Cardiac-specific overexpression of E40K active Akt prevents pressure overload-induced heart failure in mice by increasing angiogenesis and reducing apoptosis

Danlou Tablet Protects Against Cardiac Remodeling and Dysfunction after Myocardial Ischemia/Reperfusion Injury through Activating AKT/FoxO3a Pathway

Myocardial ischemia/reperfusion injury (I/RI) and ventricular remodeling are the critical pathological basis of heart failure. Danlou tablet (Dan) is a kind of Chinese patent medicine used in angina pectoris treatment in China. However, it remains unclear whether and how Dan could protect against cardiac remodeling after myocardial I/RI. In this study, both preventive and therapeutic administration of Dan attenuated ventricular remodeling and cardiac dysfunction at 3 weeks after myocardial I/RI. Dan inhibited Bax/Bcl2 ratio and Caspase3 cleavage in heart tissues and also inhibited apoptosis of human AC16 cells and neonatal rat cardiomyocytes stressed by oxygen and glucose deprivation/reperfusion. Mechanistically, Dan inhibited myocardial apoptosis through phosphorylating AKT and FoxO3a, thereby inhibiting downstream BIM and PUMA expressions. Collectively, these results demonstrate that Dan treatment is effective to protect against cardiac remodeling and dysfunction after myocardial I/RI and provide theoretical basis for its cardioprotection and clinical application in treating ischemic cardiac diseases.

Exercise training maintains cardiovascular health: signaling pathways involved and potential therapeutics

Exercise training has been widely recognized as a healthy lifestyle as well as an effective non-drug therapeutic strategy for cardiovascular diseases (CVD). Functional and mechanistic studies that employ animal exercise models as well as observational and interventional cohort studies with human participants, have contributed considerably in delineating the essential signaling pathways by which exercise promotes cardiovascular fitness and health. First, this review summarizes the beneficial impact of exercise on multiple aspects of cardiovascular health. We then discuss in detail the signaling pathways mediating exercise's benefits for cardiovascular health. The exercise-regulated signaling cascades have been shown to confer myocardial protection and drive systemic adaptations. The signaling molecules that are necessary for exercise-induced physiological cardiac hypertrophy have the potential to attenuate myocardial injury and reverse cardiac remodeling. Exercise-regulated noncoding RNAs and their associated signaling pathways are also discussed in detail for their roles and mechanisms in exercise-induced cardioprotective effects. Moreover, we address the exercise-mediated signaling pathways and molecules that can serve as potential therapeutic targets ranging from pharmacological approaches to gene therapies in CVD. We also discuss multiple factors that influence exercise's effect and highlight the importance and need for further investigations regarding the exercise-regulated molecules as therapeutic targets and biomarkers for CVD as well as the cross talk between the heart and other tissues or organs during exercise. We conclude that a deep understanding of the signaling pathways involved in exercise's benefits for cardiovascular health will undoubtedly contribute to the identification and development of novel therapeutic targets and strategies for CVD.

Centella asiatica (L.) Urb. attenuates cardiac hypertrophy and improves heart function through multi-level mechanisms revealed by systems pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Cardiac hypertrophy (CH) is an incurable heart disease, contributing to an increased risk of heart failure due to the lack of safe and effective strategies. Therefore, searching for new approaches to treat CH is urgent. Centella asiatica (L.) Urb. (CA), a traditional food and medicinal natural plant, has been turned out to be effective in the treatment of cardiovascular disease, but its efficacy and potential mechanisms in alleviating CH have not yet been investigated.

AIM OF STUDY

In this study, we aimed to elucidate the multi-level mechanisms underlying the effect of CA against CH.

STUDY DESIGN AND METHODS

A systems pharmacology approach was employed to screen active ingredients, identify potential targets, construct visual networks and systematically investigate the pathways and mechanisms of CA for CH treatment. The cardiac therapeutic potential and mechanism of action of CA on CH were verified with in vivo and in vitro experiments.

RESULTS

Firstly, we demonstrated the therapeutic effect of CA on CH and then screened 13 active compounds of CA according to the pharmacokinetic properties. Then, asiatic acid (AA) was identified as the major active molecule of CA for CH treatment. Afterwards, network and functional enrichment analyses showed that CA exerted cardioprotective effects by modulating multiple pathways mainly involved in anti-apoptotic, antioxidant and anti-inflammatory processes. Finally, in vivo, the therapeutic effects of AA and its action on the YAP/PI3K/AKT axis and NF-κB signaling pathway were validated using an isoproterenol-induced CH mouse model. In vitro, AA decreased ROS levels in hydrogen peroxide-treated HL-1 cells.

CONCLUSION

Overall, the multi-level mechanisms of CA for CH treatment were demonstrated by systems pharmacology approach, which provides a paradigm for systematically deciphering the mechanisms of action of natural plants in the treatment of diseases and offers a new idea for the development of medicinal and food products.

The Prominin-1-Derived Peptide Improves Cardiac Function Following Ischemia

Myocardial infarction (MI) remains the leading cause of death in the western world. Despite advancements in interventional revascularization technologies, many patients are not candidates for them due to comorbidities or lack of local resources. Non-invasive approaches to accelerate revascularization within ischemic tissues through angiogenesis by providing Vascular Endothelial Growth Factor (VEGF) in protein or gene form has been effective in animal models but not in humans likely due to its short half-life and systemic toxicity. Here, we tested the hypothesis that PR1P, a small VEGF binding peptide that we developed, which stabilizes and upregulates endogenous VEGF, could be used to improve outcome from MI in rodents. To test this hypothesis, we induced MI in mice and rats via left coronary artery ligation and then treated animals with every other day intraperitoneal PR1P or scrambled peptide for 14 days. Hemodynamic monitoring and echocardiography in mice and echocardiography in rats at 14 days showed PR1P significantly improved multiple functional markers of heart function, including stroke volume and cardiac output. Furthermore, molecular biology and histological analyses of tissue samples showed that systemic PR1P targeted, stabilized and upregulated endogenous VEGF within ischemic myocardium. We conclude that PR1P is a potential non-invasive candidate therapeutic for MI.

Genetic ablation of Cullin-RING E3 ubiquitin ligase 7 restrains pressure overload-induced myocardial fibrosis

Fibrosis is a pathognomonic feature of structural heart disease and counteracted by distinct cardioprotective mechanisms, e.g. activation of the phosphoinositide 3-kinase (PI3K) / AKT pro-survival pathway. The Cullin-RING E3 ubiquitin ligase 7 (CRL7) was identified as negative regulator of PI3K/AKT signalling in skeletal muscle, but its role in the heart remains to be elucidated. Here, we sought to determine whether CRL7 modulates to cardiac fibrosis following pressure overload and dissect its underlying mechanisms. For inactivation of CRL7, the Cullin 7 (Cul7) gene was deleted in cardiac myocytes (CM) by injection of adeno-associated virus subtype 9 (AAV9) vectors encoding codon improved Cre-recombinase (AAV9-CMV-iCre) in Cul7^flox/flox mice. In addition, Myosin Heavy Chain 6 (Myh6; alpha-MHC)-MerCreMer transgenic mice with tamoxifen-induced CM-specific expression of iCre were used as alternate model. After transverse aortic constriction (TAC), causing chronic pressure overload and fibrosis, AAV9-CMV-iCre induced Cul7-/- mice displayed a ~50% reduction of interstitial cardiac fibrosis when compared to Cul7+/+ animals (6.7% vs. 3.4%, p<0.01). Similar results were obtained with Cul7^flox/floxMyh6-Mer-Cre-Mer^Tg(1/0) mice which displayed a ~30% reduction of cardiac fibrosis after TAC when compared to Cul7^+/+Myh6-Mer-Cre-Mer^Tg(1/0) controls after TAC surgery (12.4% vs. 8.7%, p<0.05). No hemodynamic alterations were observed. AKT^Ser473 phosphorylation was increased 3-fold (p<0.01) in Cul7-/- vs. control mice, together with a ~78% (p<0.001) reduction of TUNEL-positive apoptotic cells three weeks after TAC. In addition, CM-specific expression of a dominant-negative CUL7^1152stop mutant resulted in a 16.3-fold decrease (p<0.001) of in situ end-labelling (ISEL) positive apoptotic cells. Collectively, our data demonstrate that CM-specific ablation of Cul7 restrains myocardial fibrosis and apoptosis upon pressure overload, and introduce CRL7 as a potential target for anti-fibrotic therapeutic strategies of the heart.

TASK-1 and TASK-3 channels modulate pressure overload-induced cardiac remodeling and dysfunction

Tandem pore domain acid-sensitive K⁺ (TASK) channels are present in cardiac tissue; however, their contribution to cardiac pathophysiology is not well understood. Here, we investigate the role of TASK-1 and TASK-3 in the pathogenesis of cardiac dysfunction using both human tissue and mouse models of genetic TASK channel loss of function. Compared with normal human cardiac tissue, TASK-1 gene expression is reduced in association with either cardiac hypertrophy alone or combined cardiac hypertrophy and heart failure. In a pressure overload cardiomyopathy model, TASK-1 global knockout (TASK-1 KO) mice have both reduced cardiac hypertrophy and preserved cardiac function compared with wild-type mice. In contrast to the TASK-1 KO mouse pressure overload response, TASK-3 global knockout (TASK-3 KO) mice develop cardiac hypertrophy and a delayed onset of cardiac dysfunction compared with wild-type mice. The cardioprotective effects observed in TASK-1 KO mice are associated with pressure overload-induced augmentation of AKT phosphorylation and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression, with consequent augmentation of cardiac energetics and fatty acid oxidation. The protective effects of TASK-1 loss of function are associated with an enhancement of physiologic hypertrophic signaling and preserved metabolic functions. These findings may provide a rationale for TASK-1 channel inhibition in the treatment of cardiac dysfunction.NEW & NOTEWORTHY The role of tandem pore domain acid-sensitive K⁺ (TASK) channels in cardiac function is not well understood. This study demonstrates that TASK channel gene expression is associated with the onset of human cardiac hypertrophy and heart failure. TASK-1 and TASK-3 strongly affect the development of pressure overload cardiomyopathies in genetic models of TASK-1 and TASK-3 loss of function. The effects of TASK-1 loss of function were associated with enhanced AKT phosphorylation and expression of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) transcription factor. These data suggest that TASK channels influence the development of cardiac hypertrophy and dysfunction in response to injury.

Histone Methyltransferase G9a Is Required for Cardiomyocyte Homeostasis and Hypertrophy

BACKGROUND

Correct gene expression programming of the cardiomyocyte underlies the normal functioning of the heart. Alterations to this can lead to the loss of cardiac homeostasis, triggering heart dysfunction. Although the role of some histone methyltransferases in establishing the transcriptional program of postnatal cardiomyocytes during heart development has been shown, the function of this class of epigenetic enzymes is largely unexplored in the adult heart. In this study, we investigated the role of G9a/Ehmt2, a histone methyltransferase that defines a repressive epigenetic signature, in defining the transcriptional program for cardiomyocyte homeostasis and cardiac hypertrophy.

METHODS

We investigated the function of G9a in normal and stressed cardiomyocytes with the use of a conditional, cardiac-specific G9a knockout mouse, a specific G9a inhibitor, and high-throughput approaches for the study of the epigenome (chromatin immunoprecipitation sequencing) and transcriptome (RNA sequencing); traditional methods were used to assess cardiac function and cardiovascular disease.

RESULTS

We found that G9a is required for cardiomyocyte homeostasis in the adult heart by mediating the repression of key genes regulating cardiomyocyte function via dimethylation of H3 lysine 9 and interaction with enhancer of zeste homolog 2, the catalytic subunit of polycomb repressive complex 2, and MEF2C-dependent gene expression by forming a complex with this transcription factor. The G9a-MEF2C complex was found to be required also for the maintenance of heterochromatin needed for the silencing of developmental genes in the adult heart. Moreover, G9a promoted cardiac hypertrophy by repressing antihypertrophic genes.

CONCLUSIONS

Taken together, our findings demonstrate that G9a orchestrates critical epigenetic changes in cardiomyocytes in physiological and pathological conditions, thereby providing novel therapeutic avenues for cardiac pathologies associated with dysregulation of these mechanisms.

H-Ras Isoform Mediates Protection Against Pressure Overload-Induced Cardiac Dysfunction in Part Through Activation of AKT

BACKGROUND

In general, Ras proteins are thought to promote cardiac hypertrophy, an important risk factor for cardiovascular disease and heart failure. However, the contribution of different Ras isoforms has not been investigated. The objective of this study was to define the role of H- and K-Ras in modulating stress-induced myocardial hypertrophy and failure.

METHODS AND RESULTS

We used H- and K-Ras gene knockout mice and subjected them to pressure overload to induce cardiac hypertrophy and dysfunction. We observed a worsened cardiac phenotype in Hras^-/- mice, while outcomes were improved in Kras^+/- mice. We also used a neonatal rat cardiomyocyte culture system to elucidate the mechanisms underlying these observations. Our findings demonstrate that H-Ras, but not K-Ras, promotes cardiomyocyte hypertrophy both in vivo and in vitro. This response was mediated in part through the phosphoinositide 3-kinase-AKT signaling pathway. Adeno-associated virus-mediated increase in AKT activation improved the cardiac function in pressure overloaded Hras null hearts in vivo. These findings further support engagement of the phosphoinositide 3-kinase-AKT signaling axis by H-Ras.

CONCLUSIONS

Taken together, these findings indicate that H- and K-Ras have divergent effects on cardiac hypertrophy and heart failure in response to pressure overload stress.

DDiT4L promotes autophagy and inhibits pathological cardiac hypertrophy in response to stress

Physiological cardiac hypertrophy, in response to stimuli such as exercise, is considered adaptive and beneficial. In contrast, pathological cardiac hypertrophy that arises in response to pathological stimuli such as unrestrained high blood pressure and oxidative or metabolic stress is maladaptive and may precede heart failure. We found that the transcript encoding DNA damage-inducible transcript 4-like (DDiT4L) was expressed in murine models of pathological cardiac hypertrophy but not in those of physiological cardiac hypertrophy. In cardiomyocytes, DDiT4L localized to early endosomes and promoted stress-induced autophagy through a process involving mechanistic target of rapamycin complex 1 (mTORC1). Exposing cardiomyocytes to various types of pathological stress increased the abundance of DDiT4L, which inhibited mTORC1 but activated mTORC2 signaling. Mice with conditional cardiac-specific overexpression of DDiT4L had mild systolic dysfunction, increased baseline autophagy, reduced mTORC1 activity, and increased mTORC2 activity, all of which were reversed by suppression of transgene expression. Genetic suppression of autophagy also reversed cardiac dysfunction in these mice. Our data showed that DDiT4L may be an important transducer of pathological stress to autophagy through mTOR signaling in the heart and that DDiT4L could be therapeutically targeted in cardiovascular diseases in which autophagy and mTOR signaling play a major role.

The IGF1-PI3K-Akt Signaling Pathway in Mediating Exercise-Induced Cardiac Hypertrophy and Protection

Regular physical activity or exercise training can lead to heart enlargement known as cardiac hypertrophy. Cardiac hypertrophy is broadly defined as an increase in heart mass. In adults, cardiac hypertrophy is often considered a poor prognostic sign because it often progresses to heart failure. Heart enlargement in a setting of cardiac disease is referred to as pathological cardiac hypertrophy and is typically characterized by cell death and depressed cardiac function. By contrast, physiological cardiac hypertrophy, as occurs in response to chronic exercise training (i.e. the 'athlete's heart'), is associated with normal or enhanced cardiac function. The following chapter describes the morphologically distinct types of heart growth, and the key role of the insulin-like growth factor 1 (IGF1) - phosphoinositide 3-kinase (PI3K)-Akt signaling pathway in regulating exercise-induced physiological cardiac hypertrophy and cardiac protection. Finally we summarize therapeutic approaches that target the IGF1-PI3K-Akt signaling pathway which are showing promise in preclinical models of heart disease.

Cardiac Stim1 Silencing Impairs Adaptive Hypertrophy and Promotes Heart Failure Through Inactivation of mTORC2/Akt Signaling

BACKGROUND

Stromal interaction molecule 1 (STIM1) is a dynamic calcium signal transducer implicated in hypertrophic growth of cardiomyocytes. STIM1 is thought to act as an initiator of cardiac hypertrophic response at the level of the sarcolemma, but the pathways underpinning this effect have not been examined.

METHODS AND RESULTS

To determine the mechanistic role of STIM1 in cardiac hypertrophy and during the transition to heart failure, we manipulated STIM1 expression in mice cardiomyocytes by using in vivo gene delivery of specific short hairpin RNAs. In 3 different models, we found that Stim1 silencing prevents the development of pressure overload-induced hypertrophy but also reverses preestablished cardiac hypertrophy. Reduction in STIM1 expression promoted a rapid transition to heart failure. We further showed that Stim1 silencing resulted in enhanced activity of the antihypertrophic and proapoptotic GSK-3β molecule. Pharmacological inhibition of glycogen synthase kinase-3 was sufficient to reverse the cardiac phenotype observed after Stim1 silencing. At the level of ventricular myocytes, Stim1 silencing or inhibition abrogated the capacity for phosphorylation of Akt(S473), a hydrophobic motif of Akt that is directly phosphorylated by mTOR complex 2. We found that Stim1 silencing directly impaired mTOR complex 2 kinase activity, which was supported by a direct interaction between STIM1 and Rictor, a specific component of mTOR complex 2.

CONCLUSIONS

These data support a model whereby STIM1 is critical to deactivate a key negative regulator of cardiac hypertrophy. In cardiomyocytes, STIM1 acts by tuning Akt kinase activity through activation of mTOR complex 2, which further results in repression of GSK-3β activity.

Phosphoinositide 3-kinase: friend and foe in cardiovascular disease

Class I phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases activated by cell membrane receptors, either receptor tyrosine kinases (RTKs) or G protein–coupled receptors (GPCRs), to catalyze the production of the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3). These enzymes engage multiple downstream intracellular signaling pathways controlling cell proliferation, survival and migration. In the cardiovascular system, the four class I PI3K isoforms, PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ are differentially expressed in distinct cell subsets which include cardiomyocytes, fibroblasts, endothelial, and vascular smooth muscle cells as well as leukocytes, suggesting specific functions for distinct PI3K isoenzymes. During the last decades, genetic disruption studies targeting different PI3K genes have elucidated the contribution of specific isoenzymes to cardiac and vascular function regulation, highlighting both beneficial and maladaptive roles. New layers of complexity in the function of PI3Ks have recently emerged, indicating that distinct PI3K isoforms are interconnected by various crosstalk events and can function not only as kinases, but also as scaffold proteins coordinating key signalosomes in cardiovascular health and disease. In this review, we will summarize major breakthroughs in the comprehension of detrimental and beneficial actions of PI3K signaling in cardiovascular homeostasis, and we will discuss recently unraveled cross-talk and scaffold mechanisms as well as the role of the less characterized class II and III PI3K isoforms.

The antioxidant compound tert-butylhydroquinone activates Akt in myocardium, suppresses apoptosis and ameliorates pressure overload-induced cardiac dysfunction

Tert-butylhydroquinone (TBHQ) is an antioxidant compound which shows multiple cytoprotective actions. We evaluated the effects of TBHQ on pathological cardiac remodeling and dysfunction induced by chronic overload. Pressure overload was created by transverse aortic constriction (TAC) in male C57BL/6 mice. TBHQ was incorporated in the diet and administered for 4 weeks. TBHQ treatment prevented left ventricular dilatation and cardiac dysfunction induced by TAC, and decreased the prevalence of myocardial apoptosis. The beneficial effects of TBHQ were associated with an increase in Akt activation, but not related to activations of Nrf2 or AMP-activated protein kinase. TBHQ-induced Akt activation was accompanied by increased phosphorylation of Bad, glycogen synthase kinase-3β (GSK-3β) and mammalian target of rapamycin (mTOR). Mechanistically, we showed that in cultured H9c2 cells and primary cardiac myocytes, TBHQ stimulated Akt phosphorylation and suppressed oxidant-induced apoptosis; this effect was abolished by wortmannin or an Akt inhibitor. Blockade of the Akt pathway in vivo accelerated cardiac dysfunction, and abrogated the protective effects of TBHQ. TBHQ also reduced the reactive aldehyde production and protein carbonylation in stressed myocardium. We suggest that TBHQ treatment may represent a novel strategy for timely activation of the cytoprotective Akt pathway in stressed myocardium.

Increased cardiac remodeling in cardiac-specific Flt-1 receptor knockout mice with pressure overload

Vascular endothelial growth factor (VEGF) inhibition has previously been shown to have damaging effects on the heart. Because the role of Flt-1 (a phosphotyrosine kinase receptor for VEGF) in cardiac function and hypertrophy is unclear, we generated mice lacking Flt-1 only in their cardiomyocytes (Flt-1 KO). The hearts from 8- to 10-week-old mice were measured by using echocardiography and histology. No significant differences were seen in fraction shortening, cross-sectional area of cardiomyocytes, and interstitial collagen fraction between littermate controls and KO mice at baseline. To test the hypothesis that Flt-1 is involved in cardiac remodeling, we performed transverse aorta constriction (TAC) by ligating the transverse ascending aorta. Four weeks after TAC, echocardiography of the mice was performed, and the hearts were excised for pathological analysis and Western blotting. No difference in mortality was found between Flt-1 KO mice and controls; however, KO mice showed a greater cardiomyocyte cross-sectional area and interstitial collagen fraction than controls. Western blotting indicated that AKT was activated less in Flt-1 KO hearts after TAC compared with that in control hearts. Thus, Flt-1 deletion in cardiomyocytes increased hypertrophy, fibrosis, and regression of AKT phosphorylation. Our study suggests that Flt-1 plays a critical role in cardiac hypertrophy induced by pressure overload via the activation of AKT, which seems to be cardioprotective.

A small molecule activator of AKT does not reduce ischemic injury of the rat heart

Background

Activation of protein kinase AKT is required for cardioprotection by ischemic preconditioning, and transgenic overexpression of AKT protects the heart against ischemia. However, it is unknown whether acute pharmacological activation of AKT alone, using a therapeutically relevant strategy, induces cardioprotection. In this study we provide the first evidence to clarify this question.

Methods

We used a recently described specific activator of AKT, the small molecule SC79, to treat rat hearts submitted to ischemia and reperfusion. Initially, isolated rat hearts were perfused with increasing doses of SC79 to verify the magnitude of AKT activation. Low and high doses were determined and used to treat hearts submitted to ischemia (35 minutes) and reperfusion (60 minutes), in a randomized and blinded design. AKT activation was verified by western immunobloting. Metabolic profile was determined by cardiac ATP content and mitochondrial enzyme activity, while cytosolic levels of cytochrome C and caspase-3 activity were used as markers of apoptosis. Ischemic injury was assessed by quantification of infarct size and cardiac release of creatine kinase and lactate dehydrogenase.

Results

SC79 activated cardiac AKT within 30 minutes in a dose-dependent fashion. ATP content was largely reduced by ischemia, but was not rescued by SC79. Similarly, mitochondrial enzyme activity was not affected by SC79. SC79 administered before ischemia or at reperfusion did not prevent cytosolic accumulation of cytochrome C and overactivation of caspase-3. Finally, SC79 failed to reduce infarct size or release of cardiac injury biomarkers at reperfusion.

Conclusion

We conclude that selective AKT activation by the synthetic molecule SC79 does not protect the rat heart against ischemic injury, indicating that acute pharmacological activation of AKT is not sufficient for cardioprotection.

Physiological activation of Akt by PHLPP1 deletion protects against pathological hypertrophy

AIMS

To examine the role of physiological Akt signalling in pathological hypertrophy through analysis of PHLPP1 (PH domain leucine-rich repeat protein phosphatase) knock-out (KO) mice.

METHODS AND RESULTS

To investigate the in vivo requirement for 'physiological' control of Akt activation in cardiac growth, we examined the effect of deleting the Akt phosphatase, PHLPP, on the induction of cardiac hypertrophy. Basal Akt phosphorylation increased nearly two-fold in the cardiomyocytes from PHLPP1 KO mice and physiological hypertrophy induced by swimming exercise was accentuated as assessed by increased heart size and myocyte cell area. In contrast, the development of pathophysiological hypertrophy induced by pressure overload and assessed by increases in heart size, myocyte cell area, and hypertrophic gene expression was attenuated. This attenuation coincided with decreased fibrosis and cell death in the KO mice. Cast moulding revealed increased capillary density basally in the KO hearts, which was further elevated relative to wild-type mouse hearts in response to pressure overload. In vitro studies with isolated myocytes in co-culture also demonstrated that PHLPP1 deletion in cardiomyocytes can enhance endothelial tube formation. Expression of the pro-angiogenic factor VEGF was also elevated basally and accentuated in response to transverse aortic constriction in hearts from KO mice.

CONCLUSION

Our data suggest that enhancing Akt activity by inhibiting its PHLPP1-mediated dephosphorylation promotes processes associated with physiological hypertrophy that may be beneficial in attenuating the development of pathological hypertrophy.

Regulation of Akt signaling by sirtuins: its implication in cardiac hypertrophy and aging

Cardiac hypertrophy is a multifactorial disease characterized by multiple molecular alterations. One of these alterations is change in the activity of Akt, which plays a central role in regulating a variety of cellular processes ranging from cell survival to aging. Akt activation is mainly achieved by its binding to phosphatidylinositol (3,4,5)-triphosphate. This results in a conformational change that exposes the kinase domain of Akt for phosphorylation and activation by its upstream kinase, 3-phosphoinositide-dependent protein kinase 1, in the cell membrane. Recent studies have shown that sirtuin isoforms, silent information regulator (SIRT) 1, SIRT3, and SIRT6, play an essential role in the regulation of Akt activation. Although SIRT1 deacetylates Akt to promote phosphatidylinositol (3,4,5)-triphosphate binding and activation, SIRT3 controls reactive oxygen species-mediated Akt activation, and SIRT6 transcriptionally represses Akt at the level of chromatin. In the first part of this review, we discuss the mechanisms by which sirtuins regulate Akt activation and how they influence other post-translational modifications of Akt. In the latter part of the review, we summarize the implications of sirtuin-dependent regulation of Akt signaling in the control of major cellular processes such as cellular growth, angiogenesis, apoptosis, autophagy, and aging, which are involved in the initiation and progression of several diseases.

Opposing roles of Akt and STAT3 in the protection of the maternal heart from peripartum stress

BACKGROUND

Peripartum cardiomyopathy (PPCM) is a pregnancy-associated cardiomyopathy in previously healthy women. Mice with a cardiomyocyte-restricted deletion of signal transducer and activator of transcription-3 (STAT3, CKO) develop PPCM. PI3K-Akt signalling is thought to promote cardiac hypertrophy and protection during pregnancy. We evaluated the role of activated Akt signalling in the maternal heart postpartum.

METHODS AND RESULTS

CKO mice were bred to mice harbouring an Akt transgene, specifically expressed in cardiomyocytes (CAkt(tg)) generating CKO; CAkt(tg), CAkt(tg), CKO, and wild-type sibling mice. CAkt(tg) and CKO;CAkt(tg) female mice developed PPCM with systolic dysfunction. Both genotypes displayed cardiac hypertrophy and lower capillary density, showed increased phosphorylation of p66 Src homology 2 domain containing protein and FoxO3A, and reduced expression of manganese superoxide dismutase as well as increased cathepsin D activity and increased miR-146a levels [indicative for generation of the anti-angiogenic 16 kDa prolactin (PRL)]. Cardiac inflammation and fibrosis was accelerated in CKO;CAkt(tg) and associated with high postpartum mortality. The PRL blocker, bromocriptine (BR), prevented heart failure and the decrease in capillary density in CKO;CAkt(tg) and CAkt(tg) mice. BR attenuated high mortality, up-regulation of CCL2, and cardiac inflammation as well as fibrosis in CKO;CAkt(tg). PRL infusion induced cardiac inflammation in CKO;CAkt(tg) independent of pregnancy. In neonatal rat cardiomyocytes, PRL and interferon γ (IFNγ) induced the expression of CCL2 via activation of Akt.

CONCLUSION

Postpartum Akt activation is detrimental for the peripartum heart as it lowers anti-oxidative defence and in combination with low STAT3 conditions, accelerate cardiac inflammation and fibrosis. PRL and its cleaved 16 kDa form are central for Akt-induced PPCM as indicated by the protection from the disease by PRL blockade.

Akt1 expression and activity at different stages in experimental heart failure

Loss of function or/and death of cardiomyocytes is one of the major contributing factors in the development of heart failure. Cytosolic Hsp60 can directly interact and regulate activation of some kinases and sequestrate certain proapoptotic molecules to avoid the cardiomyocyte apoptosis. We assumed that Akt1 kinase, a downstream effector of PI3 kinase, can interact with Hsp60. Our aim was to clarify the interaction of Akt1 and Hsp60 and to investigate the Akt1 expression in normal and failing hearts in acute and chronic stress. The experimental mouse models of inducible myocarditis and DCM-like pathology were developed in our laboratory. Akt1 and phospho-Akt1 (pS473) expression were studied by Western blot analysis. Co-immunoprecipitation method was used to test complex formation of Akt1 and Hsp60. The interaction of Hsp60 and Akt1 was detected for the first time by co-immunoprecipitation method in normal myocardium and under pathology as well. There were no significant changes in the level of Akt1 expression in both myocardia. At the same time we observed significant decrease in Akt1 phosphorylation at the final stage of DCM-like pathology but not at experimental myocarditis. The final stage of heart failure in mouse model of DCM-like pathology was characterized by reduced level of phospho-Akt1/Akt1 (pS473; -26%; P<0.05), whereas no differences were found in total Akt1 protein content. We suggest a possible involvement of cytoplasmic Hsp60 in regulation of Akt1 activity at heart failure progression.

Myocardial KRAS(G12D) expression does not cause cardiomyopathy in mice

AIMS

Germ-line mutations in genes encoding components of the RAS/mitogen-activated protein kinase (MAPK) pathway cause developmental disorders called RASopathies. Hypertrophic cardiomyopathy (HCM) is the most common myocardial pathology and a leading cause of death in RASopathy patients. KRAS mutations are found in Noonan and cardio-facio-cutaneous syndromes. KRAS mutations, unlike mutations of RAF1 and HRAS, are rarely associated with HCM. This has been attributed to the fact that germ-line KRAS mutations cause only a moderate up-regulation of the MAPK pathway. Highly bioactive KRAS mutations have been hypothesized to cause severe cardiomyopathy incompatible with life. The aim of this study was to define the impact of KRAS(G12D) expression in the heart.

METHODS AND RESULTS

To generate mice with endogenous cardiomyocyte-specific KRAS(G12D) expression (cKRAS(G12D) mice), we bred mice with a Cre-inducible allele expressing KRAS(G12D) from its endogenous promoter (Kras2(LSL)) to mice expressing Cre under control of the cardiomyocyte-specific α-myosin heavy chain promoter (αMHC-Cre). cKRAS(G12D) mice showed high levels of myocardial ERK and AKT signalling. However, surprisingly, cKRAS(G12D) mice were born in Mendelian ratios, appeared healthy, and had normal function, size, and histology of the heart.

CONCLUSION

Mice with cardiomyocyte-specific KRAS(G12D) expression do not develop heart pathology. These results challenge the view that the level of MAPK activation correlates with the severity of HCM in RASopathies and suggests that MAPK-independent strategies may be of interest in the development of new treatments for these syndromes.

Evaluation of bi-ventricular coronary flow patterns using high-frequency ultrasound in mice with transverse aortic constriction

Using high-frequency color and pulsed Doppler ultrasound, we evaluated the flow patterns of the left (LCA), septal (SCA) and right (RCA) coronary arteries in mice with and without transverse aortic constriction (TAC). Fifty-two male C57BL/6J mice were subjected to TAC or a corresponding sham operation. At 2 and 8 wk post-surgery, Doppler flow spectra from the three coronary arteries, together with morphologic and functional parameters of the left and right ventricles, were measured. Histology was performed to evaluate myocyte size and neo-angiogenesis in both ventricles. In sham-operated mice, the LCA and SCA both exhibited low-flow waveforms during systole and dominantly higher-flow waveforms during diastole. The RCA exhibited generally lower flow velocity, with similar systolic and diastolic waveforms. TAC significantly increased the systolic flow velocities of all coronary arteries, but enhanced the flow mainly in the LCA and SCA. In the left ventricle, coronary flow reserve was partially preserved 2 wk post-TAC, but decreased at 8 wk, consistent with changes in neo-angiogenesis and systolic function. In contrast, no significant change was found in the coronary flow reserve, structure or function of the right ventricle. This study has established a protocol for evaluating the flow pattern in three principal coronary arteries in mice using Doppler ultrasound and illustrated the difference among three vessels at baseline. In mice with TAC, the difference in the associating pattern of coronary flow dynamics with the myocardial structure and function between the left and right ventricles provides further insights into ventricular remodeling under pressure overload.

Human umbilical cord blood mononuclear cell-conditioned media inhibits hypoxic-induced apoptosis in human coronary artery endothelial cells and cardiac myocytes by activation of the survival protein Akt

We have previously demonstrated in acute myocardial infarctions that human umbilical cord blood mononuclear cells (HUCBCs), which contain hematopoietic, endothelial, and mesenchymal stem cells, reduce acute myocardial infarction size by ≥50% and preserve LV contractility. We hypothesize that the beneficial effects of HUCBCs are due to secretion of biologically active factors that activate in cardiac endothelial cells and myocytes the cell survival protein Akt. We determined by protein microarrays the growth factors and anti-inflammatory cytokines secreted by HUCBCs into culture media during 12 h of hypoxia (1% O2). We then determined by Western blots the effects of cell-free media from hypoxic-conditioned HUCBCs (HUCM) on activation of the cell survival protein Akt in human coronary artery endothelial cells and cardiac myocytes in culture during 24 h of 1% O2. We also determined in separate experiments endothelial cell and myocyte apoptosis by caspase-3 and Annexin V. In the present experiments, HUCBCs secreted multiple growth factors, anti-inflammatory cytokines, and inhibitors of metalloproteinase during normoxia and hypoxia. Human cord blood cells increased the concentration in culture media of angiopoietin, hepatocyte growth factor, interleukin-4, insulin-like growth factor, placental growth factor, vascular endothelial cell growth factor, angiogenin, and stem cell factor by 100 to >10,000% during 12 h of 1% O2 (p<0.001). HUCM, which contained these biological factors, significantly increased Akt phosphorylation/activation in coronary artery endothelial cells and cardiac myocytes subjected to 24 h of 1% O2 by more than 60% (p<0.05) and increased the antiapoptotic protein Bcl-2 expression by 34-50% in comparison with endothelial cells and myocytes treated without HUCM in 1% O2(p<0.05). HUCM also significantly decreased caspase-3 activity and decreased hypoxic endothelial cell and cardiac myocyte apoptosis by more than 40% in comparison with cells cultured without HUCM (p<0.05). Inhibition of Akt activation in endothelial cells and myocytes by the sensitive and specific antagonist API-1 during 24 h of hypoxia nearly completely prevented the beneficial effects of HUCM on inhibiting caspase-3 activity and apoptosis. We conclude that HUCBCs secrete biologically active factors during hypoxia that activate survival proteins in endothelial cells and myocytes that significantly limit apoptosis.

Phosphoinositide 3-Kinase p110α Is a Master Regulator of Exercise-Induced Cardioprotection and PI3K Gene Therapy Rescues Cardiac Dysfunction

Background—

Numerous molecular and biochemical changes have been linked with the cardioprotective effects of exercise, including increases in antioxidant enzymes, heat shock proteins, and regulators of cardiac myocyte proliferation. However, a master regulator of exercise-induced protection has yet to be identified. Here, we assess whether phosphoinositide 3-kinase (PI3K) p110α is essential for mediating exercise-induced cardioprotection, and if so, whether its activation independent of exercise can restore function of the failing heart.

Methods and Results—

Cardiac-specific transgenic (Tg) mice with elevated or reduced PI3K(p110α) activity (constitutively active PI3K [caPI3K] and dominant negative PI3K, respectively) and non-Tg controls were subjected to 4 weeks of exercise training followed by 1 week of pressure overload (aortic-banding) to induce pathological remodeling. Aortic-banding in untrained non-Tg controls led to pathological cardiac hypertrophy, depressed systolic function, and lung congestion. This phenotype was attenuated in non-Tg controls that had undergone exercise before aortic-banding. Banded caPI3K mice were protected from pathological remodeling independent of exercise status, whereas exercise provided no protection in banded dominant negative PI3K mice, suggesting that PI3K is necessary for exercise-induced cardioprotection. Tg overexpression of heat shock protein 70 could not rescue the phenotype of banded dominant negative PI3K mice, and deletion of heat shock protein 70 from banded caPI3K mice had no effect. Next, we used a gene therapy approach (recombinant adeno-associated viral vector 6) to deliver caPI3K expression cassettes to hearts of mice with established cardiac dysfunction caused by aortic-banding. Mice treated with recombinant adeno-associated viral 6-caPI3K vectors had improved heart function after 10 weeks.

Conclusions—

PI3K(p110α) is essential for exercise-induced cardioprotection and delivery of caPI3K vector can improve function of the failing heart.

Akt and MAPK signaling mediate pregnancy-induced cardiac adaptation

Although the signaling pathways underlying exercise-induced cardiac adaptation have been extensively studied, little is known about the molecular mechanisms that result in the response of the heart to pregnancy. The objective of this study was to define the morphological, functional, and gene expression patterns that define the hearts of pregnant mice, and to identify the signaling pathways that mediate this response. Mice were divided into three groups: nonpregnant diestrus control, midpregnancy, and late pregnancy. Both time points of pregnancy were associated with significant cardiac hypertrophy. The prosurvival signaling cascades of Akt and ERK1/2 were activated in the hearts of pregnant mice, while the stress kinase, p38, was decreased. Given the activation of Akt in pregnancy and its known role in cardiac hypertrophy, the hypertrophic response to pregnancy was tested in mice expressing a cardiac-specific activated (myristoylated) form of Akt (myrAkt) or a cardiac-specific constitutively active (antipathologic hypertrophic) form of its downstream target, glycogen synthase kinase 3β (caGSK3β). The pregnancy-induced hypertrophic responses of hearts from these mice were significantly attenuated. Finally, we tested whether pregnancy-associated sex hormones could induce hypertrophy and alter signaling pathways in isolated neonatal rat ventricular myocytes (NRVMs). In fact, progesterone, but not estradiol treatment increased NRVM cell size via phosphorylation of ERK1/2. Inhibition of MEK1 effectively blocked progesterone-induced cellular hypertrophy. Taken together, our study demonstrates that pregnancy-induced cardiac hypertrophy is mediated by activation of Akt and ERK1/2 pathways.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Effect of N-2-mercaptopropionyl glycine on exercise-induced cardiac adaptations

The purpose of this study was to test the hypothesis that exercise-induced cardiac adaptations would be attenuated by the free radical scavenger N-2-mercaptopropionyl glycine (MPG). Male Sprague-Dawley rats were divided into four groups ( n = 9–13 per group) for 3–4 wk: sedentary (S), S+MPG (100 mg/kg ip daily), exercised on a treadmill (E) (60 min/day, 5 days/wk, at a speed of 20 m/min up a 6° grade in a 6°C room), or E+MPG given 10 min prior to exercise. Additional rats ( n = 55) were used to determine acute exercise effects on myocardial redox state [nonprotein nonglutathione sulfhydryls (NPNGSH)] and PI3K/Akt signaling pathway activation. Compared with S, NPNGSH levels were 48% lower in E ( P < 0.05) and unchanged in E+MPG ( P > 0.05). MPG also attenuated exercise-induced activation of the signaling proteins Akt and S6. Hearts from the 4-wk groups were weighed, and cardiac function was evaluated using an isolated perfused working heart preparation. Similar increases ( P < 0.05) in both exercised groups were observed for heart weight and heart weight-to-body weight ratio. Cardiac function improved in E vs. S, as indicated by greater ( P < 0.05) external work performed (cardiac output × systolic pressure) and efficiency of external work (work/V̇o2). MPG prevented these exercise-induced functional improvements. Skeletal muscle mitochondria content increased to similar levels in E and E+MPG. This study provides evidence that free radicals do not play an essential role in the development of exercise-induced cardiac hypertrophy; however, they appear to be involved in functional cardiac adaptations, which may be mediated through the PI3K/Akt pathway.

MTORC1 regulates cardiac function and myocyte survival through 4E-BP1 inhibition in mice

Mechanistic target of rapamycin (MTOR) plays a critical role in the regulation of cell growth and in the response to energy state changes. Drugs inhibiting MTOR are increasingly used in antineoplastic therapies. Myocardial MTOR activity changes during hypertrophy and heart failure (HF). However, whether MTOR exerts a positive or a negative effect on myocardial function remains to be fully elucidated. Here, we show that ablation of Mtor in the adult mouse myocardium results in a fatal, dilated cardiomyopathy that is characterized by apoptosis, autophagy, altered mitochondrial structure, and accumulation of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1). 4E-BP1 is an MTOR-containing multiprotein complex-1 (MTORC1) substrate that inhibits translation initiation. When subjected to pressure overload, Mtor-ablated mice demonstrated an impaired hypertrophic response and accelerated HF progression. When the gene encoding 4E-BP1 was ablated together with Mtor, marked improvements were observed in apoptosis, heart function, and survival. Our results demonstrate a role for the MTORC1 signaling network in the myocardial response to stress. In particular, they highlight the role of 4E-BP1 in regulating cardiomyocyte viability and in HF. Because the effects of reduced MTOR activity were mediated through increased 4E-BP1 inhibitory activity, blunting this mechanism may represent a novel therapeutic strategy for improving cardiac function in clinical HF.

Distinctive ERK and p38 signaling in remote and infarcted myocardium during post-MI remodeling in the mouse

Global activation of MAP kinases has been reported in both human and experimental heart failure. Chronic remodeling of the surviving ventricular wall after myocardial infarction (MI) involves both myocyte loss and fibrosis; we hypothesized that this cardiomyopathy involves differential shifts in pro- and anti-apoptotic MAP kinase signaling in cardiac myocyte (CM) and non-myocyte. Cardiomyopathy after coronary artery ligation in mice was characterized by echocardiography, ex vivo Langendorff preparation, histologic analysis and measurements of apoptosis. Phosphorylation (activation) of signaling molecules was analyzed by Western blot, ELISA and immunohistochemistry. Post-MI remodeling involved dramatic changes in the phosphorylation of both stress-activated MAP (SAP) kinase p38 as well as ERK, a known mediator of cell survival, but not of SAP kinase JNK or the anti-apoptotic mediator of PI3K, Akt. Phosphorylation of p38 rose early after MI in the infarct, whereas a more gradual rise in the remote myocardium accompanied a rise in apoptosis in that region. In both areas, ERK phosphorylation was lowest early after MI and rose steadily thereafter, though infarct phosphorylation was consistently higher. Immunostaining of p-ERK localized to fibrotic areas populated primarily by non-myocytes, whereas staining of p38 phosphorylation was stronger in areas of progressive CM apoptosis. Relative segregation of CMs and non-myocytes in different regions of the post-MI myocardium revealed signaling patterns that imply cell type-specific changes in pro- and anti-apoptotic MAP kinase signaling. Prevention of myocyte loss and of LV remodeling after MI may therefore require cell type-specific manipulation of p38 and ERK activation.

Akt mediated mitochondrial protection in the heart: metabolic and survival pathways to the rescue

Cardiomyocyte death is now recognized as a critical factor in the development of heart disease. Mitochondria are not only responsible for energy production to ensure that cardiac output meets the body's energy demands, but they serve as critical integrators of cell survival signals. Numerous stressors are known to induce cell death by necrosis and/or apoptosis mediated through mitochondrial dysregulation. Anti- and pro-apoptotic Bcl-2 family proteins regulate apoptosis by controlling mitochondrial outer membrane permeability, whereas opening of the mitochondrial permeability transition pore (PT-pore) induces large amplitude permeability of the inner membrane and consequent rupture of the outer membrane. Akt is one of the best described survival kinases activated by receptor ligands and its activation preserves mitochondrial integrity and protects cardiomyocytes against necrotic and apoptotic death. The mechanisms responsible for Akt-mediated mitochondrial protection have not been fully elucidated. There is, however, accumulating evidence that multiple Akt target molecules, recruited through both transcriptional and post-transcriptional mechanisms, directly impinge upon and protect mitochondria. In this review we discuss mechanisms by which Akt activation can effect changes at the mitochondria that protect cardiomyocytes and attenuate pathophysiological responses of the heart.

Activation or inactivation of cardiac Akt/mTOR signaling diverges physiological from pathological hypertrophy

Cardiomyocyte hypertrophy differs according to the stress exerted on the myocardium. While pressure overload-induced cardiomyocyte hypertrophy is associated with depressed contractile function, physiological hypertrophy after exercise training associates with preserved or increased inotropy. We determined the activation state of myocardial Akt signaling with downstream substrates and fetal gene reactivation in exercise-induced physiological and pressure overload-induced pathological hypertrophies. C57BL/6J mice were either treadmill trained for 6 weeks, 5 days/week, at 85-90% of maximal oxygen uptake (VO(2max)), or underwent transverse aortic constriction (TAC) for 1 or 8 weeks. Total and phosphorylated protein levels were determined with SDS-PAGE, and fetal genes by real-time RT-PCR. In the physiologically hypertrophied heart after exercise training, total Akt protein level was unchanged, but Akt was chronically hyperphosphorylated at serine 473. This was accompanied by activation of the mammalian target of rapamycin (mTOR), measured as phosphorylation of its two substrates: the ribosomal protein S6 kinase-1 (S6K1) and the eukaryotic translation initiation factor-4E binding protein-1 (4E-BP1). Exercise training did not reactivate the fetal gene program (beta-myosin heavy chain, atrial natriuretic factor, skeletal muscle actin). In contrast, pressure overload after TAC reactivated fetal genes already after 1 week, and partially inactivated the Akt/mTOR pathway and downstream substrates after 8 weeks. In conclusion, changes in opposite directions of the myocardial Akt/mTOR signal pathway appears to distinguish between physiological and pathological hypertrophies; exercise training associating with activation and pressure overload associating with inactivation of the Akt/mTOR pathway.