Aerobic interval training reduces inducible ventricular arrhythmias in diabetic mice after myocardial infarction

High-Intensity Interval Training Mitigates Sarcopenia and Suppresses the Myoblast Senescence Regulator EEF1E1

BACKGROUND

The optimal exercise regimen for alleviating sarcopenia remains uncertain. This study aimed to investigate the efficacy of high-intensity interval training (HIIT) over moderate-intensity continuous training (MICT) in ameliorating sarcopenia.

METHODS

We conducted a randomized crossover trial to evaluate plasma proteomic reactions to acute HIIT (four 4-min high-intensity intervals at 70% maximal capacity alternating with 4 min at 30%) versus MICT (constant 50% maximal capacity) in inactive adults. We explored the relationship between a HIIT-specific protein relative to MICT, identified via comparative proteomic analysis, eukaryotic translation elongation factor 1 epsilon 1 (EEF1E1) and sarcopenia in a paired case-control study of elderly individuals (aged over 65). Young (3 months old) and aged (20 months old) mice were randomized to sedentary, HIIT and MICT groups (five sessions/week for 4 weeks; n = 8 for each group). Measurements included skeletal muscle index, hand grip strength, expression of atrophic markers Atrogin1 and MuRF1 and differentiation markers MyoD, myogenin and MyHC-II via western blotting. We examined the impact of EEF1E1 siRNA and recombinant protein on D-galactose-induced myoblast senescence, measuring senescence-associated β-galactosidase and markers like p21 and p53.

RESULTS

The crossover trial, including 10 sedentary adults (32 years old, IQR 31-32) demonstrated significant alterations in the abundance of 21 plasma proteins after HIIT compared with MICT. In the paired case-control study of 84 older adults (84 years old, IQR 69-81; 52% female), EEF1E1 was significantly increased in those with sarcopenia compared to those without (14.68 [95%CI, 2.02-27.34] pg/mL, p = 0.03) and was associated with skeletal muscle index (R2 = 0.51, p < 0.001) and hand grip strength (R2 = 0.54, p < 0.001). In the preclinical study, aged mice exhibited higher EEF1E1 mRNA and protein levels in skeletal muscle compared to young mice, accompanied by a lower muscle mass and strength, increased cellular senescence and protein degradation markers and reduced muscle differentiation efficiency (all p < 0.05). HIIT reduced EEF1E1 expression and mitigated age-related muscle decline and atrophy in aged mice more effectively than MICT. Notably, EEF1E1 downregulation via siRNA significantly counteracted D-galactose-induced myoblast senescence as evidenced by reduced markers of muscle protein degradation and improved muscle differentiation efficiency (all p < 0.05). Conversely, treatments that increased EEF1E1 levels accelerated the senescence process (p < 0.05). Further exploration indicated that the decrease in EEF1E1 was associated with increased SIRT1 level and enhanced autophagy.

CONCLUSIONS

This study highlights the potential of HIIT as a promising approach to prevent and treat sarcopenia while also highlighting EEF1E1 as a potential intervention target.

Acute aerobic exercise regulation of myocardial calcium homeostasis involves CASQ1, CASQ2, and TRDN

Exercise maintains cardiac calcium homeostasis and promotes cardiovascular health. This study explored temporal changes of calcium-related myocardial transcriptome changes during the recovery phase following a single bout of moderate-intensity aerobic exercise. Healthy male Sprague-Dawley rats were anesthetized with sodium pentobarbital after moderate-intensity aerobic exercise at four time points (0, 12, 24, and 72 h postexercise). The hearts were removed and RNA-seq and bioinformatics analyses were used to examine temporal transcriptional changes in the myocardium. Casq1, Casq2, and Trdn were identified as key genes in the regulation of calcium homeostasis during myocardial recovery. The highest expression of Casq1, Casq2, and Trdn genes and the proteins they encode occurred 24 h after exercise. An in vitro calcium overload heart model using the Langendorff heart perfusion method was used to examine myocardial calcium buffering capacity. Calcium overload caused the least changes in left ventricular developed pressure, infarct area, Lactate dehydrogenase release, and extent of morphological damage to myocardial cells, with the highest protein expressions of CASQ1, CASQ2, and TRDN at 24 h after acute exercise. This study indicates that maximal myocardial Ca2+ buffering capacity occurs 24 h postexercise in rats. Our study provides insights into exercise-mediated improvements in cardiovascular function and exercise preconditioning.NEW & NOTEWORTHY Acute aerobic exercise upregulates myocardial Casq1, Casq2, and Trdn genes and the proteins they encode in rats. Higher protein levels of CASQ1, CASQ2, and TRDN conferred an improved ability of the myocardium to resist calcium overload. Furthermore, 24 h postexercise is the time point with optimal myocardial calcium buffer capacity.

Pre-stroke exercise does not reduce atrophy in healthy young adult mice

Stroke is the main cause of acquired disability in adults. Exercise reduces the risk for stroke and protects against functional loss after stroke. An exercise-induced reduction in key risk factors probably contributes to the protective effect, but direct effects on the brain may also contribute to stroke protection. We previously reported that exercise increases angiogenesis and neurogenesis through activation of the lactate receptor HCA1. Here we exposed young adult wild-type mice and HCA1 knockout mice to interval exercise at high or medium intensity, or to intraperitoneal injections of L-lactate or saline for seven weeks before we induced experimental stroke by permanent occlusion of the distal medial cerebral artery (dMCA). The resulting cortical atrophy measured three weeks after stroke was unaffected by exercise or L-lactate pre-treatments, and independent of HCA1 activation. Our results suggest that the beneficial effect of exercise prior to stroke where no reperfusion occurs is limited in individuals who do not carry risk factors.

Sympathetic Modulation in Cardiac Arrhythmias: Where We Stand and Where We Go

The nuance of autonomic cardiac control has been studied for more than 400 years, yet little is understood. This review aimed to provide a comprehensive overview of the current understanding, clinical implications, and ongoing studies of cardiac sympathetic modulation and its anti-ventricular arrhythmias' therapeutic potential. Molecular-level studies and clinical studies were reviewed to elucidate the gaps in knowledge and the possible future directions for these strategies to be translated into the clinical setting. Imbalanced sympathoexcitation and parasympathetic withdrawal destabilize cardiac electrophysiology and confer the development of ventricular arrhythmias. Therefore, the current strategy for rebalancing the autonomic system includes attenuating sympathoexcitation and increasing vagal tone. Multilevel targets of the cardiac neuraxis exist, and some have emerged as promising antiarrhythmic strategies. These interventions include pharmacological blockade, permanent cardiac sympathetic denervation, temporal cardiac sympathetic denervation, etc. The gold standard approach, however, has not been known. Although neuromodulatory strategies have been shown to be highly effective in several acute animal studies with very promising results, the individual and interspecies variation between human autonomic systems limits the progress in this young field. There is, however, still much room to refine the current neuromodulation therapy to meet the unmet need for life-threatening ventricular arrhythmias.

Exercise training attenuates angiotensin II-induced cardiac fibrosis by reducing POU2F1 expression

PURPOSE

Exercise training protects against heart failure. However, the mechanism underlying the protective effect of exercise training on angiotensin II (Ang II)-induced cardiac fibrosis remains unclear.

METHODS

An exercise model involving C57BL/6N mice and 6 weeks of treadmill training was used. Ang II (1.44 mg/kg/day) was administered to induce cardiac fibrosis. RNA sequencing and bioinformatic analysis were used to identify the key factors mediating the effects of exercise training on cardiac fibrosis. Primary adult mouse cardiac fibroblasts (CFs) were used in vitro. Adeno-associated virus serotype 9 was used to overexpress POU domain, class 2, transcription factor 1 (POU2F1) in vivo.

RESULTS

Exercise training attenuated Ang II-induced cardiac fibrosis and reversed 39 gene expression changes. The transcription factor regulating the largest number of these genes was POU2F1. Compared to controls, POU2F1 was shown to be significantly upregulated by Ang II, which is itself reduced by exercise training. In vivo, POU2F1 overexpression nullified the benefits of exercise training on cardiac fibrosis. In CFs, POU2F1 promoted cardiac fibrosis. CCAAT enhancer-binding protein β (C/EBPβ) was predicted to be the transcription factor of POU2F1 and verified using a dual-luciferase reporter assay. In vivo, exercise training activated AMP-activated protein kinase (AMPK) and alleviated the increase in C/EBPβ induced by Ang II. In CFs, AMPK agonist inhibited the increase in C/EBPβ and POU2F1 induced by Ang II, whereas AMPK inhibitor reversed this effect.

CONCLUSION

Exercise training attenuates Ang II-induced cardiac fibrosis by reducing POU2F1. Exercise training inhibits POU2F1 by activating AMPK, which is followed by the downregulation of C/EBPβ, the transcription factor of POU2F1.

Ferroptosis and Autophagy-Related Genes in the Pathogenesis of Ischemic Cardiomyopathy

Background

Obesity plays an important role in type 2 diabetes mellitus (T2DM) and myocardial infarction (MI). Ferroptosis and ferritinophagy are related to metabolic pathways, such as fatty acid metabolism and mitochondrial respiration. We aimed to investigate the ferroptosis- and autophagy-related differentially expressed genes (DEGs) that might be potential targets for MI progression.

Methods

GSE116250 was analyzed to obtain DEGs. A Venn diagram was used to obtain the overlapping ferroptosis- and autophagy-related DEGs. The enrichment pathway analysis was performed and the hub genes were obtained. Pivotal miRNAs, transcription factors, and drugs with the hub genes interactions were also predicted. The MI mice model was constructed, and qPCR analysis and single-cell sequencing were used to validate the hub genes.

Results

Utilizing the limma package and the Venn diagram, 26 ferroptosis-related and 29 autophagy-related DEGs were obtained. The list of ferroptosis-related DEGs was analyzed, which were involved in the cellular response to a toxic substance, cellular oxidant detoxification, and the IL-17 signaling pathway. The list of autophagy-related DEGs was involved in the regulation of autophagy, the regulation of JAK-STAT signaling pathway, and the regulation of MAPK cascade. In the protein-protein interaction network, the hub DEGs, such as IL-6, PTGS2, JUN, NQO1, NOS3, LEPR, NAMPT, CDKN2A, CDKN1A, and Snai1, were obtained. After validation using qPCR analysis in the MI mice model and single-cell sequencing, the 10 hub genes can be the potential targets for MI deterioration.

Conclusion

The screened hub genes, IL-6, PTGS2, JUN, NQO1, NOS3, LEPR, NAMPT, CDKN2A, CDKN1A, and Snai1, may be therapeutic targets for patients with MI and may prevent adverse cardiovascular events.

Animal Models of Exercise From Rodents to Pythons

Acute and chronic animal models of exercise are commonly used in research. Acute exercise testing is used, often in combination with genetic, pharmacological, or other manipulations, to study the impact of these manipulations on the cardiovascular response to exercise and to detect impairments or improvements in cardiovascular function that may not be evident at rest. Chronic exercise conditioning models are used to study the cardiac phenotypic response to regular exercise training and as a platform for discovery of novel pathways mediating cardiovascular benefits conferred by exercise conditioning that could be exploited therapeutically. The cardiovascular benefits of exercise are well established, and, frequently, molecular manipulations that mimic the pathway changes induced by exercise recapitulate at least some of its benefits. This review discusses approaches for assessing cardiovascular function during an acute exercise challenge in rodents, as well as practical and conceptual considerations in the use of common rodent exercise conditioning models. The case for studying feeding in the Burmese python as a model for exercise-like physiological adaptation is also explored.

Knockout of interleukin-17A diminishes ventricular arrhythmia susceptibility in diabetic mice via inhibiting NF-κB-mediated electrical remodeling

Interleukin-17A (IL-17), a potent proinflammatory cytokine, has been shown to participate in cardiac electrical disorders. Diabetes mellitus is an independent risk factor for ventricular arrhythmia. In this study, we investigated the role of IL-17 in ventricular arrhythmia of diabetic mice. Diabetes was induced in both wild-type and IL-17 knockout mice by intraperitoneal injection of streptozotocin (STZ). High-frequency electrical stimuli were delivered into the right ventricle to induce ventricular arrhythmias. We showed that the occurrence rate of ventricular tachycardia was significantly increased in diabetic mice, which was attenuated by IL-17 knockout. We conducted optical mapping on perfused mouse hearts and found that cardiac conduction velocity (CV) was significantly decreased, and action potential duration (APD) was prolonged in diabetic mice, which were mitigated by IL-17 knockout. We performed whole-cell patch clamp recordings from isolated ventricular myocytes, and found that the densities of Ito, INa and ICa,L were reduced, the APDs at 50% and 90% repolarization were increased, and early afterdepolarization (EAD) was markedly increased in diabetic mice. These alterations were alleviated by the knockout of IL-17. Moreover, knockout of IL-17 alleviated the downregulation of Nav1.5 (the pore forming subunit of INa), Cav1.2 (the main component subunit of ICa,L) and KChIP2 (potassium voltage-gated channel interacting protein 2, the regulatory subunit of Ito) in the hearts of diabetic mice. The expression of NF-κB was significantly upregulated in the hearts of diabetic mice, which was suppressed by IL-17 knockout. In neonatal mouse ventricular myocytes, knockdown of NF-κB significantly increased the expression of Nav1.5, Cav1.2 and KChIP2. These results imply that IL-17 may represent a potential target for the development of agents against diabetes-related ventricular arrhythmias.

Animal exercise studies in cardiovascular research: Current knowledge and optimal design-A position paper of the Committee on Cardiac Rehabilitation, Chinese Medical Doctors' Association

Growing evidence has demonstrated exercise as an effective way to promote cardiovascular health and protect against cardiovascular diseases However, the underlying mechanisms of the beneficial effects of exercise have yet to be elucidated. Animal exercise studies are widely used to investigate the key mechanisms of exercise-induced cardiovascular protection. However, standardized procedures and well-established evaluation indicators for animal exercise models are needed to guide researchers in carrying out effective, high-quality animal studies using exercise to prevent and treat cardiovascular diseases. In our review, we present the commonly used animal exercise models in cardiovascular research and propose a set of standard procedures for exercise training, emphasizing the appropriate measurements and analysis in these chronic exercise models. We also provide recommendations for optimal design of animal exercise studies in cardiovascular research, including the choice of exercise models, control of exercise protocols, exercise at different stages of disease, and other considerations, such as age, sex, and genetic background. We hope that this position paper will promote basic research on exercise-induced cardiovascular protection and pave the way for successful translation of exercise studies from bench to bedside in the prevention and treatment of cardiovascular diseases.

CaMKII Inhibition is a Novel Therapeutic Strategy to Prevent Diabetic Cardiomyopathy

Increasing prevalence of diabetes mellitus worldwide has pushed the complex disease state to the foreground of biomedical research, especially concerning its multifaceted impacts on the cardiovascular system. Current therapies for diabetic cardiomyopathy have had a positive impact, but with diabetic patients still suffering from a significantly greater burden of cardiac pathology compared to the general population, the need for novel therapeutic approaches is great. A new therapeutic target, calcium/calmodulin-dependent kinase II (CaMKII), has emerged as a potential treatment option for preventing cardiac dysfunction in the setting of diabetes. Within the last 10 years, new evidence has emerged describing the pathophysiological consequences of CaMKII activation in the diabetic heart, the mechanisms that underlie persistent CaMKII activation, and the protective effects of CaMKII inhibition to prevent diabetic cardiomyopathy. This review will examine recent evidence tying cardiac dysfunction in diabetes to CaMKII activation. It will then discuss the current understanding of the mechanisms by which CaMKII activity is enhanced during diabetes. Finally, it will examine the benefits of CaMKII inhibition to treat diabetic cardiomyopathy, including contractile dysfunction, heart failure with preserved ejection fraction, and arrhythmogenesis. We intend this review to serve as a critical examination of CaMKII inhibition as a therapeutic strategy, including potential drawbacks of this approach.

L-lactate induces neurogenesis in the mouse ventricular-subventricular zone via the lactate receptor HCA1

AIM

Adult neurogenesis occurs in two major niches in the brain: the subgranular zone of the hippocampal formation and the ventricular-subventricular zone. Neurogenesis in both niches is reduced in ageing and neurological disease involving dementia. Exercise can rescue memory by enhancing hippocampal neurogenesis, but whether exercise affects adult neurogenesis in the ventricular-subventricular zone remains unresolved. Previously, we reported that exercise induces angiogenesis through activation of the lactate receptor HCA1. The aim of the present study is to investigate HCA₁ -dependent effects on neurogenesis in the two main neurogenic niches.

METHODS

Wild-type and HCA₁ knock-out mice received high intensity interval exercise, subcutaneous injections of L-lactate, or saline injections, five days per week for seven weeks. Well-established markers for proliferating cells (Ki-67) and immature neurons (doublecortin), were used to investigate neurogenesis in the subgranular zone and the ventricular-subventricular zone.

RESULTS

We demonstrated that neurogenesis in the ventricular-subventricular zone is enhanced by HCA₁ activation: Treatment with exercise or lactate resulted in increased neurogenesis in wild-type, but not in HCA₁ knock-out mice. In the subgranular zone, neurogenesis was induced by exercise in both genotypes, but unaffected by lactate treatment.

CONCLUSION

Our study demonstrates that neurogenesis in the two main neurogenic niches in the brain is regulated differently: Neurogenesis in both niches was induced by exercise, but only in the ventricular-subventricular zone was neurogenesis induced by lactate through HCA₁ activation. This opens for a role of HCA₁ in the physiological control of neurogenesis, and potentially in counteracting age-related cognitive decline.

Exercise training reveals micro-RNAs associated with improved cardiac function and electrophysiology in rats with heart failure after myocardial infarction

AIMS

Endurance training improves aerobic fitness and cardiac function in individuals with heart failure. However, the underlying mechanisms are not well characterized. Exercise training could therefore act as a tool to discover novel targets for heart failure treatment. We aimed to associate changes in Ca²⁺ handling and electrophysiology with micro-RNA (miRNA) profile in exercise trained heart failure rats to establish which miRNAs induce heart failure-like effects in Ca²⁺ handling and electrophysiology.

METHODS AND RESULTS

Post-myocardial infarction (MI) heart failure was induced in Sprague Dawley rats. Rats with MI were randomized to sedentary control (sed), moderate (mod)- or high-intensity (high) endurance training for 8 weeks. Exercise training improved cardiac function, Ca²⁺ handling and electrophysiology including reduced susceptibility to arrhythmia in an exercise intensity-dependent manner where high intensity gave a larger effect. Fifty-five miRNAs were significantly regulated (up or down) in MI-sed, of which 18 and 3 were changed towards Sham-sed in MI-high and MI-mod, respectively. Thereafter we experimentally altered expression of these "exercise-miRNAs" individually in human induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CM) in the same direction as they were changed in MI. Of the "exercise-miRNAs", miR-214-3p prolonged AP duration, whereas miR-140 and miR-208a shortened AP duration. miR-497-5p prolonged Ca²⁺ release whereas miR-214-3p and miR-31a-5p prolonged Ca²⁺ decay.

CONCLUSION

Using exercise training as a tool, we discovered that miR-214-3p, miR-497-5p, miR-31a-5p contribute to heart-failure like behaviour in Ca²⁺ handling and electrophysiology and could be potential treatment targets.

Comparative effects of two heat acclimation protocols consisting of high-intensity interval training in the heat on aerobic performance and thermoregulatory responses in exercising rats

Acclimation resulting from low- to moderate-intensity physical exertion in the heat induces several thermoregulatory adaptations, including slower exercise-induced increases in core body temperature. However, few studies have investigated the thermoregulatory adaptations induced by high-intensity interval training (HIIT) protocols. Thus, the present study aimed to compare the adaptations in rats’ thermoregulatory parameters and aerobic performance observed after two different heat acclimation regimens consisting of HIIT protocols performed in a hot environment. Twenty-three adult male Wistar rats were initially subjected to an incremental-speed exercise at 32°C until they were fatigued and then randomly assigned to one of the following three heat acclimation strategies: passive heat exposure without any exercise (untrained controls–UN; n = 7), HIIT performed at the maximal aerobic speed (HIIT_100%; n = 8) and HIIT performed at a high but submaximal speed (HIIT_85%; n = 8). Following the two weeks of interventions, the rats were again subjected to a fatiguing incremental exercise at 32°C, while their colonic temperature (T_COL) was recorded. The workload performed by the rats and their thermoregulatory efficiency were calculated. After the intervention period, rats subjected to both HIIT protocols attained greater workloads (HIIT_100%: 313.7 ± 21.9 J vs. HIIT_85%: 318.1 ± 32.6 J vs. UN: 250.8 ± 32.4 J; p < 0.01) and presented a lower ratio between the change in T_COL and the distance travelled (HIIT_100%: 4.95 ± 0.42°C/km vs. HIIT_85%: 4.33 ± 0.59°C/km vs. UN: 6.14 ± 1.03°C/km; p < 0.001) when compared to UN rats. The latter finding indicates better thermoregulatory efficiency in trained animals. No differences were observed between rats subjected to the two HIIT regimens. In conclusion, the two HIIT protocols induce greater thermoregulatory adaptations and performance improvements than passive heat exposure. These adaptations do not differ between the two training protocols investigated in the present study.

Exercise training reduces ventricular arrhythmias through restoring calcium handling and sympathetic tone in myocardial infarction mice

Exercise can improve morbidity and mortality in heart failure patients; however, the underlying mechanisms remain to be fully investigated. Thus, we investigated the effects of exercise on cardiac function and ventricular arrhythmias in myocardial infarction (MI) induced heart failure mice. Wild-type male mice underwent sham-operation or permanent left coronary artery ligation to induce MI. MI mice were divided into a sedentary (MI-Sed) and two intervention groups: MI-Ex (underwent 6-week treadmill exercise training) and MI-βb (oral bisoprolol treatment (1 mg/kg/d) without exercise). Cardiac function and structure were assessed by echocardiography and histology. Exercise capacity and cardiopulmonary function was accepted as oxygen consumption at peak exercise (peak VO2 ). Autonomic nervous system function and the incidence of spontaneous ventricular arrhythmia were evaluated via telemetry recording. mRNA and protein expressions in the left ventricle (LV) were investigated by real-time PCR and Western blotting. There were no differences in survival rate, MI size, cardiac function and structure, while exercise training improved peak VO2 . Compared with MI-Sed, MI-Ex, and MI-βb showed decreased sympathetic tone and lower incidence of spontaneous ventricular arrhythmia. By Western blot, the hyperphosphorylation of CaMKII and RyR2 were restored by exercise and β-blocker treatment. Furthermore, elevated expression of miR-1 and decreased expression of its target protein PP2A were recovered by exercise and β-blocker treatment. Continuous intensive exercise training can suppress ventricular arrhythmias in subacute to chronic phase of MI through restoring autonomic imbalance and impaired calcium handling, similarly to that for β-blockers.

CaMKII signaling in heart diseases: Emerging role in diabetic cardiomyopathy

Calcium/calmodulin-dependent protein kinase II (CaMKII) is upregulated in diabetes and significantly contributes to cardiac remodeling with increased risk of cardiac arrhythmias. Diabetes is frequently associated with atrial fibrillation, coronary artery disease, and heart failure, which may further enhance CaMKII. Activation of CaMKII occurs downstream of neurohormonal stimulation (e.g. via G-protein coupled receptors) and involve various posttranslational modifications including autophosphorylation, oxidation, S-nitrosylation and O-GlcNAcylation. CaMKII signaling regulates diverse cellular processes in a spatiotemporal manner including excitation-contraction and excitation-transcription coupling, mechanics and energetics in cardiac myocytes. Chronic activation of CaMKII results in cellular remodeling and ultimately arrhythmogenic alterations in Ca²⁺ handling, ion channels, cell-to-cell coupling and metabolism. This review addresses the detrimental effects of the upregulated CaMKII signaling to enhance the arrhythmogenic substrate and trigger mechanisms in the heart. We also briefly summarize preclinical studies using kinase inhibitors and genetically modified mice targeting CaMKII in diabetes. The mechanistic understanding of CaMKII signaling, cardiac remodeling and arrhythmia mechanisms may reveal new therapeutic targets and ultimately better treatment in diabetes and heart disease in general.

Exercise Training Has Contrasting Effects in Myocardial Infarction and Pressure Overload Due to Divergent Endothelial Nitric Oxide Synthase Regulation

The beneficial effects of exercise training (EX) on cardiac pathology are well recognized. Previously, we found that the effects of EX on cardiac dysfunction in mice critically depend on the underlying etiology. EX exerted beneficial effects after myocardial infarction (MI); however, cardiac pathology following pressure overload produced by transverse aortic constriction (TAC) was aggravated by EX. In the presented study, we investigated whether the contrasting effects of EX on cardiac dysfunction can be explained by an etiology-specific response of endothelial nitric oxide (NO) synthase (eNOS) to EX, which divergently affects the balance between nitric oxide and superoxide. For this purpose, mice were exposed to eight weeks of voluntary wheel running or sedentary housing (SED), immediately after sham, MI, or TAC surgery. Left ventricular (LV) function was assessed using echocardiography and hemodynamic measurements. EX ameliorated LV dysfunction and remodeling after MI, but not following TAC, in which EX even aggravated fibrosis. Strikingly, EX attenuated superoxide levels after MI, but exacerbated NOS-dependent superoxide levels following TAC. Similarly, elevated eNOS S-glutathionylation and eNOS monomerization, which were observed in both MI and TAC, were corrected by EX in MI, but aggravated by EX after TAC. Additionally, EX reduced antioxidant activity in TAC, while it was maintained following EX in MI. In conclusion, the present study shows that EX mitigates cardiac dysfunction after MI, likely by attenuating eNOS uncoupling-mediated oxidative stress, whereas EX tends to aggravate cardiac dysfunction following TAC, likely due to exacerbating eNOS-mediated oxidative stress.

Inhibition of calcium/calmodulin-dependent kinase II restores contraction and relaxation in isolated cardiac muscle from type 2 diabetic rats

BACKGROUND

Calcium/calmodulin-dependent kinase II-delta (CaMKIIδ) activity is enhanced during hyperglycemia and has been shown to alter intracellular calcium handling in cardiomyocytes, ultimately leading to reduced cardiac performance. However, the effects of CaMKIIδ on cardiac contractility during type 2 diabetes are undefined.

METHODS

We examined the expression and activation of CaMKIIδ in right atrial appendages from non-diabetic and type 2 diabetic patients (n = 7 patients per group) with preserved ejection fraction, and also in right ventricular tissue from Zucker Diabetic Fatty rats (ZDF) (n = 5-10 animals per group) during early diabetic cardiac dysfunction, using immunoblot. We also measured whole heart function of ZDF and control rats using echocardiography. Then we measured contraction and relaxation parameters of isolated trabeculae from ZDF to control rats in the presence and absence of CaMKII inhibitors.

RESULTS

CaMKIIδ phosphorylation (at Thr287) was increased in both the diabetic human and animal tissue, indicating increased CaMKIIδ activation in the type 2 diabetic heart. Basal cardiac contractility and relaxation were impaired in the cardiac muscles from the diabetic rats, and CaMKII inhibition with KN93 partially restored contractility and relaxation. Autocamtide-2-related-inhibitor peptide (AIP), another CaMKII inhibitor that acts via a different mechanism than KN93, fully restored cardiac contractility and relaxation.

CONCLUSIONS

Our results indicate that CaMKIIδ plays a key role in modulating performance of the diabetic heart, and moreover, suggest a potential therapeutic role for CaMKII inhibitors in improving myocardial function during type 2 diabetes.

Beneficial effects of exercise training in heart failure are lost in male diabetic rats

Exercise training has been demonstrated to have beneficial effects in patients with heart failure (HF) or diabetes. However, it is unknown whether diabetic patients with HF will benefit from exercise training. Male Wistar rats were fed either a standard (Sham, n = 53) or high-fat, high-sucrose diet ( n = 66) for 6 mo. After 2 mo of diet, the rats were already diabetic. Rats were then randomly subjected to either myocardial infarction by coronary artery ligation (MI) or sham operation. Two months later, heart failure was documented by echocardiography and animals were randomly subjected to exercise training with treadmill for an additional 8 wk or remained sedentary. At the end, rats were euthanized and tissues were assayed by RT-PCR, immunoblotting, spectrophotometry, and immunohistology. MI induced a similar decrease in ejection fraction in diabetic and lean animals but a higher premature mortality in the diabetic group. Exercise for 8 wk resulted in a higher working power developed by MI animals with diabetes and improved glycaemia but not ejection fraction or pathological phenotype. In contrast, exercise improved the ejection fraction and increased adaptive hypertrophy after MI in the lean group. Trained diabetic rats with MI were nevertheless able to develop cardiomyocyte hypertrophy but without angiogenic responses. Exercise improved stress markers and cardiac energy metabolism in lean but not diabetic-MI rats. Hence, following HF, the benefits of exercise training on cardiac function are blunted in diabetic animals. In conclusion, exercise training only improved the myocardial profile of infarcted lean rats fed the standard diet. NEW & NOTEWORTHY Exercise training is beneficial in patients with heart failure (HF) or diabetes. However, less is known of the possible benefit of exercise training for HF patients with diabetes. Using a rat model where both diabetes and MI had been induced, we showed that 2 mo after MI, 8 wk of exercise training failed to improve cardiac function and metabolism in diabetic animals in contrast to lean animals.

Exercise induces cerebral VEGF and angiogenesis via the lactate receptor HCAR1

Physical exercise can improve brain function and delay neurodegeneration; however, the initial signal from muscle to brain is unknown. Here we show that the lactate receptor (HCAR1) is highly enriched in pial fibroblast-like cells that line the vessels supplying blood to the brain, and in pericyte-like cells along intracerebral microvessels. Activation of HCAR1 enhances cerebral vascular endothelial growth factor A (VEGFA) and cerebral angiogenesis. High-intensity interval exercise (5 days weekly for 7 weeks), as well as L-lactate subcutaneous injection that leads to an increase in blood lactate levels similar to exercise, increases brain VEGFA protein and capillary density in wild-type mice, but not in knockout mice lacking HCAR1. In contrast, skeletal muscle shows no vascular HCAR1 expression and no HCAR1-dependent change in vascularization induced by exercise or lactate. Thus, we demonstrate that a substance released by exercising skeletal muscle induces supportive effects in brain through an identified receptor.

CaMKII as a target for arrhythmia suppression

Calcium/calmodulin-dependent protein kinase II (CaMKII) has emerged as key enzyme in many cardiac pathologies, especially heart failure (HF), myocardial infarction and cardiomyopathies, thus leading to contractile dysfunction and malignant arrhythmias. While many pathways leading to CaMKII activation have been elucidated in recent years, hardly any clinically viable compounds affecting CaMKII activity have progressed from basic in vitro science to in vivo studies. This review focuses on recent advances in anti-arrhythmic strategies involving CaMKII. Specifically, both inhibition of CaMKII itself to prevent arrhythmias, as well as anti-arrhythmic approaches affecting CaMKII activity via alterations in signaling cascades upstream and downstream of CaMKII will be discussed.