Akt/mTOR pathway contributes to skeletal muscle anti-atrophic effect of aerobic exercise training in heart failure mice.

BACKGROUND: Exercise intolerance is one of the main clinical symptoms of heart failure (HF) and is associated with skeletal muscle wasting due to an imbalance between proteolysis and protein synthesis. In this study, we tested whether aerobic exercise training (AET) would counteract skeletal muscle atrophy by activating IGF-I/Akt/mTOR pathway in HF mice. METHODS: Sympathetic hyperactivity induced HF mice were assigned into 8-week moderate intensity AET. Untrained wild type and HF mice were used as control. Soleus cross sectional area was evaluated by histochemistry and motor performance by rotarod. 26S proteasome activity was assessed by fluorimetric assay, and components of IGF-I/Akt/mTOR pathway or myostatin pathway by qRT-PCR or immunoblotting. A different subset of mice was used to evaluate the relative contribution of mTOR inhibition (rapamycin) or activation (leucine) on AET-induced changes in muscle mass regulation. RESULTS: AET prevented exercise intolerance and impaired motor performance in HF mice. These effects were associated with attenuation of soleus atrophy. Rapamycin treatment precluded AET effects on soleus mass in HF mice suggesting the involvement of IGF signaling pathway in this response. In fact, AET increased IGF-I Ea and IGF-I Pan mRNA levels, while it reduced myostatin and Smad2 mRNA levels in HF mice. At protein levels, AET prevented reduced expression levels of IGF-I, pAkt (at basal state), as well as, p4E-BP1 and pP70(S6K) (leucine-stimulated state) in HF mice. Additionally, AET prevented 26S proteasome hyperactivity in HF mice. CONCLUSIONS: Taken together, our data provide evidence for AET-induced activation of IGF-I/Akt/mTOR signaling pathway counteracting HF-induced muscle wasting.

Moderate exercise training promotes adaptations in coronary blood flow and adenosine production in normotensive rats.

OBJECTIVES: Aerobic exercise training prevents cardiovascular risks. Regular exercise promotes functional and structural adaptations that are associated with several cardiovascular benefits. The aim of this study is to investigate the effects of swimming training on coronary blood flow, adenosine production and cardiac capillaries in normotensive rats. METHODS: Wistar rats were randomly divided into two groups: control (C) and trained (T). An exercise protocol was performed for 10 weeks and 60 min/day with a tail overload of 5% bodyweight. Coronary blood flow was quantified with a color microsphere technique, and cardiac capillaries were quantified using light microscopy. Adenine nucleotide hydrolysis was evaluated by enzymatic activity, and protein expression was evaluated by western blot. The results are presented as the means ± SEMs (p<0.05). RESULTS: Exercise training increased the coronary blood flow and the myocardial capillary-to-fiber ratio. Moreover, the circulating and cardiac extracellular adenine nucleotide hydrolysis was higher in the trained rats than in the sedentary rats due to the increased activity and protein expression of enzymes, such as E-NTPDase and 59'-nucleotidase. CONCLUSIONS: Swimming training increases coronary blood flow, number of cardiac capillaries, and adenine nucleotide hydrolysis. Increased adenosine production may be an important contributor to the enhanced coronary blood flow and angiogenesis that were observed in the exercise-trained rats; collectively, these results suggest improved myocardial perfusion.

Angiotensin receptor blockade improves the net balance of cardiac Ca(2+) handling-related proteins in sympathetic hyperactivity-induced heart failure.

AIMS: The clinical benefits of angiotensin II type 1 (AT1) receptor blockers (ARB) in heart failure (HF) include cardiac anti-remodeling and improved ventricular function. However, the cellular mechanisms underlying the benefits of ARB on ventricular function need to be better clarified. In the present manuscript, we evaluated the effects of AT1 receptor blockade on the net balance of Ca(2+) handling proteins in hearts of mice lacking α(2A) and α(2C) adrenoceptors (α(2A)/α(2C)ARKO), which develop sympathetic hyperactivity (SH) induced-HF. MAIN METHODS: A cohort of male wild-type (WT) and congenic α(2A)/α(2C)ARKO mice in a C57BL6/J genetic background (5-7mo of age) was randomly assigned to receive either placebo or ARB (Losartan, 10mg/kg for 8wks). Ventricular function (VF) was assessed by echocardiography, and cardiac myocyte width and ventricular fibrosis by a computer-assisted morphometric system. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), phospholamban (PLN), phospho-Ser(16)-PLN, phospho-Thr(17)-PLN, phosphatase 1 (PP1), Na(+)-Ca(2+) exchanger (NCX), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and phospho-Thr(286)-CaMKII were analyzed by Western blot. KEY FINDINGS: α(2A)/α(2C)ARKO mice displayed ventricular dysfunction, cardiomyocyte hypertrophy and cardiac fibrosis paralleled by decreased SERCA2 and increased phospho-Thr(17)-PLN, CaMKII, phospho-Thr(286)-CaMKII and NCX levels. ARB induced anti-cardiac remodeling effect and improved VF in α(2A)/α(2C)ARKO associated with increased SERCA2 and phospho-Ser(16)-PLN levels, and SERCA2:NCX ratio. Additionally, ARB decreased phospho-Thr(17)-PLN levels as well as reestablished NCX, CaMKII and phospho-Thr(286)-CaMKII toward WT levels. SIGNIFICANCE: Altogether, these data provide new insights on intracellular Ca(2+) regulatory mechanisms underlying improved ventricular function by ARB therapy in HF.

Moderate exercise training promotes adaptations in coronary blood flow and adenosine production in normotensive rats

OBJECTIVES: Aerobic exercise training prevents cardiovascular risks. Regular exercise promotes functional and structural adaptations that are associated with several cardiovascular benefits. The aim of this study is to investigate the effects of swimming training on coronary blood flow, adenosine production and cardiac capillaries in normotensive rats. METHODS: Wistar rats were randomly divided into two groups: control (C) and trained (T). An exercise protocol was performed for 10 weeks and 60 min/day with a tail overload of 5 percent bodyweight. Coronary blood flow was quantified with a color microsphere technique, and cardiac capillaries were quantified using light microscopy. Adenine nucleotide hydrolysis was evaluated by enzymatic activity, and protein expression was evaluated by western blot. The results are presented as the means ± SEMs (p<0.05). RESULTS: Exercise training increased the coronary blood flow and the myocardial capillary-to-fiber ratio. Moreover, the circulating and cardiac extracellular adenine nucleotide hydrolysis was higher in the trained rats than in the sedentary rats due to the increased activity and protein expression of enzymes, such as E-NTPDase and 59- nucleotidase. CONCLUSIONS: Swimming training increases coronary blood flow, number of cardiac capillaries, and adenine nucleotide hydrolysis. Increased adenosine production may be an important contributor to the enhanced coronary blood flow and angiogenesis that were observed in the exercise-trained rats; collectively, these results suggest improved myocardial perfusion.

Resposta taquicárdica e controle autonômico no exercício físico em modelo genético de insuficiência cardíaca / Tachycardic response and autonomic control in physical exercise in genetic model of cardiac insufficiency

O aumento da atividade nervosa simpática e a taquicardia em repouso ou durante esforços físicos estão associados ao aumento da morbimortalidade, mesmo na ausência de sinais clínicos de doença cardíaca. Sabendo-se da importância dos receptores α2A/α2C-adrenérgicos na modulação da atividade nervosa e frequência cardíaca (FC), o presente trabalho utiliza um modelo genético de cardiomiopatia induzida por excesso de catecolaminas circulantes baseado na inativação gênica dos receptores α2A/α2C-adrenérgicos em camundongos (α2A/α2CKO) para verificar a resposta da FC ao exercício físico (EF), assim como o controle simpatovagal da FC ao EF. Testou-se a hipótese de que haveria resposta taquicárdica exacerbada durante o EF nos camundongos α2A/α2CKO mesmo quando a função cardíaca ainda estivesse preservada em repouso, sendo o receptor α2A-adrenérgico o principal responsável por essa resposta. Camundongos machos da linhagem C57Bl6J, controle (CO) e com inativação gênica para os receptores α2A (α2AKO), α2C α2CKO) e α2A/α2CKO foram submetidos a um teste de tolerância ao esforço físico. Outros dois grupos de camundongos, CO e α2A/α2CKO, foram submetidos ao bloqueio farmacológico dos receptores muscarínicos e β-adrenérgicos e ao EF progressivo para se avaliar a contribuição simpatovagal para a taquicardia de EF. Observou-se intolerância ao esforço físico (1.220 ± 18 e 1.460 ± 34 vs. 2.630 ± 42m, respectivamente) e maior taquicardia ao EF (765 ± 16 e 792 ± 13 vs. 603 ± 18bpm, respectivamente) nos camundongos α2AKO e α2A/α2CKO vs. CO. Além disso, o balanço autonômico estava alterado nos camundongos α2A/α2CKO pela hiperatividade simpática e menor efeito vagal cardíaco. Esses resultados demonstram a importância dos receptores α2A/α2C-adrenérgicos no controle autonômico não só no repouso, mas também durante o EF, sendo o receptor ...

Increase of sympathetic nervous activity and tachycardia at rest or during physical exertions are associated with increase of morbimortality, even in the absence of clinical signs of cardiac disease. Considering the importance of the α2A/α2C-adrenergic receptors in the modulation of the nervous activity and heart rate (HR), the present study uses a genetic model of cardiomyopathy induced by excess of circulating catecholamine in the gene inactivation of the α2A/α2 -adrenergic receptors in mice (α2A/α2CKO) to verify the HR response to physical exercise (PE), as well as the sympathetic-vagal control of the HR to PE. The hypothesis is that there would be exacerbated tachycardic response during PE in α2A/α2CKO mice even when the cardiac function was still preserved at rest, being the α2A-adrenergic receptor the main reason for this response. Male mice of the C57Bl6J lineage, control (CO) and with gene inactivation for the a2A (α2AKO), α2C α2CKO) and α2A/α2CKO receptors were submitted to tolerance to a physical exercise test. Two other groups of mice, CO and α2A/α2CKO, were submitted to pharmacological blocking of the muscarinic and β-adrenergic receptors as well as to progressive PE to assess the sympathetic-vagal contribution to PE tachycardia. Intolerance to physical exercise (1.220 ± 18 and 1.460 ± 34 vs. 2.630 ± 42m, respectively) and higher tachycardia to PE (765 ± 16 e 792 ± 13 vs. 603 ± 18 bpm, respectively) in the α2AKO and α2A/α2CKO vs. CO mice was observed. Moreover, the autonomic balance was altered in the α2A/α2CKO mice by the sympathetic hyperactivity and lower cardiac vagal effect. These outcomes demonstrated the importance of the α2A/α2C-adrenergic receptors in autonomic control not only at rest, but also during PE, being theα2A-adrenergic receptor responsible for the sympathetic hyperactivity and lower ...

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

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

Exercise training improves aortic depressor nerve sensitivity in rats with ischemia-induced heart failure.

Exercise training improves arterial baroreflex control in heart failure (HF) rabbits. However, the mechanisms involved in the amelioration of baroreflex control are unknown. We tested the hypothesis that exercise training would increase the afferent aortic depressor nerve activity (AODN) sensitivity in ischemic-induced HF rats. Twenty ischemic-induced HF rats were divided into trained (n = 11) and untrained (n = 9) groups. Nine normal control rats were also studied. Power spectral analysis of pulse interval, systolic blood pressure, renal sympathetic nerve activity (RSNA), and AODN were analyzed by means of autoregressive parametric spectral and cross-spectral algorithms. Spontaneous baroreflex sensitivity of heart rate (HR) and RSNA were analyzed during spontaneous variation of systolic blood pressure. Left ventricular end-diastolic pressure was higher in HF rats compared with that in the normal control group (P = 0.0001). Trained HF rats had a peak oxygen uptake higher than untrained rats and similar to normal controls (P = 0.01). Trained HF rats had lower low-frequency [1.8 +/- 0.2 vs. 14.6 +/- 3 normalized units (nu), P = 0.0003] and higher high-frequency (97.9 +/- 0.2 vs. 85.0 +/- 3 nu, P = 0.0005) components of pulse interval than untrained rats. Trained HF rats had higher spontaneous baroreceptor sensitivity of HR (1.19 +/- 0.2 vs. 0.51 +/- 0.1 ms/mmHg, P = 0.003) and RSNA [2.69 +/- 0.4 vs. 1.29 +/- 0.3 arbitrary units (au)/mmHg, P = 0.04] than untrained rats. In HF rats, exercise training increased spontaneous AODN sensitivity toward normal levels (trained HF rats, 1,791 +/- 215; untrained HF rats, 1,150 +/- 158; and normal control rats, 2,064 +/- 327 au/mmHg, P = 0.05). In conclusion, exercise training improves AODN sensitivity in HF rats.