrimental skeletal muscle alterations that contribute to disease severity, yet underlying mechanisms and therapeutic treatments remain poorly established. This study used a nonhuman animal model of HFpEF to better understand whether skeletal muscle abnormalities were (1) fiber-type specific and (2) reversible by various exercise training regimes. METHODS AND RESULTS: Lean control rats were compared with obese ZSF1 rats at 20 weeks and then 8 weeks after sedentary, high-intensity interval training, or moderate continuous treadmill exercise. Oxidative soleus and glycolytic extensor digitorum longus (EDL) muscles were assessed for fiber size, capillarity, glycolytic metabolism, autophagy, and contractile function. HFpEF reduced fiber size and capillarity by 20%-50% (P < .05) in both soleus and EDL, but these effects were not reversed by endurance training. In contrast, both endurance training regimes in HFpEF attenuated the elevated lactate dehydrogenase activity observed in the soleus. Autophagy was down-regulated in EDL and up-regulated in soleus (P < .05), with no influence of endurance training. HFpEF impaired contractile forces of both muscles by ∼20% (P < .05), and these were not reversed by training. CONCLUSIONS: Obesity-related HFpEF was associated with detrimental structural, cellular, and functional alterations to both slow-oxidative and fast-glycolytic skeletal muscles that could not be reversed by endurance training.

Aerobic Interval Training Prevents Age-Dependent Vulnerability to Atrial Fibrillation in Rodents.

Aims: Increasing age is the most important risk factor for atrial fibrillation (AF). Very high doses of exercise training might increase AF risk, while moderate levels seem to be protective. This study aimed to examine the effects of age on vulnerability to AF and whether long-term aerobic interval training (AIT) could modify these effects. Methods: Nine months old, male Sprague-Dawley rats were randomized to AIT for 16 weeks (old-ex) or to a sedentary control group (old-sed), and compared to young sedentary males (young-sed). After the intervention, animals underwent echocardiography, testing of exercise capacity (VO2max), and electrophysiology with AF induction before ex vivo electrophysiology. Fibrosis quantification, immunohistochemistry and western blotting of atrial tissue were performed. Results: Sustained AF was induced in vivo in 4 of 11 old-sed animals, but none of the old-ex or young-sed rats (p = 0.006). VO2max was lower in old-sed, while old-ex had comparable results to young-sed. Fibrosis was increased in old-sed (p = 0.006), with similar results in old-ex. There was a significantly slower atrial conduction in old-sed (p = 0.038), with an increase in old-ex (p = 0.027). Action potential duration was unaltered in old-sed, but prolonged in old-ex (p = 0.036). There were no differences in amount of atrial connexin 43 between groups, but a lateralization in atrial cardiomyocytes of old-sed, with similar findings in old-ex. Conclusion: AF vulnerability was higher in old-sed animals, associated with increased atrial fibrosis, lateralization of connexin-43, and reduced atrial conduction velocity. AIT reduced the age-associated susceptibility to AF, possibly through increased conduction velocity and prolongation of action potentials.

Exercise Training Reveals Inflexibility of the Diaphragm in an Animal Model of Patients With Obesity-Driven Heart Failure With a Preserved Ejection Fraction.

BACKGROUND: Respiratory muscle weakness contributes to exercise intolerance in patients with heart failure with a preserved ejection fraction (HFpEF)-a condition characterized by multiple comorbidities with few proven treatments. We aimed, therefore, to provide novel insight into the underlying diaphragmatic alterations that occur in HFpEF by using an obese cardiometabolic rat model and further assessed whether exercise training performed only after the development of overt HFpEF could reverse impairments. METHODS AND RESULTS: Obese ZSF1 rats (n=12) were compared with their lean controls (n=8) at 20 weeks, with 3 additional groups of obese ZSF1 rats compared at 28 weeks following 8 weeks of either sedentary behavior (n=13), high-intensity interval training (n=11), or moderate-continuous training (n=11). Obese rats developed an obvious HFpEF phenotype at 20 and 28 weeks. In the diaphragm at 20 weeks, HFpEF induced a shift towards an oxidative phenotype and a fiber hypertrophy paralleled by a lower protein expression in MuRF1 and MuRF2, yet mitochondrial and contractile functional impairments were observed. At 28 weeks, neither the exercise training regimen of high-intensity interval training or moderate-continuous training reversed any of the diaphragm alterations induced by HFpEF. CONCLUSIONS: This study, using a well-characterized rat model of HFpEF underpinned by multiple comorbidities and exercise intolerance (ie, one that closely resembles the patient phenotype), provides evidence that diaphragm alterations and dysfunction induced in overt HFpEF are not reversed following 8 weeks of aerobic exercise training. As such, whether alternative therapeutic interventions are required to treat respiratory muscle weakness in HFpEF warrants further investigation.

Heart failure with preserved ejection fraction induces molecular, mitochondrial, histological, and functional alterations in rat respiratory and limb skeletal muscle.

AIMS: Peripheral muscle dysfunction is a key mechanism contributing to exercise intolerance (i.e. breathlessness and fatigue) in heart failure patients with preserved ejection fraction (HFpEF); however, the underlying molecular and cellular mechanisms remain unknown. We therefore used an animal model to elucidate potential molecular, mitochondrial, histological, and functional alterations induced by HFpEF in the diaphragm and soleus, while also determining the possible benefits associated with exercise training. METHODS AND RESULTS: Female Dahl salt-sensitive rats were fed a low (CON; n = 10) or high salt (HFpEF; n = 11) diet of 0.3% or 8% NaCl, respectively, or a high salt diet in combination with treadmill exercise training (n = 11). Compared with low-salt rats, high-salt rats developed (P < 0.05) HFpEF. Compared with CON, the diaphragm of HFpEF rats demonstrated (P < 0.05): a fibre type shift from fast-to-slow twitch; fibre atrophy; a decreased pro-oxidative but increased anti-oxidant capacity; reduced proteasome activation; impaired in situ mitochondrial respiration; and in vitro muscle weakness and increased fatigability. The soleus also demonstrated numerous alterations (P < 0.05), including fibre atrophy, decreased anti-oxidant capacity, reduced mitochondrial density, and increased fatigability. Exercise training, however, prevented mitochondrial and functional impairments in both the diaphragm and soleus (P < 0.05). CONCLUSION: Our findings are the first to demonstrate that HFpEF induces significant molecular, mitochondrial, histological, and functional alterations in the diaphragm and soleus, which were attenuated by exercise training. These data therefore reveal novel mechanisms and potential therapeutic treatments of exercise intolerance in HFpEF.

Atrial myocyte function and Ca2+ handling is associated with inborn aerobic capacity.

BACKGROUND: Although high aerobic capacity is associated with effective cardiac function, the effect of aerobic capacity on atrial function, especially in terms of cellular mechanisms, is not known. We aimed to investigate whether rats with low inborn maximal oxygen uptake (VO2 max) had impaired atrial myocyte contractile function when compared to rats with high inborn VO2 max. METHODS AND RESULTS: Atrial myocyte function was depressed in Low Capacity Runners (LCR) relative to High Capacity Runners (HCR) which was associated with impaired Ca(2+) handling. Fractional shortening was 52% lower at 2 Hz and 60% lower at 5 Hz stimulation while time to 50% relengthening was 43% prolonged and 55% prolonged, respectively. Differences in Ca(2+) amplitude and diastolic Ca(2+) level were observed at 5 Hz stimulation where Ca(2+) amplitude was 70% lower and diastolic Ca(2+) level was 11% higher in LCR rats. Prolonged time to 50% Ca(2+) decay was associated with reduced sarcoplasmic reticulum (SR) Ca(2+) ATPase function in LCR (39%). Na(+)/Ca(2+) exchanger activity was comparable between the groups. Diastolic SR Ca(2+) leak was increased by 109%. This could be partly explained by increased ryanodine receptors phosphorylation at the Ca(2+)-calmodulin-dependent protein kinase-II specific Ser-2814 site in LCR rats. T-tubules were present in 68% of HCR cells whereas only 33% LCR cells had these structures. In HCR, the significantly higher numbers of cells with T-tubules were combined with greater numbers of myocytes where Ca(2+) release in the cell occurred simultaneously in central and peripheral regions, giving rise to faster and more spatial homogenous Ca(2+)-signal onset. CONCLUSION: This data demonstrates that contrasting for low or high aerobic capacity leads to diverse functional and structural remodelling of atrial myocytes, with impaired contractile function in LCR compared to HCR rats.

Late gadolinium enhancement in the assessment of the infarcted mouse heart: a longitudinal comparison with manganese-enhanced MRI.

PURPOSE: To evaluate late gadolinium-enhanced (LGE) assessment of infarct size, a comparison with manganese-enhanced magnetic resonance imaging (MEMRI), and histology was performed in a permanent infarction model in the mouse at the acute and chronic stage. MATERIALS AND METHODS: In a paired fashion at the acute and chronic stage after infarction (3-4 days and 21 days, respectively), LGE and MEMRI was performed using a self-gated fast low flip angle shot (FLASH). Infarct size was evaluated as the enhanced area relative to the complete myocardial wall area in a mid-ventricular slice. Paired comparisons were made between contrast agents and between timepoints, as well as to histology. RESULTS: At the acute stage, LGE delineated a larger infarct size as compared to both MEMRI and histology. Infarct size from LGE decreased from the acute to chronic stage, a temporal development not seen with MEMRI. At the chronic stage, no significant differences in infarct size were found between the methods. CONCLUSION: This study indicates an overenhancement of infarct size when using LGE, supported by an initial overestimation at the acute stage and a temporal decrease in infarct size from the acute to chronic stage, as compared to infarct size from MEMRI.

Intracellular mechanisms of specific beta-adrenoceptor antagonists involved in improved cardiac function and survival in a genetic model of heart failure.

beta-blockers, as class, improve cardiac function and survival in heart failure (HF). However, the molecular mechanisms underlying these beneficial effects remain elusive. In the present study, metoprolol and carvedilol were used in doses that display comparable heart rate reduction to assess their beneficial effects in a genetic model of sympathetic hyperactivity-induced HF (alpha(2A)/alpha(2C)-ARKO mice). Five month-old HF mice were randomly assigned to receive either saline, metoprolol or carvedilol for 8 weeks and age-matched wild-type mice (WT) were used as controls. HF mice displayed baseline tachycardia, systolic dysfunction evaluated by echocardiography, 50% mortality rate, increased cardiac myocyte width (50%) and ventricular fibrosis (3-fold) compared with WT. All these responses were significantly improved by both treatments. Cardiomyocytes from HF mice showed reduced peak [Ca(2+)](i) transient (13%) using confocal microscopy imaging. Interestingly, while metoprolol improved [Ca(2+)](i) transient, carvedilol had no effect on peak [Ca(2+)](i) transient but also increased [Ca(2+)] transient decay dynamics. We then examined the influence of carvedilol in cardiac oxidative stress as an alternative target to explain its beneficial effects. Indeed, HF mice showed 10-fold decrease in cardiac reduced/oxidized glutathione ratio compared with WT, which was significantly improved only by carvedilol treatment. Taken together, we provide direct evidence that the beneficial effects of metoprolol were mainly associated with improved cardiac Ca(2+) transients and the net balance of cardiac Ca(2+) handling proteins while carvedilol preferentially improved cardiac redox state.

Exercise training delays cardiac dysfunction and prevents calcium handling abnormalities in sympathetic hyperactivity-induced heart failure mice.

Exercise training (ET) is a coadjuvant therapy in preventive cardiology. It delays cardiac dysfunction and exercise intolerance in heart failure (HF); however, the molecular mechanisms underlying its cardioprotection are poorly understood. We tested the hypothesis that ET would prevent Ca(2+) handling abnormalities and ventricular dysfunction in sympathetic hyperactivity-induced HF mice. A cohort of male wild-type (WT) and congenic alpha(2A)/alpha(2C)-adrenoceptor knockout (alpha(2A)/alpha(2C)ARKO) mice with C57BL6/J genetic background (3-5 mo of age) were randomly assigned into untrained and exercise-trained groups. ET consisted of 8-wk swimming session, 60 min, 5 days/wk. Fractional shortening (FS) was assessed by two-dimensional guided M-mode echocardiography. The protein expression of ryanodine receptor (RyR), phospho-Ser(2809)-RyR, sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), Na(+)/Ca(2+) exchanger (NCX), phospholamban (PLN), phospho-Ser(16)-PLN, and phospho-Thr(17)-PLN were analyzed by Western blotting. At 3 mo of age, no significant difference in FS and exercise tolerance was observed between WT and alpha(2A)/alpha(2C)ARKO mice. At 5 mo, when cardiac dysfunction is associated with lung edema and increased plasma norepinephrine levels, alpha(2A)/alpha(2C)ARKO mice presented reduced FS paralleled by decreased SERCA2 (26%) and NCX (34%). Conversely, alpha(2A)/alpha(2C)ARKO mice displayed increased phospho-Ser(16)-PLN (76%) and phospho-Ser(2809)-RyR (49%). ET in alpha(2A)/alpha(2C)ARKO mice prevented exercise intolerance, ventricular dysfunction, and decreased plasma norepinephrine. ET significantly increased the expression of SERCA2 (58%) and phospho-Ser(16)-PLN (30%) while it restored the expression of phospho-Ser(2809)-RyR to WT levels. Collectively, we provide evidence that improved net balance of Ca(2+) handling proteins paralleled by a decreased sympathetic activity on ET are, at least in part, compensatory mechanisms against deteriorating ventricular function in HF.

Maximal lactate steady state in running mice: effect of exercise training.

1. Maximal lactate steady state (MLSS) corresponds to the highest blood lactate concentration (MLSSc) and workload (MLSSw) that can be maintained over time without continual blood lactate accumulation and is considered an important marker of endurance exercise capacity. The present study was undertaken to determine MLSSw and MLSSc in running mice. In addition, we provide an exercise training protocol for mice based on MLSSw. 2. Maximal lactate steady state was determined by blood sampling during multiple sessions of constant-load exercise varying from 9 to 21 m/min in adult male C57BL/6J mice. The constant-load test lasted at least 21 min. The blood lactate concentration was analysed at rest and then at 7 min intervals during exercise. 3. The MLSSw was found to be 15.1 +/- 0.7 m/min and corresponded to 60 +/- 2% of maximal speed achieved during the incremental exercise testing. Intra- and interobserver variability of MLSSc showed reproducible findings. Exercise training was performed at MLSSw over a period of 8 weeks for 1 h/day and 5 days/week. Exercise training led to resting bradycardia (21%) and increased running performance (28%). Of interest, the MLSSw of trained mice was significantly higher than that in sedentary littermates (19.0 +/- 0.5 vs 14.2 +/- 0.5 m/min; P = 0.05), whereas MLSSc remained unchanged (3.0 mmol/L). 4. Altogether, we provide a valid and reliable protocol to improve endurance exercise capacity in mice performed at highest workload with predominant aerobic metabolism based on MLSS assessment.

Exercise training improves the net balance of cardiac Ca2+ handling protein expression in heart failure.

The molecular basis of the beneficial effects associated with exercise training (ET) on overall ventricular function (VF) in heart failure (HF) remains unclear. We investigated potential Ca(2+) handling abnormalities and whether ET would improve VF of mice lacking alpha(2A)- and alpha(2C)-adrenoceptors (alpha(2A)/alpha(2C)ARKO) that have sympathetic hyperactivity-induced HF. A cohort of male wild-type (WT) and congenic alpha(2A)/alpha(2C)ARKO mice in a C57BL/J genetic background (5-7 mo of age) was randomly assigned into untrained and trained groups. VF was assessed by two-dimensional guided M-mode echocardiography. Cardiac myocyte width and ventricular fibrosis were evaluated with a computer-assisted morphometric system. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), phospholamban (PLN), phospho-Ser(16)-PLN, phospho-Thr(17)-PLN, phosphatase 1 (PP1), and Na(+)-Ca(2+) exchanger (NCX) were analyzed by Western blotting. ET consisted of 8-wk running sessions of 60 min, 5 days/wk. alpha(2A)/alpha(2C)ARKO mice displayed exercise intolerance, systolic dysfunction, increased cardiac myocyte width, and ventricular fibrosis paralleled by decreased SERCA2 and increased NCX expression levels. ET in alpha(2A)/alpha(2C)ARKO mice improved exercise tolerance and systolic function. ET slightly reduced cardiac myocyte width, but unchanged ventricular fibrosis in alpha(2A)/alpha(2C)ARKO mice. ET significantly increased the expression of SERCA2 (20%) and phospho-Ser(16)-PLN (63%), phospho-Thr(17)-PLN (211%) in alpha(2A)/alpha(2C)ARKO mice. Furthermore, ET restored NCX and PP1 expression in alpha(2A)/alpha(2C)ARKO to untrained WT mice levels. Thus, we provide evidence that Ca(2+) handling is impaired in this HF model and that overall VF improved upon ET, which was associated to changes in the net balance of cardiac Ca(2+) handling proteins.

Neurohumoral activation in heart failure: the role of adrenergic receptors

A insuficiência cardíaca (IC) é a via final comum da maioria das doenças cardiovasculares e uma das maiores causas de morbi-mortalidade. O desenvolvimento do estágio final da IC freqüentemente envolve um insulto inicial do miocárdio, reduzindo o débito cardíaco e levando ao aumento compensatório da atividade do sistema nervoso simpático (SNS). Existem evidências de que apesar da exposição aguda ser benéfica, exposições crônicas a elevadas concentrações de catecolaminas, liberadas pelo terminal nervoso simpático e pela glândula adrenal, são tóxicas ao tecido cardíaco e levam a deterioração da função cardíaca. Em nível molecular observa-se que a hiperatividade do SNS está associada a alterações na sinalização intracelular mediada pelos receptores beta-adrenérgicos. Sabe-se que tanto a densidade como a função dos receptores beta-adrenérgicos estão diminuídas na IC, assim como outros mecanismos intracelulares subjacentes à estimulação da via receptores beta-adrenérgicos. Nesta revisão, apresentaremos uma breve descrição da via de sinalização dos receptores beta-adrenérgicos no coração normal e as conseqüências da hiperatividade do SNS na IC. Daremos ênfase ao potencial miopático de diversos componentes da cascata de sinalização dos receptores beta-adrenérgicos discutindo estudos realizados com animais geneticamente modificados. Finalmente, discorreremos sobre o impacto clínico do conhecimento dos polimorfismos para o gene do receptor beta-adrenérgico para um melhor entendimento da progressão da IC.

Neurohumoral activation in heart failure: the role of adrenergic receptors.

Heart failure (HF) is a common endpoint for many forms of cardiovascular disease and a significant cause of morbidity and mortality. The development of end-stage HF often involves an initial insult to the myocardium that reduces cardiac output and leads to a compensatory increase in sympathetic nervous system activity. Acutely, the sympathetic hyperactivity through the activation of beta-adrenergic receptors increases heart rate and cardiac contractility, which compensate for decreased cardiac output. However, chronic exposure of the heart to elevated levels of catecholamines released from sympathetic nerve terminals and the adrenal gland may lead to further pathologic changes in the heart, resulting in continued elevation of sympathetic tone and a progressive deterioration in cardiac function. On a molecular level, altered beta-adrenergic receptor signaling plays a pivotal role in the genesis and progression of HF. beta-adrenergic receptor number and function are decreased, and downstream mechanisms are altered. In this review we will present an overview of the normal beta-adrenergic receptor pathway in the heart and the consequences of sustained adrenergic activation in HF. The myopathic potential of individual components of the adrenergic signaling will be discussed through the results of research performed in genetic modified animals. Finally, we will discuss the potential clinical impact of beta-adrenergic receptor gene polymorphisms for better understanding the progression of HF.