Exercise-induced Physiological Hypertrophy Research Articles

LncExACT1 and DCHS2 Regulate Physiological and Pathological Cardiac Growth.

The heart grows in response to pathological and physiological stimuli. The former often precedes cardiomyocyte loss and heart failure; the latter paradoxically protects the heart and enhances cardiomyogenesis. The mechanisms underlying these differences remain incompletely understood. Although long noncoding RNAs (lncRNAs) are important in cardiac development and disease, less is known about their roles in physiological hypertrophy or cardiomyogenesis. RNA sequencing was applied to hearts from mice after 8 weeks of voluntary exercise-induced physiological hypertrophy and cardiomyogenesis or transverse aortic constriction for 2 or 8 weeks to induce pathological hypertrophy or heart failure. The top lncRNA candidate was overexpressed in hearts with adeno-associated virus vectors and inhibited with antisense locked nucleic acid-GapmeRs to examine its function. Downstream effectors were identified through promoter analyses and binding assays. The functional roles of a novel downstream effector, dachsous cadherin-related 2 (DCHS2), were examined through transgenic overexpression in zebrafish and cardiac-specific deletion in Cas9-knockin mice. We identified exercise-regulated cardiac lncRNAs, called lncExACTs. lncExACT1 was evolutionarily conserved and decreased in exercised hearts but increased in human and experimental heart failure. Cardiac lncExACT1 overexpression caused pathological hypertrophy and heart failure; lncExACT1 inhibition induced physiological hypertrophy and cardiomyogenesis, protecting against cardiac fibrosis and dysfunction. lncExACT1 functioned by regulating microRNA-222, calcineurin signaling, and Hippo/Yap1 signaling through DCHS2. Cardiomyocyte DCHS2 overexpression in zebrafish induced pathological hypertrophy and impaired cardiac regeneration, promoting scarring after injury. In contrast, murine DCHS2 deletion induced physiological hypertrophy and promoted cardiomyogenesis. These studies identify lncExACT1-DCHS2 as a novel pathway regulating cardiac hypertrophy and cardiomyogenesis. lncExACT1-DCHS2 acts as a master switch toggling the heart between physiological and pathological growth to determine functional outcomes, providing a potentially tractable therapeutic target for harnessing the beneficial effects of exercise.

Cardioprotective responses to aerobic exercise-induced physiological hypertrophy in zebrafish heart

Herein, we aimed to establish an aerobic exercise-induced physiological myocardial hypertrophy zebrafish (Danio rerio) model and to explore the underlying molecular mechanism. After 4 weeks of aerobic exercise, the AMR and Ucrit of the zebrafish increased and the hearts were enlarged, with thickened myocardium, an increased number of myofilament attachment points in the Z-line, and increased compaction of mitochondrial cristae. We also found that the mTOR signaling pathway, angiogenesis, mitochondrial fusion, and fission event, and mitochondrial autophagy were associated with the adaptive changes in the heart during training. In addition, the increased mRNA expression of genes related to fatty acid oxidation and antioxidation suggested that the switch of energy metabolism and the maintenance of mitochondrial homeostasis induced cardiac physiological changes. Therefore, the zebrafish heart physiological hypertrophy model constructed in this study can be helpful in investigating the cardioprotective mechanisms in response to aerobic exercise.

Downregulation of miR-26b-5p, miR-204-5p, and miR-497-3p Expression Facilitates Exercise-Induced Physiological Cardiac Hypertrophy by Augmenting Autophagy in Rats.

Exercise-induced autophagy is associated with physiological left ventricular hypertrophy (LVH), and a growing body of evidence suggests that microRNAs (miRNAs) can regulate autophagy-related genes. However, the precise role of miRNAs in exercise induced autophagy in physiological LVH has not been fully defined. In this study, we investigated the microRNA–autophagy axis in physiological LVH and deciphered the underlying mechanism using a rat swimming exercise model. Rats were assigned to sedentary control (CON) and swimming exercise (EX) groups; those in the latter group completed a 10-week swimming exercise without any load. For in vitro studies, H9C2 cardiomyocyte cell line was stimulated with IGF-1 for hypertrophy. We found a significant increase in autophagy activity in the hearts of rats with exercise-induced physiological hypertrophy, and miRNAs showed a high score in the pathway enriched in autophagy. Moreover, the expression levels of miR-26b-5p, miR-204-5p, and miR-497-3p showed an obvious increase in rat hearts. Adenovirus-mediated overexpression of miR-26b-5p, miR-204-5p, and miR-497-3p markedly attenuated IGF-1-induced hypertrophy in H9C2 cells by suppressing autophagy. Furthermore, miR-26b-5p, miR-204-5p, and miR-497-3p attenuated autophagy in H9C2 cells through targeting ULK1, LC3B, and Beclin 1, respectively. Taken together, our results demonstrate that swimming exercise induced physiological LVH, at least in part, by modulating the microRNA–autophagy axis, and that miR-26b-5p, miR-204-5p, and miR-497-3p may help distinguish physiological and pathological LVH.

Abstract 894: Inhibition of Long Noncoding RNA lncExACT1 Induces Physiological Cardiac Hypertrophy and Protects Against Pathological Hypertrophy

Long noncoding-RNAs (lncRNAs) are critical regulators of cardiac development as well as pathological hypertrophy and heart failure (HF). However, their roles in exercise-induced physiological hypertrophy are unclear. Here, we used RNAseq to identify a novel class of cardiac lncRNAs that are dynamically regulated by exercise. We call these l ong n on c oding Ex ercise A ssociated C ardiac T ranscripts (lncExACTs). Among them, lncExACT1, a highly conserved lncRNA, is down-regulated in exercised hearts but upregulated in transverse aortic constriction (TAC)-induced pathological hypertrophy and HF. In primary neonatal cardiomyocytes (CMs), transfection of LNA antisense oligonucleotide complementary to lncExACT1 (GapmeR) was sufficient to inhibit lncExACT1 expression and increase CM size with a gene expression pattern consistent with physiological hypertrophy (increased PCG1α and α/βMHC ratio, all p <0.05 vs . control). In contrast, lentiviral overexpression of lncExACT1 in primary CMs induced a pathological gene expression pattern (decreased PCG1α and β/αMHC ratio, with increased ANP and BNP, all p <0.05 vs . control). In vivo, GapmeR treatment for two weeks reduced cardiac lncExACT1 expression (0.5-fold at 2 weeks), increased ventricular wall thickness and fractional shortening (FS, p =0.034 vs . control), increased heart weight to tibial length ratio (HW/TL) and α/βMHC. In contrast, injection of AAV9-lncExACT1 increased cardiac lncExACT1 (6-fold at 5 weeks) increased HW/TL as well as βMHC and ANP. Further, lncExACT1 acted as a sponge for microRNA-222 (a microRNA we previously reported is necessary for physiological cardiac growth) thereby increasing expression of microRNA-222 targets, including p27, a cell cycle inhibitor protein. Moreover, GapmeR injection reduced TAC-induced increase of interventricular septal end diastole (IVSd) and left Ventricular Posterior Wall Dimensions (LVPWd) without affecting FS. We conclude that inhibition of lncExACT1 is sufficient to induce physiological hypertrophy and protect against pathological hypertrophy, while induction of lncExACT1 promotes pathological hypertrophy. lncExACT1 appears to mediate these effects, at least in part, by acting as competing endogenous RNA for microRNA-222.

Melatonin differentially regulates pathological and physiological cardiac hypertrophy: Crucial role of circadian nuclear receptor RORα signaling.

Exercise-induced physiological hypertrophy provides protection against cardiovascular disease, whereas disease-induced pathological hypertrophy leads to heart failure. Emerging evidence suggests pleiotropic roles of melatonin in cardiac disease; however, the effects of melatonin on physiological vs pathological cardiac hypertrophy remain unknown. Using swimming-induced physiological hypertrophy and pressure overload-induced pathological hypertrophy models, we found that melatonin treatment significantly improved pathological hypertrophic responses accompanied by alleviated oxidative stress in myocardium but did not affect physiological cardiac hypertrophy and oxidative stress levels. As an important mediator of melatonin, the retinoid-related orphan nuclear receptor-α (RORα) was significantly decreased in human and murine pathological hypertrophic cardiomyocytes, but not in swimming-induced physiological hypertrophic murine hearts. In vivo and in vitro loss-of-function experiments indicated that RORα deficiency significantly aggravated pathological cardiac hypertrophy, and notably weakened the anti-hypertrophic effects of melatonin. Mechanistically, RORα mediated the cardioprotection of melatonin in pathological hypertrophy mainly by transactivation of manganese-dependent superoxide dismutase (MnSOD) via binding to the RORα response element located in the promoter region of the MnSOD gene. Furthermore, MnSOD overexpression reversed the pro-hypertrophic effects of RORα deficiency, while MnSOD silencing abolished the anti-hypertrophic effects of RORα overexpression in pathological cardiac hypertrophy. Collectively, our findings provide the first evidence that melatonin exerts an anti-hypertrophic effect on pathological but not physiological cardiac hypertrophy via alleviating oxidative stress through transactivation of the antioxidant enzyme MnSOD in a RORα-dependent manner.

Exercise-induced Physiological Hypertrophy: Insights from Genomics

Cardiac hypertrophy can be divided as pathological hypertrophy and physiological hypertrophy. Unlike pathological hypertrophy, physiological hypertrophy is a beneficial adaptive response, which will not cause heart failure and sudden death and can protect adverse cardiac remodeling. Exercise training is widely known to cause physiological hypertrophy. The genomic basis of pathological hypertrophy and heart failure has been well-known and is well-reviewed. In this review, we will review the genomic profiles of physiological hypertrophy and also summarize genes and microRNAs responsible for exercise-induced physiological hypertrophy. With better understanding of physiological hypertrophy, manipulation of genes or miRNAs responsible for physiological hypertrophy will offer exciting avenues for treating heart failure. Keywords: Exercise, Physiological hypertrophy, Genomics, MicroRNA

Editorial Genomics of Atrial Fibrillation and Heart Failure.

Atrial fibrillation (AF), the most common types of arrhythmia in the clinic, is an increasing health burden in developing and develped countries as well. The prevalence of AF increases with age, increasing from 1% in youth to nearly 10% in those age over 80. In the United States (US), 3 million people are affected by AF and in China, 10 million AF patients exists. Interestingly, heart failure (HF) is among the serious complications of AF, making it contributes to public health burden worldwide. Recent insights into the genomics causes of cardiovascular diseases highlighted the importance of single-gene defects and common variants in AF and HF. Besides that, microRNAs (miRNAs) dysregulation has also been implicated in the etiology and pathogenesis of AF and HF. In this issue, a group of scientists provide their insights about genomics of AF and HF, pointing out that restoration of genes and/or miRNAs expression to normal level may have therapeutic potential for AF and HF. Palatinus et al. summarized the mutations and common variants for AF while Shen et al. summarized common variants for HF risk and outcome. Both groups discussed these genetic information for the clinic therapy. Hoogen et al. discussed the current knowledge on dysfunction of miRNAs in HF caused by chronic myocarditis, which also provide potential interventions based on miRNAs in the future. Lv et al. overviewed genes and microRNAs responsible for exercise-induced physiological hypertrophy and suggested that manipulation of these critical genes and microRNAs may offer exciting avenues for the treatment of HF. The collection of articles published in this thematic issue provide the recent progress about the genomic basis for AF and HF. Advances in understanding the genomics of AF and HF will inspaire the interest in facilitating the development of novel genomic based therapies.

MicroRNA basis of physiological hypertrophy

Cardiac hypertrophy is a distinguished feature of several physiological and pathological remodeling (Frey et al., 2004). Pathological hypertrophy is commonly seen in patients with heart injury or stress, such as myocardial infarction, hypertension, and valve disease (Frey et al., 2004). Physiological hypertrophy is typically induced by exercise or pregnancy. Interestingly, physiological hypertrophy is generally accepted as an adaptive beneficial response while pathological hypertrophy can ultimately decompensate to heart failure, a common, costly, disabling, and deadly disease. Thus, dissecting the mechanisms for physiological hypertrophy will help identify novel effective therapies for a large spectrum of cardiovascular diseases (Da Costa Martins and De Windt, 2012). Distinct underlying signaling pathways for physiological and pathological hypertrophy have been identified (Maillet et al., 2013). The classic pathway for physiological hypertrophy is IGF-1/PI3K (p110a)/Akt1 while the key one for pathological hypertrophy is AngII (ET-1)/Gaq/Calcineurin/NFAT (Maillet et al., 2013). MicroRNAs (miRNAs, miRs) are a novel class of non-coding RNAs with 20–24 length of base, which posttranscriptional regulates gene expression via base-pairing with complementary sequences within mRNA (Xiao et al., 2012). It is estimated that over 1000 miRNAs were encoded by the human genome. Individual miRNAs can regulate several target genes while one gene can also be regulated by several miRNAs. Being a center player of gene regulation, miRNAs participate in many essential biological processes, including proliferation, differentiation, apoptosis, necrosis, autophagy, and stress responses (Xiao et al., 2012; Kumarswamy and Thum, 2013). Due to these multiple roles, it is naturally that miRNAs are critical in the development of various heart diseases, such as hypertrophy, heart failure, acute myocardial infarction, and arrhythmia (Xiao et al., 2011; Kumarswamy and Thum, 2013). In addition, circulating miRNAs have also been indicated to be promising biomarkers for cardiovascular diseases (Xu et al., 2012). Among them, pathological hypertrophy is the most widely studied one. Accumulating evidence has indicated that a lot of miRNAs such as miR-1, miR-133, miR-26, miR-9, miR-98, miR-29, miR-199a, miR-199b, miR-208, miR-23a, miR-499, miR-21, and mir-19b contribute to pathological hypertrophy (Da Costa Martins and De Windt, 2012). Some distinguished reviews have summarized it in detail (Da Costa Martins and De Windt, 2012; Ellison et al., 2012). Unlike pathological hypertrophy, only a little studies described how miRNAs response to physiological hypertrophy (Soci et al., 2011; Diniz et al., 2013). It has been reported that miR-1, miR-133, mir-29c, miR-27a, mir-27b, and miR-143 response to physiological hypertrophy (Soci et al., 2011; Da Costa Martins and De Windt, 2012; Ellison et al., 2012). However, these miRNAs are either compensatory or lack of direct evidence for regulating cell size. Thus, these results might only set the beginning of filling the gap in miRNAs and physiological hypertrophy. Although these studies have suggested some potential roles of miRNAs in physiological hypertrophy, more functional studies are highly needed to establish miRNAs as contributors for physiological hypertrophy. Traditionally, the adult mammalian heart is recognized as a post-mitotic organ with no regenerative capacity for cardiomyogenesis (Rosenzweig, 2012). Recently, resident endogenous cardiac stem-progenitor cells (eCSCs) in the adult heart challenged this dogma (Rosenzweig, 2012). Moreover, adult cardiomyocytes have also been reported to proliferate in response to specific stimuli (Rosenzweig, 2012). Two studies regarding physiological hypertrophy are of great importance (Bostrom et al., 2010; Waring et al., 2012). A transcriptional factor named CEBPB has been found to be down-regulated with exercise and reduction of CEBPB induces cardiomyocyte hypertrophy and proliferation (Bostrom et al., 2010). Further studies show that CEBPB promotes cardiomyocyte proliferation via increasing CITED4 (Bostrom et al., 2010). This study indicates that besides the generally accepted idea that physiological hypertrophy is solely due to the hypertrophy of existing cardiomyocytes, physiological hypertrophy also has the phenotype of new cardiomyocytes formation (Bostrom et al., 2010). A more recent study shows that c-Kit positive eCSCs increases their number and activated state in exercise-induced physiological hypertrophy, indicating that c-Kit positive eCSCs might be a source of new cardiomyocyte formation (Waring et al., 2012). Therefore, myocyte-restricted lineage tracing studies are highly needed to definitively unravel this question. Anyway, both studies indicate that it is necessary to check miRNAs roles in promoting new cardiomyocyte formation either in cardiomyocytes or in eCSCs in physiological hypertrophy. With the strategies for checking myocyte hypertrophy and new cardiomyocyte formation, the miRNA basis of physiological hypertrophy will be revealed, which will help develop a miRNA-based therapy for heart failure.

Exercise training and PI3Kα-induced electrical remodeling is independent of cellular hypertrophy and Akt signaling

In contrast with pathological hypertrophy, exercise-induced physiological hypertrophy is not associated with electrical abnormalities or increased arrhythmia risk. Recent studies have shown that increased cardiac-specific expression of phosphoinositide-3-kinase-α (PI3Kα), the key mediator of physiological hypertrophy, results in transcriptional upregulation of ion channel subunits in parallel with the increase in myocyte size (cellular hypertrophy) and the maintenance of myocardial excitability. The experiments here were undertaken to test the hypothesis that Akt1, which underlies PI3Kα-induced cellular hypertrophy, mediates the effects of augmented PI3Kα signaling on the transcriptional regulation of cardiac ion channels. In contrast to wild-type animals, chronic exercise (swim) training of mice (Akt1−/−) lacking Akt1 did not result in ventricular myocyte hypertrophy. Ventricular K+ current amplitudes and the expression of K+ channel subunits, however, were increased markedly in Akt1−/− animals with exercise training. Expression of the transcripts encoding inward (Na+ and Ca2+) channel subunits were also increased in Akt1−/− ventricles following swim training. Additional experiments in a transgenic mouse model of inducible cardiac-specific expression of constitutively active PI3Kα (icaPI3Kα) revealed that short-term activation of PI3Kα signaling in the myocardium also led to the transcriptional upregulation of ion channel subunits. Inhibition of cardiac Akt activation with triciribine in this (inducible caPI3Kα expression) model did not prevent the upregulation of myocardial ion channel subunits. These combined observations demonstrate that chronic exercise training and enhanced PI3Kα expression/activity result in transcriptional upregulation of myocardial ion channel subunits independent of cellular hypertrophy and Akt signaling.

Estrogens Mediate Cardiac Hypertrophy in a Stimulus-Dependent Manner

The incidence of cardiac hypertrophy, an established risk factor for heart failure, is generally lower in women compared with men, but this advantage is lost after menopause. Although it is widely believed that estrogens are cardioprotective, there are contradictory reports, including increased cardiac events in postmenopausal women receiving estrogens and enhanced cardiac protection from ischemic injury in female mice without estrogens. We exposed aromatase knockout (ArKO) mice, which produce no estrogens, to both pathologic and physiologic stimuli. This model allows an investigation into the effects of a complete, chronic lack of estrogens in male and female hearts. At baseline, female ArKO mice had normal-sized hearts but decreased cardiac function and paradoxically increased phosphorylation of many progrowth kinases. When challenged with the pathological stimulus, isoproterenol, ArKO females developed 2-fold more hypertrophy than wild-type females. In contrast, exercise-induced physiological hypertrophy was unaffected by the absence of estrogens in either sex, although running performance was blunted in ArKO females. Thus, loss of estrogen signaling in females, but not males, impairs cardiac function and sensitizes the heart to pathological insults through up-regulation of multiple hypertrophic pathways. These findings provide insight into the apparent loss of cardioprotection after menopause and suggest that caution is warranted in the long-term use of aromatase inhibitors in the setting of breast cancer prevention.

Swim-exercised mice show a decreased level of proteinO-GlcNAcylation and expression ofO-GlcNAc transferase in heart

Swim-training exercise in mice leads to cardiac remodeling associated with an improvement in contractile function. Protein O-linked N-acetylglucosamine (O-GlcNAcylation) is a posttranslational modification of serine and threonine residues capable of altering protein-protein interactions affecting gene transcription, cell signaling pathways, and general cell physiology. Increased levels of protein O-GlcNAcylation in the heart have been associated with pathological conditions such as diabetes, ischemia, and hypertrophic heart failure. In contrast, the impact of physiological exercise on protein O-GlcNAcylation in the heart is currently unknown. Swim-training exercise in mice was associated with the development of a physiological hypertrophy characterized by an improvement in contractile function relative to sedentary mice. General protein O-GlcNAcylation was significantly decreased in swim-exercised mice. This effect was mirrored in the level of O-GlcNAcylation of individual proteins such as SP1. The decrease in protein O-GlcNAcylation was associated with a decrease in the expression of O-GlcNAc transferase (OGT) and glutamine-fructose amidotransferase (GFAT) 2 mRNA. O-GlcNAcase (OGA) activity was actually lower in swim-trained than sedentary hearts, suggesting that it did not contribute to the decreased protein O-GlcNAcylation. Thus it appears that exercise-induced physiological hypertrophy is associated with a decrease in protein O-GlcNAcylation, which could potentially contribute to changes in gene expression and other physiological changes associated with exercise.

Transcriptional profile of isoproterenol-induced cardiomyopathy and comparison to exercise-induced cardiac hypertrophy and human cardiac failure

BackgroundIsoproterenol-induced cardiac hypertrophy in mice has been used in a number of studies to model human cardiac disease. In this study, we compared the transcriptional response of the heart in this model to other animal models of heart failure, as well as to the transcriptional response of human hearts suffering heart failure.ResultsWe performed microarray analyses on RNA from mice with isoproterenol-induced cardiac hypertrophy and mice with exercise-induced physiological hypertrophy and identified 865 and 2,534 genes that were significantly altered in pathological and physiological cardiac hypertrophy models, respectively. We compared our results to 18 different microarray data sets (318 individual arrays) representing various other animal models and four human cardiac diseases and identified a canonical set of 64 genes that are generally altered in failing hearts. We also produced a pairwise similarity matrix to illustrate relatedness of animal models with human heart disease and identified ischemia as the human condition that most resembles isoproterenol treatment.ConclusionThe overall patterns of gene expression are consistent with observed structural and molecular differences between normal and maladaptive cardiac hypertrophy and support a role for the immune system (or immune cell infiltration) in the pathology of stress-induced hypertrophy. Cross-study comparisons such as the results presented here provide targets for further research of cardiac disease that might generally apply to maladaptive cardiac stresses and are also a means of identifying which animal models best recapitulate human disease at the transcriptional level.