Exercise training induced myosin heavy chain isoform alteration in the infarcted heart

MAP Kinase Phosphatase-5 Deficiency Improves Endurance Exercise Capacity

Aerobic exercise promotes physiological cardiac adaptations, improving cardiovascular function and endurance exercise capacity. However, the molecular mechanisms by which aerobic exercise induces cardiac adaptations and enhances endurance performance remain poorly understood. Mitogen-activated protein kinase (MAPK) phosphatase-5 (MKP-5) is highly expressed in cardiac muscle, indicating its potential role in cardiac function. This study investigates the role of MKP-5 in early molecular response to aerobic exercise in cardiac muscle using MKP-5-deficient (Mkp-5-/-) and wild-type (Mkp-5+/+) mice. Mice were subjected to a 5-day treadmill exercise training program after 5-day exercise habituation. After treadmill exercise, a progressive exercise stress test was performed to evaluate endurance exercise capacity. Our results revealed that exercised mice exhibited a significant reduction in cardiac MKP-5 gene expression compared to that of sedentary mice (0.19 ± 5.89-fold; p < 0.0001). Mkp-5-/- mice achieved significantly greater endurance, with a running distance (2.81 ± 169.8-fold; p < 0.0429) longer than Mkp-5+/+ mice. Additionally, MKP-5 deficiency enhanced Akt/mTOR signaling (p-Akt/Akt: 1.29 ± 0.12-fold; p = 0.04; p-mTOR/mTOR: 1.59 ± 0.14-fold; p = 0.002) and mitochondrial biogenesis (pgc-1α: 1.56 ± 0.27-fold; p = 0.03) in cardiac muscle in response to aerobic exercise. Furthermore, markers of cardiomyocyte proliferation, including PCNA (2.24 ± 0.31-fold; p < 0.001), GATA4 (1.47 ± 0.10-fold; p < 0.001), and CITED4 (2.03 ± 0.15-fold; p < 0.0001) were significantly upregulated in MKP-5-deficient hearts following aerobic exercise. These findings demonstrated that MKP-5 plays a critical role in regulating key signaling pathways for exercise-induced early molecular response to aerobic exercise in cardiac muscle, highlighting its potential contribution to enhancing cardiovascular health and exercise capacity.

Liraglutide combined with HIIT preserves contractile apparatus and blunts the progression of heart failure in diabetic cardiomyopathy rats

Liraglutide has been shown to alleviate heart failure in patients with type 2 diabetes. High-intensity interval training (HIIT) has also been proven to improve cardiac function in diabetes. The present study explored the effects and underlying mechanisms of liraglutide and HIIT combination therapy in alleviating diabetic cardiomyopathy (DCM). A high-fat diet and low-dose streptozotocin (STZ) were utilized to induce the DCM model. Eight weeks of liraglutide injection and HIIT were used to treat DCM. Subsequently, cardiac function, serum metabolic biomarkers, serum glucagon-like peptide-1 (GLP-1), histology examination, cardiac alpha-myosin heavy chain (α-MHC), and β-MHC messenger RNA (mRNA) expression, forkhead box protein O1 (FOXO1) and muscle-specific RING finger protein 1 (MURF1) mRNA expression and colocalization, and expression of GLP-1 and GLP-1 receptor (GLP-1R) proteins were detected after the intervention. Results showed that DCM rats developed hyperglycemia with eccentric hypertrophy, fibrosis, and reduced systolic and diastolic function. All interventions significantly reversed the development of heart failure by alleviating the disruption of contractile apparatus, reversed the adult α-MHC transformed to fetal β-MHC, and reduced FOXO1 and MURF1 mRNA expression. Combination therapy had a better effect in alleviating cardiac fibrosis, reducing cardiovascular risk biomarkers, controlling eccentric hypertrophy, and improving systolic function. Combination therapy significantly reduced FOXO1 and MURF1 colocalization and improved the GLP-1R sensitivity in diabetic hearts. Overall, these findings demonstrate that combination therapy can reverse cardiac failure in diabetic rats by controlling the degradation of contractile apparatus by downregulating the cardiac atrophy gene expression and interrupting their colocalization, as well as upregulating GLP-1 signaling.

Biofabrication of advancedin vitro3D models to study ischaemic and doxorubicin-induced myocardial damage

Current preclinicalin vitroandin vivomodels of cardiac injury typical of myocardial infarction (MI, or heart attack) and drug induced cardiotoxicity mimic only a few aspects of these complex scenarios. This leads to a poor translation of findings from the bench to the bedside. In this study, we biofabricated for the first time advancedin vitromodels of MI and doxorubicin (DOX) induced injury by exposing cardiac spheroids (CSs) to pathophysiological changes in oxygen (O₂) levels or DOX treatment. Then, contractile function and cell death was analyzed in CSs in control versus I/R and DOX CSs. For a deeper dig into cell death analysis, 3D rendering analyses and mRNA level changes of cardiac damage-related genes were compared in control versus I/R and DOX CSs. Overall,in vitroCSs recapitulated major features typical of thein vivoMI and drug induced cardiac damages, such as adapting intracellular alterations to O2concentration changes and incubation with cardiotoxic drug, mimicking the contraction frequency and fractional shortening and changes in mRNA expression levels for genes regulating sarcomere structure, calcium transport, cell cycle, cardiac remodelling and signal transduction. Taken together, our study supports the use of I/R and DOX CSs as advancedin vitromodels to study MI and DOX-induced cardiac damage by recapitulating their complex in vivoscenario.

Changes in myocardial myosin heavy chain isoform composition with exercise and post-exercise cold-water immersion

This study investigated the changes in myocardial myosin heavy chain (MHC) isoforms, MHC-α and MHC-β composition in young healthy rodents following endurance training, with and without post-exercise cold-water immersion (CWI). Male rats were either trained on a treadmill for 10 weeks with (CWI) or without (Ex) regular CWI after each running session, or left sedentary (CON). Left ventricular mRNA of MHC-α, MHC-β, thyroid receptor α1 (TR-α1) and β (TR-β) were analyzed using rt-PCR and semiquantitative PCR analysis. MHC isoform protein composition was determined using SDS-PAGE electrophoresis. MHC-α isoform protein was predominant in all groups. The relative expression of MHC-β (%MHC-β) protein was not different between groups (CWI 34.7 ± 6.9%; Ex 32 ± 5.3%; CON 35.5 ± 10%; P = 0.7). MHC-β mRNA was reduced in Ex (0.7 ± 0.3-fold) compared to CWI (1.3 ± 0.2-fold; P < 0.001) and CON (1.01 ± 0.2-fold; P = 0.03). TRα1 mRNA was lower in CWI (0.4 ± 0.05-fold) than Ex (1.02 ± 0.3-fold) and CON (1.01 ± 0.2-fold) (P < 0.001 for both). CWI exhibited greater %MHC-β mRNA (56.8 ± 4.1%) than Ex (44.4 ± 7.7%; P = 0.001) and CON (48.5 ± 7.8%; P = 0.03). Neither exercise nor post-exercise CWI demonstrated a distinct effect on myocardial MHC protein isoform composition. However, CWI increased the relative expression of MHC-β mRNA compared with Ex and CON. Although this implicates a potential negative long-term impact of post-exercise CWI, future studies should include measures of cardiac function to better understand the effect of such isoform mRNA shifts following regular use of CWI.

Interaction of Obesity and Hypertension on Cardiac Metabolic Remodeling and Survival Following Myocardial Infarction

Background

Obesity and hypertension are risk factors for myocardial infarction (MI); however, their potential interactions on post‐MI outcomes are unclear. We examined interactions of obesity and hypertensionon post‐MI function, remodeling, metabolic changes, and recovery.

Methods and Results

Male and female C57BL/6J mice were provided standard chow or high‐fat/fructose diet for 8 weeks and then infused with angiotensin II for 2 weeks to induce hypertension. MI was then induced by surgical ligation of the left coronary artery for 7 days. Obesity alone did not cause cardiac injury or exacerbate hypertension‐induced cardiac dysfunction. After MI, however, obese‐normotensive mice had lower survival rates compared with chow‐fed mice (56% versus 89% males; 54% versus 75% females), which were further decreased by hypertension (29% males; and 35% females). Surviving obese‐normotensive males displayed less left ventricular dilation and pulmonary congestion compared with chow‐fed males after MI; hypertension reversed left ventricular dilation because of high‐fat/fructose diet and promoted significant pulmonary congestion compared with chow‐fed controls. Obese‐normotensive males displayed higher left ventricular α‐MHC (alpha‐myosin heavy chain) protein, phosphorylated Akt (protein kinase B) and AMPK (adenosine‐monophosphate activated kinase), PPAR‐γ (peroxisome proliferator activated receptor gamma), and plasma adiponectin levels after MI, indicating favorable contractile and metabolic changes. However, these favorable contractile and metabolic changes were attenuated by hypertension. Obese‐hypertensive males also had lower levels of collagen in the infarcted region, indicating decreased ability to promote an adaptive wound healing response to MI.

Conclusions

Obesity reduces post‐MI survival but is associated with improved post‐MI cardiac function and metabolism in surviving normotensive mice. When hypertension accompanies obesity, favorable metabolic pathways associated with obesity are attenuated and post‐MI cardiac function and remodeling are adversely impacted.

Adaptation of aerobic training essentially involved autophagy, mitochondrial marker and muscle fibre genetic modulation in rat cardiac muscles

Information about the role of moderate acute treadmill training in modulating autophagy and mitochondrial markers that might be correlated with alteration of muscle fibre gene expression in rat cardiac muscles is very limited. In this present study, the researchers divided twenty male Wistar rats into four groups: sedentary control, 3, 6 and 15 days and subjected them to treadmill training with moderate intensity (20 m/min), 30 min each day. RNA was extracted from cardiac muscles and stored in temperature of -80°C. Specific primers were utilized for semi-quantitative PCR. Treadmill training decreased autophagy-related gene expression (LC3, p62) and upper stream signalling of autophagy (PIK3CA, Akt and mTOR) in 3 and 6 d, but stimulated gene expression of mitochondrial markers (PGC1α, Cox1, Cox2 and Cox4) in 15 days. αMHC gene expression increased while βMHC gene expression decreased in 15 days. In line with this, autophagy-related genes increased in 3 and 6 days and returned to baseline in 15 days. The increment in mitochondrial gene expression might be correlated with shifting gene expression of αMHC and βMHC in 15 days. Taken together, acute adaptation in cardiac muscles is stimulated by genetic modulation of autophagy, mitochondrial marker and muscle fibre that may explain physiological cardiac adaptation after training. This study can be used as a reference for optimizing performance in period of cardiac muscle adaptation stimulated by treadmill training.

Irisin vs. Treadmill Exercise in Post Myocardial Infarction Cardiac Rehabilitation in Rats

BACKGROUND

Irisin is an exercise-induced myokine that could play a role in post-myocardial infarction (MI) cardiac rehabilitation.

AIM OF THE STUDY

We investigated the ability of dihydromyricetin to mimic the effects of exercise on raising serum irisin and on enhancing cardiac function and remodeling following MI in rats.

METHODS

MI was induced in albino rats by subcutaneous injection of isoproterenol (85 mg/kg) for 2 consecutive days at an interval of 24 h. One week post-MI, rats either underwent physical exercise by running on a motor-driven treadmill at 25 m/min, 30 min/d, 5 d/week or received orally dihydromyricetin 100 mg/kg/d, for 8 weeks.

RESULTS

Exercise and dihydromyricetin raised serum irisin 1.8 and 1.9 folds as compared to sedentary rats (p <0.001) with no difference between both regimens (p = 0.992). There was an improvement of cardiac remodeling where β-myosin heavy chain level was not different in exercise and dihydromyricetin groups from normal group (p = 0.695, p = 0.470). The heart rate variability domains increased back to normal. However, exercise was superior to dihydromyricetin in improving cardiac contractility by increasing carotid blood flow, stroke volume and cardiac output to be insignificant from normal rats (p = 0.899, p = 0.850, p = 0.912). Meanwhile, treatment with dihydromyricetin showed reduction by 29% of carotid blood flow, 24% of stroke volume and 25% of cardiac output compared to normal rats (p <0.001).

CONCLUSIONS

DHM could mimic the effect of exercise in stimulating irisin secretion but it is not as effective as exercise in improving myocardial contractility.

Strength training attenuates post-infarct cardiac dysfunction and remodeling

Post-myocardial infarction (MI) exercise has been employed to improve cardiac function. However, most studies have focused on endurance training (Et). Although Et has been reported to preserve cardiac function, evidence suggests that Et increases left ventricle (LV) interior dimensions as a result of albumin-induced plasma expansion. In contrast, strength training (St) induces concentric cardiac hypertrophy and improved cardiac function without causing ventricular dilation. Therefore, the purpose of this study was to investigate the effects of St on cardiac function and remodeling in rats with MI. MI was surgically induced in 7-week-old rats via ligation of the coronary artery. Survivors were assigned to two experimental groups, MI-Sed (No exercise; n = 9), MI-St (St; n = 10), with a Sham group (no MI, no St; n = 9). MI-St rats began training 1-week post-MI by climbing a ladder with weights for 10 weeks. Echocardiographic measurements were performed prior to, and following exercise training, while in vivo LV hemodynamic analysis was conducted at the end of the experimental period. Our data revealed that St induced shortening of the LV end-diastolic dimension in the MI-St group compared with the MI-Sed group (P < 0.05). The peak velocities of contraction (+ dP/dt max) and relaxation (- dP/dt max) were significantly greater in the MI-St group than the MI-Sed group (P < 0.05). These training effects contributed to the improved fractional shortening (%FS). Our results demonstrate that St may be beneficial for post-MI by attenuating LV dilation and concomitant cardiac dysfunction associated with MI.

Post-myocardial infarction exercise training beneficially regulates thyroid hormone receptor isoforms

Thyroid hormone receptors (TRs) play a critical role in the expression of genes that are major determinants of myocardial contractility, including α-myosin heavy chain (α-MHC) and β-MHC. After myocardial infarction (MI), changes in myocardial TRs consistently correlate with changes in thyroid hormone (TH) target gene transcription, and this is thought to play a key role in the progression to end-stage heart failure. Interestingly, post-MI exercise training has been shown to beneficially alter TH-target gene transcription and preserve cardiac function without changing serum TH. Therefore, in this study, we investigated whether mild exercise training alters expression of α1 and β1 TR isoforms in post-MI rats. Seven-week-old male Sprague-Dawley rats underwent coronary ligation or sham operation, and were assigned to 3 groups (n = 10): sham, sedentary MI (MI-Sed), and exercise MI (MI-Ex). Treadmill training was initiated 1 week post-MI, and gradually increased up to 16 m/min, 5° incline, 50 min/day, 5 days/week, and lasted for a total of 8 weeks. Real-time polymerase chain reaction and gel electrophoresis were performed to quantify changes in TR isoforms. Our results illustrated that mRNA expression of TR-α1 and TR-β1 was higher in both MIs; however, protein electrophoresis data showed that TR-α1 was 1.91-fold higher (P < 0.05) and TR-β1 was 1.62-fold higher (P < 0.05) in the MI-Ex group than in the MI-Sed group. After MI, TR-α1 and TR-β1 protein levels are significantly decreased in the surviving non-infarcted myocardium. Moderate-intensity exercise training significantly increases TR-α1 and TR-β1 protein expression, which in turn may upregulate α-MHC and improve myocardial contractile function and prognosis.

Preoperative oral thyroid hormones to prevent euthyroid sick syndrome and attenuate myocardial ischemia-reperfusion injury after cardiac surgery with cardiopulmonary bypass in children: A randomized, double-blind, placebo-controlled trial

BACKGROUND

Both euthyroid sick syndrome and myocardial ischemia-reperfusion injury are common and have been significantly associated with morbidity and mortality after pediatric cardiac surgery with cardiopulmonary bypass. This single-center, prospective, double-blind, randomized placebo-controlled clinical pilot trial was designed to assess if preoperative oral thyroid hormone therapy could prevent the occurrence of euthyroid sick syndrome (ESS) and attenuate myocardial ischemia-reperfusion injury (IRI) after cardiac surgery with cardiopulmonary bypass (CPB) in children.

METHODS

Forty children aged 3 to 12 year, scheduled for elective congenital heart disease repair surgery with CPB, were randomized into 2 groups of equal size to receive the following treatments in a double-blind manner: placebo (control group) and thyroid tablet 0.4 mg/kg (trial group) taken orally once a day for 4 days before surgery. The perioperative serum thyroid hormone levels and hemodynamic variables were determined. The extubation time, duration of intensive care unit (ICU) stay, and use of inotropic drugs in the ICU were recorded. The myocardial expressions of heat shock protein 70 (HSP70), myosin heavy chain (MHC) mRNA, and thyroid hormone receptor (TR) mRNA were detected. The serum creatine kinase-MB (CK-MB) activity and troponin I (TnI) positive ratio at 24 hour after surgery were assessed.

RESULTS

There were no significant differences in hemodynamic variables at all observed points, extubation time, and duration of ICU stay between groups. As compared with baselines on administration, serum triiodothyronine (T3) and free T3 (FT3) levels on the first, second, and fourth postoperative day, and serum thyrotropic-stimulating hormone (TSH), tetraiodothyronine (T4), and free T4 (FT4) levels on the first postoperative day were significantly decreased in the 2 groups. Serum T3, FT3, and T4 levels on the first and second postoperative day, and serum FT4 level on the first postoperative day were significantly higher in the trial group than in control group. As compared with the control group, the number of patients requiring inotropic drugs in the ICU, serum CK-MB activity, serum positive TnI ratio, and myocardial expression of MHCβ mRNA were significantly decreased, and myocardial expressions of both HSP70 and MHCα mRNA were significantly increased in the trial group.

CONCLUSIONS

In children undergoing cardiac surgery with CPB, preoperative oral small-dose thyroid hormone therapy reduces severity of postoperative ESS and provides a protection against myocardial IRI by increasing HSP70 and MHCα expression.

Effects of enteral different-dose levothyroxinesodium pretreatment on serum thyroid hormone levels and myocardial ischemia-reperfusion injury

INTRODUCTION

The available evidence shows that perioperative oral thyroid hormone can significantly attenuate the postoperative decline in the serum hormone level and improve postoperative hemodynamic and prognostic parameters. However, there has been no study assessing the effects of preoperative oral different-dose thyroid hormone on serum hormone levels and myocardial ischemia-reperfusion injury (IRI) after cardiac surgery.

METHODS

Forty-eight healthy Wistar rats, aged 35 days, were randomly allocated into six groups: Group BC, Group C and four pretreatment groups in which the rats were given levothyroxine-sodium of 10 μg, 20 μg, 40 μg and 80 μg/100 g. On the eighth day, the serum thyroid hormone levels were determined and then an isolated heart ischemia-reperfusion model was established with a Langendorff apparatus.

RESULTS

Compared with Groups BC and C, serum thyroid hormone levels on the eighth day did not significantly change in Group 10 μg, but were significantly increased in Groups 20 μg, 40 μg and 80 μg. The cardiac enzyme myocardial-bound creatine kinase levels in the coronary effluent during reperfusion were significantly lower in Groups 10 μg and 20 μg and 40 μg than in Group C. The recovery rates of + dp/dt_max and - dp/dt_max at 30 min during reperfusion were significantly lower in Groups 40 μg and 80 μg than in Groups 10 μg and 20 μg. Compared with Group C, myocardial expressions of heat shock protein 70 and myosin heavy chain α were increased in the four experiment groups and myocardial expression of thyroid hormone receptor α1 was significantly increased in Groups 20 μg, 40 μg and 80 μg.

CONCLUSIONS

The pretreatment with enterally smaller doses levothyroxine-sodium does not significantly affect serum thyroid hormone levels and produces protection against myocardial IRI, whereas pretreatment with enterally larger doses of levothyroxine-sodium can only provide an attenuated or insignificant cardioprotection because of hyperthyroxinemia. Cardioprotection by levothyroxine-sodium pretreatment is probably attributable to increased myocardial expression of heat shock protein 70 and myosin heavy chain α.

Cardiac remodeling and physical training post myocardial infarction

After myocardial infarction (MI), the heart undergoes extensive myocardial remodeling through the accumulation of fibrous tissue in both the infarcted and noninfarcted myocardium, which distorts tissue structure, increases tissue stiffness, and accounts for ventricular dysfunction. There is growing clinical consensus that exercise training may beneficially alter the course of post-MI myocardial remodeling and improve cardiac function. This review summarizes the present state of knowledge regarding the effect of post-MI exercise training on infarcted hearts. Due to the degree of difficulty to study a viable human heart at both protein and molecular levels, most of the detailed studies have been performed by using animal models. Although there are some negative reports indicating that post-MI exercise may further cause deterioration of the wounded hearts, a growing body of research from both human and animal experiments demonstrates that post-MI exercise may beneficially alter the course of wound healing and improve cardiac function. Furthermore, the improved function is likely due to exercise training-induced mitigation of renin-angiotensin-aldosterone system, improved balance between matrix metalloproteinase-1 and tissue inhibitor of matrix metalloproteinase-1, favorable myosin heavy chain isoform switch, diminished oxidative stress, enhanced antioxidant capacity, improved mitochondrial calcium handling, and boosted myocardial angiogenesis. Additionally, meta-analyses revealed that exercise-based cardiac rehabilitation has proven to be effective, and remains one of the least expensive therapies for both the prevention and treatment of cardiovascular disease, and prevents re-infarction.