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

Vasohibin inhibition improves myocardial relaxation in a rat model of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome associated with increased myocardial stiffness and cardiac filling abnormalities. Prior studies implicated increased α-tubulin detyrosination, which is catalyzed by the vasohibin enzymes, as a contributor to increased stabilization of the cardiomyocyte microtubule network (MTN) and stiffness in failing human hearts. We explored whether increased MTN detyrosination contributed to impaired diastolic function in the ZSF1 obese rat model of HFpEF and designed a small-molecule vasohibin inhibitor to ablate MTN detyrosination in vivo. Compared with ZSF1 lean and Wistar Kyoto rats, obese rats exhibited increased tubulin detyrosination concomitant with diastolic dysfunction, left atrial enlargement, and cardiac hypertrophy with a preserved left ventricle ejection fraction, consistent with an HFpEF phenotype. Ex vivo myocardial phenotyping assessed cardiomyocyte mechanics and contractility. Vasohibin inhibitor treatment of isolated cardiomyocytes from obese rats resulted in reduced stiffness and faster relaxation. Acute in vivo treatment with vasohibin inhibitor improved diastolic relaxation in ZSF1 obese rats compared with ZSF1 lean and Wistar Kyoto rats. Vasohibin inhibition also improved relaxation in isolated human cardiomyocytes from both failing and nonfailing hearts. Our data suggest the therapeutic potential for vasohibin inhibition to reduce myocardial stiffness and improve relaxation in HFpEF.

Modulation of Titin and Contraction-Regulating Proteins in a Rat Model of Heart Failure with Preserved Ejection Fraction: Limb vs. Diaphragmatic Muscle

Heart failure with preserved ejection fraction (HFpEF) is characterized by biomechanically dysfunctional cardiomyocytes. Underlying cellular changes include perturbed myocardial titin expression and titin hypophosphorylation leading to titin filament stiffening. Beside these well-studied alterations at the cardiomyocyte level, exercise intolerance is another hallmark of HFpEF caused by molecular alterations in skeletal muscle (SKM). Currently, there is a lack of data regarding titin modulation in the SKM of HFpEF. Therefore, the aim of the present study was to analyze molecular alterations in limb SKM (tibialis anterior (TA)) and in the diaphragm (Dia), as a more central SKM, with a focus on titin, titin phosphorylation, and contraction-regulating proteins. This study was performed with muscle tissue, obtained from 32-week old female ZSF-1 rats, an established a HFpEF rat model. Our results showed a hyperphosphorylation of titin in limb SKM, based on enhanced phosphorylation at the PEVK region, which is known to lead to titin filament stiffening. This hyperphosphorylation could be reversed by high-intensity interval training (HIIT). Additionally, a negative correlation occurring between the phosphorylation state of titin and the muscle force in the limb SKM was evident. For the Dia, no alterations in the phosphorylation state of titin could be detected. Supported by data of previous studies, this suggests an exercise effect of the Dia in HFpEF. Regarding the expression of contraction regulating proteins, significant differences between Dia and limb SKM could be detected, supporting muscle atrophy and dysfunction in limb SKM, but not in the Dia. Altogether, these data suggest a correlation between titin stiffening and the appearance of exercise intolerance in HFpEF, as well as a differential regulation between different SKM groups.

Effects of qigong Training on Muscle Strengths, Flexibility, Cardiopulmonary Fitness, and Antioxidant/Oxidant Responses in Sedentary Middle-Aged and Elderly Type 2 Diabetes Mellitus Women: A Quasi-Experimental Design, Placebo-Controlled Study

Background: Qigong exercise training has been suggested to elicit beneficial effects on physical functioning, reduction of oxidative stress, and improved antioxidant capacity in women. However, regular exercise training may support the development of antioxidant defense mechanisms and beneficially modulate oxidant/antioxidant responses. Objective: To evaluate the effects of an 8-week qigong exercise training on exercise performance and oxidative stress responses in sedentary middle-aged and elderly women suffering from type 2 diabetic mellitus (T2DM). Method/design: Quasi-experimental design, placebo-controlled study. Setting: The Department of Physical Therapy, Faculty of Allied Health Science, Burapha University, Thailand. Participants: Thirty-six sedentary middle-aged and elderly women with T2DM. Intervention: Participants were allocated to qigong exercise (n = 20) or to the control group (CG, n = 20). Primary outcome measures: Muscle strengths, flexibility, VO2 max predicted, and walking intensity derived from the 6-minute walk test. Secondary outcome measures: Fasting plasma glucose, antioxidant/oxidant stress parameters, and body composition. Results: Leg strength and trunk flexibility were improved after qigong training and changes were significantly different compared with the CG (all p < 0.05). VO2 max predicted, 6-min walking distance, and walking intensity were all increased (p < 0.05), and oxidative stress markers were diminished after qigong training (p < 0.05). The antioxidant/oxidant balance was improved after qigong training (p < 0.05). Conclusion: The presented findings indicate that 8 weeks of qigong training significantly improved leg strength and trunk flexibility in middle-aged and elderly women with T2DM, partly associated with a more favorable antioxidant/oxidant balance. These effects may beneficially impact on health in this specific population. Clinical Trial Number: TCTR20221003001.

Caloric Restriction Rejuvenates Skeletal Muscle Growth in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a major clinical problem, with limited treatments. HFpEF is characterized by a distinct, but poorly understood, skeletal muscle pathology, which could offer an alternative therapeutic target. In a rat model, we identified impaired myonuclear accretion as a mechanism for low myofiber growth in HFpEF following resistance exercise. Acute caloric restriction rescued skeletal muscle pathology in HFpEF, whereas cardiac therapies had no effect. Mechanisms regulating myonuclear accretion were dysregulated in patients with HFpEF. Overall, these findings may have widespread implications in HFpEF, indicating combined dietary with exercise interventions as a beneficial approach to overcome skeletal muscle pathology.

Exploring the Mechanistic Link Between Obesity and Heart Failure

PURPOSE OF REVIEW

Among subtypes of cardiovascular disease, obesity has a potent and unique association with heart failure (HF) that is unexplained by traditional cardiovascular risk mediators. The concomitant rise in the prevalence of obesity and HF necessitates better understanding of their relationship to develop effective prevention and treatment strategies. The purpose of this review is to provide mechanistic insight regarding the link between obesity and HF by elucidating the direct and indirect pathways linking the two conditions.

RECENT FINDINGS

Several direct pathophysiologic mechanisms contribute to HF risk in individuals with excess weight, including hemodynamic alterations, neurohormonal activation, hormonal effects of dysfunctional adipose tissue, ectopic fat deposition with resulting lipotoxicity and microvascular dysfunction. Obesity further predisposes to HF indirectly through causal associations with hypertension, dyslipidemia, and most importantly, diabetes via insulin resistance. Low levels of physical activity and fitness further influence HF risk in the context of obesity. These various processes lead to myocardial injury and cardiac remodeling that are reflected by abnormalities in cardiac biomarkers and cardiac function on myocardial imaging. Understanding and addressing obesity-associated HF is a pressing clinical and public health challenge which can be informed by a deeper understanding of the complex pathways linking these two conditions together.

Locomotor and respiratory muscle abnormalities in HFrEF and HFpEF

Heart failure (HF) is a chronic and progressive syndrome affecting worldwide billions of patients. Exercise intolerance and early fatigue are hallmarks of HF patients either with a reduced (HFrEF) or a preserved (HFpEF) ejection fraction. Alterations of the skeletal muscle contribute to exercise intolerance in HF. This review will provide a contemporary summary of the clinical and molecular alterations currently known to occur in the skeletal muscles of both HFrEF and HFpEF, and thereby differentiate the effects on locomotor and respiratory muscles, in particular the diaphragm. Moreover, current and future therapeutic options to address skeletal muscle weakness will be discussed focusing mainly on the effects of exercise training.

Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training

This review highlights some established and some more contemporary mechanisms responsible for heart failure (HF)-induced skeletal muscle wasting and weakness. We first describe the effects of HF on the relationship between protein synthesis and degradation rates, which determine muscle mass, the involvement of the satellite cells for continual muscle regeneration, and changes in myofiber calcium homeostasis linked to contractile dysfunction. We then highlight key mechanistic effects of both aerobic and resistance exercise training on skeletal muscle in HF and outline its application as a beneficial treatment. Overall, HF causes multiple impairments related to autophagy, anabolic-catabolic signaling, satellite cell proliferation, and calcium homeostasis, which together promote fiber atrophy, contractile dysfunction, and impaired regeneration. Although both wasting and weakness are partly rescued by aerobic and resistance exercise training in HF, the effects of satellite cell dynamics remain poorly explored.

Exercise training impacts skeletal muscle remodelling induced by metabolic syndrome in ZSF1 rats through metabolism regulation

Metabolic syndrome (MetS), characterized by a set of conditions that include obesity, hypertension, and dyslipidemia, is associated with increased cardiovascular risk. Exercise training (EX) has been reported to improve MetS management, although the underlying metabolic adaptations that drive its benefits remain poorly understood. This work aims to characterize the molecular changes induced by EX in skeletal muscle in MetS, focusing on gastrocnemius metabolic remodelling. ¹H NMR metabolomics and molecular assays were employed to assess the metabolic profile of skeletal muscle tissue from lean male ZSF1 rats (CTL), obese sedentary male ZSF1 rats (MetS-SED), and obese male ZF1 rats submitted to 4 weeks of treadmill EX (5 days/week, 60 min/day, 15 m/min) (MetS-EX). EX did not counteract the significant increase of body weight and circulating lipid profile, but had an anti-inflammatory effect and improved exercise capacity. The decreased gastrocnemius mass observed in MetS was paralleled with glycogen degradation into small glucose oligosaccharides, with the release of glucose-1-phosphate, and an increase in glucose-6-phosphate and glucose levels. Moreover, sedentary MetS animals' muscle exhibited lower AMPK expression levels and higher amino acids' metabolism such as glutamine and glutamate, compared to lean animals. In contrast, the EX group showed changes suggesting an increase in fatty acid oxidation and oxidative phosphorylation. Additionally, EX mitigated MetS-induced fiber atrophy and fibrosis in the gastrocnemius muscle. EX had a positive effect on gastrocnemius metabolism by enhancing oxidative metabolism and, consequently, reducing susceptibility to fatigue. These findings reinforce the importance of prescribing EX programs to patients with MetS.

The Effects of Resistance Exercise on the Cardiorespiratory Tissue of Rats with Parkinson's Disease

Parkinson's Disease (PD) affects the cardiorespiratory system, causing an increase in the left ventricular mass in the heart and respiratory muscle weakness in relation to healthy individuals. The objective of this study was to investigate the effects of progressive resistive physical exercise on the vertical ladder on the histomorphometry of cardiac tissue and respiratory muscles in rats with PD. Seventy male Wistar rats, aged 40 days old, were divided into Parkinson's (PD) and Sham (SH) groups; they were also subdivided into groups that performed progressive resistive physical exercise on the vertical ladder Before Surgery (ExBS), After Surgery (ExAS), and Before and After Surgery (ExBAS). The physical training was carried out before and/or after PD induction. Exercise was performed five times a week for 25 min/day for four or eight weeks. PD induction was conducted via electrolytic stimulation of the Substantia nigra of the animals' brains, adopting the following stereotaxic table coordinates: -4.9; lateral medium equal to 1.7, and dorsoventral equal to 8.1. For the morphometric analysis of the heart, the following variables were calculated: relative weight and diameter and thickness of the left ventricle. The diaphragm and the myocardial, intercostal, and abdominal muscles were stained with Hematoxylin and Eosin (HE). The histomorphometric analysis was performed using the ImageJ software to assess the cross-sectional area of muscles and the number of muscle fibers. Progressive resistance exercise promoted the hypertrophy of respiratory muscles and the left ventricle in animals with PD.

Skeletal muscle abnormalities in heart failure with preserved ejection fraction

Almost half of all heart failure (HF) disease burden is due to HF with preserved ejection fraction (HFpEF). The primary symptom in patients with HFpEF, even when well compensated, is severe exercise intolerance and is associated with their reduced quality of life. Recently, studies showed that HFpEF patients have multiple skeletal muscle (SM) abnormalities, and these are associated with decreased exercise intolerance. The SM abnormalities are likely intrinsic to the HFpEF syndrome, not a secondary consequence of an epiphenomenon. These abnormalities are decreased muscle mass, reduced type I (oxidative) muscle fibers, and reduced type I-to-type II fiber ratio as well as a reduced capillary-to-fiber ratio, abnormal fat infiltration into the thigh SM, increased levels of atrophy genes and proteins, reduction in mitochondrial content, and rapid depletion of high-energy phosphate during exercise with markedly delayed repletion of high-energy phosphate during recovery in mitochondria. In addition, patients with HFpEF have impaired nitric oxide bioavailability, particularly in the microvasculature. These SM abnormalities may be responsible for impaired diffusive oxygen transport and/or impaired SM oxygen extraction. To date, exercise training (ET) and caloric restriction are some of the interventions shown to improve outcomes in HFpEF patients. Improvements in exercise tolerance following aerobic ET are largely mediated through peripheral SM adaptations with minimal change in central hemodynamics and highlight the importance of targeting SM to improve exercise intolerance in HFpEF. Focusing on the abnormalities mentioned above may improve the clinical condition of patients with HFpEF.

Skeletal myopathy in a rat model of postmenopausal heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for ∼50% of all patients with heart failure and frequently affects postmenopausal women. The HFpEF condition is phenotype-specific, with skeletal myopathy that is crucial for disease development and progression. However, most of the current preclinical models of HFpEF have not addressed the postmenopausal phenotype. We sought to advance a rodent model of postmenopausal HFpEF and examine skeletal muscle abnormalities therein. Female, ovariectomized, spontaneously hypertensive rats (SHRs) were fed a high-fat, high-sucrose diet to induce HFpEF. Controls were female sham-operated Wistar-Kyoto rats on a lean diet. In a complementary, longer-term cohort, controls were female sham-operated SHRs on a lean diet to evaluate the effect of strain difference in the model. Our model developed key features of HFpEF that included increased body weight, glucose intolerance, hypertension, cardiac hypertrophy, diastolic dysfunction, exercise intolerance, and elevated plasma cytokines. In limb skeletal muscle, HFpEF decreased specific force by 15%-30% (P < 0.05) and maximal mitochondrial respiration by 40%-55% (P < 0.05), increased oxidized glutathione by approximately twofold (P < 0.05), and tended to increase mitochondrial H2O2 emission (P = 0.10). Muscle fiber cross-sectional area, markers of mitochondrial content, and indices of capillarity were not different between control and HFpEF in our short-term cohort. Overall, our preclinical model of postmenopausal HFpEF recapitulates several key features of the disease. This new model reveals contractile and mitochondrial dysfunction and redox imbalance that are potential contributors to abnormal metabolism, exercise intolerance, and diminished quality of life in patients with postmenopausal HFpEF.NEW & NOTEWORTHY Heart failure with preserved ejection fraction (HFpEF) is a condition with phenotype-specific features highly prevalent in postmenopausal women and skeletal myopathy contributing to disease development and progression. We advanced a rat model of postmenopausal HFpEF with key cardiovascular and systemic features of the disease. Our study shows that the skeletal myopathy of postmenopausal HFpEF includes loss of limb muscle-specific force independent of atrophy, mitochondrial dysfunction, and oxidized shift in redox balance.

Profile of urinary amino acids and their post-translational modifications (PTM) including advanced glycation end-products (AGEs) of lysine, arginine and cysteine in lean and obese ZSF1 rats

Heart failure with preserved ejection fraction (HFpEF) is associated with high mortality and has an increasing prevalence associated with the demographic change and limited therapeutic options. Underlying mechanisms are largely elusive and need to be explored to identify specific biomarkers and new targets, which mirror disease progression and intervention success. Obese ZSF1 (O-ZSF1) rats are a useful animal model, as they spontaneously develop hypertension, hyperlipidemia and glucose intolerance and finally HFpEF. The urinary profile of amino acids and their metabolites of post-translational modifications (PTM), including the advanced glycation end-products (AGEs) of lysine, arginine and cysteine, are poorly investigated in HFpEF and ZSF1 rats. The aim of the present study was to characterize the status of free amino acids and their metabolites of PTM and glycation in lean ZSF1 (L-ZSF1) and O-ZSF1 rats in urine aiming to find possible effects of glucose on the excretion of native and modified amino acids. In the urine of twelve L-ZSF1 and twelve O-ZFS1 rats collected at the age of 20 weeks, we measured the concentration of native and modified amino acids by reliable previously validated stable-isotope dilution gas chromatography-mass spectrometry (GC–MS) approaches. Serum glucose was 1.39-fold higher in the O-ZSF1 rats, while urinary creatinine concentration was 2.5-fold lower in the O-ZSF1 rats. We observed many differences in urinary amino acids excretion between L-ZSF1 and O-ZSF1 rats. The creatinine-corrected homoarginine excretion was twofold lower in the O-ZSF1 rats. We also observed distinct associations between the concentrations of serum glucose and urinary amino acids including their PTM and AGE metabolites in the L-ZSF1 and O-ZSF1 rats. Our study shows that PTM metabolites and AGEs are consistently lower in the L-ZSF1 than in the O-ZSF1 rats. Serum malondialdehyde (MDA) concentration was higher in the O-ZSF1 rats. These results suggest that hyperglycemia, hyperlipidemia and elevated oxidative stress in the O-ZSF1 rats favor PTM methylation of arginine and lysine and the glycation of lysine and cysteine. The area under the receiver operation characteristic (ROC) curve values were 0.996 for serum glucose, 0.951 for urinary creatinine, 0.939 for serum MDA, 0.885 for N^ε-carboxyethyl-lysine, 0.830 for carboxyethyl-cysteine, and 0.792 for monomethyl-lysine. Non-invasive measurement of methylation and glycation products of arginine, lysine and cysteine residues in proteins in urine of L-ZSF1 and O-ZSF1 rats may be useful in studying pathophysiology and pharmacology of HFpEF.

Mitochondrial function, dynamics and quality control in the pathophysiology of HFpEF

Heart failure (HF) is one of the leading causes of hospitalization for the adult population and a major cause of mortality worldwide. The HF syndrome is characterized by the heart's inability to supply the cardiac output required to meet the body's metabolic requirements or only at the expense of elevated filling pressures. HF without overt impairment of left ventricular ejection fraction (LVEF) was initially labeled as "diastolic HF" until recognizing the coexistence of both systolic and diastolic abnormalities in most cases. Acknowledging these findings, the preferred nomenclature is HF with preserved EF (HFpEF). This syndrome primarily affects the elderly population and is associated with a heterogeneous overlapping of comorbidities that makes its diagnosis challenging. Despite extensive research, there is still no evidence-based therapy for HFpEF, reinforcing the need for a thorough understanding of the pathophysiology underlying its onset and progression. The role of mitochondrial dysfunction in developing the pathophysiological changes that accompany HFpEF onset and progression (low-grade systemic inflammation, oxidative stress, endothelial dysfunction, and myocardial remodeling) has just begun to be acknowledged. This review summarizes our current understanding of the participation of the mitochondrial network in the pathogenesis of HFpEF, with particular emphasis on the signaling pathways involved, which may provide future therapeutic targets.

Impaired skeletal muscle fatigue resistance during cardiac hypertrophy is prevented by functional overload- or exercise-induced functional capillarity

KEY POINTS

Capillary rarefaction is hypothesized to contribute to impaired exercise tolerance in cardiovascular disease, but it remains a poorly exploited therapeutic target for improving skeletal muscle performance. Using an abdominal aortic coarctation rat model of compensatory cardiac hypertrophy, we determine the efficacy of aerobic exercise for the prevention of, and mechanical overload for, restoration of hindlimb muscle fatigue resistance and microvascular impairment in the early stages of heart disease. Impaired muscle fatigue resistance was found after development of cardiac hypertrophy, but this impairment was prevented by low-intensity aerobic exercise and recovered after mechanical stretch due to muscle overload. Changes in muscle fatigue resistance were closely related to functional (i.e. perfused) microvascular density, independent of arterial blood flow, emphasizing the critical importance of optimal capillary diffusion for skeletal muscle function. Pro-angiogenic therapies are an important tool for improving skeletal muscle function in the incipient stages of heart disease.

ABSTRACT

Microvascular rarefaction may contribute to declining skeletal muscle performance in cardiac and vascular diseases. It remains uncertain to what extent microvascular rarefaction occurs in the earliest stages of these conditions, if impaired blood flow is an aggravating factor and whether angiogenesis restores muscle performance. To investigate this, the effects of aerobic exercise (voluntary wheel running) and functional muscle overload on the performance, femoral blood flow (FBF) and microvascular perfusion of the extensor digitorum longus (EDL) were determined in a chronic rat model of compensatory cardiac hypertrophy (CCH, induced by surgically imposed abdominal aortic coarctation). CCH was associated with hypertension (P = 0.001 vs. Control) and increased relative heart mass (P < 0.001). Immediately upon placing the aortic band (i.e. before development of CCH), post-fatigue test FBF was reduced (P < 0.003), coinciding with attenuated fatigue resistance (P = 0.039) indicating an acute arterial perfusion constraint on muscle performance. While FBF was normalized during CCH in chronic groups (P > 0.05) fatigue resistance remained reduced (P = 0.039) and was associated with reduced (P = 0.009) functional capillarity after development of CCH without intervention, indicating a microvascular limitation to muscle performance. Normalization of functional capillarity after aerobic exercise (P = 0.065) and overload (P = 0.329) in CCH coincided with restoration to control levels of muscle fatigue resistance (P > 0.999), although overload-induced EDL hypertrophy (P = 0.027) and wheel-running velocity and duration (both P < 0.05) were attenuated after aortic banding. These data show that reductions in skeletal muscle performance during CCH can be countered by improving functional capillarity, providing a therapeutic target to improve skeletal muscle function in chronic diseases.

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.

Skeletal muscle (dys)function in heart failure with preserved ejection fraction

PURPOSE OF REVIEW

Skeletal muscle dysfunction contributes to exercise intolerance, which manifests as dyspnea and fatiguability in patients with heart failure with preserved ejection fraction (HFpEF). This review aims to summarize the current understanding of skeletal muscle dysfunction in HFpEF.

RECENT FINDINGS

Animal and human studies in HFpEF provide insights into the pathophysiological alterations in skeletal muscle structure and function with the identification of several molecular mechanisms. Exercise training and novel pharmacological therapies that target skeletal muscle are proposed as therapeutic interventions to treat HFpEF.

SUMMARY

There is evidence that skeletal muscle dysfunction plays a pathophysiological role in HFpEF. However, precise mechanistic insights are needed to understand the contribution of skeletal muscle dysfunction in HFpEF.

Abnormal skeletal muscle blood flow, contractile mechanics and fibre morphology in a rat model of obese-HFpEF

KEY POINTS

Heart failure is characterised by limb and respiratory muscle impairments that limit functional capacity and quality of life. However, compared with heart failure with reduced ejection fraction (HFrEF), skeletal muscle alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly explored. Here we report that obese-HFpEF induces multiple skeletal muscle alterations in the rat hindlimb, including impaired muscle mechanics related to shortening velocity, fibre atrophy, capillary loss, and an impaired blood flow response to contractions that implies a perfusive oxygen delivery limitation. We also demonstrate that obese-HFpEF is characterised by diaphragmatic alterations similar to those caused by denervation - atrophy in Type IIb/IIx (fast/glycolytic) fibres and hypertrophy in Type I (slow/oxidative) fibres. These findings extend current knowledge in HFpEF skeletal muscle physiology, potentially underlying exercise intolerance, which may facilitate future therapeutic approaches.

ABSTRACT

Peripheral skeletal muscle and vascular alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly identified, with limited therapeutic targets. This study used a cardiometabolic obese-HFpEF rat model to comprehensively phenotype skeletal muscle mechanics, blood flow, microvasculature and fibre atrophy. Lean (n = 8) and obese-HFpEF (n = 8) ZSF1 rats were compared. Skeletal muscles (soleus and diaphragm) were assessed for in vitro contractility (isometric and isotonic properties) alongside indices of fibre-type cross-sectional area, myosin isoform, and capillarity, and estimated muscle PO₂ . In situ extensor digitorum longus (EDL) contractility and femoral blood flow were assessed. HFpEF soleus demonstrated lower absolute maximal force by 22%, fibre atrophy by 24%, a fibre-type shift from I to IIa, and a 17% lower capillary-to-fibre ratio despite increased capillary density (all P < 0.05) with preserved muscle PO₂ (P = 0.115) and isometric specific force (P > 0.05). Soleus isotonic properties (shortening velocity and power) were impaired by up to 17 and 22%, respectively (P < 0.05), while the magnitude of the exercise hyperaemia was attenuated by 73% (P = 0.012) in line with higher muscle fatigue by 26% (P = 0.079). Diaphragm alterations (P < 0.05) included Type IIx fibre atrophy despite Type I/IIa fibre hypertrophy, with increased indices of capillarity alongside preserved contractile properties during isometric, isotonic, and cyclical contractions. In conclusion, obese-HFpEF rats demonstrated blunted skeletal muscle blood flow during contractions in parallel to microvascular structural remodelling, fibre atrophy, and isotonic contractile dysfunction in the locomotor muscles. In contrast, diaphragm phenotype remained well preserved. This study identifies numerous muscle-specific impairments that could exacerbate exercise intolerance in obese-HFpEF.

Dual SGLT-1 and SGLT-2 inhibition improves left atrial dysfunction in HFpEF

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, Ca2+ transients (CaT; electrically stimulated, caffeine-induced) and spontaneous Ca2+ release were recorded by ratiometric microscopy using Ca2+-sensitive fluorescent dyes (Fura-2) during various experimental protocols. Mitochondrial structure (dye: Mitotracker), Ca2+ 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 Ca2+ release events (SCaEs). Sotagliflozin significantly reduced the magnitude of SCaEs, while their frequency was unaffected. Sotagliflozin lowered diastolic [Ca2+] 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 Ca2+ buffer capacity in HFpEF. Sotagliflozin improved mitochondrial fission and reactive oxygen species (ROS) production during glucose starvation and averted Ca2+ accumulation upon glycolytic inhibition.

CONCLUSION

The SGLT-1&2 inhibitor sotagliflozin ameliorated LA remodeling in metabolic HFpEF. It also improved distinct features of Ca2+-mediated cellular arrhythmogenesis in-vitro (i.e. magnitude of SCaEs, mitochondrial Ca2+ buffer capacity, diastolic Ca2+ 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.

Muscular changes in animal models of heart failure with preserved ejection fraction: what comes closest to the patient?

AIMS

Heart failure with preserved ejection fraction (HFpEF) is associated with reduced exercise capacity elicited by skeletal muscle (SM) alterations. Up to now, no clear medical treatment advice for HFpEF is available. Identification of the ideal animal model mimicking the human condition is a critical step in developing and testing treatment strategies. Several HFpEF animals have been described, but the most suitable in terms of comparability with SM alterations in HFpEF patients is unclear. The aim of the present study was to investigate molecular changes in SM of three different animal models and to compare them with alterations of muscle biopsies obtained from human HFpEF patients.

METHODS AND RESULTS

Skeletal muscle tissue was obtained from HFpEF and control patients and from three different animal models including the respective controls-ZSF1 rat, Dahl salt-sensitive rat, and transverse aortic constriction surgery/deoxycorticosterone mouse. The development of HFpEF was verified by echocardiography. Protein expression and enzyme activity of selected markers were assessed in SM tissue homogenates. Protein expression between SM tissue obtained from HFpEF patients and the ZSF1 rats revealed similarities for protein markers involved in muscle atrophy (MuRF1 expression, protein ubiquitinylation, and LC3) and mitochondrial metabolism (succinate dehydrogenase and malate dehydrogenase activity, porin expression). The other two animal models exhibited far less similarities to the human samples.

CONCLUSIONS

None of the three tested animal models mimics the condition in HFpEF patients completely, but among the animal models tested, the ZSF1 rat (ZSF1-lean vs. ZSF1-obese) shows the highest overlap to the human condition. Therefore, when studying therapeutic interventions to treat HFpEF and especially alterations in the SM, we suggest that the ZSF1 rat is a suitable model.

Oxygen transport kinetics underpin rapid and robust diaphragm recovery following chronic spinal cord injury

Key points

Spinal treatment can restore diaphragm function in all animals 1 month following C2 hemisection induced paralysis. Greater recovery occurs the longer after injury the treatment is applied.

Through advanced assessment of muscle mechanics, innovative histology and oxygen tension modelling, we have comprehensively characterized in vivo diaphragm function and phenotype.

Muscle work loops reveal a significant deficit in diaphragm functional properties following chronic injury and paralysis, which are normalized following restored muscle activity caused by plasticity‐induced spinal reconnection.

Injury causes global and local alterations in diaphragm muscle vascular supply, limiting oxygen diffusion and disturbing function. Restoration of muscle activity reverses these alterations, restoring oxygen supply to the tissue and enabling recovery of muscle functional properties.

There remain metabolic deficits following restoration of diaphragm activity, probably explaining only partial functional recovery. We hypothesize that these deficits need to be resolved to restore complete respiratory motor function.

Abstract

Months after spinal cord injury (SCI), respiratory deficits remain the primary cause of morbidity and mortality for patients. It is possible to induce partial respiratory motor functional recovery in chronic SCI following 2 weeks of spinal neuroplasticity. However, the peripheral mechanisms underpinning this recovery are largely unknown, limiting development of new clinical treatments with potential for complete functional restoration. Utilizing a rat hemisection model, diaphragm function and paralysis was assessed and recovered at chronic time points following trauma through chondroitinase ABC induced neuroplasticity. We simulated the diaphragm's in vivo cyclical length change and activity patterns using the work loop technique at the same time as assessing global and local measures of the muscles histology to quantify changes in muscle phenotype, microvascular composition, and oxidative capacity following injury and recovery. These data were fed into a physiologically informed model of tissue oxygen transport. We demonstrate that hemidiaphragm paralysis causes muscle fibre hypertrophy, maintaining global oxygen supply, although it alters isolated muscle kinetics, limiting respiratory function. Treatment induced recovery of respiratory activity normalized these effects, increasing oxygen supply, restoring optimal diaphragm functional properties. However, metabolic demands of the diaphragm were significantly reduced following both injury and recovery, potentially limiting restoration of normal muscle performance. The mechanism of rapid respiratory muscle recovery following spinal trauma occurs through oxygen transport, metabolic demand and functional dynamics of striated muscle. Overall, these data support a systems‐wide approach to the treatment of SCI, and identify new targets to mediate complete respiratory recovery.

Spinal treatment can restore diaphragm function in all animals 1 month following C2 hemisection induced paralysis. Greater recovery occurs the longer after injury the treatment is applied.

Through advanced assessment of muscle mechanics, innovative histology and oxygen tension modelling, we have comprehensively characterized in vivo diaphragm function and phenotype.

Muscle work loops reveal a significant deficit in diaphragm functional properties following chronic injury and paralysis, which are normalized following restored muscle activity caused by plasticity‐induced spinal reconnection.

Injury causes global and local alterations in diaphragm muscle vascular supply, limiting oxygen diffusion and disturbing function. Restoration of muscle activity reverses these alterations, restoring oxygen supply to the tissue and enabling recovery of muscle functional properties.

There remain metabolic deficits following restoration of diaphragm activity, probably explaining only partial functional recovery. We hypothesize that these deficits need to be resolved to restore complete respiratory motor function.

Heart Failure Results in Inspiratory Muscle Dysfunction Irrespective of Left Ventricular Ejection Fraction

BACKGROUND

Exercise intolerance in heart failure with reduced ejection fraction (HFrEF) or heart failure with preserved ejection fraction (HFpEF) results from both cardiac dysfunction and skeletal muscle weakness. Respiratory muscle dysfunction with restrictive ventilation disorder may be present irrespective of left ventricular ejection fraction and might be mediated by circulating pro-inflammatory cytokines.

OBJECTIVE

To determine lung and respiratory muscle function in patients with HFrEF/HFpEF and to determine its associations with exercise intolerance and markers of systemic inflammation.

METHODS

Adult patients with HFrEF (n = 22, 19 male, 61 ± 14 years) and HFpEF (n = 8, 7 male, 68 ± 8 years) and 19 matched healthy control subjects underwent spirometry, measurement of maximum mouth occlusion pressures, diaphragm ultrasound, and recording of transdiaphragmatic and gastric pressures following magnetic stimulation of the phrenic nerves and the lower thoracic nerve roots. New York Heart Association (NYHA) class and 6-min walking distance (6MWD) were used to quantify exercise intolerance. Levels of circulating interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) were measured using ELISAs.

RESULTS

Compared with controls, both patient groups showed lower forced vital capacity (FVC) (p < 0.05), maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax) (p < 0.05), diaphragm thickening ratio (p = 0.01), and diaphragm strength (twitch transdiaphragmatic pressure in response to supramaximal cervical magnetic phrenic nerve stimulation) (p = 0.01). In patients with HFrEF, NYHA class and 6MWD were both inversely correlated with FVC, PImax, and PEmax. In those with HFpEF, there was an inverse correlation between amino terminal pro B-type natriuretic peptide levels and FVC (r = -0.77, p = 0.04). In all HF patients, IL-6 and TNF-α were statistically related to FVC.

CONCLUSIONS

Irrespective of left ventricular ejection fraction, HF is associated with respiratory muscle dysfunction, which is associated with increased levels of circulating IL-6 and TNF-α.

Impact of experimental obesity on diaphragm structure, function, and bioenergetics

Obesity is associated with bioenergetic dysfunction of peripheral muscles; however, little is known regarding the impact of obesity on the diaphragm. We hypothesized that obesity would be associated with diaphragm dysfunction attributable to mitochondrial oxygen consumption and structural and ultrastructural changes. Wistar rat litters were culled to 3 pups to induce early postnatal overfeeding and consequent obesity. Control animals were obtained from unculled litters. From postnatal day 150, diaphragm ultrasound, computed tomography, high-resolution respirometry, immunohistochemical, biomolecular, and ultrastructural histological analyses were performed. The diaphragms of obese animals, compared with those of controls, presented changes in morphology as increased thickening fraction, diaphragm excursion, and diaphragm dome height, as well as increased mitochondrial respiratory capacity coupled to ATP synthesis and maximal respiratory capacity. Fatty acid synthase gene expression was also higher in obese animals, suggesting a source of energy for the respiratory chain. Myosin heavy chain-IIA was increased, indicating shift from glycolytic toward oxidative muscle fiber profile. Diaphragm tissue also exhibited ultrastructural changes, such as compact, round, and swollen mitochondria with fainter cristae and more lysosomal bodies. Dynamin-1 expression in the diaphragm was reduced in obese rats, suggesting decreased mitochondrial fission. Furthermore, gene expressions of peroxisome γ proliferator-activated receptor coactivator-1α and superoxide dismutase-2 were lower in obese animals than in controls, which may indicate a predisposition to oxidative injury. In conclusion, in the obesity model used herein, muscle fiber phenotype was altered in a manner likely associated with increased mitochondrial respiratory capability, suggesting respiratory adaptation to increased metabolic demand.NEW & NOTEWORTHY Obesity has been associated with peripheral muscle dysfunction; however, little is known about its impact on the diaphragm. In the current study, we found high oxygen consumption in diaphragm tissue and changes in muscle fiber phenotypes toward a more oxidative profile in experimental obesity.

ZSF1 rat as animal model for HFpEF: Development of reduced diastolic function and skeletal muscle dysfunction

AIMS

The prevalence of heart failure with preserved ejection fraction (HFpEF) is still increasing, and so far, no pharmaceutical treatment has proven to be effective. A key obstacle for testing new pharmaceutical substances is the availability of suitable animal models for HFpEF, which realistically reflect the clinical picture. The aim of the present study was to characterize the development of HFpEF and skeletal muscle (SM) dysfunction in ZSF1 rats over time.

METHODS AND RESULTS

Echocardiography and functional analyses of the SM were performed in 6-, 10-, 15-, 20-, and 32-week-old ZSF1-lean and ZSF1-obese. Furthermore, myocardial and SM tissue was collected for molecular and histological analyses. HFpEF markers were evident as early as 10 weeks of age. Diastolic dysfunction, confirmed by a significant increase in E/e', was detectable at 10 weeks. Increased left ventricular mRNA expression of collagen and BNP was detected in ZSF1-obese animals as early as 15 and 20 weeks, respectively. The loss of muscle force was measurable in the extensor digitorum longus starting at 15 weeks, whereas the soleus muscle function was impaired at Week 32. In addition, at Week 20, markers for aortic valve sclerosis were increased.

CONCLUSIONS

Our measurements confirmed the appearance of HFpEF in ZSF1-obese rats as early as 10 weeks of age, most likely as a result of the pre-existing co-morbidities. In addition, SM function was reduced after the manifestation of HFpEF. In conclusion, the ZSF1 rat may serve as a suitable animal model to study pharmaceutical strategies for the treatment of HFpEF.

Mechanisms of atrial fibrillation in aged rats with heart failure with preserved ejection fraction

BACKGROUND

Although ∼20% of the elderly population develops atrial fibrillation (AF), little is known about the mechanisms. Heart failure with preserved ejection fraction (HFpEF), which is associated with AF, is more common in aged women than in men.

OBJECTIVE

The purpose of this study was to identify potential mechanisms of AF in an age-related HFpEF model.

METHODS

In aged female Fischer F344 rats (21- to 24-month-old), which are prone to HFpEF, we induced AF by atrial pacing. Young Fischer F344 female rats (3- to 4-month-old) and age-matched Sprague Dawley female rats (27-month-old) served as controls. Phenotyping included echocardiography to assess left ventricular structure/function; in vivo electrophysiology and ex vivo high-resolution optical mapping to assess AF vulnerability; systemic and atrial inflammatory profiling; atrial histology; and expression of inflammasome signaling proteins.

RESULTS

Aged rats developed left ventricular hypertrophy, left atrial enlargement, diastolic dysfunction, and pulmonary congestion, without ejection fraction impairment, thus meeting the criteria for HFpEF. Increased serum inflammatory markers, hypertension, and obesity further characterize aged females. Sinoatrial and atrioventricular node dysfunction was associated with the high inducibility of AF in aged rats. Ex vivo electrical activation mapping revealed abnormal β-adrenergic responsiveness and slowed conduction velocity. Atrial inflammasome signaling was enhanced in aged rats, which may contribute to fibrotic remodeling and high AF susceptibility.

CONCLUSION

Together, our data demonstrate that aging-related atrial remodeling and HFpEF are associated with atrial enlargement, fibrosis, conduction abnormalities, and nodal dysfunction, favoring a substrate conducive to AF.

Towards a personalised approach in exercise-based cardiovascular rehabilitation: How can translational research help? A 'call to action' from the Section on Secondary Prevention and Cardiac Rehabilitation of the European Association of Preventive Cardiology

The benefit of regular physical activity and exercise training for the prevention of cardiovascular and metabolic diseases is undisputed. Many molecular mechanisms mediating exercise effects have been deciphered. Personalised exercise prescription can help patients in achieving their individual greatest benefit from an exercise-based cardiovascular rehabilitation programme. Yet, we still struggle to provide truly personalised exercise prescriptions to our patients. In this position paper, we address novel basic and translational research concepts that can help us understand the principles underlying the inter-individual differences in the response to exercise, and identify early on who would most likely benefit from which exercise intervention. This includes hereditary, non-hereditary and sex-specific concepts. Recent insights have helped us to take on a more holistic view, integrating exercise-mediated molecular mechanisms with those influenced by metabolism and immunity. Unfortunately, while the outline is recognisable, many details are still lacking to turn the understanding of a concept into a roadmap ready to be used in clinical routine. This position paper therefore also investigates perspectives on how the advent of 'big data' and the use of animal models could help unravel inter-individual responses to exercise parameters and thus influence hypothesis-building for translational research in exercise-based cardiovascular rehabilitation.

Heart Failure With Preserved Ejection Fraction and Adipose Tissue: A Story of Two Tales

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of heart failure in the presence of a normal left ventricular ejection fraction. Although it accounts for up to 50% of all clinical presentations of heart failure, there are no evidence-based therapies for HFpEF to reduce morbidity and mortality. Additionally there is a lack of mechanistic understanding about the pathogenesis of HFpEF. HFpEF is associated with many comorbidities (such as obesity, hypertension, type 2 diabetes, atrial fibrillation, etc.) and is coupled with both cardiac and extra-cardiac abnormalities. Large outcome trials and registries reveal that being obese is a major risk factor for HFpEF. There is increasing focus on investigating the link between obesity and HFpEF, and the role that the adipose tissue and the heart, and the circulating milieu play in development and pathogenesis of HFpEF. This review discusses features of the obese-HFpEF phenotype and highlights proposed mechanisms implicated in the inter-tissue communication between adipose tissue and the heart in obesity-associated HFpEF.

Mitochondrial respiration and H2O2 emission in saponin-permeabilized murine diaphragm fibers: optimization of fiber separation and comparison to limb muscle

Diaphragm abnormalities in aging or chronic diseases include impaired mitochondrial respiration and H₂O₂ emission, which can be measured using saponin-permeabilized muscle fibers. Mouse diaphragm presents a challenge for isolation of fibers due to relatively high abundance of connective tissue in healthy muscle that is exacerbated in disease states. We tested a new approach to process mouse diaphragm for assessment of intact mitochondria respiration and ROS emission in saponin-permeabilized fibers. We used the red gastrocnemius (RG) as "standard" limb muscle. Markers of mitochondrial content were two- to fourfold higher in diaphragm (Dia) than in RG (P < 0.05). Maximal O₂ consumption (JO₂: pmol·s^-1·mg^-1) in Dia was higher with glutamate, malate, and succinate (Dia 399 ± 127, RG 148 ± 60; P < 0.05) and palmitoyl-CoA + carnitine (Dia 15 ± 5, RG 7 ± 1; P < 0.05) than in RG, but not different between muscles when JO₂ was normalized to citrate synthase activity. Absolute JO₂ for Dia was two- to fourfold higher than reported in previous studies. Mitochondrial JH₂O₂ was higher in Dia than in RG (P < 0.05), but lower in Dia than in RG when JH₂O₂ was normalized to citrate synthase activity. Our findings are consistent with an optimized diaphragm preparation for assessment of intact mitochondria in permeabilized fiber bundles. The data also suggest that higher mitochondrial content potentially makes the diaphragm more susceptible to "mitochondrial onset" myopathy. Overall, the new approach will facilitate testing and understanding of diaphragm mitochondrial function in mouse models that are used to advance biomedical research and human health.

Heart Failure With Preserved Ejection Fraction: A Review of Cardiac and Noncardiac Pathophysiology

Heart failure with preserved ejection fraction (HFpEF) is one of the largest unmet clinical needs in 21st-century cardiology. It is a complex disorder resulting from the influence of several comorbidities on the endothelium. A derangement in nitric oxide bioavailability leads to an intricate web of physiological abnormalities in the heart, blood vessels, and other organs. In this review, we examine the contribution of cardiac and noncardiac factors to the development of HFpEF. We zoom in on recent insights on the role of comorbidities and microRNAs in HFpEF. Finally, we address the potential of exercise training, which is currently the only available therapy to improve aerobic capacity and quality of life in HFpEF patients. Unraveling the underlying mechanisms responsible for this improvement could lead to new biomarkers and therapeutic targets for HFpEF.

The role of fibroblast - Cardiomyocyte interaction for atrial dysfunction in HFpEF and hypertensive heart disease

AIMS

Atrial contractile dysfunction is associated with increased mortality in heart failure (HF). We have shown previously that a metabolic syndrome-based model of HFpEF and a model of hypertensive heart disease (HHD) have impaired left atrial (LA) function in vivo (rat). In this study we postulate, that left atrial cardiomyocyte (CM) and cardiac fibroblast (CF) paracrine interaction related to the inositol 1,4,5-trisphosphate signalling cascade is pivotal for the manifestation of atrial mechanical dysfunction in HF and that quantitative atrial remodeling is highly disease-dependent.

METHODS AND RESULTS

Differential remodeling was observed in HHD and HFpEF as indicated by an increase of atrial size in vivo (HFpEF), unchanged fibrosis (HHD and HFpEF) and a decrease of CM size (HHD). Baseline contractile performance of rat CM in vitro was enhanced in HFpEF. Upon treatment with conditioned medium from their respective stretched CF (CM-SF), CM (at 21 weeks) of WT showed increased Ca²⁺ transient (CaT) amplitudes related to the paracrine activity of the inotrope endothelin (ET-1) and inositol 1,4,5-trisphosphate induced Ca²⁺ release. Concentration of ET-1 was increased in CM-SF and atrial tissue from WT as compared to HHD and HFpEF. In HHD, CM-SF had no relevant effect on CaT kinetics. However, in HFpEF, CM-SF increased diastolic Ca²⁺ and slowed Ca²⁺ removal, potentially contributing to an in-vivo decompensation. During disease progression (i.e. at 27 weeks), HFpEF displayed dysfunctional excitation-contraction-coupling (ECC) due to lower sarcoplasmic-reticulum Ca²⁺ content unrelated to CF-CM interaction or ET-1, but associated with enhanced nuclear [Ca²⁺]. In human patients, tissue ET-1 was not related to the presence of arterial hypertension or obesity.

CONCLUSIONS

Atrial remodeling is a complex entity that is highly disease and stage dependent. The activity of fibrosis related to paracrine interaction (e.g. ET-1) might contribute to in vitro and in vivo atrial dysfunction. However, during later stages of disease, ECC is impaired unrelated to CF.

Skeletal Muscle Fiber Type in Hypoxia: Adaptation to High-Altitude Exposure and Under Conditions of Pathological Hypoxia

Skeletal muscle is able to modify its size, and its metabolic/contractile properties in response to a variety of stimuli, such as mechanical stress, neuronal activity, metabolic and hormonal influences, and environmental factors. A reduced oxygen availability, called hypoxia, has been proposed to induce metabolic adaptations and loss of mass in skeletal muscle. In addition, several evidences indicate that muscle fiber-type composition could be affected by hypoxia. The main purpose of this review is to explore the adaptation of skeletal muscle fiber-type composition to exposure to high altitude (ambient hypoxia) and under conditions of pathological hypoxia, including chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF) and obstructive sleep apnea syndrome (OSAS). The muscle fiber-type composition of both adult animals and humans is not markedly altered during chronic exposure to high altitude. However, the fast-to-slow fiber-type transition observed in hind limb muscles during post-natal development is impaired in growing rats exposed to severe altitude. A slow-to-fast transition in fiber type is commonly found in lower limb muscles from patients with COPD and CHF, whereas a transition toward a slower fiber-type profile is often found in the diaphragm muscle in these two pathologies. A slow-to-fast transformation in fiber type is generally observed in the upper airway muscles in rodent models of OSAS. The factors potentially responsible for the adaptation of fiber type under these hypoxic conditions are also discussed in this review. The impaired locomotor activity most likely explains the changes in fiber type composition in growing rats exposed to severe altitude. Furthermore, chronic inactivity and muscle deconditioning could result in the slow-to-fast fiber-type conversion in lower limb muscles during COPD and CHF, while the factors responsible for the adaptation of muscle fiber type during OSAS remain hypothetical. Finally, the role played by cellular hypoxia, hypoxia-inducible factor-1 alpha (HIF-1α), and other molecular regulators in the adaptation of muscle fiber-type composition is described in response to high altitude exposure and conditions of pathological hypoxia.

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.

Increasing quality of life in pulmonary arterial hypertension: is there a role for nutrition?

Pulmonary arterial hypertension (PAH) is a progressive disease primarily affecting the pulmonary vasculature and heart. PAH patients suffer from exercise intolerance and fatigue, negatively affecting their quality of life. This review summarizes current insights in the pathophysiological mechanisms underlying PAH. It zooms in on the potential involvement of nutritional status and micronutrient deficiencies on PAH exercise intolerance and fatigue, also summarizing the potential benefits of exercise and nutritional interventions. Pubmed/Medline, Scopus, and Web of Science were searched for publications on pathophysiological mechanisms of PAH negatively affecting physical activity potential and nutritional status, and for potential effects of interventions involving exercise or nutritional measures known to improve exercise intolerance. Pathophysiological processes that contribute to exercise intolerance and impaired quality of life of PAH patients include right ventricular dysfunction, inflammation, skeletal muscle alterations, and dysfunctional energy metabolism. PAH-related nutritional deficiencies and metabolic alterations have been linked to fatigue, exercise intolerance, and endothelial dysfunction. Available evidence suggests that exercise interventions can be effective in PAH patients to improve exercise tolerance and decrease fatigue. By contrast, knowledge on the prevalence of micronutrient deficiencies and the possible effects of nutritional interventions in PAH patients is limited. Although data on nutritional status and micronutrient deficiencies in PAH are scarce, the available knowledge, including that from adjacent fields, suggests that nutritional intervention to correct deficiencies and metabolic alterations may contribute to a reduction of disease burden.

Endothelial function is disturbed in a hypertensive diabetic animal model of HFpEF: Moderate continuous vs. high intensity interval training

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with endothelial dysfunction, but the molecular mechanisms still remain unclear. Whether exercise training (ET) along with which optimal modality can improve endothelial function is controversial. The present study used a hypertensive, diabetic-driven HFpEF animal model (ZSF1 rats) to determine whether different training modalities (moderate-continuous (MCT) and high-intensity interval training (HIIT)) could reverse endothelial dysfunction and to understand the underlying molecular mechanisms.

METHODS AND RESULTS

The development of HFpEF in ZSF1 obese animals was confirmed by echocardiography and hemodynamic measurements. Thereafter, animals were randomized into following groups: 1) sedentary, 2) 8 weeks of MCT, 3) 8 weeks of HIIT. ZSF1 lean animals served as control. In vitro measurement of endothelial function in aortic rings revealed significantly impaired endothelial-dependent and -independent vasodilation in HFpEF, which was reversed by MCT and HIIT. At the molecular level, the development of endothelial dysfunction was associated with a reduced expression / activation of endothelial nitric oxide synthase (eNOS), an increase in NADPH and activation of c-Jun N-terminal protein kinase (JNK), a reduced collagen I/III ratio and a reduced lining of the vessel wall by endothelial cells. ET primarily decreased NADPH oxidase expression, and JNK activation, elevated collagen I/III ratio while further improving aortic endothelial cell coverage.

CONCLUSIONS

The present study provides evidence that endothelial dysfunction occurs in experimental HFpEF and that ET, independent of the studied training modality, reverses endothelial dysfunction and specific molecular alterations. ET may therefore provide an important therapeutic intervention for HFpEF patients.

Skeletal muscle alterations in HFrEF vs. HFpEF

PURPOSE OF REVIEW

Severe exercise intolerance and early fatigue are hallmarks of heart failure patients either with a reduced (HFrEF) or a still preserved (HFpEF) ejection fraction. This review, therefore, will provide a contemporary summary of the alterations currently known to occur in the skeletal muscles of both HFrEF and HFpEF, and provide some further directions that will be required if we want to improve our current understanding of this area.

RECENT FINDINGS

Skeletal muscle alterations are well documented for over 20 years in HFrEF, and during the recent years also data are presented that in HFpEF muscular alterations are present. Alterations are ranging from a shift in fiber type and capillarization to an induction of atrophy and modulation of mitochondrial energy supply. In general, the molecular alterations are more severe in the skeletal muscle of HFrEF when compared to HFpEF. The alterations occurring in the skeletal muscle at the molecular level may contribute to exercise intolerance in HFrEF and HFpEF. Nevertheless, the knowledge of changes in the skeletal muscle of HFpEF is still sparsely available and more studies in this HF cohort are clearly warranted.