AKT signalling in the failing heart

Irisin Controls Growth, Intracellular Ca2+ Signals, and Mitochondrial Thermogenesis in Cardiomyoblasts

Exercise offers short-term and long-term health benefits, including an increased metabolic rate and energy expenditure in myocardium. The newly-discovered exercise-induced myokine, irisin, stimulates conversion of white into brown adipocytes as well as increased mitochondrial biogenesis and energy expenditure. Remarkably, irisin is highly expressed in myocardium, but its physiological effects in the heart are unknown. The objective of this work is to investigate irisin’s potential multifaceted effects on cardiomyoblasts and myocardium. For this purpose, H9C2 cells were treated with recombinant irisin produced in yeast cells (r-irisin) and in HEK293 cells (hr-irisin) for examining its effects on cell proliferation by MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and on gene transcription profiles by qRT-PCR. R-irisin and hr-irisin both inhibited cell proliferation and activated genes related to cardiomyocyte metabolic function and differentiation, including myocardin, follistatin, smooth muscle actin, and nuclear respiratory factor-1. Signal transduction pathways affected by r-irisin in H9C2 cells and C57BL/6 mice were examined by detecting phosphorylation of PI3K-AKT, p38, ERK or STAT3. We also measured intracellular Ca²⁺ signaling and mitochondrial thermogenesis and energy expenditure in r-irisin-treated H9C2 cells. The results showed that r-irisin, in a certain concentration rage, could activate PI3K-AKT and intracellular Ca²⁺ signaling and increase cellular oxygen consumption in H9C2 cells. Our study also suggests the existence of irisin-specific receptor on the membrane of H9C2 cells. In conclusion, irisin in a certain concentration rage increased myocardial cell metabolism, inhibited cell proliferation and promoted cell differentiation. These effects might be mediated through PI3K-AKT and Ca²⁺ signaling, which are known to activate expression of exercise-related genes such as follistatin and myocardin. This work supports the value of exercise, which promotes irisin release.

Effects of 3-methyladenine on isolated left atria subjected to simulated ischaemia-reperfusion

Although autophagy is a prominent feature of myocardial ischaemia and reperfusion, its functional significance is unclear and controversial. In order to gain a deeper insight into the role of autophagy in myocardial ischaemia-reperfusion, we explored the effects of the pharmacological inhibitor of autophagy 3-methyladenine (3-MA). Isolated rat atria subjected to simulated 75-min ischaemia/75-min reperfusion (Is-Rs) in the presence or absence of 3-MA were used. The LC3-II/LC3-I ratio, an indicator of autophagosome formation, did not increase after ischaemia either in the presence or absence of 3-MA, but there was significant enhancement during reperfusion, which was prevented by the presence of 3-MA. The autophagy inhibitor also increased p62 protein, one of the specific substrates degraded through the autophagy-lysosomal pathway. Electron micrographs showed double membrane autophagosome-like structures during reperfusion, which were absent in atria subjected to Is-Rs in the presence of 3-MA. These findings suggest that this agent inhibited the autophagic flux under the present experimental conditions. Inhibition of autophagy during Is-Rs was accompanied by a high incidence of tachyarrhythmias during reperfusion, and a decrease in the maximal inotropic response to β-adrenergic and to calcium stimulation at the end of Is-Rs. Deterioration of mitochondrial morphology and function, without affecting cell viability, was observed in atria subjected to Is-Rs in the presence of 3-MA. The present results suggest an association between the inhibition of autophagy and functional alterations of the cells that have undergone sublethal stress, and have been able to recover in this experimental model of ischaemia-reperfusion.

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.

Augmentation of autophagy by atorvastatin via Akt/mTOR pathway in spontaneously hypertensive rats

Autophagy is activated in hypertension-induced cardiac hypertrophy. However, the mechanisms and significance of an activated autophagy are not clear. This study was designed to determine the role of atorvastatin (ATO) in cardiac autophagy and associated benefits on cardiac remodeling and left ventricular function in spontaneously hypertensive rats (SHRs). Twenty-eight male SHRs at 8 weeks of age were randomized to treatment with vehicle (saline solution; SHR+V) or ATO (SHR+ATO; 50 mg kg(-1) per day) for 6 or 12 months. Age-matched male Wistar-Kyoto (WKY) rats were used as normotensive controls. Cardiac magnetic resonance was used to evaluate cardiac function and structure. Compared with WKY rats, SHRs showed significant left ventricle (LV) dysfunction, remodeling and increases in cardiomyocyte size, which were all attenuated by 6 and 12 months of ATO treatment. Compared with WKY rats, autophagy was activated in the hearts of SHRs and this effect was amplified by chronic ATO treatment, particularly following 12 months of treatment. Protein expression levels of microtubule-associated protein-1 light chain 3-II and beclin-1, the biomarkers of an activated cardiac autophagy, were significantly elevated in ATO-treated versus vehicle-treated SHRs and control WKY rats. Cardiac Akt and phosphorylated mammalian target of rapamycin (mTOR) expression were also increased in the hearts of SHR versus WKY rats, and this effect was attenuated by ATO treatment. These findings suggest that ATO-mediated improvements in LV function and structure in SHRs may be, in part, through its regulation of cardiac autophagy via the Akt/mTOR pathway.

Trastuzumab cardiac toxicity: a problem we put our heart into

Trastuzumab has gained a central role in the treatment of HER2-positive breast cancer, revolutionizing care in this setting. However, since the beginning of its use there have been concerns about its cardiac safety. Trastuzumab can give rise to cardiac toxicity, in some cases leading to discontinuation of treatment. Growing evidence shows that trastuzumab toxicity can be detected early or averted by means of new chemotherapy regimens using different anthracycline formulations or avoiding anthracyclines altogether. Moreover, patients in whom cardiac toxicity develops can be treated effectively and full cardiac function can be restored thanks to progress in drug management. Knowing the characteristics and proper management of trastuzumab toxicity is of paramount importance to grant patients in this setting the best available treatment.

Cross talk of the first-line defense TLRs with PI3K/Akt pathway, in preconditioning therapeutic approach

Toll-like receptor family (TLRs), pattern recognition receptors, is expressed not only on immune cells but also on non-immune cells, including cardiomyocytes, fibroblasts, and vascular endothelial cells. One main function of TLRs in the non-immune system is to regulate apoptosis. TLRs are the central mediators in hepatic, pulmonary, brain, and renal ischemic/reperfusion (I/R) injury. Up-regulation of TLRs and their ligation by either exogenous or endogenous danger signals plays critical roles in ischemia/reperfusion-induced tissue damage. Conventional TLR-NF-κB pathways are markedly activated in failing and ischemic myocardium. Recent studies have identified a cross talk between TLR activation and the PI3K/Akt pathway. The activation of TLRs is proposed to be the most potent preconditioning method after ischemia, to improve the cell survival via the mechanism involved the PI3K/Akt signaling pathway and to attenuate the subsequent TLR-NF-κB pathway stimulation. Thus, TLRs could be a great target in the new treatment approaches for myocardial I/R injury.

Cross talk of the first-line defense TLRs with PI3K/Akt pathway, in preconditioning therapeutic approach

Toll-like receptor family (TLRs), pattern recognition receptors, is expressed not only on immune cells but also on non-immune cells, including cardiomyocytes, fibroblasts, and vascular endothelial cells. One main function of TLRs in the non-immune system is to regulate apoptosis. TLRs are the central mediators in hepatic, pulmonary, brain, and renal ischemic/reperfusion (I/R) injury. Up-regulation of TLRs and their ligation by either exogenous or endogenous danger signals plays critical roles in ischemia/reperfusion-induced tissue damage. Conventional TLR-NF-κB pathways are markedly activated in failing and ischemic myocardium. Recent studies have identified a cross talk between TLR activation and the PI3K/Akt pathway. The activation of TLRs is proposed to be the most potent preconditioning method after ischemia, to improve the cell survival via the mechanism involved the PI3K/Akt signaling pathway and to attenuate the subsequent TLR-NF-κB pathway stimulation. Thus, TLRs could be a great target in the new treatment approaches for myocardial I/R injury.

Atorvastatin protects cardiomyocytes from oxidative stress by inhibiting LOX-1 expression and cardiomyocyte apoptosis

Coronary artery disease (CAD) is a major health problem worldwide. The most severe form of CAD is acute coronary syndrome (ACS). Recent studies have demonstrated the beneficial role of atorvastatin in ACS; however, the mechanisms underlying this effect have not been fully clarified. Growing evidence indicates that activation of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) plays an important role in oxidative stress-induced cardiomyocyte apoptosis during ACS. In this study, we examined whether atorvastatin inhibits H2O2-induced LOX-1 expression and H9c2 cardiomyocyte apoptosis, and investigated the underlying signaling pathway. Treatment of H9c2 cardiomyocytes with H2O2 resulted in elevated expression of LOX-1 mRNA and protein, as well as increased caspase-3 and -9 protein expression and cell apoptosis. H2O2-induced LOX-1 expression, caspase protein expression, and cardiomyocyte apoptosis were attenuated by pretreatment with atorvastatin. Atorvastatin activated H2O2-inhibited phosphorylation of Akt in a concentration-dependent manner. The Akt inhibitor, LY294002, inhibited the effect of atorvastatin on inducing Akt phosphorylation and on suppressing H2O2-mediated caspase up-regulation and cell apoptosis. These findings indicate that atorvastatin protects cardiomyocyte from oxidative stress via inhibition of LOX-1 expression and apoptosis, and that activation of H2O2-inhibited phosphorylation of Akt may play an important role in the protective function of atorvastatin.

Phosphatidylinositol-3,4,5-triphosphate and cellular signaling: implications for obesity and diabetes

Phosphatidylinositol-3,4,5-triphosphate (PtdIns(3,4,5)P₃) is one of the most important phosphoinositides and is capable of activating a wide range of proteins through its interaction with their specific binding domains. Localization and activation of these effector proteins regulate a number of cellular functions, including cell survival, proliferation, cytoskeletal rearrangement, intracellular vesicle trafficking, and cell metabolism. Phosphoinositides have been investigated as an important agonist-dependent second messenger in the regulation of diverse physiological events depending upon the phosphorylation status of their inositol group. Dysregulation in formation as well as metabolism of phosphoinositides is associated with various pathophysiological disorders such as inflammation, allergy, cardiovascular diseases, cancer, and metabolic diseases. Recent studies have demonstrated that the impaired metabolism of PtdIns(3,4,5)P₃ is a prime mediator of insulin resistance associated with various metabolic diseases including obesity and diabetes. This review examines the current status of the role of PtdIns(3,4,5)P₃ signaling in the regulation of various cellular functions and the implications of dysregulated PtdIns(3,4,5)P₃ signaling in obesity, diabetes, and their associated complications.

It's all in the timing: modeling isovolumic contraction through development and disease with a dynamic dual electromechanical bioreactor system

This commentary discusses the rationale behind our recently reported work entitled "Mimicking isovolumic contraction with combined electromechanical stimulation improves the development of engineered cardiac constructs," introduces new data supporting our hypothesis, and discusses future applications of our bioreactor system. The ability to stimulate engineered cardiac tissue in a bioreactor system that combines both electrical and mechanical stimulation offers a unique opportunity to simulate the appropriate dynamics between stretch and contraction and model isovolumic contraction in vitro. Our previous study demonstrated that combined electromechanical stimulation that simulated the timing of isovolumic contraction in healthy tissue improved force generation via increased contractile and calcium handling protein expression and improved hypertrophic pathway activation. In new data presented here, we further demonstrate that modification of the timing between electrical and mechanical stimulation to mimic a non-physiological process negatively impacts the functionality of the engineered constructs. We close by exploring the various disease states that have altered timing between the electrical and mechanical stimulation signals as potential future directions for the use of this system.

Astragalus polysaccharide suppresses doxorubicin-induced cardiotoxicity by regulating the PI3k/Akt and p38MAPK pathways

Background. Doxorubicin, a potent chemotherapeutic agent, is associated with acute and chronic cardiotoxicity, which is cumulatively dose-dependent. Astragalus polysaccharide (APS), the extract of Astragalus membranaceus with strong antitumor and antiglomerulonephritis activity, can effectively alleviate inflammation. However, whether APS could ameliorate chemotherapy-induced cardiotoxicity is not understood. Here, we investigated the protective effects of APS on doxorubicin-induced cardiotoxicity and elucidated the underlying mechanisms of the protective effects of APS. Methods. We analyzed myocardial injury in cancer patients who underwent doxorubicin chemotherapy and generated a doxorubicin-induced neonatal rat cardiomyocyte injury model and a mouse heart failure model. Echocardiography, reactive oxygen species (ROS) production, TUNEL, DNA laddering, and Western blotting were performed to observe cell survival, oxidative stress, and inflammatory signal pathways in cardiomyocytes. Results. Treatment of patients with the chemotherapeutic drug doxorubicin led to heart dysfunction. Doxorubicin reduced cardiomyocyte viability and induced C57BL/6J mouse heart failure with concurrent elevated ROS generation and apoptosis, which, however, was attenuated by APS treatment. In addition, there was profound inhibition of p38MAPK and activation of Akt after APS treatment. Conclusions. These results demonstrate that APS could suppress oxidative stress and apoptosis, ameliorating doxorubicin-mediated cardiotoxicity by regulating the PI3k/Akt and p38MAPK pathways.

Phosphoproteomic profiling of human myocardial tissues distinguishes ischemic from non-ischemic end stage heart failure

The molecular differences between ischemic (IF) and non-ischemic (NIF) heart failure are poorly defined. A better understanding of the molecular differences between these two heart failure etiologies may lead to the development of more effective heart failure therapeutics. In this study extensive proteomic and phosphoproteomic profiles of myocardial tissue from patients diagnosed with IF or NIF were assembled and compared. Proteins extracted from left ventricular sections were proteolyzed and phosphopeptides were enriched using titanium dioxide resin. Gel- and label-free nanoscale capillary liquid chromatography coupled to high resolution accuracy mass tandem mass spectrometry allowed for the quantification of 4,436 peptides (corresponding to 450 proteins) and 823 phosphopeptides (corresponding to 400 proteins) from the unenriched and phospho-enriched fractions, respectively. Protein abundance did not distinguish NIF from IF. In contrast, 37 peptides (corresponding to 26 proteins) exhibited a ≥ 2-fold alteration in phosphorylation state (p<0.05) when comparing IF and NIF. The degree of protein phosphorylation at these 37 sites was specifically dependent upon the heart failure etiology examined. Proteins exhibiting phosphorylation alterations were grouped into functional categories: transcriptional activation/RNA processing; cytoskeleton structure/function; molecular chaperones; cell adhesion/signaling; apoptosis; and energetic/metabolism. Phosphoproteomic analysis demonstrated profound post-translational differences in proteins that are involved in multiple cellular processes between different heart failure phenotypes. Understanding the roles these phosphorylation alterations play in the development of NIF and IF has the potential to generate etiology-specific heart failure therapeutics, which could be more effective than current therapeutics in addressing the growing concern of heart failure.

Investigation into the effects of varying frequency of mechanical stimulation in a cycle-by-cycle manner on engineered cardiac construct function

Mechanical stimulation has been used extensively to improve the function of cardiac engineered tissue, as it mimics the physical environment in which the tissue is situated during normal development. However, previous mechanical stimulation has been carried out under a constant frequency that more closely resembles a diseased heart. The goal of this study was to create a bioreactor system that would allow us to control the mechanical stimulation of engineered cardiac tissue on a cycle-by-cycle basis. This unique system allows us to determine the effects on cardiac construct function of introducing variability to the mechanical stretch. To test our bioreactor system, constructs created from neonatal rat cardiomyocytes entrapped in fibrin hydrogels were stimulated under various regimes for 2 weeks and then assessed for functional outcomes. No differences were observed in the final cell number in each condition, indicating that variability in frequency did not have a negative effect on viability. The forces were higher for all mechanical stimulation groups compared to static controls, although no differences were observed between the mechanically stimulated conditions, indicating that variable frequency on a cycle-by-cycle basis has limited effects on the resulting force. Although differences in the observed twitch force were not observed, differences in the protein expression indicate that variable-frequency mechanical stimulation had an effect on cell-cell coupling and growth pathway activation in the constructs. Thus, this bioreactor system provides a valuable tool for further development and optimization of engineered myocardial tissue as a repair or replacement strategy for patients undergoing heart failure. Copyright © 2014 John Wiley & Sons, Ltd.

Screening for acute IKr block is insufficient to detect torsades de pointes liability: role of late sodium current

BACKGROUND

New drugs are routinely screened for IKr blocking properties thought to predict QT prolonging and arrhythmogenic liability. However, recent data suggest that chronic (hours) drug exposure to phosphoinositide 3-kinase inhibitors used in cancer can prolong QT by inhibiting potassium currents and increasing late sodium current (INa-L) in cardiomyocytes. We tested the extent to which IKr blockers with known QT liability generate arrhythmias through this pathway.

METHODS AND RESULTS

Acute exposure to dofetilide, an IKr blocker without other recognized electropharmacologic actions, produced no change in ion currents or action potentials in adult mouse cardiomyocytes, which lack IKr. By contrast, 2 to 48 hours of exposure to the drug generated arrhythmogenic afterdepolarizations and ≥15-fold increases in INa-L. Including phosphatidylinositol 3,4,5-trisphosphate, a downstream effector for the phosphoinositide 3-kinase pathway, in the pipette inhibited these effects. INa-L was also increased, and inhibitable by phosphatidylinositol 3,4,5-trisphosphate, with hours of dofetilide exposure in human-induced pluripotent stem cell-derived cardiomyocytes and in Chinese hamster ovary cells transfected with SCN5A, encoding sodium current. Cardiomyocytes from dofetilide-treated mice similarly demonstrated increased INa-L and afterdepolarizations. Other agents with variable IKr-blocking potencies and arrhythmia liability produced a range of effects on INa-L, from marked increases (E-4031, d-sotalol, thioridazine, and erythromycin) to little or no effect (haloperidol, moxifloxacin, and verapamil).

CONCLUSIONS

Some but not all drugs designated as arrhythmogenic IKr blockers can generate arrhythmias by augmenting INa-L through the phosphoinositide 3-kinase pathway. These data identify a potential mechanism for individual susceptibility to proarrhythmia and highlight the need for a new paradigm to screen drugs for QT prolonging and arrhythmogenic liability.

Tongxinluo protects against pressure overload-induced heart failure in mice involving VEGF/Akt/eNOS pathway activation

Background

It has been demonstrated that Tongxinluo (TXL), a traditional Chinese medicine compound, improves ischemic heart disease in animal models via vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). The present study aimed to investigate whether TXL protects against pressure overload–induced heart failure in mice and explore the possible mechanism of action.

Methods and Results

Transverse aortic constriction (TAC) surgery was performed in mice to induce heart failure. Cardiac function was evaluated by echocardiography. Myocardial pathology was detected using hematoxylin and eosin or Masson trichrome staining. We investigated cardiomyocyte ultrastructure using transmission electron microscopy. Angiogenesis and oxidative stress levels were determined using CD31 and 8-hydroxydeoxyguanosine immunostaining and malondialdehyde assay, respectively. Fetal gene expression was measured using real-time PCR. Protein expression of VEGF, phosphorylated (p)-VEGF receptor 2 (VEGFR2), p–phosphatidylinositol 3-kinase (PI3K), p-Akt, p-eNOS, heme oxygenase-1 (HO-1), and NADPH oxidase 4 (Nox4) were measured with western blotting. Twelve-week low- and high-dose TXL treatment following TAC improved cardiac systolic and diastolic function and ameliorated left ventricular hypertrophy, fibrosis, and myocardial ultrastructure derangement. Importantly, TXL increased myocardial capillary density significantly and attenuated oxidative stress injury in failing hearts. Moreover, TXL upregulated cardiac nitrite content and the protein expression of VEGF, p-VEGFR2, p-PI3K, p-Akt, p-eNOS, and HO-1, but decreased Nox4 expression in mouse heart following TAC.

Conclusion

Our findings indicate that TXL protects against pressure overload–induced heart failure in mice. Activation of the VEGF/Akt/eNOS signaling pathway might be involved in TXL improvement of the failing heart.

Mimicking isovolumic contraction with combined electromechanical stimulation improves the development of engineered cardiac constructs

Electrical and mechanical stimulation have both been used extensively to improve the function of cardiac engineered tissue as each of these stimuli is present in the physical environment during normal development in vivo. However, to date, there has been no direct comparison between electrical and mechanical stimulation and current published data are difficult to compare due to the different systems used to create the engineered cardiac tissue and the different measures of functionality studied as outcomes. The goals of this study were twofold. First, we sought to directly compare the effects of mechanical and electrical stimulation on engineered cardiac tissue. Second, we aimed to determine the importance of the timing of the two stimuli in relation to each other in combined electromechanical stimulation. We hypothesized that delaying electrical stimulation after the beginning of mechanical stimulation to mimic the biophysical environment present during isovolumic contraction would improve construct function by improving proteins responsible for cell-cell communication and contractility. To test this hypothesis, we created a bioreactor system that would allow us to electromechanically stimulate engineered tissue created from neonatal rat cardiac cells entrapped in fibrin gel during 2 weeks in culture. Contraction force was higher for all stimulation groups as compared with the static controls, with the delayed combined stimulation constructs having the highest forces. Mechanical stimulation alone displayed increased final cell numbers but there were no other differences between electrical and mechanical stimulation alone. Delayed combined stimulation resulted in an increase in SERCA2a and troponin T expression levels, which did not happen with synchronous combined stimulation, indicating that the timing of combined stimulation is important to maximize the beneficial effect. Increases in Akt protein expression levels suggest that the improvements are at least in part induced by hypertrophic growth. In summary, combined electromechanical stimulation can create engineered cardiac tissue with improved functional properties over electrical or mechanical stimulation alone, and the timing of the combined stimulation greatly influences its effects on engineered cardiac tissue.

Cardioprotective effects of dietary lipids evident in the time-dependent alterations of cardiac function and gene expression following myocardial infarction

We have previously shown that prolonged high–saturated fat feeding (SAT) for 8 weeks after myocardial infarction (MI) improves ventricular function and prevents the metabolic remodeling commonly observed in heart failure. The current study was designed to delineate the interplay between markers of energy metabolism and indices of cardiac remodeling with 2 and 4 weeks of post‐MI SAT in male Wistar rats. By 2 weeks, less remodeling was noted in MI‐SAT evidenced by diminished chamber dilation and greater ejection fraction assessed by echocardiography and hemodynamic measures. In addition, gene expression of energy metabolism targets involved in FA uptake, oxidation, and glucose oxidation regulation was increased in MI‐SAT with respect to MI alone, although no change in PDH phosphorylation was observed. The regulatory kinase, phosphoinositide 3 kinase (Pi3k), was strongly induced by 2 weeks in the MI‐SAT group, although AKT protein content (a primary downstream target of PI3K that affects metabolism) was decreased by both MI and SAT alone, indicating early involvement of cellular signaling pathways in lipid‐mediated cardioprotection. Our results demonstrate that cardioprotection occurs acutely with SAT following MI, with improvement in indices of both cardiac function and fatty acid oxidation, suggesting a mechanistic role for energy metabolism in the beneficial effects of high dietary fat following cardiac injury.

e12019

A diet rich in saturated fats is cardioprotective after myocardial infarction. The cardioprotective effect is noted by 2 weeks and includes functional and genomic changes indicative of a relationship with preservation of metabolic flexibility.

Bioreducible polymers for therapeutic gene delivery

Most currently available cationic polymers have significant acute toxicity concerns such as cellular toxicity, aggregation of erythrocytes, and entrapment in the lung capillary bed, largely due to their poor biocompatibility and non-degradability under physiological conditions. To develop more intelligent polymers, disulfide bonds are introduced in the design of biodegradable polymers. Herein, the sustained innovations of biomimetic nano-sized constructs with bioreducible poly(disulfide amine)s demonstrate a viable clinical tool for the treatment of cardiovascular disease, anemia, diabetes, and cancer.

Nitrite therapy improves left ventricular function during heart failure via restoration of nitric oxide-mediated cytoprotective signaling

RATIONALE

Nitric oxide (NO) bioavailability is reduced in the setting of heart failure. Nitrite (NO2) is a critically important NO intermediate that is metabolized to NO during pathological states. We have previously demonstrated that sodium nitrite ameliorates acute myocardial ischemia/reperfusion injury.

OBJECTIVE

No evidence exists as to whether increasing NO bioavailability via nitrite therapy attenuates heart failure severity after pressure-overload-induced hypertrophy.

METHODS AND RESULTS

Serum from patients with heart failure exhibited significantly decreased nitrosothiol and cGMP levels. Transverse aortic constriction was performed in mice at 10 to 12 weeks. Sodium nitrite (50 mg/L) or saline vehicle was administered daily in the drinking water postoperative from day 1 for 9 weeks. Echocardiography was performed at baseline and at 1, 3, 6, and 9 weeks after transverse aortic constriction to assess left ventricular dimensions and ejection fraction. We observed increased cardiac nitrite, nitrosothiol, and cGMP levels in mice treated with nitrite. Sodium nitrite preserved left ventricular ejection fraction and improved left ventricular dimensions at 9 weeks (P<0.001 versus vehicle). In addition, circulating and cardiac brain natriuretic peptide levels were attenuated in mice receiving nitrite (P<0.05 versus vehicle). Western blot analyses revealed upregulation of Akt-endothelial nitric oxide-nitric oxide-cGMP-GS3Kβ signaling early in the progression of hypertrophy and heart failure.

CONCLUSIONS

These results support the emerging concept that nitrite therapy may be a viable clinical option for increasing NO levels and may have a practical clinical use in the treatment of heart failure.

Thyroid Hormone-Regulated Cardiac microRNAs are Predicted to Suppress Pathological Hypertrophic Signaling

Cardiomyocyte size in the healthy heart is in part determined by the level of circulating thyroid hormone (TH). Higher levels of TH induce ventricular hypertrophy, primarily in response to an increase in hemodynamic load. Normal cardiac function is maintained in this form of hypertrophy, whereas progressive contractile dysfunction is a hallmark of pathological hypertrophy. MicroRNAs (miRNAs) are important modulators of signal-transduction pathways driving adverse remodeling. Because little is known about the involvement of miRNAs in cardiac TH action and hypertrophy, we examined the miRNA expression profile of the hypertrophied left ventricle (LV) using a mouse model of TH-induced cardiac hypertrophy. C57Bl/6J mice were rendered hypothyroid by treatment with propylthiouracil and were subsequently treated for 3 days with TH (T3) or saline. T3 treatment increased LV weight by 38% (p < 0.05). RNA was isolated from the LV and expression of 641 mouse miRNAs was determined using Taqman Megaplex arrays. Data were analyzed using RQ-manager and DataAssist. A total of 52 T3-regulated miRNAs showing a >2-fold change (p < 0.05) were included in Ingenuity Pathway Analysis to predict target mRNAs involved in cardiac hypertrophy. The analysis was further restricted to proteins that have been validated as key factors in hypertrophic signal transduction in mouse models of ventricular remodeling. A total of 27 mRNAs were identified as bona fide targets. The predicted regulation of 19% of these targets indicates enhancement of physiological hypertrophy, while 56% indicates suppression of pathological remodeling. Our data suggest that cardiac TH action includes a novel level of regulation in which a unique set of TH-dependent miRNAs primarily suppresses pathological hypertrophic signaling. This may be relevant for our understanding of the progression of adverse remodeling, since cardiac TH levels are known to decrease substantially in various forms of pathological hypertrophy.

Loss of the AE3 Cl(-)/HCO(-) 3 exchanger in mice affects rate-dependent inotropy and stress-related AKT signaling in heart

Cl(-)/HCO(-) 3 exchangers are expressed abundantly in cardiac muscle, suggesting that HCO(-) 3 extrusion serves an important function in heart. Mice lacking Anion Exchanger Isoform 3 (AE3), a major cardiac Cl(-)/HCO(-) 3 exchanger, appear healthy, but loss of AE3 causes decompensation in a hypertrophic cardiomyopathy (HCM) model. Using intra-ventricular pressure analysis, in vivo pacing, and molecular studies we identified physiological and biochemical changes caused by loss of AE3 that may contribute to decompensation in HCM. AE3-null mice had normal cardiac contractility under basal conditions and after β-adrenergic stimulation, but pacing of hearts revealed that frequency-dependent inotropy was blunted, suggesting that AE3-mediated HCO(-) 3 extrusion is required for a robust force-frequency response (FFR) during acute biomechanical stress in vivo. Modest changes in expression of proteins that affect Ca(2+)-handling were observed, but Ca(2+)-transient analysis of AE3-null myocytes showed normal twitch-amplitude and Ca(2+)-clearance. Phosphorylation and expression of several proteins implicated in HCM and FFR, including phospholamban (PLN), myosin binding protein C, and troponin I were not altered in hearts of paced AE3-null mice; however, phosphorylation of Akt, which plays a central role in mechanosensory signaling, was significantly higher in paced AE3-null hearts than in wild-type controls and phosphorylation of AMPK, which is affected by Akt and is involved in energy metabolism and some cases of HCM, was reduced. These data show loss of AE3 leads to impaired rate-dependent inotropy, appears to affect mechanical stress-responsive signaling, and reduces activation of AMPK, which may contribute to decompensation in heart failure.

Chronic alcohol consumption disrupts myocardial protein balance and function in aged, but not adult, female F344 rats

The purpose of this study was to assess whether the deleterious effect of chronic alcohol consumption differs in adult and aged female rats. To address this aim, adult (4 mo) and aged (18 mo) F344 rats were fed a nutritionally complete liquid diet containing alcohol (36% total calories) or an isocaloric isonitrogenous control diet for 20 wk. Cardiac structure and function, assessed by echocardiography, as well as myocardial protein synthesis and proteolysis did not differ in either alcohol- versus control-fed adult rats or in adult versus aged control-fed rats. In contrast, cardiac function was impaired in alcohol-fed aged rats compared with age-matched control rats. Additionally, alcohol feeding decreased cardiac protein synthesis that was associated with decreased phosphorylation of 4E-BP1 and S6K1. This reduction in mammalian target of rapamycin (mTOR) kinase activity was associated with reduced eIF3f and binding of both Raptor and eIF4G to eIF3. Proteasome activity was increased in alcohol-fed aged rats with a coordinate elevation in the E3 ligases atrogin-1 and muscle RING-finger protein-1 (MuRF1). These changes were associated with increased regulated in development and DNA damage response 1 (REDD1) and phosphorylation of AMP-activated protein kinase (AMPK) but no increase in AKT or forkhead transcription factor (FOXO)3 phosphorylation. Finally, markers of autophagy (e.g., LC3B, Atg7, Atg12) and TNF-α were increased to a greater extent in alcohol-fed aged rats. These data demonstrate that aged female rats exhibit an enhanced sensitivity to alcohol compared with adult animals. Our data are consistent with a model whereby alcohol increases proteolysis via FOXO-independent increase in atrogin-1, which degrades eIF3f and therefore impairs formation of a functional preinitiation complex and protein synthesis.

Molecular aspects of the cardioprotective effect of exercise in the elderly

Aging is a well-recognized risk factor for several different forms of cardiovascular disease. However, mechanisms by which aging exerts its negative effect on outcome have been only partially clarified. Numerous evidence indicate that aging is associated with alterations of several mechanisms whose integrity confers protective action on the heart and vasculature. The present review aims to focus on the beneficial effects of exercise, which plays a pivotal role in primary and secondary prevention of cardiovascular diseases, in counteracting age-related deterioration of protective mechanisms that are crucially involved in the homeostasis of cardiovascular system. In this regard, animal and human studies indicate that exercise training is able: (1) to improve the inotropic reserve of the aging heart through restoration of cardiac β-adrenergic receptor signaling; (2) to rescue the mechanism of cardiac preconditioning and angiogenesis whose integrity has been shown to confer cardioprotection against ischemia and to improve post-myocardial infarction left ventricular remodeling; (3) to counteract age-related reduction of antioxidant systems that is associated to decreased cellular resistance to reactive oxygen species accumulation. Moreover, this review also describes the molecular effects induced by different exercise training protocols (endurance vs. resistance) in the attempt to better explain what kind of exercise strategy could be more efficacious to improve cardiovascular performance in the elderly population.

GDNF-independent ureteric budding: role of PI3K-independent activation of AKT and FOSB/JUN/AP-1 signaling

A significant fraction of mice deficient in either glial cell-derived neurotrophic factor (GDNF) or its co-receptors (Gfrα1, Ret), undergoes ureteric bud (UB) outgrowth leading to the formation of a rudimentary kidney. Previous studies using the isolated Wolffian duct (WD) culture indicate that activation of fibroblast growth factor (FGF) receptor signaling, together with suppression of BMP/Activin signaling, is critical for GDNF-independent WD budding (Maeshima et al., 2007). By expression analysis of embryonic kidney from Ret((-/-)) mice, we found the upregulation of several FGFs, including FGF7. To examine the intracellular pathways, we then analyzed GDNF-dependent and GDNF-independent budding in the isolated WD culture. In both conditions, Akt activation was found to be important; however, whereas this occurred through PI3-kinase in GDNF-dependent budding, in the case of GDNF-independent budding, Akt activation was apparently via a PI3-kinase independent mechanism. Jnk signaling and the AP-1 transcription factor complex were also implicated in GDNF-independent budding. FosB, a binding partner of c-Jun in the formation of AP-1, was the most highly upregulated gene in the ret knockout kidney (in which budding had still occurred), and we found that its siRNA-mediated knockdown in isolated WDs also blocked GDNF-independent budding. Taken together with the finding that inhibition of Jnk signaling does not block Akt activation/phosphorylation in GDNF-independent budding, the data support necessary roles for both FosB/Jun/AP-1 signaling and PI3-kinase-independent activation of Akt in GDNF-independent budding. A model is proposed for signaling events that involve Akt and JNK working to regulate GDNF-independent WD budding.

Puerarin attenuates pressure overload-induced cardiac hypertrophy

BACKGROUND

Puerarin is the most abundant isoflavonoid in kudzu root. It has been used to treat angina pectoris and myocardial infarction clinically. However, little is known about the effect of puerarin on cardiac hypertrophy.

METHODS

Aortic banding (AB) was performed to induce cardiac hypertrophy in mice. Puerarin premixed in diets was administered to mice after one week of AB. Echocardiography and catheter-based measurements of hemodynamic parameters were performed at 7 weeks after starting puerarin treatment (8 weeks post-surgery). The extent of cardiac hypertrophy was also evaluated by pathological and molecular analyses of heart samples. Cardiomyocyte apoptosis was assessed by measuring Bax and Bcl-2 protein expression and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. In addition, the inhibitory effect of puerarin (1 μM, 5 μM, 10 μM, 20 μM, 40 μM) on mRNA expression of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in Ang II (1 μM)-stimulated H9c2 cells was investigated using quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

Echocardiography and catheter-based measurements of hemodynamic parameters at 7 weeks revealed the amelioration of systolic and diastolic abnormalities. Puerarin also decreased cardiac fibrosis in AB mice. Moreover, the beneficial effect of puerarin was associated with the normalization in gene expression of hypertrophic and fibrotic markers. Further studies showed that pressure overload significantly induced the activation of phosphoinositide 3-kinase (PI3K)/Akt signaling and c-Jun N-terminal kinase (JNK) signaling, which was blocked by puerarin treatment. Cardiomyocyte apoptosis and induction of Bax in response to AB were suppressed by puerarin. Furthermore, the increased mRNA expression of ANP and BNP induced by Ang II (1 μM) was restrained to a different extent by different concentrations of puerarin.

CONCLUSION

Puerarin may have an ability to retard the progression of cardiac hypertrophy and apoptosis which is probably mediated by the blockade of PI3K/Akt and JNK signaling pathways.

Dipeptidylpeptidase inhibition is associated with improvement in blood pressure and diastolic function in insulin-resistant male Zucker obese rats

Diastolic dysfunction is a prognosticator for future cardiovascular events that demonstrates a strong correlation with obesity. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon-like peptide-1 is an emerging therapy for control of glycemia in type 2 diabetes patients. Accumulating evidence suggests that glucagon-like peptide-1 has insulin-independent actions in cardiovascular tissue. However, it is not known whether DPP-4 inhibition improves obesity-related diastolic dysfunction. Eight-week-old Zucker obese (ZO) and Zucker lean rats were fed normal chow diet or diet containing the DPP-4 inhibitor, linagliptin (LGT), for 8 weeks. Plasma DPP-4 activity was 3.3-fold higher in ZO compared with Zucker lean rats and was reduced by 95% with LGT treatment. LGT improved echocardiographic and pressure volume-derived indices of diastolic function that were impaired in ZO control rats, without altering food intake or body weight gain during the study period. LGT also blunted elevated blood pressure progression in ZO rats involving improved skeletal muscle arteriolar function, without reducing left ventricular hypertrophy, fibrosis, or oxidative stress in ZO hearts. Expression of phosphorylated- endothelial nitric oxide synthase (eNOS)(Ser1177), total eNOS, and sarcoplasmic reticulum calcium ATPase 2a protein was elevated in the LGT-treated ZO heart, suggesting improved Ca(2+) handling. The ZO myocardium had an abnormal mitochondrial sarcomeric arrangement and cristae structure that were normalized by LGT. These studies suggest that LGT reduces blood pressure and improves intracellular Cai(2+) mishandling and cardiomyocyte ultrastructure, which collectively result in improvements in diastolic function in the absence of reductions in left ventricular hypertrophy, fibrosis, or oxidative stress in insulin-resistant ZO rats.

The effects of neuregulin on cardiac Myosin light chain kinase gene-ablated hearts

BACKGROUND

Activation of ErbB2/4 receptor tyrosine kinases in cardiomyocytes by neuregulin treatment is associated with improvement in cardiac function, supporting its use in human patients with heart failure despite the lack of a specific mechanism. Neuregulin infusion in rodents increases cardiac myosin light chain kinase (cMLCK) expression and cardiac myosin regulatory light chain (RLC) phosphorylation which may improve actin-myosin interactions for contraction. We generated a cMLCK knockout mouse to test the hypothesis that cMLCK is necessary for neuregulin-induced improvement in cardiac function by increasing RLC phosphorylation.

PRINCIPAL FINDINGS

The cMLCK knockout mice have attenuated RLC phosphorylation and decreased cardiac performance measured as fractional shortening. Neuregulin infusion for seven days in wildtype mice increased cardiac cMLCK protein expression and RLC phosphorylation while increasing Akt phosphorylation and decreasing phospholamban phosphorylation. There was no change in fractional shortening. In contrast, neuregulin infusion in cMLCK knockout animals increased cardiac performance in the absence of cMLCK without increasing RLC phosphorylation. In addition, CaMKII signaling appeared to be enhanced in neuregulin-treated knockout mice.

CONCLUSIONS

Thus, Neuregulin may improve cardiac performance in the failing heart without increasing cMLCK and RLC phosphorylation by activating other signaling pathways.

CpG-ODN attenuates pathological cardiac hypertrophy and heart failure by activation of PI3Kα-Akt signaling

Phosphoinositide-3-kinase α (PI3Kα) represents a potential novel drug target for pathological cardiac hypertrophy (PCH) and heart failure. Oligodeoxynucleotides containing CpG motifs (CpG-ODN) are classic agonists of Toll-like receptor 9 (TLR9), which typically activates PI3K-Akt signaling in immune cells; however, the role of the nucleotide TLR9 agonists in cardiac myocytes is largely unknown. Here we report that CpG-ODN C274 could both attenuate PCH and improve cardiac dysfunction by activating PI3Kα-Akt signaling cascade. In vitro studies indicated that C274 could blunt reactivation of fetal cardiac genes and cell enlargement induced by a hypertrophic agent, isoproterenol. The anti-hypertrophic effect of C274 was suppressed by a pan-PI3K inhibitor, LY294002, or a small interfering RNA targeting PI3Kα. In vivo studies demonstrated that PCH, as marked by increased heart weight (HW) and cardiac ANF mRNA, was normalized by pre-administration with C274. In addition, Doppler echocardiography detected cardiac ventricular dilation, and contractile dysfunction in isoproterenol-treated animals, consistent with massive replacement fibrosis, reflecting cardiac cell death. As expected, pre-treatment of mice with C274 could prevent cardiac dysfunction associated with diminished cardiac cell death and fibrosis. In conclusion, CpG-ODNs are novel cardioprotective agents possessing antihypertrophic and anti-cell death activity afforded by engagement of the PI3Kα-Akt signaling. CpG-ODNs may have clinical use curbing the progression of PCH and preventing heart failure.

Primary proteasome inhibition results in cardiac dysfunction

AIMS

The proteasome prevents the intracellular accumulation of proteins and its impairment can lead to structural and functional alterations, as noted for the coronary vasculature in a previous study. Utilizing the same model, this study was designed to test the hypothesis that chronic proteasome inhibition (PSI) also leads to structural and functional changes of the heart.

METHODS AND RESULTS

Female domestic pigs were randomized to a normal diet without (N) or with twice-weekly subcutaneous injections of the proteasome inhibitor MLN-273 (0.08 mg/kg, N + PSI, n = 5 each group). In vivo data on cardiac structure and function as well as myocardial perfusion and microvascular permeability response to adenosine and dobutamine were obtained by electron beam computed tomography after 11 weeks. Subsequent ex vivo myocardial analyses included immunoblotting, immunostaining, TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labelling), Masson trichrome, and Congo red staining. Compared with N, an increase in LV mass was observed in N + PSI (106.5 ± 16.4 g vs. 183.1 ± 24.2 g, P < 0.05). The early to late diastolic filling ratio was increased in N + PSI vs. N (3.5 ± 0.6 vs. 1.8 ± 0.1, P < 0.05). The EF tended to be lower (46 ± 12% and 53 ± 9%, respectively) and cardiac output was significantly lower in N + PSI than in N (2.9 ± 1.1 vs. 4.7 ± 1.1 L/min, P < 0.05). Tissue analyses demonstrated an accumulation of proteasome substrates, apoptosis, and fibrosis in the PSI group. Compared with N, the myocardial perfusion response was reduced and microvascular permeability was increased in N + PSI.

CONCLUSION

The current study demonstrates that chronic proeasome inhibition affects the cardiovascular system, leading to functional and structural alteration of the heart consistent with a hypertrophic-restrictive cardiomyopathy phenotype.

Neuregulin-1 protects against doxorubicin-induced apoptosis in cardiomyocytes through an Akt-dependent pathway

In previous studies, it has been shown that recombinant human neuregulin-1(rhNRG-1) is capable of improving the survival rate in animal models of doxorubicin (DOX)-induced cardiomyopathy; however, the underlying mechanism of this phenomenon remains unknown. In this study, the role of rhNRG-1 in attenuating doxorubicin-induce apoptosis is confirmed. Neonatal rat ventricular myocytes (NRVMs) were subjected to various treatments, in order to both induce apoptosis and determine the effects of rhNRG-1 on the process. Activation of apoptosis was determined by observing increases in the protein levels of classic apoptosis markers (including cleaved caspase-3, cytochrome c, Bcl-2, BAX and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining). The activation of Akt was detected by means of western blot analysis. The study results showed that doxorubicin increased the number of TUNEL positive cells, as well as the protein levels of cleaved caspase-3 and cytochrome c, and reduced the ratio of Bcl-2/Bax. However, all of these effects were markedly antagonized by pretreament with rhNRG-1. It was then further demonstrated that the effects of rhNRG-1 could be blocked by the phosphoinositole-3-kinase inhibitor LY294002, indicating the involvement of the Akt process in mediating the process. RhNRG-1 is a potent inhibitor of doxorubicin-induced apoptosis, which acts through the PI3K-Akt pathway. RhNRG-1 is a novel therapeutic drug which may be effective in preventing further damage from occurring in DOX-induced damaged myocardium.

Ageing as a risk factor for disease

Age is the main risk factor for the prevalent diseases of developed countries: cancer, cardiovascular disease and neurodegeneration. The ageing process is deleterious for fitness, but can nonetheless evolve as a consequence of the declining force of natural selection at later ages, attributable to extrinsic hazards to survival: ageing can then occur as a side-effect of accumulation of mutations that lower fitness at later ages, or of natural selection in favour of mutations that increase fitness of the young but at the cost of a higher subsequent rate of ageing. Once thought of as an inexorable, complex and lineage-specific process of accumulation of damage, ageing has turned out to be influenced by mechanisms that show strong evolutionary conservation. Lowered activity of the nutrient-sensing insulin/insulin-like growth factor/Target of Rapamycin signalling network can extend healthy lifespan in yeast, multicellular invertebrates, mice and, possibly, humans. Mitochondrial activity can also promote ageing, while genome maintenance and autophagy can protect against it. We discuss the relationship between evolutionarily conserved mechanisms of ageing and disease, and the associated scientific challenges and opportunities.

H₂S protects against pressure overload-induced heart failure via upregulation of endothelial nitric oxide synthase

BACKGROUND

Cystathionine γ-lyase (CSE) produces H2S via enzymatic conversion of L-cysteine and plays a critical role in cardiovascular homeostasis. We investigated the effects of genetic modulation of CSE and exogenous H2S therapy in the setting of pressure overload-induced heart failure.

METHODS AND RESULTS

Transverse aortic constriction was performed in wild-type, CSE knockout, and cardiac-specific CSE transgenic mice. In addition, C57BL/6J or CSE knockout mice received a novel H2S donor (SG-1002). Mice were followed up for 12 weeks with echocardiography. We observed a >60% reduction in myocardial and circulating H2S levels after transverse aortic constriction. CSE knockout mice exhibited significantly greater cardiac dilatation and dysfunction than wild-type mice after transverse aortic constriction, and cardiac-specific CSE transgenic mice maintained cardiac structure and function after transverse aortic constriction. H2S therapy with SG-1002 resulted in cardioprotection during transverse aortic constriction via upregulation of the vascular endothelial growth factor-Akt-endothelial nitric oxide synthase-nitric oxide-cGMP pathway with preserved mitochondrial function, attenuated oxidative stress, and increased myocardial vascular density.

CONCLUSIONS

Our results demonstrate that H2S levels are decreased in mice in the setting of heart failure. Moreover, CSE plays a critical role in the preservation of cardiac function in heart failure, and oral H2S therapy prevents the transition from compensated to decompensated heart failure in part via upregulation of endothelial nitric oxide synthase and increased nitric oxide bioavailability.

Cathepsin K knockout mitigates high-fat diet-induced cardiac hypertrophy and contractile dysfunction

The cysteine protease cathepsin K has been implicated in pathogenesis of cardiovascular disease. We hypothesized that ablation of cathepsin K protects against obesity-associated cardiac dysfunction. Wild-type mice fed a high-fat diet exhibited elevated heart weight, enlarged cardiomyocytes, increased left ventricular wall thickness, and decreased fractional shortening. All these changes were reconciled in cathepsin K knockout mice. Cathepsin K knockout partly reversed the impaired cardiomyocyte contractility and dysregulated calcium handling associated with high-fat diet. Additionally, cathepsin K knockout alleviated whole-body glucose intolerance and improved insulin-stimulated Akt phosphorylation in high-fat diet-fed mice. High-fat feeding increased the expression of cardiac hypertrophic proteins and apoptotic markers, which were inhibited by cathepsin K knockout. Furthermore, high-fat feeding resulted in cathepsin K release from lysosomes into the cytoplasm. In H9c2 myoblasts, silencing of cathepsin K inhibited palmitic acid-induced release of cytochrome c from mitochondria and expression of proapoptotic signaling molecules. Collectively, our data indicate that cathepsin K contributes to the development of obesity-associated cardiac hypertrophy and may represent a potential target for the treatment to obesity-associated cardiac anomalies.

Role of phosphatidylinositol 3,4,5-trisphosphate in cell signaling

Many lipids present in cellular membranes are phosphorylated as part of signaling cascades and participate in the recruitment, localization, and activation of downstream protein effectors. Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) is one of the most important second messengers and is capable of interacting with a variety of proteins through specific PtdIns(3,4,5)P3 binding domains. Localization and activation of these effector proteins controls a myriad of cellular functions including cell survival, proliferation, cytoskeletal rearrangement, and gene expression. Aberrations in the production and metabolism of PtdIns(3,4,5)P3 have been implicated in many human diseases including cancer, diabetes, inflammation, and heart disease. This chapter provides an overview of the role of PtdIns(3,4,5)P3 in cellular regulation and the implications of PtdIns(3,4,5)P3 dysregulation in human diseases. Additionally, recent attempts at targeting PtdIns(3,4,5)P3 signaling via small molecule inhibitors are summarized.

The orphan receptor TR3 participates in angiotensin II-induced cardiac hypertrophy by controlling mTOR signalling

Angiotensin II (AngII) induces cardiac hypertrophy and increases the expression of TR3. To determine whether TR3 is involved in the regulation of the pathological cardiac hypertrophy induced by AngII, we established mouse and rat hypertrophy models using chronic AngII administration. Our results reveal that a deficiency of TR3 in mice or the knockdown of TR3 in the left ventricle of rats attenuated AngII-induced cardiac hypertrophy compared with the respective controls. A mechanistic analysis demonstrates that the TR3-mediated activation of mTORC1 is associated with AngII-induced cardiac hypertrophy. TR3 was shown to form a trimer with the TSC1/TSC2 complex that specifically promoted TSC2 degradation via a proteasome/ubiquitination pathway. As a result, mTORC1, but not mTORC2, was activated; this was accompanied by increased protein synthesis, enhanced production of reactive oxygen species and enlarged cell size, thereby resulting in cardiac hypertrophy. This study demonstrates that TR3 positively regulates cardiac hypertrophy by influencing the effect of AngII on the mTOR pathway. The elimination or reduction of TR3 may reduce cardiac hypertrophy; therefore, TR3 is a potential target for clinical therapy.

Heart failure highlights in 2011

Heart failure (HF) remains a major medical problem, and the European Journal of Heart Failure is dedicated to publishing research further investigating its pathophysiology and diagnosis in order to help clinicians alleviate symptoms and improve patient outcomes.( 1) This review reports on important studies in the field of HF published in 2011. All research areas are addressed, including experimental studies, biomarkers, clinical trials, arrhythmias, and new insights into the role of device therapy.

Stem cell antigen 1 protects against cardiac hypertrophy and fibrosis after pressure overload

Stem cell antigen (Sca) 1, a glycosyl phosphatidylinositol-anchored protein localized to lipid rafts, is upregulated in the heart during myocardial infarction and renovascular hypertension-induced cardiac hypertrophy. It has been suggested that Sca-1 plays an important role in myocardial infarction. To investigate the role of Sca-1 in cardiac hypertrophy, we performed aortic banding in Sca-1 cardiac-specific transgenic mice, Sca-1 knockout mice, and their wild-type littermates. Cardiac hypertrophy was evaluated by echocardiographic, hemodynamic, pathological, and molecular analyses. Sca-1 expression was upregulated and detected in cardiomyocytes after aortic banding surgery in wild-type mice. Sca-1 transgenic mice exhibited significantly attenuated cardiac hypertrophy and fibrosis and preserved cardiac function compared with wild-type mice after 4 weeks of aortic banding. Conversely, Sca-1 knockout dramatically worsened cardiac hypertrophy, fibrosis, and dysfunction after pressure overload. Furthermore, aortic banding-induced activation of Src, mitogen-activated protein kinases, and Akt was blunted by Sca-1 overexpression and enhanced by Sca-1 deficiency. Our results suggest that Sca-1 protects against cardiac hypertrophy and fibrosis via regulation of multiple pathways in cardiomyocytes.

Nuclear inositol 1,4,5-trisphosphate is a necessary and conserved signal for the induction of both pathological and physiological cardiomyocyte hypertrophy

It is well established that inositol 1,4,5-trisphosphate (IP3) dependent Ca(2+) signaling plays a crucial role in cardiomyocyte hypertrophy. However, it is not yet known whether nuclear IP3 represents a Ca(2+) mobilizing pathway involved in this process. The goal of the current work was to investigate the specific role of nuclear IP3 in cardiomyocyte hypertrophic response. In this work, we used an adenovirus construct that selectively buffers IP3 in the nuclear region of neonatal cardiomyocytes. We showed for the first time that nuclear IP3 mediates endothelin-1 (ET-1) induced hypertrophy. We also found that both calcineurin (Cn)/nuclear factor of activated T Cells (NFAT) and histone deacetylase-5 (HDAC5) pathways require nuclear IP3 to mediate pathological cardiomyocyte growth. Additionally, we found that nuclear IP3 buffering inhibited insulin-like growth factor-1 (IGF-1) induced hypertrophy and prevented reexpression of fetal gene program. Together, these results demonstrated that nuclear IP3 is an essential and a conserved signal for both pathological and physiological forms of cardiomyocyte hypertrophy.

Cancer Therapy Targeting the HER2-PI3K Pathway: Potential Impact on the Heart

The HER2-PI3K pathway is the one of the most mutated pathways in cancer. Several drugs targeting the major kinases of this pathway have been approved by the Food and Drug Administration and many are being tested in clinical trials for the treatment of various cancers. However, the HER2-PI3K pathway is also pivotal for maintaining the physiological function of the heart, especially in the presence of cardiac stress. Clinical studies have shown that in patients treated with doxorubicin concurrently with Trastuzumab, a monoclonal antibody that blocks the HER2 receptor, the New York Heart Association class III/IV heart failure was significantly increased compared to those who were treated with doxorubicin alone (16 vs. 3%). Studies in transgenic mice have also shown that other key kinases of this pathway, such as PI3Kα, PDK1, Akt, and mTOR, are important for protecting the heart from ischemia-reperfusion and aortic stenosis induced cardiac dysfunction. Studies, however, have also shown that inhibition of PI3Kγ improve cardiac function of a failing heart. In addition, results from transgenic mouse models are not always consistent with the outcome of the pharmacological inhibition of this pathway. Here, we will review these findings and discuss how we can address the cardiac side-effects caused by inhibition of this important pathway in both cancer and cardiac biology.

Disruption of mindin exacerbates cardiac hypertrophy and fibrosis

Cardiac hypertrophy is a response of the myocardium to increased workload and is characterised by an increase of myocardial mass and an accumulation of extracellular matrix (ECM). As an ECM protein, an integrin ligand, and an angiogenesis inhibitor, all of which are key players in cardiac hypertrophy, mindin is an attractive target for therapeutic intervention to treat or prevent cardiac hypertrophy and heart failure. In this study, we investigated the role of mindin in cardiac hypertrophy using littermate Mindin knockout (Mindin ( -/- )) and wild-type (WT) mice. Cardiac hypertrophy was induced by aortic banding (AB) or angiotensin II (Ang II) infusion in Mindin ( -/- ) and WT mice. The extent of cardiac hypertrophy was quantitated by echocardiography and by pathological and molecular analyses of heart samples. Mindin ( -/- ) mice were more susceptible to cardiac hypertrophy and fibrosis in response to AB or Ang II stimulation than wild type. Cardiac function was also markedly exacerbated during both systole and diastole in Mindin ( -/- ) mice in response to hypertrophic stimuli. Western blot assays further showed that the activation of AKT/glycogen synthase kinase 3β (GSK3β) signalling in response to hypertrophic stimuli was significantly increased in Mindin ( -/- ) mice. Moreover, blocking AKT/GSK3β signalling with a pharmacological AKT inhibitor reversed cardiac abnormalities in Mindin ( -/- ) mice. Our data show that mindin, as an intrinsic cardioprotective factor, prevents maladaptive remodelling and the transition to heart failure by blocking AKT/GSK3β signalling.