Nuclear targeting of Akt enhances kinase activity and survival of cardiomyocytes

Mineralocorticoid receptor antagonism attenuates vascular apoptosis and injury via rescuing protein kinase B activation

Emerging evidence indicates that mineralocorticoid receptor (MR) blockade reduces the risk of cardiovascular events beyond those predicted by its blood pressure-lowering actions; however, the underlying mechanisms remain unclear. To investigate whether protection elicited by MR blockade is through attenuation of vascular apoptosis and injury, independently of blood pressure lowering, we administered a low dose of the MR antagonist spironolactone or vehicle for 21 days to hypertensive transgenic Ren2 rats with elevated plasma aldosterone levels. Although Ren2 rats developed higher systolic blood pressures compared with Sprague-Dawley littermates, low-dose spironolactone treatment did not reduce systolic blood pressure compared with untreated Ren2 rats. Ren2 rats exhibited vascular injury as evidenced by increased apoptosis, hemidesmosome-like structure loss, mitochondrial abnormalities, and lipid accumulation compared with Sprague-Dawley rats, and these abnormalities were attenuated by MR antagonism. Protein kinase B activation is critical to vascular homeostasis via regulation of cell survival and expression of apoptotic genes. Protein kinase B serine(473) phosphorylation was impaired in Ren2 aortas and restored with MR antagonism. In vivo MR antagonist treatment promoted antiapoptotic effects by increasing phosphorylation of BAD serine(136) and expression of Bcl-2 and Bcl-xL, decreasing cytochrome c release and BAD expression, and suppressing caspase-3 activation. Furthermore, MR antagonism substantially reduced the elevated NADPH oxidase activity and lipid peroxidation, expression of angiotensin II, angiotensin type 1 receptor, and MR in Ren2 vasculature. These results demonstrate that MR antagonism protects the vasculature from aldosterone-induced vascular apoptosis and structural injury via rescuing protein kinase B activation, independent of blood pressure effects.

Are transgenic mice the 'alkahest' to understanding myocardial hypertrophy and failure?

Murine transgenesis using cardioselective promoters has become increasingly common in studies of cardiac hypertrophy and heart failure, with expression mediated by pronuclear microinjection being the commonest format. Without wishing to decry their usefulness, in our view, such studies are not necessarily as unambiguous as sometimes portrayed and clarity is not always their consequence. We describe broadly the types of approach undertaken in the heart and point out some of the drawbacks. We provide three arbitrarily-chosen examples where, in spite of a number of often-independent studies, no consensus has yet been achieved. These include glycogen synthase kinase 3, the extracellular signal-regulated kinase pathway and the ryanodine receptor 2. We believe that the transgenic approach should not be viewed in an empyreal light and, depending on the questions asked, we suggest that other experimental systems provide equal (or even more) valuable outcomes.

Pim-1 kinase antagonizes aspects of myocardial hypertrophy and compensation to pathological pressure overload

Pim-1 kinase exerts potent cardioprotective effects in the myocardium downstream of AKT, but the participation of Pim-1 in cardiac hypertrophy requires investigation. Cardiac-specific expression of Pim-1 (Pim-WT) or the dominant-negative mutant of Pim-1 (Pim-DN) in transgenic mice together with adenoviral-mediated overexpression of these Pim-1 constructs was used to delineate the role of Pim-1 in hypertrophy. Transgenic overexpression of Pim-1 protects mice from pressure-overload-induced hypertrophy relative to wild-type controls as evidenced by improved hemodynamic function, decreased apoptosis, increases in antihypertrophic proteins, smaller myocyte size, and inhibition of hypertrophic signaling after challenge. Similarly, Pim-1 overexpression in neonatal rat cardiomyocyte cultures inhibits hypertrophy induced by endothelin-1. On the cellular level, hearts of Pim-WT mice show enhanced incorporation of BrdU into myocytes and a hypercellular phenotype compared to wild-type controls after hypertrophic challenge. In comparison, transgenic overexpression of Pim-DN leads to dilated cardiomyopathy characterized by increased apoptosis, fibrosis, and severely depressed cardiac function. Furthermore, overexpression of Pim-DN leads to reduced contractility as evidenced by reduced Ca(2+) transient amplitude and decreased percentage of cell shortening in isolated myocytes. These data support a pivotal role for Pim-1 in modulation of hypertrophy by impacting responses on molecular, cellular, and organ levels.

Molecular mechanisms underlying the transition of cardiac hypertrophy to heart failure

Heart failure is a condition in which the heart cannot supply enough blood to the body's organs, and is a final common consequence of various heart diseases. In the past 2 decades, much progress has been made in understanding the molecular and cellular processes that contribute to cardiac hypertrophy and heart failure, leading to the development of effective therapies. However, heart failure remains a leading cause of mortality worldwide and the precise molecular mechanisms that mediate the transition of cardiac hypertrophy to heart failure are largely undefined. This review discusses the potential mechanisms of heart failure progression focusing on (1) cardiac myocyte loss, (2) abnormalities of calcium handling, and (3) myocardial ischemia and hypoxia. These factors are closely related, and are considered to contribute to the pathogenesis of contractile dysfunction and heart failure in a cooperative manner. Elucidation of the molecular mechanisms underlying the transition of cardiac hypertrophy to heart failure will lead to the development of novel therapeutic strategies for heart diseases.

Temporally controlled overexpression of cardiac-specific PI3Kalpha induces enhanced myocardial contractility--a new transgenic model

The phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates multiple cellular processes including cell survival/apoptosis and growth. In the cardiac context, PI3Kalpha plays important roles in cardiac growth. We have shown that cardiac PI3K activity is highly regulated during development, with the highest levels found during the fetal-neonatal transition period and the lowest levels in the adult. There is a close relationship between cardiomyocyte proliferation and cardiac PI3K activity. In adult transgenic mice, however, the prolonged constitutive activation of PI3Kalpha in the heart results in hypertrophy. To develop a strategy to allow temporally controlled overexpression of cardiac PI3Kalpha, we engineered a tetracycline (tet) transactivator tet-off controlled transgenic mouse line with a conditional overexpression of a cardiac-specific fusion protein of the SH2 domain of p85 and p110alpha. Cardiac PI3K activity and Akt phosphorylation were significantly increased in adult mice after transgene induction following the removal of doxycycline for 2 wk. The heart weight-to-body weight ratio was not changed, and there were no signs of cardiomyopathy. The overexpression of PI3Kalpha resulted in increased left ventricular (LV) developed pressure and the maximal and minimal positive values of the first derivative of LV pressure, but not heart rate, as assessed in Langendorff hearts. Mice overexpressing PI3Kalpha also had increases in the levels of Ca(2+)-regulating proteins, including the L-type Ca(2+) channels, ryanodine receptors, and sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a. Thus the temporally controlled overexpression of cardiac PI3Kalpha does not induce hypertrophy or cardiomyopathy but results in increased contractility, probably via the increased expression of multiple Ca(2+)-regulating proteins. These distinct phenotypes suggest a fundamental difference between transgenic mice with temporal or prolonged activation of cardiac PI3Kalpha.

Blockade of NF-kappaB using IkappaB alpha dominant-negative mice ameliorates cardiac hypertrophy in myotrophin-overexpressed transgenic mice

Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor that regulates various kinds of genes including inflammatory molecules, macrophage infiltration factors, cell adhesion molecules, and so forth, in various disease processes including cardiac hypertrophy and heart failure. Previously, we have demonstrated that activation of NF-kappaB was required in myotrophin-induced cardiac hypertrophy, in spontaneously hypertensive rats, and in dilated cardiomyopathy human hearts. Moreover, our recent study using the myotrophin-overexpressed transgenic mouse (Myo-Tg) model showed that short hairpin RNA-mediated knockdown of NF-kappaB significantly attenuated cardiac mass associated with improved cardiac function. Although it has been shown that NF-kappaB is substantially involved in cardiovascular remodeling, it is not clear whether the continuous blockade of NF-kappaB is effective in cardiovascular remodeling. To address this question, we took a genetic approach using IkappaB alpha triple mutant mice (3M) bred with Myo-Tg mice (a progressive hypertrophy/heart failure model). The double transgenic mice (Myo-3M) displayed an attenuated cardiac hypertrophy (9.8+/-0.62 versus 5.4+/-0.34, p<0.001) and improved cardiac function associated with significant inhibition of the NF-kappaB signaling cascade, hypertrophy marker gene expression, and inflammatory and macrophage gene expression at 24 weeks of age compared to Myo-Tg mice. NF-kappaB-targeted gene array profiling displayed several important genes that were significantly downregulated in Myo-3M mice compared to Myo-Tg mice. Furthermore, Myo-3M did not show any changes of apoptotic gene expression, indicating that significant inhibition of NF-kappaB activation reduces further proinflammatory reactions without affecting susceptibility to apoptosis. Therefore, development of therapeutic strategies targeting NF-kappaB may provide an effective approach to prevent adverse cardiac pathophysiological consequences.

Follistatin-like 1 is an Akt-regulated cardioprotective factor that is secreted by the heart

BACKGROUND

The Akt protein kinase is an important mediator of cardiac myocyte growth and survival. To identify factors with novel therapeutic applications in cardiac diseases, we focused on the identification of factors secreted from Akt1-activated cells that have cardioprotective effects through autocrine/paracrine mechanisms.

METHODS AND RESULTS

Using an inducible Akt1 transgenic mouse model, we have found that follistatin-like 1 (Fstl1) protein and transcript expression are increased 4.0- and 2.0-fold, respectively, by Akt activation in the heart (P<0.05). Fstl1 transcript was also upregulated in response to myocardial stresses including transverse aortic constriction, ischemia/reperfusion injury, and myocardial infarction. Adenovirus-mediated overexpression of Fstl1 protected cultured neonatal rat ventricular myocytes from hypoxia/reoxygenation-induced apoptosis (P<0.01), and this protective effect was dependent on the upregulation of both Akt and ERK activities. Conversely, knockdown of Fstl1 in cardiac myocytes decreased basal Akt signaling and increased the frequency of apoptotic death in vitro (P<0.01). The intravenous administration of an adenoviral encoding Fstl1 to mice resulted in a 66.0% reduction in myocardial infarct size after ischemia/reperfusion injury that was accompanied by a 70.9% reduction in apoptosis in the heart (P<0.01).

CONCLUSIONS

These results indicate that Fstl1 is a cardiac-secreted factor that functions as an antiapoptotic protein. Fstl1 could play a role in myocardial maintenance and repair in response to harmful stimuli.

Tackling heart failure in the twenty-first century

Heart failure, or congestive heart failure, is a condition in which the heart cannot supply the body's tissues with enough blood. The result is a cascade of changes that lead to severe fatigue, breathlessness and, ultimately, death. In the past quarter century, much progress has been made in understanding the molecular and cellular processes that contribute to heart failure, leading to the development of effective therapies. Despite this, chronic heart failure remains a major cause of illness and death. And because the condition becomes more common with increasing age, the number of affected individuals is rising with the rapidly ageing global population. New treatments that target disease mechanisms at the cellular and whole-organ level are needed to halt and reverse the devastating consequences of this disease.

Activation of Notch-mediated protective signaling in the myocardium

The Notch network regulates multiple cellular processes, including cell fate determination, development, differentiation, proliferation, apoptosis, and regeneration. These processes are regulated via Notch-mediated activity that involves hepatocyte growth factor (HGF)/c-Met receptor and phosphatidylinositol 3-kinase/Akt signaling cascades. The impact of HGF on Notch signaling was assessed following myocardial infarction as well as in cultured cardiomyocytes. Notch1 is activated in border zone cardiomyocytes coincident with nuclear c-Met following infarction. Intramyocardial injection of HGF enhances Notch1 and Akt activation in adult mouse myocardium. Corroborating evidence in cultured cardiomyocytes shows treatment with HGF or insulin increases levels of Notch effector Hes1 in immunoblots, whereas overexpression of activated Notch intracellular domain prompts a 3-fold increase in phosphorylated Akt. Infarcted hearts injected with adenoviral vector expressing Notch intracellular domain treatment exhibit improved hemodynamic function in comparison with control mice after 4 weeks, implicating Notch signaling in a cardioprotective role following cardiac injury. These results indicate Notch activation in cardiomyocytes is mediated through c-Met and Akt survival signaling pathways, and Notch1 signaling in turn enhances Akt activity. This mutually supportive crosstalk suggests a positive survival feedback mechanism between Notch and Akt signaling in adult myocardium following injury.

Bromelain induces cardioprotection against ischemia-reperfusion injury through Akt/FOXO pathway in rat myocardium

Bromelain (Br), a proteolytic enzyme extracted from the stem of the pineapple, is known to possess anti-inflammatory activity and has been shown to reduce blood viscosity, prevent the aggregation of blood platelets, and improve ischemia-reperfusion (I/R) injury in a skeletal muscle model. We investigated the capacity of Br to limit myocardial injury in a global I/R model. Adult male Sprague-Dawley rats were divided into two groups: control (PBS) and Br at 10 mg/kg in PBS administered via intraperitoneal injection (twice/day) for 15 consecutive days. On day 16, the hearts were excised and subjected to 30 min of global ischemia followed by 2 h of reperfusion. Br treatment showed higher left ventricular functional recovery throughout reperfusion compared with the controls [maximum rate of rise in intraventricular pressure (dP/d tmax), 2,225 vs. 1,578 mmHg/s at 2 h reperfusion]. Aortic flow was also found to be increased in Br treatment when compared with that in untreated rats (11 vs. 1 ml). Furthermore, Br treatment reduced both the infarct size (34% vs. 43%) and the degree of apoptosis (28% vs. 37%) compared with the control animals. Western blot analysis showed an increased phosphorylation of both Akt and FOXO3A in the treatment group compared with the control. These results demonstrated for the first time that Br triggers an Akt-dependent survival pathway in the heart, revealing a novel mechanism of cardioprotective action and a potential therapeutic target against I/R injury.

"AKT"ing lessons for stem cells: regulation of cardiac myocyte and progenitor cell proliferation

Cardiac development and postnatal growth depend on activation of AKT, but initial strategies to improve myocardial repair using AKT were stymied by undesirable corollary alterations in myocardial structure and function. These unfortunate precedents were based on high-level expression of constitutively activated AKT, predominantly in the cytoplasm of the cell. Based on subsequent studies establishing that activated AKT accumulates in the nucleus, we reasoned that the location of AKT, not simply the activity level, would be a critical determinant of the phenotypic outcome resulting from AKT activation. Using myocardial-specific expression of nuclear-targeted AKT (AKT/nuc), the proliferation of myocardial stem and progenitor cell populations is enhanced, casting new light on the implementation of AKT activity as a molecular interventional approach for treatment of cardiomyopathic damage resulting from acute injury, chronic stress, or the debilitating changes of aging.

Akt mediates mitochondrial protection in cardiomyocytes through phosphorylation of mitochondrial hexokinase-II

Akt activation supports survival of cardiomyocytes against ischemia/reperfusion, which induces cell death through opening of the mitochondrial permeability transition pore (PT-pore). Mitochondrial depolarization induced by treatment of cardiomyocytes with H(2)O(2) is prevented by activation of Akt with leukemia inhibitory factor (LIF). This protective effect is observed even when cardiomyocytes treated with LIF are permeabilized and mitochondrial depolarization is elicited by elevating Ca(2+). Cell fractionation studies demonstrate that LIF treatment increases both total and phosphorylated Akt in the mitochondrial fraction. Furthermore, the association of Akt with HK-II is increased by LIF. HK-II contains consensus sequences for phosphorylation by Akt and LIF treatment induces PI3K- and Akt-dependent HK-II phosphorylation. Addition of recombinant kinase-active Akt to isolated adult mouse heart mitochondria stimulates phosphorylation of HK-II and concomitantly inhibits the ability of Ca(2+) to induce cytochrome c release. This protection is prevented when HK-II is dissociated from mitochondria by incubation with glucose 6-phosphate or HK-II-dissociating peptide. Finally LIF increases HK-II association with mitochondria and dissociation of HK-II from mitochondria attenuates the protective effect of LIF on H(2)O(2)-induced mitochondrial depolarization in cardiomyocytes. We conclude that Akt has a direct effect at the level of the mitochondrion, which is mediated via phosphorylation of HK-II and results in protection of mitochondria against oxidant or Ca(2+)-stimulated PT-pore opening.

Akt is transferred to the nucleus of cells treated with apoptin, and it participates in apoptin-induced cell death

OBJECTIVES

The phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is well known for the regulation of cell survival, proliferation, and some metabolic routes.

MATERIALS AND METHODS

In this study, we document a novel role for the PI3-K/Akt pathway during cell death induced by apoptin, a tumour-selective inducer of apoptosis.

RESULTS

We show for the first time that apoptin interacts with the p85 regulatory subunit, leading to constitutive activation of PI3-K. The inhibition of PI3-K activation either by chemical inhibitors or by genetic approaches severely impairs cell death induced by apoptin. Downstream of PI3-K, Akt is activated and translocated to the nucleus together with apoptin. Direct interaction between apoptin and Akt is documented. Co-expression of nuclear Akt significantly potentiates cell death induced by apoptin. Thus, apoptin-facilitated nuclear Akt, in contrast to when in its cytoplasmic pool, appears to be a positive regulator, rather than repressor of apoptosis.

CONCLUSIONS

Our observations indicate that PI3-K/Akt pathways have a dual role in both survival and cell death processes depending on the stimulus. Nuclear Akt acts as apoptosis stimulator rather than as a repressor, as it likely gains access to a new set of substrates in the nucleus. The implicated link between survival and cell death pathways during apoptosis opens new pharmacological opportunities to modulate apoptosis in cancer, for example through the manipulation of Akt's cellular localization.

Pim-1 regulates cardiomyocyte survival downstream of Akt

The serine-threonine kinases Pim-1 and Akt regulate cellular proliferation and survival. Although Akt is known to be a crucial signaling protein in the myocardium, the role of Pim-1 has been overlooked. Pim-1 expression in the myocardium of mice decreased during postnatal development, re-emerged after acute pathological injury in mice and was increased in failing hearts of both mice and humans. Cardioprotective stimuli associated with Akt activation induced Pim-1 expression, but compensatory increases in Akt abundance and phosphorylation after pathological injury by infarction or pressure overload did not protect the myocardium in Pim-1-deficient mice. Transgenic expression of Pim-1 in the myocardium protected mice from infarction injury, and Pim-1 expression inhibited cardiomyocyte apoptosis with concomitant increases in Bcl-2 and Bcl-X(L) protein levels, as well as in Bad phosphorylation levels. Relative to nontransgenic controls, calcium dynamics were significantly enhanced in Pim-1-overexpressing transgenic hearts, associated with increased expression of SERCA2a, and were depressed in Pim-1-deficient hearts. Collectively, these data suggest that Pim-1 is a crucial facet of cardioprotection downstream of Akt.

DIVERSE CARDIOPROTECTIVE SIGNALING MECHANISMS OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-γ LIGANDS, 15-DEOXY-Δ12,14-PROSTAGLANDIN J2 AND CIGLITAZONE, IN REPERFUSION INJURY

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear receptor that regulates diverse biological functions including inflammation. The PPARgamma ligands have been reported to exert cardioprotective effects and attenuate myocardial reperfusion injury. Here, we examined the molecular mechanisms of their anti-inflammatory effects. Male Wistar rats were subjected to myocardial ischemia and reperfusion and were treated with the PPAR-gamma ligands, 15-deoxy-Delta-prostaglandin J2 (15d-PGJ2) or ciglitazone, or with vehicle only, in the absence or presence of the selective PPAR-gamma antagonist GW-9662. In vehicle-treated rats, myocardial injury was associated with elevated tissue activity of myeloperoxidase, indicating infiltration of neutrophils, and elevated plasma levels of creatine kinase and tumor necrosis factor-alpha. These events were preceded by activation of the nuclear factor-kappaB pathway. The PPAR-gamma DNA binding was also increased in the heart after reperfusion. Treatment with ciglitazone or 15d-PGJ2 reduced myocardial damage and neutrophil infiltration and blunted creatine kinase levels and cytokine production. The beneficial effects of both ligands were associated with enhancement of PPAR-gamma DNA binding and reduction of nuclear factor-kappaB activation. Treatment with 15d-PGJ2, but not ciglitazone, enhanced DNA binding of heat shock factor 1 and upregulated the expression of the cardioprotective heat shock protein 70. Treatment with 15d-PGJ2, but not ciglitazone, also induced a significant increase in nuclear phosphorylation of the prosurvival kinase Akt. The cardioprotection afforded by ciglitazone was attenuated by the PPAR-gamma antagonist GW-9662. In contrast, GW-9662 did not affect the beneficial effects afforded by 15d-PGJ2. Thus, our data suggest that treatment with these chemically unrelated PPAR-gamma ligands results in diverse anti-inflammatory mechanisms.

Antioxidant administration attenuates mechanical ventilation-induced rat diaphragm muscle atrophy independent of protein kinase B (PKB Akt) signalling

Oxidative stress promotes controlled mechanical ventilation (MV)-induced diaphragmatic atrophy. Nonetheless, the signalling pathways responsible for oxidative stress-induced muscle atrophy remain unknown. We tested the hypothesis that oxidative stress down-regulates insulin-like growth factor-1-phosphotidylinositol 3-kinase-protein kinase B serine threonine kinase (IGF-1-PI3K-Akt) signalling and activates the forkhead box O (FoxO) class of transcription factors in diaphragm fibres during MV-induced diaphragm inactivity. Sprague-Dawley rats were randomly assigned to one of five experimental groups: (1) control (Con), (2) 6 h of MV, (3) 6 h of MV with infusion of the antioxidant Trolox, (4) 18 h of MV, (5) 18 h of MV with Trolox. Following 6 h and 18 h of MV, diaphragmatic Akt activation decreased in parallel with increased nuclear localization and transcriptional activation of FoxO1 and decreased nuclear localization of FoxO3 and FoxO4, culminating in increased expression of the muscle-specific ubiquitin ligases, muscle atrophy factor (MAFbx) and muscle ring finger-1 (MuRF-1). Interestingly, following 18 h of MV, antioxidant administration was associated with attenuation of MV-induced atrophy in type I, type IIa and type IIb/IIx myofibres. Collectively, these data reveal that the antioxidant Trolox attenuates MV-induced diaphragmatic atrophy independent of alterations in Akt regulation of FoxO transcription factors and expression of MAFbx or MuRF-1. Further, these results also indicate that differential regulation of diaphragmatic IGF-1-PI3K-Akt signalling exists during the early and late stages of MV.

Metabolic gene switching in the murine female heart parallels enhanced mitochondrial respiratory function in response to oxidative stress

The mechanisms underlying increased cardioprotection in younger female mice are unclear. We hypothesized that serine-threonine protein kinase (protein kinase B; Akt) triggers a metabolic gene switch (decreased fatty acids, increased glucose) in female hearts to enhance mitochondrial bioenergetic capacity, conferring protection against oxidative stress. Here, we employed male and female control (db/+) and obese (db/db) mice. We found diminished transcript levels of peroxisome proliferator-activated receptor-alpha, muscle-type carnitine palmitoyltransferase 1 and pyruvate dehydrogenase kinase 4 in female control hearts versus male hearts. Moreover, females displayed improved recovery of cardiac mitochondrial respiratory function and higher ATP levels versus males in response to acute oxygen deprivation. All these changes were reversed in female db/db hearts. However, we found no significant gender-based differences in levels of Akt, suggesting that Akt-independent signaling mechanisms are responsible for the resilient mitochondrial phenotype observed in female mouse hearts. As glucose is a more energetically efficient fuel substrate when oxygen is limiting, this gene program may be a crucial component that enhances tolerance to oxygen deprivation in female hearts.

Detection of TUNEL-positive cardiomyocytes and C-kit-positive progenitor cells in children with congenital heart disease

The loss of cardiomyocytes by apoptosis and the subsequent replacement by fibrous connective tissues are important features of cardiac remodeling in adult heart disease. In children with CHD, however, the cellular and molecular mechanisms of heart failure have not yet been fully understood because of the anatomical and hemodynamic complexities. To investigate the apoptotic death of cardiomyocytes and mobilization of cardiac progenitor cells in children with congenital heart disease (CHD), terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling (TUNEL) assay and immunohistochemistry with antibody against c-kit were performed. The incidence of TUNEL-positive cardiomyocytes in children with CHD (n=17) was higher (0.39+/-0.21%) than that in the child controls (0.072+/-0.037%, p<0.001, n=6), however, the incidence was lower than that in adults with heart disease (1.35+/-0.54%, p<0.005, n=7). Significant cardiomyocyte hypertrophy or fibrosis was not observed in children with CHD. The CHD patients hemodynamically demonstrating a volume overload showed more TUNEL-positive cardiomyocytes (0.58+/-0.17%, n=4) than those with severe cyanosis (0.20+/-0.12%, p<0.05, n=4). C-kit-positive cells were more abundantly detected in CHD in comparison to the child control (p<0.01) and the adults with heart disease (p<0.005). The incidence of c-kit-positive cells correlated with that of TUNEL-positive cardiomyocytes (r=0.513). In contrast to adult patients with heart disease where cardiomyocyte apoptosis and the subsequent replacement by fibrous connective tissue are characteristic features of remodeling process, stress in children with CHD was found to induce less cardiomyocyte apoptosis and fibrosis. This study also provides a possible relationship between cardiomyocyte apoptosis and mobilization of c-kit-positive cells in children with CHD.

Differences between pathological and physiological cardiac hypertrophy: novel therapeutic strategies to treat heart failure

1. In general, cardiac hypertrophy (an increase in heart mass) is a poor prognostic sign. Cardiac enlargement is a characteristic of most forms of heart failure. Cardiac hypertrophy that occurs in athletes (physiological hypertrophy) is a notable exception. 2. Physiological cardiac hypertrophy in response to exercise training differs in its structural and molecular profile to pathological hypertrophy associated with pressure or volume overload in disease. Physiological hypertrophy is characterized by normal organization of cardiac structure and normal or enhanced cardiac function, whereas pathological hypertrophy is commonly associated with upregulation of fetal genes, fibrosis, cardiac dysfunction and increased mortality. 3. It is now clear that several signalling molecules play unique roles in the regulation of pathological and physiological cardiac hypertrophy. 4. The present review discusses the possibility of targeting cardioprotective signalling pathways and genes activated in the athlete's heart to treat or prevent heart failure.

Periostin induces proliferation of differentiated cardiomyocytes and promotes cardiac repair

Adult mammalian hearts respond to injury with scar formation and not with cardiomyocyte proliferation, the cellular basis of regeneration. Although cardiogenic progenitor cells may maintain myocardial turnover, they do not give rise to a robust regenerative response. Here we show that extracellular periostin induced reentry of differentiated mammalian cardiomyocytes into the cell cycle. Periostin stimulated mononucleated cardiomyocytes to go through the full mitotic cell cycle. Periostin activated alphaV, beta1, beta3 and beta5 integrins located in the cardiomyocyte cell membrane. Activation of phosphatidylinositol-3-OH kinase was required for periostin-induced reentry of cardiomyocytes into the cell cycle and was sufficient for cell-cycle reentry in the absence of periostin. After myocardial infarction, periostin-induced cardiomyocyte cell-cycle reentry and mitosis were associated with improved ventricular remodeling and myocardial function, reduced fibrosis and infarct size, and increased angiogenesis. Thus, periostin and the pathway that it regulates may provide a target for innovative strategies to treat heart failure.

Cardioprotective and anti-inflammatory effects of interleukin converting enzyme inhibition in experimental diabetic cardiomyopathy

OBJECTIVE

We investigated the effect of pharmacological inhibition of the interleukin converting enzyme (ICE) on cardiac inflammation, apoptosis, fibrosis, and left ventricular function in an animal model of diabetes.

RESEARCH DESIGN AND METHODS

Diabetes was induced in 24 Sprague-Dawley rats by injection of streptozotozin (STZ) (70 mg/kg). Diabetic animals were treated with the interleukin converting enzyme (ICE) inhibitor (ICEI) (n = 12) or with a placebo (n = 12). Nondiabetic rats served as controls (n = 12). Left ventricular function was documented 6 weeks after induction of diabetes. Cardiac tissue was analyzed for the expression of cytokines, intracellular adhesion molecule-1 and vascular cell adhesion molecule-1, leukocyte and macrophage integrins, and collagen. Phosphorylation of Akt was analyzed by Western blot and apoptosis by Blc-2 and Bax measurements.

RESULTS

Left ventricular function was significantly impaired in diabetic animals. This was accompanied by a significant increase of cytokines, cell adhesion molecules, leukocytes and macrophages, and collagen content. In addition, the phosphorylation state of Akt was reduced. These changes were significantly attenuated in the diabetic group treated with ICEI.

CONCLUSIONS

Cardiac dysfunction is associated with cardiac inflammation in experimental diabetic cardiomyopathy. Both of these--cardiac dysfunction and inflammation--are attenuated after treatment with ICEI. These data suggest that anticytokine-based therapies might be beneficial in diabetic cardiomyopathy.

Hsp70/Hsc70 regulates the effect phosphorylation has on stabilizing ataxin-1

Spinocerebellar ataxia type 1 (SCA1) is an inherited neurodegenerative disorder. The mutation causing SCA1 is an expansion in the polyglutamine tract of the ATXN1 protein. Previous work demonstrated that phosphorylation of mutant ATXN1 at serine 776 (S776), a putative Akt phosphorylation site, is critical for pathogenesis. To examine this pathway further, we utilized a cell-transfection system that allowed the targeting of Akt to either the cytoplasm or the nucleus. In contrast to HeLa cells, we found that Akt targeted to the cytoplasm increased the degradation of ATXN1 in Chinese hamster ovary cells. However, Akt targeted to the cytoplasm failed to destabilize ATXN1 if Hsp70/Hsc70 was present. Thus, Hsp70/Hsc70 can regulate ATXN1 levels in concert with phosphorylation of ATXN1 at S776.

Therapeutic Potential of H11 Kinase for the Ischemic Heart

H11 kinase (H11K) is a small heat shock protein expressed predominantly in the heart and skeletal muscle, which plays a critical role in the maintenance of cardiac cell survival and in promoting cell growth through the activation of complementary signaling pathways. An overexpression of H11K was detected in various forms of heart disease, both in animal models and in patients, including acute and chronic ventricular dysfunction, and myocardial hypertrophy. Overexpression of H11K was reproduced in a cardiac-specific transgenic model, which led to significant progress in understanding the role and mechanism of action of the protein. Increased expression of H11K confers a cardioprotection that is equivalent to ischemic preconditioning; it promotes cardiac hypertrophy while maintaining contractile function. The overexpression of H11K is sufficient to activate most of the signaling pathways involved in cardiac cell growth and survival, including the phosphatidylinositol-3-kinase/Akt pathway, the AMP-dependent protein kinase, the PKCepsilon pathway of ischemic preconditioning, the nitric oxide pathway of delayed cardioprotection, and the mTOR pathway of cell growth. As a result, the survival response triggered by H11K in the heart includes antiapoptosis, cytoprotection, preconditioning, growth, and metabolic stimulation. In addition to activating signaling pathways, H11K promotes the subcellular translocation and crosstalk of intracellular messengers. This review discusses the biological function of H11K, its molecular mechanisms of action, and its potential therapeutic relevance. In particular, we discuss how preemptive conditioning of the heart by H11K might be beneficial for patients with ischemic heart disease who would be at risk of further irreversible cardiac damage.

Sphingosine 1-phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocardial ischemia-reperfusion injury

Sphingosine 1-phosphate (S1P) is released at sites of tissue injury and effects cellular responses through activation of G protein-coupled receptors. The role of S1P in regulating cardiomyocyte survival following in vivo myocardial ischemia-reperfusion (I/R) injury was examined by using mice in which specific S1P receptor subtypes were deleted. Mice lacking either S1P(2) or S1P(3) receptors and subjected to 1-h coronary occlusion followed by 2 h of reperfusion developed infarcts equivalent to those of wild-type (WT) mice. However, in S1P(2,3) receptor double-knockout mice, infarct size following I/R was increased by >50%. I/R leads to activation of ERK, JNK, and p38 MAP kinases; however, these responses were not diminished in S1P(2,3) receptor knockout compared with WT mice. In contrast, activation of Akt in response to I/R was markedly attenuated in S1P(2,3) receptor knockout mouse hearts. Neither S1P(2) nor S1P(3) receptor deletion alone impaired I/R-induced Akt activation, which suggests redundant signaling through these receptors and is consistent with the finding that deletion of either receptor alone did not increase I/R injury. The involvement of cardiomyocytes in S1P(2) and S1P(3) receptor mediated activation of Akt was tested by using cells from WT and S1P receptor knockout hearts. Akt was activated by S1P, and this was modestly diminished in cardiomyocytes from S1P(2) or S1P(3) receptor knockout mice and completely abolished in the S1P(2,3) receptor double-knockout myocytes. Our data demonstrate that activation of S1P(2) and S1P(3) receptors plays a significant role in protecting cardiomyocytes from I/R damage in vivo and implicate the release of S1P and receptor-mediated Akt activation in this process.

Regulation of cardiac growth and coronary angiogenesis by the Akt/PKB signaling pathway

Postnatal growth of the heart is primarily achieved through hypertrophy of individual myocytes. Cardiac growth observed in athletes represents adaptive or physiological hypertrophy, whereas cardiac growth observed in patients with hypertension or valvular heart diseases is called maladaptive or pathological hypertrophy. These two types of hypertrophy are morphologically, functionally, and molecularly distinct from each other. The serine/threonine protein kinase Akt is activated by various extracellular stimuli in a phosphatidylinositol-3 kinase-dependent manner and regulates multiple aspects of cellular functions including survival, growth and metabolism. In this review we will discuss the role of the Akt signaling pathway in the heart, focusing on the regulation of cardiac growth, contractile function, and coronary angiogenesis. How this signaling pathway contributes to the development of physiological/pathological hypertrophy and heart failure will also be discussed.

Alpha1-adrenergic receptors activate AKT via a Pyk2/PDK-1 pathway that is tonically inhibited by novel protein kinase C isoforms in cardiomyocytes

AKT is a potent antiapoptotic kinase, but its role in the cardioprotective actions of alpha(1)-adrenergic receptors (ARs) remains uncertain, because alpha(1)-ARs typically induce little-to-no AKT activation in most cardiomyocyte models. This study identifies a prominent alpha(1)-AR-dependent AKT activation pathway that is under tonic inhibitory control by novel protein kinase Cs (nPKCs) in neonatal rat cardiomyocyte cultures. We also implicate Pyk2, Pyk2 complex formation with PDK-1 and paxillin, and increased PDK-1-Y373/376 phosphorylation as the mechanism that links alpha(1)-AR activation to increased AKT phosphorylation. nPKCs (which are prominent alpha(1)-AR effectors) interfere with this alpha(1)-AR-dependent AKT activation by blocking Pyk2/PDK-1/paxillin complex formation and PDK-1-Y373/376 phosphorylation. Additional studies used an adenoviral-mediated overexpression strategy to show that Pyk2 exerts dual controls on antiapoptotic PDK-1/AKT and proapoptotic c-Jun N-terminal kinase (JNK) pathways. Although the high nPKC activity of most cardiomyocyte models favors Pyk2 signaling to JNK (and cardiac apoptosis), the cardioprotective actions of Pyk2 through the PDK-1/AKT pathway are exposed when PKC or JNK activation is prevented. Collectively, these studies identify JNK and AKT as functionally distinct downstream components of the alpha(1)-AR/Pyk2 signaling pathway. We also implicate nPKCs as molecular switches that control the balance of signaling via proapoptotic JNK and antiapoptotic PDK-1/AKT pathways, exposing a novel mechanism for nPKC-dependent regulation of cardiac hypertrophy and failure.

Regulation of cardiac hypertrophy by intracellular signalling pathways

The mammalian heart is a dynamic organ that can grow and change to accommodate alterations in its workload. During development and in response to physiological stimuli or pathological insults, the heart undergoes hypertrophic enlargement, which is characterized by an increase in the size of individual cardiac myocytes. Recent findings in genetically modified animal models implicate important intermediate signal-transduction pathways in the coordination of heart growth following physiological and pathological stimulation.

Protection against myocardial ischemia/reperfusion injury by short-term diabetes: enhancement of VEGF formation, capillary density, and activation of cell survival signaling

The aims of this study were to determine effects of diabetes duration on myocardial ischemia/reperfusion (I/R) injury and test whether time-dependent differences in sensitivity of the streptozotocin diabetic rat heart to I/R are related to differences in vascular density, levels of vascular endothelial growth factor (VEGF) or endothelial nitric oxide synthase (eNOS) expression, NO formation, activation of Akt, and/or oxidative stress. After 2 or 6 weeks of streptozotocin-induced diabetes, I/R injury was induced by occlusion (30 min) and reperfusion of the left descending coronary artery. After 2 weeks of diabetes, infarct size and cleavage of caspase-3, a proapoptosis signal, were decreased as compared with normoglycemic controls or rats that had been diabetic for 6 weeks, whereas capillary density and levels of VEGF and eNOS protein and cardiac NO(x) levels were all increased. Phosphorylation of Akt, a prosurvival signal, was also significantly increased after 2 weeks of diabetes. Cardiac lipid peroxidation was comparable to controls after 2 weeks of diabetes, whereas levels of nitrotyrosine, a peroxynitrite biomarker, were reduced. After 6 weeks of diabetes, lipid peroxidation was increased and levels of VEGF and plasma NO were reduced as compared with controls or rats diabetic for 2 weeks. Our results indicate endogenous cardioprotective mechanisms become transiently activated in this early stage of diabetes and that this may protect the heart from I/R injury through enhancement of VEGF and eNOS expression, NO formation, activation of cell survival signals, and decreased oxidative stress.

Local Controlled Intramyocardial Delivery of Platelet-Derived Growth Factor Improves Postinfarction Ventricular Function Without Pulmonary Toxicity

Background— Local delivery methods can target therapies to specific tissues and potentially avoid toxicity to other organs. Platelet-derived growth factor can protect the myocardium, but it also plays an important role in promoting pulmonary hypertension. It is not known whether local myocardial delivery of platelet-derived growth factor during myocardial infarction (MI) can lead to sustained cardiac benefit without causing pulmonary hypertension.

Methods and Results— We performed a randomized and blinded experiment of 127 rats that survived experimental MI or sham surgery. We delivered platelet-derived growth factor (PDGF)-BB with self-assembling peptide nanofibers (NFs) to provide controlled release within the myocardium. There were 6 groups with n≥20 in each group: sham, sham+NF, sham+NF/PDGF, MI, MI+NF, and MI+NF/PDGF. Serial echocardiography from 1 day to 3 months showed significant improvement of ventricular fractional shortening, end-systolic dimension, and end-diastolic dimension with local PDGF delivery ( P <0.05 for MI+NF/PDGF versus MI or MI+NF). Catheterization at 4 months revealed improved ventricular function in the controlled delivery group (left ventricular end-diastolic pressure, cardiac index, +dP/dt, −dP/dt, and time constant of exponential decay all P <0.05 for MI+NF/P versus MI or MI+NF). Infarcted myocardial volume was reduced by NF/PDGF therapy (34.0±13.3% in MI, 28.9±12.9% in MI+NF, and 12.0±5.8% in MI+NF/PDGF; P <0.001). There was no evidence of pulmonary toxicity from the therapy, with no differences in right ventricular end-systolic pressure, right ventricular dP/dt, bromodeoxyuridine staining, or pulmonary artery medial wall thickness.

Conclusions— Intramyocardial delivery of PDGF by self-assembling peptide NFs leads to long-term improvement in cardiac performance after experimental infarction without apparent pulmonary toxicity. Local myocardial protection may allow prevention of heart failure without systemic toxicity.

Gene 33/RALT is induced by hypoxia in cardiomyocytes, where it promotes cell death by suppressing phosphatidylinositol 3-kinase and extracellular signal-regulated kinase survival signaling

Ischemia in the heart deprives cardiomyocytes of oxygen, triggering cell death (myocardial infarction). Ischemia and its cell culture model, hypoxia, elicit a stress response program that contributes to cardiomyocyte death; however, the molecular components required to promote this process remain nebulous. Gene 33 is a 50-kDa cytosolic adapter protein that suppresses signaling from receptor Tyr kinases of the epidermal growth factor receptor/ErbB family. Here we show that adenoviral expression of Gene 33 swiftly stimulates cardiomyocyte death coincident with reduced Akt and extracellular signal-regulated kinase (ERK) signaling. Subjecting cardiomyocytes to hypoxia and then reoxygenation induces gene 33 mRNA and Gene 33 protein. RNA interference experiments indicate that endogenous Gene 33 reduces Akt and ERK signaling and is required for maximal hypoxia-induced cardiomyocyte death. Gene 33 levels are also strikingly increased in myocardial ischemic injury and infarction. Our results identify a new role for Gene 33 as a component in the molecular pathophysiology of ischemic injury.

Nuclear targeting of Akt antagonizes aspects of cardiomyocyte hypertrophy

The serine/threonine kinase Akt regulates cellular survival, proliferation, gene transcription, protein translation, metabolism, and differentiation. Although Akt substrates are found throughout the cell, activated Akt normally accumulates in the nucleus, suggesting that biologically relevant targets are located there. Consequences of nuclear Akt signaling in cardiomyocytes were explored by using nuclear-targeted Akt (Akt-nuc). Accumulation of Akt-nuc did not provoke hypertrophy, unlike constitutively activated Akt. Instead, Akt-nuc inhibited hypertrophy concurrent with increased atrial natriuretic peptide (ANP) expression that depended upon phosphatidylinositol-3 kinase activity. Akt-nuc antihypertrophic effects were blocked by inhibition of either guanylyl cyclase A receptor or cyclic guanosine monophosphate-dependent protein kinase in cultured cardiomyocytes. Corroborating evidence showed blunted acute hypertrophic remodeling in Akt-nuc transgenic mice after transverse aortic constriction coincident with higher ANP expression and smaller myocyte volume. In addition, Akt-nuc expression improved systolic function and survival in the chronic phase of transverse aortic constriction-induced hypertrophy. Thus, Akt-nuc antagonizes certain aspects of hypertrophy through autocrine/paracrine stimulation of a phosphatidylinositol-3 kinase-dependent signaling cascade that promotes ANP expression, resulting in a unique combination of prosurvival coupled with antihypertrophic signaling.

Microarray analysis of Akt1 activation in transgenic mouse hearts reveals transcript expression profiles associated with compensatory hypertrophy and failure

To investigate molecular mechanisms involved in the development of cardiac hypertrophy and heart failure, we developed a tetracycline-regulated transgenic system to conditionally switch a constitutively active form of the Akt1 protein kinase on or off in the adult heart. Short-term activation (2 wk) of Akt1 resulted in completely reversible hypertrophy with maintained contractility. In contrast, chronic Akt1 activation (6 wk) induced extensive cardiac hypertrophy, severe contractile dysfunction, and massive interstitial fibrosis. The focus of this study was to create a transcript expression profile of the heart as it undergoes reversible Akt1-mediated hypertrophy and during the transition from compensated hypertrophy to heart failure. Heart tissue was analyzed before transgene induction, 2 wk after transgene induction, 2 wk of transgene induction followed by 2 days of repression, 6 wk after transgene induction, and 6 wk of transgene induction followed by 2 wk of repression. Acute overexpression of Akt1 (2 wk) leads to changes in the expression of 826 transcripts relative to noninduced hearts, whereas chronic induction (6 wk) led to changes in the expression of 1,611, of which 65% represented transcripts that were regulated during the pathological phase of heart growth. Another set of genes identified was uniquely regulated during heart regression but not growth, indicating that nonoverlapping transcription programs participate in the processes of cardiac hypertrophy and atrophy. These data define the gene regulatory programs downstream of Akt that control heart size and contribute to the transition from compensatory hypertrophy to heart failure.

Hypertrophic response of Duchenne and limb-girdle muscular dystrophies is associated with activation of Akt pathway

Dystrophic muscle undergoes repeated cycles of degeneration/regeneration, characterized by the presence of hypertrophic fibers. In order to elucidate the signaling pathways that govern these events, we investigated Akt activation in normal and dystrophic muscle. Akt is activated in neonatal muscle and in actively dividing myoblasts, supporting a developmental role for Akt signaling. Akt activation was detected at very early, prenecrotic stages of disease pathogenesis, and maximal activation was observed during peak stages of muscle hypertrophy. Duchenne muscular dystrophy patients exhibit a similar pattern of Akt activation. Mice with sarcoglycan-deficient muscular dystrophy possess more severe muscle pathology and display elevated Akt signaling. However, the highest levels of Akt activation were found in dystrophin-utrophin-deficient muscle with very advanced dystrophy. We propose that Akt may serve as an early biomarker of disease and that Akt activation mediates hypertrophy in muscular dystrophy. Current investigations are focused on introducing constitutively active and dominant-negative Akt into prenecrotic mdx mice to determine how early modification of Akt activity influences disease pathogenesis.

Akt promotes increased cardiomyocyte cycling and expansion of the cardiac progenitor cell population

Activation of Akt is associated with enhanced cell cycling and cellular proliferation in nonmyocytes, but this effect of nuclear Akt accumulation has not been explored in the context of the myocardium. Cardiac-specific expression of nuclear-targeted Akt (Akt/nuc) in transgenics prolongs postnatal cell cycling as evidenced by increased numbers of Ki67+ cardiomyocytes at 2 to 3 weeks after birth. Similarly, nuclear-targeting of Akt promotes expansion of the presumptive cardiac progenitor cell population as assessed by immunolabeling for c-kit in combination with myocyte-specific markers Nkx 2.5 or MEF 2C. Increases in pro-proliferative cytokines, including tumor-necrosis superfamily 8, interleukin-17e, and hepatocyte growth factor, were found in nuclear-targeted Akt myocardial samples. Concurrent signaling mediated by paracrine factors downstream of Akt/nuc expression may be responsible for phenotypic effects of nuclear-targeted Akt in the myocardium, including enhanced cell proliferation and expansion of the stem cell population.

Thyroid hormone stimulates protein synthesis in the cardiomyocyte by activating the Akt-mTOR and p70S6K pathways

Thyroid hormones affect cardiac growth and phenotype; however, the mechanisms by which the hormones induce cardiomyocyte hypertrophy remain uncharacterized. Tri-iodo-L-thyronine (T3) treatment of cultured cardiomyocytes for 24 h resulted in a 41 +/- 5% (p < 0.001) increase in [(3)H]leucine incorporation into total cellular protein. This response was abrogated by the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin. Co-immunoprecipitation studies showed a direct interaction of cytosol-localized thyroid hormone receptor TRalpha1 and the p85alpha subunit of PI3K. T3 treatment rapidly increased PI3K activity by 52 +/- 3% (p < 0.005), which resulted in increased phosphorylation of downstream kinases Akt and mammalian target of rapamycin (mTOR). This effect was abrogated by pretreatment with wortmannin or LY294002. Phosphorylation of p70(S6K), a known target of mTOR, occurred rapidly following T3 treatment and was inhibited by rapamycin and wortmannin. In contrast, phosphorylation of the p85 variant of S6K in response to T3 was not blocked by LY294002, wortmannin, or rapamycin, thus supporting a T3-activated pathway independent of PI3K and mTOR. 40 S ribosomal protein S6, a target of p70(S6K), and 4E-BP1, a target of mTOR, were both phosphorylated within 15-25 min of T3 treatment and could be inhibited by wortmannin and rapamycin. Thus, rapid T3-mediated activation of PI3K by cytosolic TRalpha1 and subsequent activation of the Akt-mTOR-S6K signaling pathway may underlie one of the mechanisms by which thyroid hormone regulates physiological cardiac growth.

PIKE GTPase-mediated nuclear signalings promote cell survival

The nuclear GTPase PIKE (PI 3-kinase Enhancer) binds PI 3-kinase and enhances it lipid kinase activity. PIKE predominantly distributes in the brain, and nerve growth factor stimulation triggers PIKE activation by provoking nuclear translocation of PLC-gamma1, which acts as a physiologic guanine nucleotide exchange factor (GEF) for PIKE through its SH3 domain. PIKE contains GTPase and ArfGAP domains, which are separated by a PH domain. C-terminal ArfGAP domain activates its internal GTPase activity, and this process is regulated by the interaction between phosphatidylinositols and PH domain. PI 3-kinase occurs in the nuclei of a broad range of cell types, and various stimuli elicit its nuclear translocation. The nuclei from NGF-treated PC12 cells are resistant to DNA fragmentation initiated by activated cell-free apoptosome, for which PIKE/nuclear PI 3-kinase signaling through nuclear PI(3,4,5)P(3) and Akt plays an essential role. As a nuclear receptor for PI(3,4,5)P(3,) B23 binds to PI(3,4,5)P(3) in an NGF-dependent way. The PI(3,4,5)P(3)/B23 complex inhibits DNA fragmentation activity of CAD. Nuclear Akt regulation of apoptosis is dependent on its phosphorylation of key substrates in the nucleus, but the identities of these substrates are unknown. Identification of its nuclear substrates will further our understanding of the physiological roles of nuclear PI 3-kinase/Akt signaling.

Nuclear Akt associates with PKC-phosphorylated Ebp1, preventing DNA fragmentation by inhibition of caspase-activated DNase

Akt promotes cell survival through phosphorylation. The physiological functions of cytoplasmic Akt have been well defined, but little is known about the nuclear counterpart. Employing a cell-free apoptotic assay and NGF-treated PC12 nuclear extracts, we purified Ebp1 as a factor, which contributes to inhibition of DNA fragmentation by CAD. Depletion of Ebp1 from nuclear extracts or knockdown of Ebp1 in PC12 cells abolishes the protective effects of nerve growth factor, whereas overexpression of Ebp1 prevents apoptosis. Ebp1 (S360A), which cannot be phosphorylated by PKC, barely binds Akt or inhibits DNA fragmentation, whereas Ebp1 S360D, which mimics phosphorylation, strongly binds Akt and suppresses apoptosis. Further, phosphorylated nuclear but not cytoplasmic Akt interacts with Ebp1 and enhances its antiapoptotic action independent of Akt kinase activity. Moreover, knocking down of Akt diminishes the antiapoptotic effect of Ebp1 in the nucleus. Thus, nuclear Akt might contribute to suppressing apoptosis through interaction with Ebp1.

Heat shock-induced cardioprotection activates cytoskeletal-based cell survival pathways

To define better the subcellular mechanism of heat shock (HS)-induced cardioprotection, we examined the effect of HS, as well as selective expression of individual HS proteins (HSPs), on cell injury in neonatal rat ventricular myocytes (NRVM). HS was induced in NRVM by a rapid elevation of temperature to 42 degrees C for 20 min followed by 20-24 h of recovery at 37 degrees C. Other NRVM were infected with a replication-deficient adenovirus encoding HSP27 or HSP70. On the same day, all groups were subjected to metabolic inhibition (MI). Cell injury was assayed by measurement of the percentage of total lactate dehydrogenase released, the percentage of cells staining with trypan blue, or TdT-mediated dUTP nick-end labeling, whereas cell signaling was assayed by immunoblot analysis and coimmunoprecipitation. Before MI, the viability of all treated groups did not differ significantly from control NRVM. HS resulted in a significant increase in HSP70 and HSP27 expression. Infection with either virus caused a significant increase in selective HSP content compared with control NRVM. HS protected NRVM from injury. Selective expression of HSP27 or HSP70 alone was not protective in NRVM, but dual infection with both viral vectors (HSP27 + HSP70) was protective. HS and HSP27 + HSP70 expression caused increased paxillin localization in the membrane fraction, which persisted in response to MI, compared with control NRVM. HS increased the integrin-paxillin-focal adhesion kinase interaction, whereas targeted inhibition of focal adhesion kinase activity abolished the integrin-paxillin association and resulted in an increase in cell death. HS and HSP27 + HSP70 expression increased the association of members of the focal adhesion complex and protected NRVM against irreversible injury. Cytoskeletal-based signaling pathways at focal adhesion junctions may represent a unique pathway of cardioprotection.

Intranuclear 3'-phosphoinositide metabolism and Akt signaling: new mechanisms for tumorigenesis and protection against apoptosis?

Lipid second messengers, particularly those derived from the polyphosphoinositide metabolism, play a pivotal role in multiple cell signaling networks. Phosphoinositide 3-kinase (PI3K) generate 3'-phosphorylated inositol lipids that are key players in a multitude of cell functions. One of the best characterized targets of PI3K lipid products is the serine/threonine protein kinase Akt (protein kinase B, PKB). Recent findings have implicated the PI3K/Akt pathway in tumorigenesis because it stimulates cell proliferation and suppresses apoptosis. However, it was thought that this signal transduction network would exert its carcinogenetic effects mainly by operating in the cytoplasm. Evidence accumulated over the past 15 years has highlighted the presence of an autonomous nuclear inositol lipid cycle, and strongly suggests that lipid molecules are important components of signaling pathways operating at the nuclear level. PI3K, its lipid product phosphatidylinositol (3,4,5) trisphosphate (PtdIns(3,4,5)P3), and Akt have been identified within the nucleus and recent data suggest that they counteract apoptosis also by operating in this cell compartment through a block of caspase-activated DNase and inhibition of chromatin condensation. In this review, we shall summarize the most updated and intriguing findings about nuclear PI3K/PtdIns(3,4,5)P3/Akt in relationship with tumorigenesis and suppression of apoptotic stimuli.

Prevention of left ventricular remodeling with granulocyte colony-stimulating factor after acute myocardial infarction: final 1-year results of the Front-Integrated Revascularization and Stem Cell Liberation in Evolving Acute Myocardial Infarction by Granulocyte Colony-Stimulating Factor (FIRSTLINE-AMI) Trial

BACKGROUND

Experimental and clinical evidence has recently shown that pluripotent stem cells can be mobilized by granulocyte colony-stimulating factor (G-CSF) and may enhance myocardial regeneration early after primary percutaneous coronary intervention (PCI) management of acute myocardial infarction. Sustained or long-term effects of mobilized CD34-positive mononuclear stem cells, however, are unknown.

METHODS AND RESULTS

Thirty consecutive patients with ST-elevation myocardial infarction undergoing primary PCI with stenting and abciximab were selected for the study 85+/-30 minutes after PCI; 15 patients were randomly assigned to receive subcutaneous G-CSF at 10 microg/kg body weight for 6 days in addition to standard care including aspirin, clopidogrel, an angiotensin-converting enzyme inhibitor, beta-blocking agents, and statins. In patients with comparable demographics and clinical and infarct-related characteristics, G-CSF stimulation led to sustained mobilization of CD34 positive mononuclear cells (MNC(CD34+)), with a 20-fold increase (from 3+/-2 at baseline to 66+/-54 MNC(CD34+)/microL on day 6; P<0.001); there was no evidence of leukocytoclastic effects, accelerated restenosis rate, or any late adverse events. Within 4 months, G-CSF-induced MNC(CD34+) mobilization led to enhanced resting wall thickening in the infarct zone of 1.16+/-0.29 mm (P<0.05 versus control), which was sustained at 1.20+/-0.28 after 12 months (P<0.001 versus control). Similarly, left ventricular ejection fraction improved from 48+/-4% at baseline to 54+/-8% at 4 months (P<0.005 versus control) and 56+/-9% at 12 months (P<0.003 versus control and paralleled by sustained improvement of wall-motion score index from 1.70+/-0.22 to 1.42+/-0.26 and 1.33+/-0.21 at 4 and 12 months, respectively), after G-CSF (P<0.05 versus baseline and P<0.03 versus controls). Accordingly, left ventricular end-diastolic diameter showed no remodeling and stable left ventricular dimensions after G-CSF stimulation, whereas left ventricular end-diastolic diameter in controls revealed enlargement from 55+/-4 mm at baseline to 58+/-4 mm (P<0.05 versus baseline) at 12 months after infarction and no improvement in diastolic function.

CONCLUSIONS

Mobilization of MNC(CD34+) by G-CSF after primary PCI may offer a pragmatic strategy for improvement in ventricular function and prevention of left ventricular remodeling 1 year after acute myocardial infarction.

H11 Kinase Prevents Myocardial Infarction by Preemptive Preconditioning of the Heart

Ischemic preconditioning confers powerful protection against myocardial infarction through pre-emptive activation of survival signaling pathways, but it remains difficult to apply to patients with ischemic heart disease, and its effects are transient. Promoting a sustained activation of preconditioning mechanisms in vivo would represent a novel approach of cardioprotection. We tested the role of the protein H11 kinase (H11K), which accumulates by 4- to 6-fold in myocardium of patients with chronic ischemic heart disease and in experimental models of ischemia. This increased expression was quantitatively reproduced in cardiac myocytes using a transgenic (TG) mouse model. After 45 minutes of coronary artery occlusion and reperfusion, hearts from TG mice showed an 82+/-5% reduction in infarct size compared with wild-type (WT), which was similar to the 84+/-4% reduction of infarct size observed in WT after a protocol of ischemic preconditioning. Hearts from TG mice showed significant activation of survival kinases participating in preconditioning, including Akt and the 5'AMP-activated protein kinase (AMPK). H11K directly binds to both Akt and AMPK and promotes their nuclear translocation and their association in a multiprotein complex, which results in a stimulation of survival mechanisms in cytosol and nucleus, including inhibition of proapoptotic effectors (glycogen synthase kinase-3beta, Bad, and Foxo), activation of antiapoptotic effectors (protein kinase Cepsilon, endothelial and inducible NO synthase isoforms, and heat shock protein 70), increased expression of the hypoxia-inducible factor-1alpha, and genomic switch to glucose utilization. Therefore, activation of survival pathways by H11K preemptively triggers the antiapoptotic and metabolic response to ischemia and is sufficient to confer cardioprotection in vivo equally potent to preconditioning.