Cellular remodeling in heart failure disrupts K(ATP) channel-dependent stress tolerance

Cardiopoietic programming of embryonic stem cells for tumor-free heart repair

Embryonic stem cells have the distinct potential for tissue regeneration, including cardiac repair. Their propensity for multilineage differentiation carries, however, the liability of neoplastic growth, impeding therapeutic application. Here, the tumorigenic threat associated with embryonic stem cell transplantation was suppressed by cardiac-restricted transgenic expression of the reprogramming cytokine TNF-α, enhancing the cardiogenic competence of recipient heart. The in vivo aptitude of TNF-α to promote cardiac differentiation was recapitulated in embryoid bodies in vitro. The procardiogenic action required an intact endoderm and was mediated by secreted cardio-inductive signals. Resolved TNF-α–induced endoderm-derived factors, combined in a cocktail, secured guided differentiation of embryonic stem cells in monolayers produce cardiac progenitors termed cardiopoietic cells. Characterized by a down-regulation of oncogenic markers, up-regulation, and nuclear translocation of cardiac transcription factors, this predetermined population yielded functional cardiomyocyte progeny. Recruited cardiopoietic cells delivered in infarcted hearts generated cardiomyocytes that proliferated into scar tissue, integrating with host myocardium for tumor-free repair. Thus, cardiopoietic programming establishes a strategy to hone stem cell pluripotency, offering a tumor-resistant approach for regeneration.

KATP channel knockout worsens myocardial calcium stress load in vivo and impairs recovery in stunned heart

Gene knockout of the KCNJ11-encoded Kir6.2 ATP-sensitive K(+) (K(ATP)) channel implicates this stress-response element in the safeguard of cardiac homeostasis under imposed demand. K(ATP) channels are abundant in ventricular sarcolemma, where subunit expression appears to vary between the sexes. A limitation, however, in establishing the full significance of K(ATP) channels in the intact organism has been the inability to monitor in vivo the contribution of the channel to intracellular calcium handling and the superimposed effect of sex that ultimately defines heart function. Here, in vivo manganese-enhanced cardiac magnetic resonance imaging revealed, under dobutamine stress, a significantly greater accumulation of calcium in both male and female K(ATP) channel knockout (Kir6.2-KO) mice compared with sex- and age-matched wild-type (WT) counterparts, with greatest calcium load in Kir6.2-KO females. This translated, poststress, into a sustained contracture manifested by reduced end-diastolic volumes in K(ATP) channel-deficient mice. In response to ischemia-induced stunning, male and female Kir6.2-KO hearts demonstrated accelerated time to contracture and increased peak contracture compared with WT. The outcome on reperfusion, in both male and female Kir6.2-KO hearts, was a transient reduction in systolic performance, measured as rate-pressure product compared with WT, with protracted increase in left ventricular end-diastolic pressure, exaggerated in female knockout hearts, despite comparable leakage of creatine kinase across groups. Kir6.2-KO hearts were rescued from diastolic dysfunction by agents that target alternative pathways of calcium handling. Thus K(ATP) channel deficit confers a greater susceptibility to calcium overload in vivo, accentuated in female hearts, impairing contractile recovery under various conditions of high metabolic demand.

Gene knockout of the KCNJ8-encoded Kir6.1 K(ATP) channel imparts fatal susceptibility to endotoxemia

Sepsis, the systemic inflammatory response to infection, imposes a high demand for bodily adaptation, with the cardiovascular response a key determinant of outcome. The homeostatic elements that secure cardiac tolerance in the setting of the sepsis syndrome are poorly understood. Here, in a model of acute septic shock induced by endotoxin challenge with Escherichia coli lipopolysaccharide (LPS), knockout of the KCNJ8 gene encoding the vascular Kir6.1 K(ATP) channel pore predisposed to an early and profound survival disadvantage. The exaggerated susceptibility provoked by disruption of this stress-responsive sensor of cellular metabolism was linked to progressive deterioration in cardiac activity, ischemic myocardial damage, and contractile dysfunction. Deletion of KCNJ8 blunted the responsiveness of coronary vessels to cytokine- or metabolic-mediated vasodilation necessary to support myocardial perfusion in the wild-type (WT), creating a deficit in adaptive response in the Kir6.1 knockout. Application of a K(ATP) channel opener drug improved survival in the endotoxic WT but had no effect in the Kir6.1 knockout. Restoration of the dilatory capacity of coronary vessels was required to rescue the Kir6.1 knockout phenotype and reverse survival disadvantage in lethal endotoxemia. Thus, the Kir6.1-containing K(ATP) channel, by coupling vasoreactivity with metabolic demand, provides a vital feedback element for cardiovascular tolerance in endotoxic shock.

Derivation of a cardiopoietic population from human mesenchymal stem cells yields cardiac progeny

Stem cells have emerged as a next-generation therapy for cardiovascular disease. Initial clinical trials in patients with myocardial infarction document improved cardiac performance after administration of stem cells, translating their regenerative potential from the bench to the bedside. However, the promise of stem cell-based therapy has yet to be fully exploited, in part due to varying degrees of efficacy on follow-up. Contributing to the uncertain outcome is the variable cardiogenic potential of patient-derived stem cells. A strategy mimicking cardiogenic signaling was here formulated to transform mesenchymal stem cells, derived from human bone marrow, into cardiac progenitors. We identified a set of recombinant trophic factors capable of collectively inducing nuclear translocation of cardiac-specific transcription factors, engaging mesenchymal stem cells into cardiopoiesis, and ultimately securing a phenotype with functional excitation-contraction coupling. Maximizing the cardiogenic potential of human mesenchymal stem cells achieves a critical step in optimizing therapeutic translation.

Protection conferred by myocardial ATP-sensitive K+ channels in pressure overload-induced congestive heart failure revealed in KCNJ11 Kir6.2-null mutant

Ventricular load can precipitate development of the heart failure syndrome, yet the molecular components that control the cardiac adaptive response to imposed demand remain partly understood. Compromised ATP-sensitive K(+) (K(ATP)) channel function renders the heart vulnerable to stress, implicating this metabolic sensor in the homeostatic response that would normally prevent progression of cardiac disease. Here, pressure overload was imposed on the left ventricle by transverse aortic constriction in the wild-type and in mice lacking sarcolemmal K(ATP) channels through Kir6.2 pore knockout (Kir6.2-KO). Despite equivalent haemodynamic loads, within 30 min of aortic constriction, Kir6.2-KO showed an aberrant prolongation of action potentials with intracellular calcium overload and ATP depletion, whereas wild-type maintained ionic and energetic handling. On catheterization, constricted Kir6.2-KO displayed compromised myocardial performance with elevated left ventricular end-diastolic pressure, not seen in the wild-type. Glyburide, a K(ATP) channel inhibitor, reproduced the knockout phenotype in the wild-type, whereas the calcium channel antagonist, verapamil, prevented abnormal outcome in Kir6.2-KO. Within 48 h following aortic constriction, fulminant biventricular congestive heart failure, characterized by exercise intolerance, cardiac contractile dysfunction, hepatopulmonary congestion and ascites, halved the Kir6.2-KO cohort, while no signs of organ failure or mortality were seen in wild-type. Surviving Kir6.2-KO developed premature and exaggerated fibrotic myocardial hypertrophy associated with nuclear up-regulation of calcium-dependent pro-remodelling MEF2 and NF-AT pathways, precipitating chamber dilatation within 3 weeks. Thus, K(ATP) channels appear mandatory in acute and chronic cardiac adaptation to imposed haemodynamic load, protecting against congestive heart failure and death.

Thioredoxin and ventricular remodeling

Increasing bodies of evidence indicate that reactive oxygen species (ROS) produced by mitochondria and other sources play an essential role in mediating ventricular remodeling after myocardial infarction and the development of heart failure. Antioxidants scavenge ROS, thereby maintaining the reduced environment of cells and inhibiting ventricular remodeling in the heart. Thioredoxin not only functions as a major antioxidant in the heart but also interacts with important signaling molecules and transcription factors, thereby modulating various cellular functions. The activity of thioredoxin is regulated by a variety of mechanisms, such as transcription, localization, protein-protein interaction, and post-translational modification. In this review, we will summarize the cardiac effects of thioredoxin and the mechanisms by which thioredoxin mediates inhibition of ventricular remodeling.

Cardiac and vascular KATP channels in rats are activated by endogenous epoxyeicosatrienoic acids through different mechanisms

We have reported that epoxyeicosatrienoic acids (EETs), the cytochrome P450 (CYP) epoxygenase metabolites of arachidonic acid (AA), are potent sarcolemmal ATP-sensitive K+ (KATP) channel activators. However, activation of cardiac and vascular KATP channels by endogenously produced EETs under physiological intracellular conditions has not been demonstrated and direct comparison of the mechanisms whereby EETs activate the KATP channels in cardiac myocytes versus vascular smooth muscle cells has not been made. In this study, we examined the effects of AA on KATP channels in freshly isolated cardiac myocytes from rats, wild-type (WT) and transgenic mice overexpressing CYP2J2 cDNA, and mesenteric arterial smooth muscle cells from rats. We also compared the activation of cardiac and vascular KATP channels by extracellularly and intracellularly applied 11,12-EET. We found that 1 microm AA enhanced KATP channel activities in both cardiac and vascular smooth muscle cells, and the AA effects were inhibited by preincubation with CYP epoxygenase inhibitors. Baseline cardiac KATP current densities in CYP2J2 transgenic mice were 190% higher than those of WT mice, and both were reduced to similar levels by CYP epoxygenase inhibition. Western blot analysis showed that expression of Kir6.2 and SUR2A was similar between WT and CYP2J2 transgenic hearts. 11,12-EET (5 microm) applied intracellularly enhanced the KATP currents by 850% in cardiac myocytes, but had no effect in vascular smooth muscle cells. In contrast, 11,12-EET (5 microm) applied extracellularly increased KATP currents by 520% in mesenteric arterial smooth muscle cells, but by only 209% in cardiac myocytes. Preincubation with 100 microm m-iodobenzylguanidine or 5 microm myristoylated PKI amide did not alter the activation of cardiac KATP channels by 5 microm 11,12-EET, but significantly inhibited activation of vascular KATP channels. Moreover, EET only enhanced the inward component of cardiac KATP currents, but activated both the inward and outward components of vascular KATP currents. Our results indicate that endogenously derived CYP metabolites of AA potently activate cardiac and vascular KATP channels. EETs regulate cardiac electrophysiology and vascular tone by KATP channel activation, albeit through different mechanisms: the cardiac KATP channels are directly activated by EETs, whereas activation of the vascular KATP channels by EETs is protein kinase A dependent.

KCNJ11 gene knockout of the Kir6.2 KATP channel causes maladaptive remodeling and heart failure in hypertension

Heart failure is a growing epidemic, with systemic hypertension a major risk factor for development of disease. However, the molecular determinants that prevent the transition from a state of hypertensive load to that of overt cardiac failure remain largely unknown. Here in experimental hypertension, knockout of the KCNJ11 gene, encoding the Kir6.2 pore-forming subunit of the sarcolemmal ATP-sensitive potassium (K(ATP)) channel, predisposed to heart failure and death. Defective decoding of hypertension-induced metabolic distress signals in the K(ATP) channel knockout set in motion pathological calcium overload and aggravated cardiac remodeling through a calcium/calcineurin-dependent cyclosporine-sensitive pathway. Rescue of the failing K(ATP) knockout phenotype was achieved by alternative control of myocardial calcium influx, bypassing uncoupled metabolic-electrical integration. The intact KCNJ11-encoded K(ATP) channel is thus a required safety element preventing hypertension-induced heart failure, with channel dysfunction a molecular substrate for stress-associated channelopathy in cardiovascular disease.

Cardiac system bioenergetics: metabolic basis of the Frank-Starling law

The fundamental principle of cardiac behaviour is described by the Frank-Starling law relating force of contraction during systole with end-diastolic volume. While both work and respiration rates increase linearly with imposed load, the basis of mechano-energetic coupling in heart muscle has remained a long-standing enigma. Here, we highlight advances made in understanding of complex cellular and molecular mechanisms that orchestrate coupling of mitochondrial oxidative phosphorylation with ATP utilization for muscle contraction. Cardiac system bioenergetics critically depends on an interrelated metabolic infrastructure regulating mitochondrial respiration and energy fluxes throughout cellular compartments. The data reviewed indicate the significance of two interrelated systems regulating mitochondrial respiration and energy fluxes in cells: (1) the creatine kinase, adenylate kinase and glycolytic pathways that communicate flux changes generated by cellular ATPases within structurally organized enzymatic modules and networks; and (2) a secondary system based on mitochondrial participation in cellular calcium cycle, which adjusts substrate oxidation and energy-transducing processes to meet increasing cellular energy demands. By conveying energetic signals to metabolic sensors, coupled phosphotransfer reactions provide a high-fidelity regulation of the excitation-contraction cycle. Such integration of energetics with calcium signalling systems provides the basis for 'metabolic pacing', synchronizing the cellular electrical and mechanical activities with energy supply processes.

The genetic basis for cardiac remodeling

Cardiomyopathies are primary disorders of cardiac muscle associated with abnormalities of cardiac wall thickness, chamber size, contraction, relaxation, conduction, and rhythm. They are a major cause of morbidity and mortality at all ages and, like acquired forms of cardiovascular disease, often result in heart failure. Over the past two decades, molecular genetic studies of humans and analyses of model organisms have made remarkable progress in defining the pathogenesis of cardiomyopathies. Hypertrophic cardiomyopathy can result from mutations in 11 genes that encode sarcomere proteins, and dilated cardiomyopathy is caused by mutations at 25 chromosome loci where genes encoding contractile, cytoskeletal, and calcium regulatory proteins have been identified. Causes of cardiomyopathies associated with clinically important cardiac arrhythmias have also been discovered: Mutations in cardiac metabolic genes cause hypertrophy in association with ventricular pre-excitation and mutations causing arrhythmogenic right ventricular dysplasia were recently discovered in protein constituents of desmosomes. This considerable genetic heterogeneity suggests that there are multiple pathways that lead to changes in heart structure and function. Defects in myocyte force generation, force transmission, and calcium homeostasis have emerged as particularly critical signals driving these pathologies. Delineation of the cell and molecular events triggered by cardiomyopathy gene mutations provide new fundamental knowledge about myocyte biology and organ physiology that accounts for cardiac remodeling and defines mechanistic pathways that lead to heart failure.

Bioenergetic protection of failing atrial and ventricular myocardium by vasopeptidase inhibitor omapatrilat

Deficient bioenergetic signaling contributes to myocardial dysfunction and electrical instability in both atrial and ventricular cardiac chambers. Yet, approaches capable to prevent metabolic distress are only partially established. Here, in a canine model of tachycardia-induced congestive heart failure, we compared atrial and ventricular bioenergetics and tested the efficacy of metabolic rescue with the vasopeptidase inhibitor omapatrilat. Despite intrinsic differences in energy metabolism, failing atria and ventricles demonstrated profound bioenergetic deficiency with reduced ATP and creatine phosphate levels and compromised adenylate kinase and creatine kinase catalysis. Depressed phosphotransfer enzyme activities correlated with reduced tissue ATP levels, whereas creatine phosphate inversely related with atrial and ventricular load. Chronic treatment with omapatrilat maintained myocardial ATP, the high-energy currency, and protected adenylate and creatine kinase phosphotransfer capacity. Omapatrilat-induced bioenergetic protection was associated with maintained atrial and ventricular structural integrity, albeit without full recovery of the creatine phosphate pool. Thus therapy with omapatrilat demonstrates the benefit in protecting phosphotransfer enzyme activities and in preventing impairment of atrial and ventricular bioenergetics in heart failure.

K(ATP) channel therapeutics at the bedside

The family of potassium channel openers regroups drugs that share the property of activating adenosine triphosphate-sensitive potassium (K(ATP)) channels, metabolic sensors responsible for adjusting membrane potential-dependent functions to match cellular energetic demands. K(ATP) channels, widely represented in metabolically-active tissue, are heteromultimers composed of an inwardly rectifying potassium channel pore and a regulatory sulfonylurea receptor subunit, the site of action of potassium channel opening drugs that promote channel activity by antagonizing ATP-induced pore inhibition. The activity of K(ATP) channels is critical in the cardiovascular adaptive response to stress, maintenance of neuronal electrical stability, and hormonal homeostasis. Thereby, K(ATP) channel openers have a unique therapeutic spectrum, ranging from applications in myopreservation and vasodilatation in patients with heart or vascular disease to potential clinical use as bronchodilators, bladder relaxants, islet cell protector, antiepileptics and promoters of hair growth. While the current experience in practice with potassium channel openers remains limited, multitude of ongoing investigations aims at defining the benefit of this emerging family of therapeutics in diverse disease conditions associated with metabolic distress.

Cardiac KATP channels in health and disease

ATP-sensitive potassium (K(ATP)) channels are evolutionarily conserved plasma-membrane protein complexes, widely represented in tissue beds with high metabolic activity. There, they are formed through physical association of the inwardly rectifying potassium channel pore, most typically Kir6.2, and the regulatory sulfonylurea receptor subunit, an ATP-binding cassette protein. Energetic signals, received via tight integration with cellular metabolic pathways, are processed by the sulfonylurea receptor subunit that in turn gates the nucleotide sensitivity of the channel pore thereby controlling membrane potential dependent cellular functions. Recent findings, elicited from genetic disruption of channel proteins, have established in vivo the requirement of intact K(ATP) channels in the proper function of cardiac muscle under stress. In the heart, where K(ATP) channels were originally discovered, channel ablation compromises cardioprotection under ischemic insult. New data implicate the requirement of intact K(ATP) channels for the cardiac adaptive response to acute stress. K(ATP) channels have been further implicated in the adaptive cardiac response to chronic (patho)physiologic hemodynamic load, with K(ATP) channel deficiency affecting structural remodeling, rendering the heart vulnerable to calcium-dependent maladaptation and predisposing to heart failure. These findings are underscored by the identification in humans that defective K(ATP) channels induced by mutations in ABCC9, the gene encoding the cardiac sulfonylurea receptor subunit, confer susceptibility to dilated cardiomyopathy. Thus, in parallel with the developed understanding of the molecular identity and mode of action of K(ATP) channels since their discovery, there is now an expanded understanding of their critical significance in the cardiac stress response in health and disease.

ATP-sensitive K+ channel channel/enzyme multimer: metabolic gating in the heart

Cardiac ATP-sensitive K(+) (K(ATP)) channels, gated by cellular metabolism, are formed by association of the inwardly rectifying potassium channel Kir6.2, the potassium conducting subunit, and SUR2A, the ATP-binding cassette protein that serves as the regulatory subunit. Kir6.2 is the principal site of ATP-induced channel inhibition, while SUR2A regulates K(+) flux through adenine nucleotide binding and catalysis. The ATPase-driven conformations within the regulatory SUR2A subunit of the K(ATP) channel complex have determinate linkage with the states of the channel's pore. The probability and life-time of ATPase-induced SUR2A intermediates, rather than competitive nucleotide binding alone, defines nucleotide-dependent K(ATP) channel gating. Cooperative interaction, instead of independent contribution of individual nucleotide binding domains within the SUR2A subunit, serves a decisive role in defining K(ATP) channel behavior. Integration of K(ATP) channels with the cellular energetic network renders these channel/enzyme heteromultimers high-fidelity metabolic sensors. This vital function is facilitated through phosphotransfer enzyme-mediated transmission of controllable energetic signals. By virtue of coupling with cellular energetic networks and the ability to decode metabolic signals, K(ATP) channels set membrane excitability to match demand for homeostatic maintenance. This new paradigm in the operation of an ion channel multimer is essential in providing the basis for K(ATP) channel function in the cardiac cell, and for understanding genetic defects associated with life-threatening diseases that result from the inability of the channel complex to optimally fulfill its physiological role.

Molecular determinants of cardiac K(ATP) channel activation by epoxyeicosatrienoic acids

We have previously reported that epoxyeicosatrienoic acids (EETs), the cytochrome P450 epoxygenase metabolites of arachidonic acid, are potent stereospecific activators of the cardiac K(ATP) channel. The epoxide group in EET is critical for reducing channel sensitivity to ATP, thereby activating the channel. This study is to identify the molecular sites on the K(ATP) channels for EET-mediated activation. We investigated the effects of EETs on Kir6.2delta C26 with or without the coexpression of SUR2A and on Kir6.2 mutants of positively charged residues known to affect channel activity coexpressed with SUR2A in HEK293 cells. The ATP IC50 values were significantly increased in Kir6.2 R27A, R50A, K185A, and R201A but not in R16A, K47A, R54A, K67A, R192A, R195A, K207A, K222A, and R314A mutants. Similar to native cardiac K(ATP) channel, 5 microM 11,12-EET increased the ATP IC50 by 9.6-fold in Kir6.2/SUR2A wild type and 8.4-fold in Kir6.2delta C26. 8,9- and 14,15-EET regioisomers activated the Kir6.2 channel as potently as 11,12-EET. 8,9- and 11,12-EET failed to change the ATP sensitivity of Kir6.2 K185A, R195A, and R201A, whereas their effects were intact in the other mutants. 14,15-EET had a similar effect with K185A and R201A mutants, but instead of R195A, it failed to activate Kir6.2R192A. These results indicate that activation of Kir6.2 by EETs does not require the SUR2A subunit, and the region in the Kir6.2 C terminus from Lys-185 to Arg-201 plays a critical role in EET-mediated Kir6.2 channel activation. Based on computer modeling of the Kir6.2 structure, we infer that the EET-Kir6.2 interaction may allosterically change the ATP binding site on Kir6.2, reducing the channel sensitivity to ATP.

Genetic disruption of Kir6.2, the pore-forming subunit of ATP-sensitive K+ channel, predisposes to catecholamine-induced ventricular dysrhythmia

Metabolic-sensing ATP-sensitive K+ channels (KATP channels) adjust membrane excitability to match cellular energetic demand. In the heart, KATP channel activity has been linked to homeostatic shortening of the action potential under stress, yet the requirement of channel function in securing cardiac electrical stability is only partially understood. Here, upon catecholamine challenge, disruption of KATP channels, by genetic deletion of the pore-forming Kir6.2 subunit, produced defective cardiac action potential shortening, predisposing the myocardium to early afterdepolarizations. This deficit in repolarization reserve, demonstrated in Kir6.2-knockout hearts, translated into a high risk for induction of triggered activity and ventricular dysrhythmia. Thus, intact KATP channel function is mandatory for adequate repolarization under sympathetic stress providing electrical tolerance against triggered arrhythmia.

ATP-sensitive K+ channel knockout compromises the metabolic benefit of exercise training, resulting in cardiac deficits

Exercise training elicits a metabolic and cardiovascular response that underlies fitness. The molecular mechanisms that orchestrate this adaptive response and secure the wide-ranging gains of a regimented exercise program are poorly understood. Formed through association of the Kir6.2 pore and the sulfonylurea receptor, the stress-responsive ATP-sensitive K(+) channels (K(ATP) channels), with their metabolic-sensing capability and broad tissue expression, are potential candidates for integrating the systemic adaptive response to repetitive exercise. Here, the responses of mice lacking functional Kir6.2-containing K(ATP) channels (Kir6.2-KO) were compared with wild-type controls following a 28-day endurance swimming protocol. While chronic aquatic training resulted in lighter, leaner, and fitter wild-type animals, the Kir6.2-KO manifested less augmentation in exercise capacity and lacked metabolic improvement in body fat composition and glycemic handling with myocellular defects. Moreover, the repetitive stress of swimming unmasked a survival disadvantage in the Kir6.2-KO, associated with pathologic calcium-dependent structural damage in the heart and impaired cardiac performance. Thus, Kir6.2-containing K(ATP) channel activity is required for attainment of the physiologic benefits of exercise training without injury.

Cardiac myocyte apoptosis provokes adverse cardiac remodeling in transgenic mice with targeted TNF overexpression

Although cardiac myocyte apoptosis has been detected in explanted hearts from patients with end-stage dilated and ischemic cardiomyopathy, the relative contribution of apoptotic cell death to left ventricular (LV) remodeling and cardiac decompensation is not known. To determine whether progressive cardiac myocyte apoptosis contributes to the transition from a hypertrophic to a dilated cardiac phenotype that is observed in transgenic myosin heavy chain secreted TNF (MHCsTNF) mice with cardiac restricted overexpression of tumor necrosis factor (TNF), we assessed cardiac myocyte apoptosis (using a DNA ligase technique) in MHCsTNF mice and littermate control mice in relation to serial changes in LV structure, which was assessed using MRI. The prevalence of cardiac myocyte apoptosis increased progressively from 4 to 12 wk as the hearts of the MHCsTNF mice underwent the transition from a concentric hypertrophic to a dilated cardiac phenotype. Treatment of the MHCsTNF mice with the broad-based caspase inhibitor N-[(1,3-dimethylindole-2-carbonyl)-valinyl]-3-amino4-oxo-5-fluoropentanoic acid significantly decreased cardiac myocyte apoptosis and significantly attenuated LV wall thinning and adverse cardiac remodeling. Additional studies suggested that the TNF-induced decrease in Bcl-2 expression and activation of the intrinsic mitochondrial death pathway were responsible for the cardiac myocyte apoptosis observed in the MHCsTNF mice. These studies show that progressive cardiac myocyte apoptosis is sufficient to contribute to adverse cardiac remodeling in the adult mammalian heart through progressive LV wall thinning.

Stable benefit of embryonic stem cell therapy in myocardial infarction

Conventional therapies for myocardial infarction attenuate disease progression without contributing significantly to repair. Because of the capacity for de novo cardiogenesis, embryonic stem cells are considered a potential source for myocardial regeneration, yet limited information is available on their ultimate therapeutic value. We treated infarcted rat hearts with CGR8 embryonic stem cells preexamined for cardiogenicity, serially probed left ventricular function, and determined final pathological outcome. Stem cell delivery generated new cardiomyocytes of embryonic stem cell origin that integrated with host myocardium within infarct regions. This resulted in a functional benefit within 3 wk that remained sustained over 12 wk of continuous follow-up and included a vigorous inotropic response to beta-adrenergic challenge. Integration of stem cell-derived cardiomyocytes was associated with normalized ventricular architecture, little scar, and a decrease in signs of myocardial necrosis. In contrast, sham-treated infarcted hearts exhibited ventricular cavity dilation and aneurysm formation, poor ventricular function, and a lack of response to beta-adrenergic stimulation. No evidence of graft rejection, ectopy, sudden cardiac death, or tumor formation was observed after therapy. These findings indicate that embryonic stem cells, through differentiation within the host myocardium, can contribute to a stable beneficial outcome on contractile function and ventricular remodeling in the infarcted heart.

Transgenic overexpression of human DMPK accumulates into hypertrophic cardiomyopathy, myotonic myopathy and hypotension traits of myotonic dystrophy

Abnormal expression of human myotonic dystrophy protein kinase (hDMPK) gene products has been implicated in myotonic dystrophy type 1 (DM1), yet the impact of distress accumulation produced by persistent overexpression of this poorly understood member of the Rho kinase-related protein kinase gene-family remains unknown. Here, in the aged transgenic murine line carrying approximately 25 extra copies of a complete hDMPK gene with all exons and an intact promoter region (Tg26-hDMPK), overexpression of mRNA and protein transgene products in cardiac, skeletal and smooth muscles resulted in deficient exercise endurance, an integrative index of muscle systems underperformance. In contrast to age-matched (11-15 months) wild-type controls, hearts from Tg26-hDMPK developed cardiomyopathic remodeling with myocardial hypertrophy, myocyte disarray and interstitial fibrosis. Hypertrophic cardiomyopathy was associated with a propensity for dysrhythmia and characterized by overt intracellular calcium overload promoting nuclear translocation of transcription factors responsible for maladaptive gene reprogramming. Skeletal muscles in distal limbs of Tg26-hDMPK showed myopathy with myotonic discharges coupled with deficit in sarcolemmal chloride channels, required regulators of hyperexcitability. Fiber degeneration in Tg26-hDMPK resulted in sarcomeric disorganization, centralization of nuclei and tubular aggregation. Moreover, the reduced blood pressure in Tg26-hDMPK indicated deficient arterial smooth muscle tone. Thus, the cumulative stress induced by permanent overexpression of hDMPK gene products translates into an increased risk for workload intolerance, hypertrophic cardiomyopathy with dysrhythmia, myotonic myopathy and hypotension, all distinctive muscle traits of DM1. Proper expression of hDMPK is, therefore, mandatory in supporting the integral balance among cytoarchitectural infrastructure, ion-homeostasis and viability control in various muscle cell types.

ABCC9 mutations identified in human dilated cardiomyopathy disrupt catalytic KATP channel gating

Stress tolerance of the heart requires high-fidelity metabolic sensing by ATP-sensitive potassium (K(ATP)) channels that adjust membrane potential-dependent functions to match cellular energetic demand. Scanning of genomic DNA from individuals with heart failure and rhythm disturbances due to idiopathic dilated cardiomyopathy identified two mutations in ABCC9, which encodes the regulatory SUR2A subunit of the cardiac K(ATP) channel. These missense and frameshift mutations mapped to evolutionarily conserved domains adjacent to the catalytic ATPase pocket within SUR2A. Mutant SUR2A proteins showed aberrant redistribution of conformations in the intrinsic ATP hydrolytic cycle, translating into abnormal K(ATP) channel phenotypes with compromised metabolic signal decoding. Defective catalysis-mediated pore regulation is thus a mechanism for channel dysfunction and susceptibility to dilated cardiomyopathy.