Mechanisms of exercise-induced improvements in the contractile apparatus of the mammalian myocardium

HAPI Fit: An Exercise Intervention to Improve Peak Aerobic Capacity in Young Adults Born Very Preterm

INTRODUCTION

Individuals born preterm have reduced aerobic capacity, which could be related to impaired organ development. Their capacity to improve aerobic capacity with exercise training could therefore be limited, but this remains unknown. We aimed to test an exercise intervention to improve cardiorespiratory fitness in adults born preterm.

METHODS

Twenty-one very preterm and 37 full-term individuals aged 18-33 yr took part in a 14-wk supervised exercise intervention of cardiovascular, resistance, and flexibility training (two group and one individual sessions per week). Adherence and compliance to intervention were recorded. Primary outcome was change in peak oxygen consumption (peak V̇O 2 ) measured before and after the intervention. Within- and between-group differences were estimated using nonparametric tests.

RESULTS

Of 219 eligible individuals, 58 were enrolled and 14 participants dropped out over the course of the intervention. Among the 44 who completed the intervention, mean adherence was 82% and 66% for group and individual sessions, respectively. Compliance with training requirement varied between 71% and 100%. There was no difference in adherence between the preterm and full-term groups. Because only one preterm male met the adherence criteria, subsequent analyses were done exclusively on females. Both the term and preterm groups achieved higher peak V̇O 2 after the intervention [term = +4.2 (SD 4.3) mL·min -1 ·kg -1 , P < 0.01; preterm = +4.7 (2.9) mL·min -1 ·kg -1 , P < 0.01]. There was no between-group difference in the response to the intervention ( P = 0.729).

CONCLUSIONS

Recruitment and adherence to an exercise intervention are challenging. Results could indicate improvements in cardiorespiratory fitness in young women born preterm after current exercise program. Adaptation of this intervention is needed for wider uptake.

Electrically stimulated in vitro heart cell mimic of acute exercise reveals novel immediate cellular responses to exercise: Reduced contractility and metabolism, but maintained calcium cycling and increased myofilament calcium sensitivity

Cardiac cellular responses to acute exercise remain undescribed. We present a model for mimicking acute aerobic endurance exercise to freshly isolated cardiomyocytes by evoking exercise-like contractions over prolonged periods of time with trains of electrical twitch stimulations. We then investigated immediate contractile, Ca2+ , and metabolic responses to acute exercise in perfused freshly isolated left ventricular rat cardiomyocytes, after a matrix-design optimized protocol and induced a mimic for acute aerobic endurance exercise by trains of prolonged field twitch stimulations. Acute exercise decreased cardiomyocyte fractional shortening 50%-80% (p < .01). This was not explained by changes to intracellular Ca2+ handling (p > .05); rather, we observed a weak insignificant Ca2+ transient increase (p = .11), while myofilament Ca2+ sensitivity increased 20%-70% (p < .05). Acidic pH 6.8 decreased fractional shortening 20%-70% (p < .05) because of 20%-30% decreased Ca2+ transients (p < .05), but no difference occurred between control and acute exercise (p > .05). Addition of 1 or 10 mM La- increased fractional shortening in control (1 mM La- : no difference, p > .05; 10 mM La- : 20%-30%, p < .05) and acute exercise (1 mM La- : 40%-90%, p < .01; 10 mM La- : 50%-100%, p < .01) and rendered acute exercise indifferent from control (p > .05). Intrinsic autofluorescence showed a resting NADstate of 0.59 ± 0.04 and FADstate of 0.17 ± 0.03, while acute exercise decreased NADH/FAD ratio 8% (p < .01), indicating intracellular oxidation. In conclusion, we show a novel approach for studying immediate acute cardiomyocyte responses to aerobic endurance exercise. We find that acute exercise in cardiomyocytes decreases contraction, but Ca2+ handling and myofilament Ca2+ sensitivity compensate for this, while acidosis and reduced energy substrate and mitochondrial ATP generation explain this.

When one says yes and the other says no; does calcineurin participate in physiologic cardiac hypertrophy?

Developing engaging activities that build skills for understanding and appreciating research is important for undergraduate and postgraduate science students. Comparing and contrasting opposing research studies does this, and more: it also appropriately for these cohorts challenges higher level cognitive processing. Here, we present and discuss one such scenario, that of calcineurin in the heart and its response to exercise training. This scenario is further accentuated by the existence of only two studies. The background is that regular aerobic endurance exercise training stimulates the heart to physiologically adapt to chronically increase its ability to produce a greater cardiac output to meet the increased demand for oxygenated blood in working muscles, and this happens by two main mechanisms: 1) increased cardiac contractile function and 2) physiologic hypertrophy. The major underlying mechanisms have been delineated over the last decades, but one aspect has not been resolved: the potential role of calcineurin in modulating physiologic hypertrophy. This is partly because the existing research has provided opposing and contrasting findings, one line showing that exercise training does activate cardiac calcineurin in conjunction with myocardial hypertrophy, but another line showing that exercise training does not activate cardiac calcineurin even if myocardial hypertrophy is blatantly occurring. Here, we review and present the current evidence in the field and discuss reasons for this controversy. We present real-life examples from physiology research and discuss how this may enhance student engagement and participation, widen the scope of learning, and thereby also further facilitate higher level cognitive processing.

HIIE Protocols Promote Better Acute Effects on Blood Glucose and Pressure Control in People with Type 2 Diabetes than Continuous Exercise

This study compared the acute effects of a session of different high-intensity interval exercise (HIIE) protocols and a session of moderate-intensity continuous exercise (MICE) on blood glucose, blood pressure (BP), and heart rate (HR) in people with Type 2 Diabetes Mellitus (DM2). The trial included 44 participants (age: 55.91 ± 1.25 years; BMI: 28.95 ± 0.67 kg/m²; Hb1Ac: 9.1 ± 2.3%; 76 mmol/mol) randomized into three exercise protocols based on the velocity at which maximum oxygen consumption was obtained (vVO2 max): long HIIE (2 min at 100% vV̇o2peak + 2 min of passive rest); short HIIE (30 s at 100% vV̇o2peak + 30 s of passive rest); or MICE (14 min at 70% vV̇o2peak) on a treadmill. Capillary blood glucose, BP, and HR measurements were taken at rest, during peak exercise, immediately after the end of exercise, and 10 min after exercise. Long and short HIIE protocols reduced capillary blood glucose by 32.14 mg/dL and 31.40 mg/dL, respectively, and reduced systolic BP by 12.43 mmHg and 8.73 mmHg, respectively. No significant changes were observed for MICE. HIIE was found to promote more acute effects than MICE on glycemia and BP in people with DM2.

Structure-Function Relationships and Modifications of Cardiac Sarcoplasmic Reticulum Ca2+-Transport

Sarcoplasmic reticulum (SR) is a specialized tubular network, which not only maintains the intracellular concentration of Ca2+ at a low level but is also known to release and accumulate Ca2+ for the occurrence of cardiac contraction and relaxation, respectively. This subcellular organelle is composed of several phospholipids and different Ca2+-cycling, Ca2+-binding and regulatory proteins, which work in a coordinated manner to determine its function in cardiomyocytes. Some of the major proteins in the cardiac SR membrane include Ca2+-pump ATPase (SERCA2), Ca2+-release protein (ryanodine receptor), calsequestrin (Ca2+-binding protein) and phospholamban (regulatory protein). The phosphorylation of SR Ca2+-cycling proteins by protein kinase A or Ca2+-calmodulin kinase (directly or indirectly) has been demonstrated to augment SR Ca2+-release and Ca2+-uptake activities and promote cardiac contraction and relaxation functions. The activation of phospholipases and proteases as well as changes in different gene expressions under different pathological conditions have been shown to alter the SR composition and produce Ca2+-handling abnormalities in cardiomyocytes for the development of cardiac dysfunction. The post-translational modifications of SR Ca2+ cycling proteins by processes such as oxidation, nitrosylation, glycosylation, lipidation, acetylation, sumoylation, and O GlcNacylation have also been reported to affect the SR Ca2+ release and uptake activities as well as cardiac contractile activity. The SR function in the heart is also influenced in association with changes in cardiac performance by several hormones including thyroid hormones and adiponectin as well as by exercise-training. On the basis of such observations, it is suggested that both Ca2+-cycling and regulatory proteins in the SR membranes are intimately involved in determining the status of cardiac function and are thus excellent targets for drug development for the treatment of heart disease.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

The effect of eight weeks of moderate and high intensity aerobic training on the gene expression of Mir-145, Wnt3a and Dab2 in the heart tissue of type 2 diabetic rats

Purpose

Pathological hypertrophy of heart tissue has been attributed to changes in some microRNAs and their target genes in heart tissue. This study intended to study the effects of eight weeks of moderate and high intensity aerobic training (MIT&HIT) on the mRNA of Mir-145, Wnt3a, and Dab2 in heart tissue of type 2 diabetic rats.

Methods

To implement this experimental research, 60 male Wistar rats were randomly divided into 6 groups, including Healthy-control (HC), Diabetic-control (DC), Moderate intensity training (MIT), Diabetes-MIT (DMIT), high intensity training (HIT) and Diabetes-HIT (DHIT). The aerobic training was conducted with moderate (50-60% VO2max) and high (85-90% VO2max) intensity, 5 days a week, for 8 weeks. The Mir-145, Wnt3a and Dab2 gene expression in the heart tissue samples was measured by Real Time PCR. Data were analyzed by one-way ANOVA and Tukey post hoc test at the P < 0.05.

Results

Moderate and high intensity aerobic training was associated with non-significant increase in Mir-145 mRNA of Heart tissue in type 2 diabetic rats than the diabetic control group(P < 0.05). Moderate and high intensity aerobic training was associated with significant increase in Wnt3a mRNA (P = 0.001) and significant decrease in Dab-2 mRNA (P = 0.001) of Heart tissue in type 2 diabetic rats than the diabetic control group. The Dab-2 mRNA was significantly lower of heart tissue in the diabetes- high intensity training group than the diabetes- moderate intensity training group (P = 0.001).

Conclusion

It seems that moderate and high intensity aerobic exercise can help regulate the genes of the physiological hypertrophy pathway of the heart tissue in diabetes.

Evidence of region-specific right ventricular functional adaptation in endurance-trained men in response to an acute volume infusion

NEW FINDINGS

What is the central question of this study? Endurance athletes demonstrate altered regional right ventricular (RV) wall mechanics, characterized by lower basal deformation, in comparison to non-athletic control subjects at rest. We hypothesized that regional adaptations at the RV base reflect an enhanced functional reserve capacity in response to haemodynamic volume loading. What is the main finding and its importance? Free wall RV longitudinal strain is elevated in response to acute volume loading in both endurance athletes and control subjects. However, the RV basal segment longitudinal strain response to acute volume infusion is greater in endurance athletes. Our findings suggest that training-induced cardiac remodelling might involve region-specific adaptation in the RV functional response to volume manipulation.

ABSTRACT

Eccentric remodelling of the right ventricle (RV) in response to increased blood volume and repetitive haemodynamic load during endurance exercise is well established. Structural remodelling is accompanied by decreased deformation at the base of the RV free wall, which might reflect an enhanced functional reserve capacity in response to haemodynamic perturbation. Therefore, in this study we examined the impact of acute blood volume expansion on RV wall mechanics in 16 young endurance-trained men (aged 24 ± 3 years) and 13 non-athletic male control subjects (aged 27 ± 5 years). Conventional echocardiographic parameters and the longitudinal strain and strain rate were quantified at the basal and apical levels of the RV free wall. Measurements were obtained at rest and after 7 ml/kg i.v. Gelofusine infusion, with and without a passive leg raise. After infusion, blood volume increased by 12 ± 4 and 14 ± 5% in endurance-trained individuals versus control subjects, respectively (P = 0.264). Both endurance-trained individuals (8 ± 10%) and control subjects (7 ± 9%) experienced an increase in free wall strain from baseline, which was also similar following leg raise (7 ± 10 and 6 ± 10%, respectively; P = 0.464). However, infusion evoked a greater increase in basal longitudinal strain in endurance-trained versus control subjects (16 ± 14 vs. 6 ± 11%; P = 0.048), which persisted after leg raise (16 ± 18 vs. 3 ± 11%; P = 0.032). Apical longitudinal strain and RV free wall strain rates were not different between groups and remained unchanged after infusion across all segments. Endurance training results in a greater contribution of longitudinal myocardial deformation at the base of the RV in response to a haemodynamic volume challenge, which might reflect a greater region-specific functional reserve capacity.

Digoxin Combined with Aerobic Interval Training Improved Cardiomyocyte Contractility

Digoxin is a cardiotonic that increases the cardiac output without causing deleterious effects on heart, as well as improves the left ventricular performance during physical exercise. We tested whether the association between chronic digoxin administration and aerobic interval training (AIT) promotes beneficial cardiovascular adaptations by improving the myocardial contractility and calcium (Ca²⁺⁾ handling. Male Wistar rats were randomly assigned to sedentary control (C), interval training (T), sedentary digoxin (DIGO) and T associated to digoxin (TDIGO). AIT was performed on a treadmill (1h/day, 5 days/week) for 60 days, consisting of successive 8-min periods at 80% and 20% of VO₂máx for 2 min. Digoxin was administered by orogastric gavage for 60 days. Left ventricle samples were collected to analysis of Ca²⁺ handling proteins; contractility and Ca²⁺ handling were performed on isolated cardiomyocytes. TDIGO group had a greater elevation in fractional shortening (44%) than DIGO, suggesting a cardiomyocyte contractile improvement. In addition, T or TDIGO groups showed no change in cardiomyocytes properties after Fura2-acetoxymethyl ester, as well as in sarcoplasmic reticulum Ca^2+-ATPase (SERCA2a), phospholamban and calcineurin expressions. The main findings indicate that association of digoxin and aerobic interval training improved the cardiomyocyte contractile function, but these effects seem to be unrelated to Ca²⁺ handling.

RESISTANCE TRANING PROTOCOLS PROMOTE STRENGTH INCREASE WITHOUT MORPHOLOGICAL CHANGES

ABSTRACT Introduction Resistance training (RT) has been related to increased protein synthesis, and in the myocardium it triggers morphological adaptations that result in improved cardiac contractility. In skeletal muscle, RT promotes an improvement in functional capacity and in sarcopenia caused by aging. However, the efficacy of this training method in the cardiac and skeletal systems has not yet been clarified. Objective To investigate the effect of different vertical ladder RT protocols on cardiac and skeletal structure and morphology. Materials and Methods: Wistar rats (n = 28) were randomized into four groups: sedentary (C); RT protocol with 4 to 9 climbs, 3 sessions/week, 120 second interval and intensity of 50% to 100% of the maximum load (ML) with progressive addition of 30 g (RT1); RT protocol with 4 to 5 climbs, 3 sessions/week, 60 second interval and intensity of 50% to 100% of the ML, where a 30 g overload was added in the 5th climb (RT2); RT protocol with 4 to 5 climbs, 5 sessions/week, 60 second interval and intensity of 50% to 100% of the ML; the animals that completed the 4th climb underwent the 5th climb with 100% ML plus 30 g (RT3). RT protocols were performed for 9 weeks with a duration of 30 to 45 minutes/day. The nutritional profile and cardiac/skeletal muscle morphology were evaluated along with the cross sectional area and collagen fraction. Results RT did not promote adaptations in cardiac and musculoskeletal structure and morphology, nor was it able to reduce body weight and body fat deposits. However, RT brought about an increase in absolute and relative strength. Conclusion Vertical ladder RT protocols, regardless of weekly frequency, lead to increased muscle strength without cardiac and skeletal structural adaptations. Level of evidence I, Therapeutic studies - Investigating treatment results.

Exercise training protects the heart against ischemia-reperfusion injury: A central role for mitochondria?

Ischemic heart disease is one of the main causes of morbidity and mortality worldwide. Physical exercise is an effective lifestyle intervention to reduce the risk factors for cardiovascular disease and also to improve cardiac function and survival in patients with ischemic heart disease. Among the strategies that contribute to reduce heart damages during ischemia and reperfusion, regular physical exercise is efficient both in rodent experimental models and in humans. However, the cellular and molecular mechanisms of the cardioprotective effects of exercise remain unclear. During ischemia and reperfusion, mitochondria are crucial players in cell death, but also in cell survival. Although exercise training can influence mitochondrial function, the consequences on heart sensitivity to ischemic insults remain elusive. In this review, we describe the effects of physical activity on cardiac mitochondria and their potential key role in exercise-induced cardioprotection against ischemia-reperfusion damage. Based on recent scientific data, we discuss the role of different pathways that might help to explain why mitochondria are a key target of exercise-induced cardioprotection.

Moderate Exercise in Spontaneously Hypertensive Rats Is Unable to Activate the Expression of Genes Linked to Mitochondrial Dynamics and Biogenesis in Cardiomyocytes

Hypertension (HTN) is a public health concern and a major preventable cause of cardiovascular disease (CVD). When uncontrolled, HTN may lead to adverse cardiac remodeling, left ventricular hypertrophy, and ultimately, heart failure. Regular aerobic exercise training exhibits blood pressure protective effects, improves myocardial function, and may reverse pathologic cardiac hypertrophy. These beneficial effects depend at least partially on improved mitochondrial function, decreased oxidative stress, endothelial dysfunction, and apoptotic cell death, which supports the general recommendation of moderate exercise in CVD patients. However, most of these mechanisms have been described on healthy individuals; the effect of moderate exercise on HTN subjects at a cellular level remain largely unknown. We hypothesized that hypertension in adult spontaneously hypertensive rats (SHRs) reduces the mitochondrial response to moderate exercise in the myocardium. Methods: Eight-month-old SHRs and their normotensive control-Wistar-Kyoto rats (WKYR)-were randomly assigned to moderate exercise on a treadmill five times per week with a running speed set at 10 m/min and 15° inclination. The duration of each session was 45 min with a relative intensity of 70-85% of the maximum O₂ consumption for a total of 8 weeks. A control group of untrained animals was maintained in their cages with short sessions of 10 min at 10 m/min two times per week to maintain them accustomed to the treadmill. After completing the exercise protocol, we assessed maximum exercise capacity and echocardiographic parameters. Animals were euthanized, and heart and muscle tissue were harvested for protein determinations and gene expression analysis. Measurements were compared using a nonparametric ANOVA (Kruskal-Wallis), with post-hoc Dunn's test. Results: At baseline, SHR presented myocardial remodeling evidenced by left ventricular hypertrophy (interventricular septum 2.08 ± 0.07 vs. 1.62 ± 0.08 mm, p < 0.001), enlarged left atria (0.62 ± 0.1 mm vs. 0.52 ± 0.1, p = 0.04), and impaired diastolic function (E/A ratio 2.43 ± 0.1 vs. 1.56 ± 0.2) when compared to WKYR. Moderate exercise did not induce changes in ventricular remodeling but improved diastolic filling pattern (E/A ratio 2.43 ± 0.1 in untrained SHR vs. 1.89 ± 0.16 trained SHR, p < 0.01). Histological analysis revealed increased myocyte transversal section area, increased Myh7 (myosin heavy chain 7) expression, and collagen fiber accumulation in SHR-control hearts. While the exercise protocol did not modify cardiac size, there was a significant reduction of cardiomyocyte size in the SHR-exercise group. Conversely, titin expression increased only WYK-exercise animals but remained unchanged in the SHR-exercise group. Mitochondrial response to exercise also diverged between SHR and WYKR: while moderate exercise showed an apparent increase in mRNA levels of Ppargc1α, Opa1, Mfn2, Mff, and Drp1 in WYKR, mitochondrial dynamics proteins remained unchanged in response to exercise in SHR. This finding was further confirmed by decreased levels of MFN2 and OPA1 in SHR at baseline and increased OPA1 processing in response to exercise in heart. In summary, aerobic exercise improves diastolic parameters in SHR but fails to activate the cardiomyocyte mitochondrial adaptive response observed in healthy individuals. This finding may explain the discrepancies on the effect of exercise in clinical settings and evidence of the need to further refine our understanding of the molecular response to physical activity in HTN subjects.

Resistance training promotes reduction in Visceral Adiposity without improvements in Cardiomyocyte Contractility and Calcium handling in Obese Rats

Resistance training (RT) improves the cardiomyocyte calcium (Ca²⁺) cycling during excitation-contraction coupling. However, the role of RT in cardiomyocyte contractile function associated with Ca²⁺ handling in obesity is unclear. Wistar rats were distributed into four groups: control, sedentary obese, control plus RT, and obesity plus RT. The 10-wk RT protocol was used (4-5 vertical ladder climbs, 60-second interval, 3× a week, 50-100% of maximum load). Metabolic, hormonal, cardiovascular and biochemical parameters were determined. Reduced leptin levels, epididymal, retroperitoneal and visceral fat pads, lower body fat, and adiposity index were observed in RT. Obesity promoted elevation of collagen, but RT did not promote modifications of LV collagen in ObRT. RT induced elevation in maximum rates of contraction and relaxation, and reduction of time to 50% relaxation. ObRT group did not present improvement in the cardiomyocyte contractile function in comparison to Ob group. Reduced cardiac PLB serine¹⁶ phosphorylation (pPLB Ser¹⁶) and pPLB Ser¹⁶/PLB ratio with no alterations in sarcoplasmic reticulum Ca²⁺ ATPase (SERCA2a) and phospholamban (PLB) expression were observed in Ob groups. Resistance training improved body composition reduced fat pads and plasma leptin levels but did not promote positive alterations in cardiomyocyte contractile function, Ca²⁺ handling and phospholamban phosphorylation.

Sedentary Behavior, Exercise, and Cardiovascular Health

Sedentary behavior and physical inactivity are among the leading modifiable risk factors worldwide for cardiovascular disease and all-cause mortality. The promotion of physical activity and exercise training (ET) leading to improved levels of cardiorespiratory fitness is needed in all age groups, race, and ethnicities and both sexes to prevent many chronic diseases, especially cardiovascular disease. In this state-of-the-art review, we discuss the negative impact of sedentary behavior and physical inactivity, as well as the beneficial effects of physical activity /ET and cardiorespiratory fitness for the prevention of chronic noncommunicable diseases, including cardiovascular disease. We review the prognostic utility of cardiorespiratory fitness compared with obesity and the metabolic syndrome, as well as the increase of physical activity /ET for patients with heart failure as a therapeutic strategy, and ET dosing. Greater efforts at preventing sedentary behavior and physical inactivity while promoting physical activity, ET, and cardiorespiratory fitness are needed throughout the healthcare system worldwide and particularly in the United States in which the burden of cardiometabolic diseases remains extremely high.

LOW-INTENSITY ENDURANCE TRAINING AND RIGHT VENTRICULAR MYOCYTES OF HYPERTENSIVE RATS

ABSTRACT Introduction The structural and mechanical adaptations of the right ventricular (RV) myocytes in response to hypertension associated with low-intensity endurance training (LIET) have not been studied in experimental models. Objective To determine the effects of LIET on the structural and mechanical properties of RV myocytes in spontaneously hypertensive rats (SHRs). Methods Male SHRs and normotensive Wistar rats (age: 16 weeks) were allocated to groups (n=7): WIS (Wistar Controls); SHR-C (SHR Controls) and SHR-T (SHR Trained; 60 min/day, 50-60% of maximal exercise capacity, 5 days/week for 8 weeks). Systolic arterial pressure (SAP), isolated RV myocyte dimensions, contractility, intracellular Ca2+ transient ([Ca2+]i), and ventricular Ca2+ regulatory proteins were measured. The statistical analysis was performed by one-way ANOVA followed by the Tukey post hoc test (α=5%). Results LIET reduced the SAP in SHR animals (SHR-C, 164 ± 2 mmHg vs. SHR-T, 152 ± 4 mmHg; P<0.05). Hypertension increased cell length (WIS, 156.8 ± 2.7 µm; SHR-C, 166.6 ± 3.1 µm; P<0.05) but did not affect cell width or volume (P>0.05). LIET did not change the cell dimensions in the SHR-T. Neither hypertension nor LIET affected myocyte contractility or the expression of Ca2+ regulatory proteins in the RV of the SHR-C and SHR-T groups. Hypertension did not affect the amplitude of the [Ca2+]i transient or the time to half resting level (P>0.05), but increased the time to peak (WIS, 58 ± 1 ms vs. SHR-C, 79 ± 2 ms; P<0.05). LIET increased the amplitude of the [Ca2+]i transient (WIS, 2.28 ± 0.07 F/F0 and SHR-C, 2.48 ± 0.08 F/F0 vs. SHR-T, 2.87 ± 0.08 F/F0 P<0.05), but did not alter the times to peak or to half resting level. Conclusion LIET had no effect on the structural and mechanical properties of RV myocytes in the SHRs, although it increased the amplitude of the [Ca2+]i transient and reduced the SAP. Level of evidence I, Therapeutic Studies - Investigating the Results of Treatment.

Plasma matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs and aging and lifelong exercise adaptations in ventricular and arterial stiffness

The age-associated increase in cardiac and central arterial stiffness is attenuated with lifelong (>25 years) endurance exercise in a dose-dependent manner. Remodelling of the extracellular matrix of cardiovascular structures may underpin these lifelong exercise adaptations in structural stiffness. The primary aim was to examine whether matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) levels are associated with aging and lifelong exercise-related changes in cardiac and central arterial stiffness. Plasma MMPs and TIMPs, left ventricular (LV) (LV stiffness constant) and central arterial stiffness (pulse wave velocity) were examined in healthy adults stratified into five groups based on age and lifelong weekly exercise frequency: (1) young sedentary adults (28-50 years), and older adults (>60 years) who had performed either: (a) sedentary (0-1 sessions/week), (b) casual (2-3 sessions/week), (c) committed (4-5 sessions/week) or (d) athletic (≥6 sessions/week) frequency of exercise. MMP-1 was significantly lower in young compared to older sedentary (p = 0.049). Except for TIMP-2 (p = 0.018 versus committed) and the ratio of MMP-2/TIMP-4 (p = 0.047 versus committed), MMP and TIMP expression was not significantly different in lifelong exercise groups (≥casual) compared to the older sedentary group. MMP-1, -3 had a weak positive relationship with central PWV (r = 0.17-0.25, p ≤ 0.050) but there were no significant relationships between MMPs or TIMPs and LV stiffness constant (p ≥ 0.148). In conclusion, there was not a clear or consistent difference in plasma MMPs and TIMPs with lifelong exercise dose despite exhibiting lower cardiovascular stiffness at the highest exercise levels.

Understanding Key Mechanisms of Exercise-Induced Cardiac Protection to Mitigate Disease: Current Knowledge and Emerging Concepts

The benefits of exercise on the heart are well recognized, and clinical studies have demonstrated that exercise is an intervention that can improve cardiac function in heart failure patients. This has led to significant research into understanding the key mechanisms responsible for exercise-induced cardiac protection. Here, we summarize molecular mechanisms that regulate exercise-induced cardiac myocyte growth and proliferation. We discuss in detail the effects of exercise on other cardiac cells, organelles, and systems that have received less or little attention and require further investigation. This includes cardiac excitation and contraction, mitochondrial adaptations, cellular stress responses to promote survival (heat shock response, ubiquitin-proteasome system, autophagy-lysosomal system, endoplasmic reticulum unfolded protein response, DNA damage response), extracellular matrix, inflammatory response, and organ-to-organ crosstalk. We summarize therapeutic strategies targeting known regulators of exercise-induced protection and the challenges translating findings from bench to bedside. We conclude that technological advancements that allow for in-depth profiling of the genome, transcriptome, proteome and metabolome, combined with animal and human studies, provide new opportunities for comprehensively defining the signaling and regulatory aspects of cell/organelle functions that underpin the protective properties of exercise. This is likely to lead to the identification of novel biomarkers and therapeutic targets for heart disease.

Cardiovascular Effects and Benefits of Exercise

It is widely accepted that regular physical activity is beneficial for cardiovascular health. Frequent exercise is robustly associated with a decrease in cardiovascular mortality as well as the risk of developing cardiovascular disease. Physically active individuals have lower blood pressure, higher insulin sensitivity, and a more favorable plasma lipoprotein profile. Animal models of exercise show that repeated physical activity suppresses atherogenesis and increases the availability of vasodilatory mediators such as nitric oxide. Exercise has also been found to have beneficial effects on the heart. Acutely, exercise increases cardiac output and blood pressure, but individuals adapted to exercise show lower resting heart rate and cardiac hypertrophy. Both cardiac and vascular changes have been linked to a variety of changes in tissue metabolism and signaling, although our understanding of the contribution of the underlying mechanisms remains incomplete. Even though moderate levels of exercise have been found to be consistently associated with a reduction in cardiovascular disease risk, there is evidence to suggest that continuously high levels of exercise (e.g., marathon running) could have detrimental effects on cardiovascular health. Nevertheless, a specific dose response relationship between the extent and duration of exercise and the reduction in cardiovascular disease risk and mortality remains unclear. Further studies are needed to identify the mechanisms that impart cardiovascular benefits of exercise in order to develop more effective exercise regimens, test the interaction of exercise with diet, and develop pharmacological interventions for those unwilling or unable to exercise.

Nandrolone alter left ventricular contractility and promotes remodelling involving calcium-handling proteins and renin-angiotensin system in male SHR

AIMS

Hypertension is a highly prevalent disease that has been correlated to severe organ damage and mortality. However, the role of androgens in hypertension is controversial. The aim of this study was to evaluate the cardiac effects of the nandrolone decanoate (NDL) in male SHR.

MAIN METHODS

At 12 weeks of age, male SHR rats were separated into three groups: Control (CON), Nandrolone 10 mg/kg twice weekly (NDL), and NDL plus Enalapril 10 mg/kg/day (NDL-E) groups. The animals were treated for 4 weeks. Haemodynamic parameters were acquired through ventricular catheter implantation. The left ventricle was stained with haematoxylin/eosin or picrosirius red. Western blot analysis of TNF-α, ACE, AT₁R, β₁-AR, PLB, p-PLB^ser16 and SERCA2a was performed.

KEY FINDINGS

Nandrolone increased hypertension in SHR rats and enalapril reduced blood pressure to values below those of the control. NDL increased +dP/dt_max, -dP/dt_max and cardiac hypertrophy, which were prevented in the NDL-E group. Cardiac collagen deposition was increased in the NDL group, with this effect being attenuated by enalapril in NDL-E animals. TNF-α, ACE, AT₁R and β1-AR proteins were increased in the NDL, and enalapril decreased them, except for TNF-α. The ratio p-PLB^ser16/PLB revealed an increase after nandrolone, which was prevented in the NDL-E group. The SERCA2a expression protein and SERCA2a/PLB were increased in NDL animals, which did not occur in the NDL-E group.

SIGNIFICANCE

Nandrolone has distinct effects on cardiac function and remodelling in male SHR, altering the hypertension development process in the heart through modulation of calcium handling proteins and the renin-angiotensin system.

Chronic low-intensity exercise attenuates cardiomyocyte contractile dysfunction and impaired adrenergic responsiveness in aortic-banded mini-swine

Exercise improves clinical outcomes in patients diagnosed with heart failure with reduced ejection fraction (HFrEF), in part via beneficial effects on cardiomyocyte Ca²⁺ cycling during excitation-contraction coupling (ECC). However, limited data exist regarding the effects of exercise training on cardiomyocyte function in patients diagnosed with heart failure with preserved ejection fraction (HFpEF). The purpose of this study was to investigate cardiomyocyte Ca²⁺ handling and contractile function following chronic low-intensity exercise training in aortic-banded miniature swine and test the hypothesis that low-intensity exercise improves cardiomyocyte function in a large animal model of pressure overload. Animals were divided into control (CON), aortic-banded sedentary (AB), and aortic-banded low-intensity trained (AB-LIT) groups. Left ventricular cardiomyocytes were electrically stimulated (0.5 Hz) to assess Ca²⁺ homeostasis (fura-2-AM) and unloaded shortening during ECC under conditions of baseline pacing and pacing with adrenergic stimulation using dobutamine (1 μM). Cardiomyocytes in AB animals exhibited depressed Ca²⁺ transient amplitude and cardiomyocyte shortening vs. CON under both conditions. Exercise training attenuated AB-induced decreases in cardiomyocyte Ca²⁺ transient amplitude but did not prevent impaired shortening vs. CON. With dobutamine, AB-LIT exhibited both Ca²⁺ transient and shortening amplitude similar to CON. Adrenergic sensitivity, assessed as the time to maximum inotropic response following dobutamine treatment, was depressed in the AB group but normal in AB-LIT animals. Taken together, our data suggest exercise training is beneficial for cardiomyocyte function via the effects on Ca²⁺ homeostasis and adrenergic sensitivity in a large animal model of pressure overload-induced heart failure. NEW & NOTEWORTHY Conventional treatments have failed to improve the prognosis of heart failure with preserved ejection fraction (HFpEF) patients. Our findings show chronic low-intensity exercise training can prevent cardiomyocyte dysfunction and impaired adrenergic responsiveness in a translational large animal model of chronic pressure overload-induced heart failure with relevance to human HFpEF.

The Role of MicroRNAs in the Cardiac Response to Exercise

Noncoding microRNAs (miRNAs) have emerged as central regulators of cardiac biology, modulating cardiac development and the response to pathological stress in disease. Although less well developed, emerging evidence suggests miRNAs are likely also important in the heart's response to the physiological stress of exercise. Given the well-recognized cardiovascular benefits of exercise, elucidating the contribution of miRNAs to this response has the potential not only to reveal novel aspects of cardiovascular biology but also to identify new targets for therapeutic intervention that may complement those discovered through studies of diseased hearts. Here, we first provide an overview of the cardiovascular effects of exercise as well as some of the major protein signaling mechanisms contributing to these effects. We then review the evidence that both cardiac and circulating miRNAs are dynamically regulated by exercise and regulate these mechanisms and phenotypes.

Peroxisome proliferator-activated receptor-γ coactivator 1 α1 induces a cardiac excitation-contraction coupling phenotype without metabolic remodelling

KEY POINTS

Transcriptional co-activator PGC-1α1 has been shown to regulate energy metabolism and to mediate metabolic adaptations in pathological and physiological cardiac hypertrophy but other functional implications of PGC-1α1 expression are not known. Transgenic PGC-1α1 overexpression within the physiological range in mouse heart induces purposive changes in contractile properties, electrophysiology and calcium signalling but does not induce substantial metabolic remodelling. The phenotype of the PGC-1α1 transgenic mouse heart recapitulates most of the functional modifications usually associated with the exercise-induced heart phenotype, but does not protect the heart against load-induced pathological hypertrophy. Transcriptional effects of PGC-1α1 show clear dose-dependence with diverse changes in genes in circadian clock, heat shock, excitability, calcium signalling and contraction pathways at low overexpression levels, while metabolic genes are recruited at much higher PGC-1α1 expression levels. These results imply that the physiological role of PGC-1α1 is to promote a beneficial excitation-contraction coupling phenotype in the heart.

ABSTRACT

The transcriptional coactivator PGC-1α1 has been identified as a central factor mediating metabolic adaptations of the heart. However, to what extent physiological changes in PGC-1α1 expression levels actually contribute to the functional adaptation of the heart is still mostly unresolved. The aim of this study was to characterize the transcriptional and functional effects of physiologically relevant, moderate PGC-1α1 expression in the heart. In vivo and ex vivo physiological analysis shows that expression of PGC-1α1 within a physiological range in mouse heart does not induce the expected metabolic alterations, but instead induces a unique excitation-contraction (EC) coupling phenotype recapitulating features typically seen in physiological hypertrophy. Transcriptional screening of PGC-1α1 overexpressing mouse heart and myocyte cultures with higher, acute adenovirus-induced PGC-1α1 expression, highlights PGC-1α1 as a transcriptional coactivator with a number of binding partners in various pathways (such as heat shock factors and the circadian clock) through which it acts as a pleiotropic transcriptional regulator in the heart, to both augment and repress the expression of its target genes in a dose-dependent fashion. At low levels of overexpression PGC-1α1 elicits a diverse transcriptional response altering the expression state of circadian clock, heat shock, excitability, calcium signalling and contraction pathways, while metabolic targets of PGC-1α1 are recruited at higher PGC-1α1 expression levels. Together these findings demonstrate that PGC-1α1 elicits a dual effect on cardiac transcription and phenotype. Further, our results imply that the physiological role of PGC-1α1 is to promote a beneficial EC coupling phenotype in the heart.

Muscle Stem Cell and Physical Activity: What Point is the Debate at?

In the last 15 years, it emerged that the practice of regular physical activity reduces the risks of many diseases (cardiovascular diseases, diabetes, etc.) and it is fundamental in weight control and energy consuming to contrast obesity. Different groups proposed many molecular mechanisms as responsible for the positive effects of physical activity in healthy life. However, many points remain to be clarified. In this mini-review we reported the latest observations on the effects of physical exercise on healthy skeletal and cardiac muscle focusing on muscle stem cells. The last ones represent the fundamental elements for muscle regeneration post injury, but also for healthy muscle homeostasis.

Interestingly, in both muscle tissues the morphological consequence of physical activity is a physiological hypertrophy that depends on different phenomena both in differentiated cells and stem cells. The signaling pathways for physical exercise effects present common elements in skeletal and cardiac muscle, like activation of specific transcription factors, proliferative pathways, and cytokines. More recently, post translational (miRNAs) or epigenetic (DNA methylation) modifications have been demonstrated. However, several points remain unresolved thus requiring new research on the effect of exercise on muscle stem cells.

Physical Activity Is Associated With Reduced Left Ventricular Mass in Obese and Hypertensive African Americans

BACKGROUND

Physical activity (PA) has been associated with decreased left ventricular (LV) hypertrophy in previous studies. However, little is known about the relationship between PA and LV structure and factors which influence this relationship among African Americans.

METHODS

We evaluated 1,300 African Americans with preserved LV ejection fraction (EF > 50%) from the Genetic Epidemiology Network of Arteriopathy (GENOA) Study (mean age 62.4 years, 73% women). PA index was calculated as 3 * heavy activity hours + 2 * moderate activity hours + slight activity hours/day. The relationship between PA index and LV structure was evaluated using generalized estimating equation. The association between PA index and LV mass index by age group, sex, body mass index (BMI), history of hypertension, diabetes or coronary heart disease, estimated glomerular filtration rate, and current smoking status were plotted.

RESULTS

After adjustment for these factors, higher PA index was independently associated with lower LV mass index (P < 0.05). There were significant interactions between PA index and obesity (BMI ≥ 30) and history of hypertension on LV mass index (P for interaction <0.05, for both). Higher PA index was associated with lower LV mass index more in obese or hypertensive participants compared with nonobese or nonhypertensive participants.

CONCLUSIONS

Higher PA index was associated with reduced LV hypertrophy in obese and hypertensive African Americans. Prospective studies aimed at assessing whether increasing PA prevents LV hypertrophy and potentially reduces the risk of heart failure in these at risk groups are warranted.

Caryocar brasiliense oil improves cardiac function by increasing Serca2a/PLB ratio despite no significant changes in cardiovascular risk factors in rats

Background

Caryocar brasiliense (pequi) oil is high in monounsaturated fat acids (MUFA), especially oleic, and in carotenoids, which have been associated with protection against cardiovascular disease. However, this food is poorly studied in this context, especially in the cardiac function. Therefore, we investigated the effects of a long-term intake of pequi oil in systemic cardiovascular risk factors and in the ex vivo cardiac function of rats.

Methods

Previously, we determined fatty acids and carotenoids in pequi oil. Next, male rats were divided in C – control group feed a standard diet, and PO – pequi oil group fed the same diet added pequi oil (+2.25 g.100 g⁻¹). After 15 weeks, plasma lipids, glucose, insulin, blood pressure, heart rate, hepatic lipids were accessed and visceral fat pads were harvested. Hearts were used for the ex vivo cardiac function, histologic assays, SERCA2a and phospholanban (PLB) determinations.

Results

In agreement with scientific data, pequi oil had expressive amounts MUFA, especially oleic acid, and carotenoids. Hepatic triglycerides (TG) were reduced by pequi oil intake (p < 0.05). All others cardiovascular risk factors were not changed. The intrinsic heart rate was lower in PO group (p < 0.05). SERCA2a content was higher in this group (p < 0.05), without affecting PLB. Also, SERCA2a/PLB ratio increased in PO group (p < 0.05).

Conclusion

Pequi oil intake improved cardiac function ex vivo, despite no significant changes in systemic cardiovascular risk factors. The higher lipid offer in pequi oil diet, its composition in oleic acid and carotenoids could be related to those effects.

Molecular Aspects of Exercise-induced Cardiac Remodeling

Exercise-induced cardiac remodeling is typically an adaptive response associated with cardiac myocyte hypertrophy and renewal, increased cardiac myocyte contractility, sarcomeric remodeling, cell survival, metabolic and mitochondrial adaptations, electrical remodeling, and angiogenesis. Initiating stimuli/triggers of cardiac remodeling include increased hemodynamic load, increased sympathetic activity, and the release of hormones and growth factors. Prolonged and strenuous exercise may lead to maladaptive exercise-induced cardiac remodeling including cardiac dysfunction and arrhythmia. In addition, this article describes novel therapeutic approaches for the treatment of heart failure that target mechanisms responsible for adaptive exercise-induced cardiac remodeling, which are being developed and tested in preclinical models.

Endurance exercise and selective breeding for longevity extend Drosophila healthspan by overlapping mechanisms

Endurance exercise has emerged as a powerful intervention that promotes healthy aging by maintaining the functional capacity of critical organ systems. In addition, long-term exercise reduces the incidence of age-related diseases in humans and in model organisms. Despite these evident benefits, the genetic pathways required for exercise interventions to achieve these effects are still relatively poorly understood. Here, we compare gene expression changes during endurance training in Drosophila melanogaster to gene expression changes during selective breeding for longevity. Microarrays indicate that 65% of gene expression changes found in flies selectively bred for longevity are also found in flies subjected to three weeks of exercise training. We find that both selective breeding and endurance training increase endurance, cardiac performance, running speed, flying height, and levels of autophagy in adipose tissue. Both interventions generally upregulate stress defense, folate metabolism, and lipase activity, while downregulating carbohydrate metabolism and odorant receptor expression. Several members of the methuselah-like (mthl) gene family are downregulated by both interventions. Knockdown of mthl-3 was sufficient to provide extension of negative geotaxis behavior, endurance and cardiac stress resistance. These results provide support for endurance exercise as a broadly acting anti-aging intervention and confirm that exercise training acts in part by targeting longevity assurance pathways.

CITED4 induces physiologic hypertrophy and promotes functional recovery after ischemic injury

The mechanisms by which exercise mediates its multiple cardiac benefits are only partly understood. Prior comprehensive analyses of the cardiac transcriptional components and microRNAs dynamically regulated by exercise suggest that the CBP/p300-interacting protein CITED4 is a downstream effector in both networks. While CITED4 has documented functional consequences in neonatal cardiomyocytes in vitro, nothing is known about its effects in the adult heart. To investigate the impact of cardiac CITED4 expression in adult animals, we generated transgenic mice with regulated, cardiomyocyte-specific CITED4 expression. Cardiac CITED4 expression in adult mice was sufficient to induce an increase in heart weight and cardiomyocyte size with normal systolic function, similar to the effects of endurance exercise training. After ischemia-reperfusion, CITED4 expression did not change initial infarct size but mediated substantial functional recovery while reducing ventricular dilation and fibrosis. Forced cardiac expression of CITED4 also induced robust activation of the mTORC1 pathway after ischemic injury. Moreover, pharmacological inhibition of mTORC1 abrogated CITED4's effects in vitro and in vivo. Together, these data establish CITED4 as a regulator of mTOR signaling that is sufficient to induce physiologic hypertrophy at baseline and mitigate adverse ventricular remodeling after ischemic injury.

Exercise training reverses myocardial dysfunction induced by CaMKIIδC overexpression by restoring Ca2+ homeostasis

Several conditions of heart disease, including heart failure and diabetic cardiomyopathy, are associated with upregulation of cytosolic Ca(2+)/calmodulin-dependent protein kinase II (CaMKIIδC) activity. In the heart, CaMKIIδC isoform targets several proteins involved in intracellular Ca(2+) homeostasis. We hypothesized that high-intensity endurance training activates mechanisms that enable a rescue of dysfunctional cardiomyocyte Ca(2+) handling and thereby ameliorate cardiac dysfunction despite continuous and chronic elevated levels of CaMKIIδC CaMKIIδC transgenic (TG) and wild-type (WT) mice performed aerobic interval exercise training over 6 wk. Cardiac function was measured by echocardiography in vivo, and cardiomyocyte shortening and intracellular Ca(2+) handling were measured in vitro. TG mice had reduced global cardiac function, cardiomyocyte shortening (47% reduced compared with WT, P < 0.01), and impaired Ca(2+) homeostasis. Despite no change in the chronic elevated levels of CaMKIIδC, exercise improved global cardiac function, restored cardiomyocyte shortening, and reestablished Ca(2+) homeostasis to values not different from WT. The key features to explain restored Ca(2+) homeostasis after exercise training were increased L-type Ca(2+) current density and flux by 79 and 85%, respectively (P < 0.01), increased sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a) function by 50% (P < 0.01), and reduced diastolic SR Ca(2+) leak by 73% (P < 0.01), compared with sedentary TG mice. In conclusion, exercise training improves global cardiac function as well as cardiomyocyte function in the presence of a maintained high CaMKII activity. The main mechanisms of exercise-induced improvements in TG CaMKIIδC mice are mediated via increased L-type Ca(2+) channel currents and improved SR Ca(2+) handling by restoration of SERCA2a function in addition to reduced diastolic SR Ca(2+) leak.

Knockout of p21-activated kinase-1 attenuates exercise-induced cardiac remodelling through altered calcineurin signalling

AIMS

Despite its known cardiovascular benefits, the intracellular signalling mechanisms underlying physiological cardiac growth remain poorly understood. Therefore, the purpose of this study was to investigate a novel role of p21-activated kinase-1 (Pak1) in the regulation of exercise-induced cardiac hypertrophy.

METHODS AND RESULTS

Wild-type (WT) and Pak1 KO mice were subjected to 6 weeks of treadmill endurance exercise training (ex-training). Cardiac function was assessed via echocardiography, in situ haemodynamics, and the pCa-force relations in skinned fibre preparations at baseline and at the end of the training regimen. Post-translational modifications to the sarcomeric proteins and expression levels of calcium-regulating proteins were also assessed following ex-training. Heart weight/tibia length and echocardiography data revealed that there was marked hypertrophy following ex-training in the WT mice, which was not evident in the KO mice. Additionally, following ex-training, WT mice demonstrated an increase in cardiac contractility, myofilament calcium sensitivity, and phosphorylation of cardiac myosin-binding protein C, cardiac TnT, and tropomyosin compared with KO mice. With ex-training in WT mice, there were also increased protein levels of calcineurin and increased phosphorylation of phospholamban.

CONCLUSIONS

Our data suggest that Pak1 is essential for adaptive physiological cardiac remodelling and support previous evidence that demonstrates Pak1 signalling is important for cardiac growth and survival.

Influence of Physical Activity on Hypertension and Cardiac Structure and Function

The global burden of hypertension is rising and accounts for substantial morbidity and mortality. Lifestyle factors such as diet and physical inactivity contribute to this burden, further highlighting the need for prevention efforts to curb this public health epidemic. Regular physical activity is associated with lower blood pressure, reduced cardiovascular risk, and cardiac remodeling. While exercise and hypertension can both be associated with the development of left ventricular hypertrophy (LVH), the cardiac remodeling from hypertension is pathologic with an associated increase in myocyte hypertrophy, fibrosis, and risk of heart failure and mortality, whereas LVH in athletes is generally non-pathologic and lacks the fibrosis seen in hypertension. In hypertensive patients, physical activity has been associated with paradoxical regression or prevention of LVH, suggesting a mechanism by which exercise can benefit hypertensive patients. Further studies are needed to better understand the mechanisms underlying the benefits of physical activity in the hypertensive heart.

Effects of high-intensity interval versus continuous moderate-intensity aerobic exercise on apoptosis, oxidative stress and metabolism of the infarcted myocardium in a rat model

The optimal aerobic exercise training (AET) protocol for patients following myocardial infarction (MI) has remained under debate. The present study therefore aimed to compare the effects of continuous moderate-intensity training (CMT) and high-intensity interval training (HIT) on cardiac functional recovery, and to investigate the potential associated mechanisms in a post-MI rat model. Female Sprague Dawley rats (8-10 weeks old) undergoing MI or sham surgery were subsequently submitted to CMT or HIT, or kept sedentary for eight weeks. Prior to and following AET, echocardiographic parameters and exercise capacity of the rats were measured. Western blotting was used to evaluate the levels of apoptosis and associated signaling pathway protein expression. The concentrations of biomarkers of oxidative stress were also determined by ELISA assay. Messenger (m)RNA levels and activity of the key enzymes for glycolysis and fatty acid oxidation, as well as the rate of adenosine triphosphate (ATP) synthesis, were also measured. Compared with the MI group, exercise capacity and cardiac function were significantly improved following AET, particularly following HIT. Left ventricular ejection fraction and fraction shortening were further improved in the MI-HIT group in comparison to that of the MI-CMT group. The two forms of AET almost equally attenuated apoptosis of the post-infarction myocardium. CMT and HIT also alleviated oxidative stress by decreasing the concentration of malondialdehyde and increasing the concentration of superoxide dismutase and glutathione peroxidase (GPx). In particular, HIT induced a greater increase in the concentration of GPx than that of CMT. AET, and HIT in particular, significantly increased the levels of mRNA and the maximal activity of phosphofructokinase-1 and carnitine palmitoyl transferase-1, as well as the maximal ratio of ATP synthesis. In addition, compared with the MI group, the expression of signaling proteins PI3K, Akt, p38mapk and AMPK was significantly altered in the MI-CMT and MI-HIT groups. HIT was superior to CMT in its ability to improve cardiac function and exercise capability in a post-MI rat model. HIT was also superior to CMT with regard to attenuating oxidative stress and improving glucolipid metabolism of the post-MI myocardium.

Using exercise to measure and modify cardiac function

Exercise is the archetype of physiologic demands placed on the cardiovascular system. Acute responses provide an informative assessment of cardiovascular function and fitness, while repeated exercise promotes cardiovascular health and evokes important molecular, structural, and functional changes contributing to its effects in primary and secondary prevention. Here we examine the use of exercise in murine models, both as a phenotypic assay and as a provocative intervention. We first review the advantages and limitations of exercise testing for assessing cardiac function, then highlight the cardiac structural and cellular changes elicited by chronic exercise and key molecular pathways that mediate these effects.

Exercise training starting at weaning age preserves cardiac pacemaker function in adulthood of diet-induced obese rats

Peripheral sympathetic overdrive in young obese subjects contributes to further aggravation of insulin resistance, diabetes, and hypertension, thus inducing worsening clinical conditions in adulthood. Exercise training has been considered a strategy to repair obesity autonomic dysfunction, thereby reducing the cardiometabolic risk. Therefore, the aim of this study was to assess the effect of early exercise training, starting immediately after weaning, on cardiac autonomic control in diet-induced obese rats. Male Wistar rats (weaning) were divided into four groups: (i) a control group (n = 6); (ii) an exercise-trained control group (n = 6); (iii) a diet-induced obesity group (n = 6); and (iv) an exercise-trained diet-induced obesity group (n = 6). The development of obesity was induced by 9 weeks of palatable diet intake, and the training program was implemented in a motor-driven treadmill (5 times per week) during the same period. After this period, animals were submitted to vein and artery catheter implantation to assess cardiac autonomic balance by methylatropine (3 mg/kg) and propranolol (4 mg/kg) administration. Exercise training increased running performance in both groups (p < 0.05). Exercise training also prevented the increased resting heart rate in obese rats, which seemed to be related to cardiac pacemaker activity preservation (p < 0.05). Additionally, the training program preserved the pressure and bradycardia responses to autonomic blockade in obese rats (p < 0.05). An exercise program beginning at weaning age prevents cardiovascular dysfunction in obese rats, indicating that exercise training may be used as a nonpharmacological therapeutic strategy for the treatment of cardiometabolic diseases.

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 (VO_{2 max}) had impaired atrial myocyte contractile function when compared to rats with high inborn VO_{2 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 Ca²⁺ 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 Ca²⁺ amplitude and diastolic Ca²⁺ level were observed at 5 Hz stimulation where Ca²⁺ amplitude was 70% lower and diastolic Ca²⁺ level was 11% higher in LCR rats. Prolonged time to 50% Ca²⁺ decay was associated with reduced sarcoplasmic reticulum (SR) Ca²⁺ ATPase function in LCR (39%). Na⁺/Ca²⁺ exchanger activity was comparable between the groups. Diastolic SR Ca²⁺ leak was increased by 109%. This could be partly explained by increased ryanodine receptors phosphorylation at the Ca²⁺-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 Ca²⁺ release in the cell occurred simultaneously in central and peripheral regions, giving rise to faster and more spatial homogenous Ca²⁺-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.

Regional effects of low-intensity endurance training on structural and mechanical properties of rat ventricular myocytes

We tested the effects of low-intensity endurance training (LIET) on the structural and mechanical properties of right (RV) and left ventricular (LV) myocytes. Male Wistar rats (4 mo old) were randomly divided into control (C, n = 7) and trained (T, n = 7, treadmill running at 50–60% of maximal running speed for 8 wk) groups. Isolated ventricular myocyte dimensions, contractility, Ca2+ transients {intracellular Ca2+ concentration ([Ca2+]i)}, and ventricular [Ca2+]i regulatory proteins were measured. LIET augmented cell length (C, 152.5 ± 2.0 μm vs. T, 162.2 ± 2.1 μm; P < 0.05) and volume (C, 5,162 ± 131 μm3 vs. T, 5,506 ± 132 μm3; P < 0.05) in the LV but not in the RV. LIET increased cell shortening (C, 7.5 ± 0.3% vs. T, 8.6 ± 0.3%; P < 0.05), the [Ca2+]i transient amplitude (C, 2.49 ± 0.06 F/F0 vs. T, 2.82 ± 0.06 F/F0; P < 0.05), the expression of sarcoplasmic reticulum Ca2+-ATPase 2a (C, 1.07 ± 0.13 vs. T, 1.59 ± 0.12; P < 0.05), and the levels of phosphorylated phospholamban at serine 16 (C, 0.99 ± 0.11 vs. T, 1.34 ± 0.10; P < 0.05), and reduced the total phospholamban-to-sarcoplasmic reticulum Ca2+-ATPase 2a ratio (C, 1.19 ± 0.15 vs. T, 0.40 ± 0.16; P < 0.05) in the LV without changing such parameters in the RV. In conclusion, LIET affected the structure and improved the mechanical properties of LV but not of RV myocytes in rats, helping to characterize the functional and morphological changes that accompany the endurance training-induced cardiac remodeling.

Mitogen-activated protein kinase-activated protein kinases 2 and 3 regulate SERCA2a expression and fiber type composition to modulate skeletal muscle and cardiomyocyte function

The mitogen-activated protein kinase (MAPK)-activated protein kinases 2 and 3 (MK2/3) represent protein kinases downstream of the p38 MAPK. Using MK2/3 double-knockout (MK2/3(-/-)) mice, we analyzed the role of MK2/3 in cross-striated muscle by transcriptome and proteome analyses and by histology. We demonstrated enhanced expression of the slow oxidative skeletal muscle myofiber gene program, including the peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC-1α). Using reporter gene and electrophoretic gel mobility shift assays, we demonstrated that MK2 catalytic activity directly regulated the promoters of the fast fiber-specific myosin heavy-chain IId/x and the slow fiber-specific sarco/endoplasmic reticulum Ca(2+)-ATPase 2 (SERCA2) gene. Elevated SERCA2a gene expression caused by a decreased ratio of transcription factor Egr-1 to Sp1 was associated with accelerated relaxation and enhanced contractility in MK2/3(-/-) cardiomyocytes, concomitant with improved force parameters in MK2/3(-/-) soleus muscle. These results link MK2/3 to the regulation of calcium dynamics and identify enzymatic activity of MK2/3 as a critical factor for modulating cross-striated muscle function by generating a unique muscle phenotype exhibiting both reduced fatigability and enhanced force in MK2/3(-/-) mice. Hence, the p38-MK2/3 axis may represent a novel target for the design of therapeutic strategies for diseases related to fiber type changes or impaired SERCA2 function.

Role of exercise in the prevention of cardiovascular disease: results, mechanisms, and new perspectives

On an empirical basis, exercise has been regarded as a fundamental pre-requisite for human well-being and physical integrity since classical times. Only in the last decades, however, scientific evidence has accumulated proving its role in the prevention and treatment of multiple chronic diseases beyond any reasonable doubt. Few treatment strategies in medicine have been tested so rigorously in large cohorts of patients as regular physical exercise. With the advent of molecular biology, the underlying mechanisms, such as NO bioavailability and mobilization of progenitor cells, could be identified. This enhances our understanding of this therapeutic tool. Unfortunately, the low compliance rate of the patients is the major drawback of the intervention exercise training (ET). The objective of this manuscript is to summarize the current knowledge with respect to ET on cardiovascular disease (CVD) and the molecular changes elicited by ET. Finally, we will critically assess reasons why ET as therapeutic option is not as effective at the population level in preventing CVD and what we may change in the future to make ET the most effective intervention to fight the development of CVD.

Physical exercise and its effects on coronary artery disease

The beneficial effects of physical exercise on stable coronary artery disease (CAD) have been shown by an increasing number of studies. Exercise training leads to an improved bioavailability of the endothelial nitric oxide and partially attenuates endothelial dysfunction. Further effects are an economization of ventricular function and a reduction of cardiovascular risk factors. In clinical studies exercise training was associated with a decreased total and cardiovascular mortality and a reduced angina pectoris threshold. Thus exercise training has developed to an evidence-based therapeutic option of stable CAD with a Class Ia recommendation in the guidelines.

Does aerobic exercise training promote changes in structural and biomechanical properties of the tendons in experimental animals? A systematic review

To develop a systematic review to evaluate, through the best scientific evidence available, the effectiveness of aerobic exercise in improving the biomechanical characteristics of tendons in experimental animals. Two independent assessors conducted a systematic search in the databases Medline/PUBMED and Lilacs/BIREME, using the following descriptors of Mesh in animal models. The ultimate load of traction and the elastic modulus tendon were used as primary outcomes and transverse section area, ultimate stress and tendon strain as secondary outcomes. The assessment of risk of bias in the studies was carried out using the following methodological components: light/dark cycle, temperature, nutrition, housing, research undertaken in conjunction with an ethics committee, randomization, adaptation of the animals to the training and preparation for the mechanical test. Eight studies, comprising 384 animals, were selected; it was not possible to combine them into one meta-analysis due to the heterogeneity of the samples. There was a trend to increasing ultimate load without changes in the other outcomes studied. Only one study met more than 80% of the quality criteria. Physical training performed in a structured way with imposition of overloads seems to be able to promote changes in tendon structure of experimental models by increasing the ultimate load supported. However, the results of the influence of exercise on the elastic modulus parameters, strain, transverse section area and ultimate stress, remain controversial and inconclusive. Such a conclusion must be evaluated with reservation as there was low methodological control in the studies included in this review.

dFatp regulates nutrient distribution and long-term physiology in Drosophila

Nutrient allocation and usage plays an important part in regulating the onset and progression of age-related functional declines. Here, we describe a heterozygous mutation in Drosophila (dFatp) that alters nutrient distribution and multiple aspects of physiology. dFatp mutants have increased lifespan and stress resistance, altered feeding behavior and fat storage, and increased mobility. Concurrently, mutants experience impairment of cardiac function. We show that endurance exercise reverses increased lipid storage in the myocardium and the deleterious cardiac function conferred by dFatp mutation. These findings establish a novel conserved genetic target for regulating lifespan and physiology in aging animals. These findings also highlight the importance of varying exercise conditions in assessing aging functions of model organisms.

The effect of creatine supplementation on myocardial function, mitochondrial respiration and susceptibility to ischaemia/reperfusion injury in sedentary and exercised rats

AIM

To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium.

METHODS

Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified.

RESULTS

Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption.

CONCLUSION

This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.