Walter J. Koch

Adiponectin Cardioprotection After Myocardial Ischemia/Reperfusion Involves the Reduction of Oxidative/Nitrative Stress

Background— Several clinical studies have demonstrated that levels of adiponectin are significantly reduced in patients with type 2 diabetes and that adiponectin levels are inversely related to the risk of myocardial ischemia. The present study was designed to determine the mechanism by which adiponectin exerts its protective effects against myocardial ischemia/reperfusion. Methods and Results— Adiponectin−/− or wild-type mice were subjected to 30 minutes of myocardial ischemia followed by 3 hours or 24 hours (infarct size and cardiac function) of reperfusion. Myocardial infarct size and apoptosis, production of peroxynitrite, nitric oxide (NO) and superoxide, and inducible NO synthase (iNOS) and gp91phox protein expression were compared. Myocardial apoptosis and infarct size were markedly enhanced in adiponectin−/− mice (P<0.01). Formation of NO, superoxide, and their cytotoxic reaction product, peroxynitrite, were all significantly higher in cardiac tissue obtained from adiponectin−/− than from wild-type mice (P<0.01). Moreover, myocardial ischemia/reperfusion–induced iNOS and gp91phox protein expression was further enhanced, but endothelial NOS phosphorylation was reduced in cardiac tissue from adiponectin−/− mice. Administration of the globular domain of adiponectin 10 minutes before reperfusion reduced myocardial ischemia/reperfusion–induced iNOS/gp91phox protein expression, decreased NO/superoxide production, blocked peroxynitrite formation, and reversed proapoptotic and infarct-enlargement effects observed in adiponectin−/− mice. Conclusion— The present study demonstrates that adiponectin is a natural molecule that protects hearts from ischemia/reperfusion injury by inhibition of iNOS and nicotinamide adenine dinucleotide phosphate-oxidase protein expression and resultant oxidative/nitrative stress.

A Novel and Efficient Model of Coronary Artery Ligation and Myocardial Infarction in the Mouse

Rationale: Coronary artery ligation to induce myocardial infarction (MI) in mice is typically performed by an invasive and time-consuming approach that requires ventilation and chest opening (classic method), often resulting in extensive tissue damage and high mortality. We developed a novel and rapid surgical method to induce MI that does not require ventilation. Objective: The purpose of this study was to develop and comprehensively describe this method and directly compare it to the classic method. Methods and Results: Male C57/B6 mice were grouped into 4 groups: new method MI (MI-N) or sham (S-N) and classic method MI (MI-C) or sham (S-C). In the new method, heart was manually exposed without intubation through a small incision and MI was induced. In the classic method, MI was induced through a ventilated thoracotomy. Similar groups were used in an ischemia/reperfusion injury model. This novel MI procedure is rapid, with an average procedure time of 1.22±0.05 minutes, whereas the classic method requires 23.2±0.6 minutes per procedure. Surgical mortality was 3% in MI-N and 15.9% in MI-C. The rate of arrhythmia was significantly lower in MI-N. The postsurgical levels of tumor necrosis factor-&agr; and myeloperoxidase were lower in new method, indicating less inflammation. Overall, 28-day post-MI survival rate was 68% with MI-N and 48% with MI-C. Importantly, there was no difference in infarct size or post-MI cardiac function between the methods. Conclusions: This new rapid method of MI in mice represents a more efficient and less damaging model of myocardial ischemic injury compared with the classic method.

Regulation of β-Adrenergic Receptor Signaling by S-Nitrosylation of G-Protein-Coupled Receptor Kinase 2

beta-adrenergic receptors (beta-ARs), prototypic G-protein-coupled receptors (GPCRs), play a critical role in regulating numerous physiological processes. The GPCR kinases (GRKs) curtail G-protein signaling and target receptors for internalization. Nitric oxide (NO) and/or S-nitrosothiols (SNOs) can prevent the loss of beta-AR signaling in vivo, but the molecular details are unknown. Here we show in mice that SNOs increase beta-AR expression and prevent agonist-stimulated receptor downregulation; and in cells, SNOs decrease GRK2-mediated beta-AR phosphorylation and subsequent recruitment of beta-arrestin to the receptor, resulting in the attenuation of receptor desensitization and internalization. In both cells and tissues, GRK2 is S-nitrosylated by SNOs as well as by NO synthases, and GRK2 S-nitrosylation increases following stimulation of multiple GPCRs with agonists. Cys340 of GRK2 is identified as a principal locus of inhibition by S-nitrosylation. Our studies thus reveal a central molecular mechanism through which GPCR signaling is regulated.

Catecholamines, Cardiac b-Adrenergic Receptors, and Heart Failure

It is now generally accepted that chronically elevated stimulation of the cardiac b-adrenergic system is toxic to the heart and that such stimulation may contribute to the pathogenesis of congestive heart failure of various causes. Administration of either b-adrenergic agonists or phosphodiesterase inhibitors has been shown to decrease survival of patients with chronic heart failure, even though they produce immediate and long-term hemodynamic benefits. 1 Moreover, in human heart failure, as well as in several animal models, elevated circulating catecholamines lead, via various compensatory mechanisms, to decreased levels and functional activity of cardiac b1-adrenergic receptors (b1ARs) and thus to marked desensitization of the heart to inotropic b-adrenergic stimulation.2

Animal models of heart failure: a scientific statement from the American Heart Association.

Heart failure (HF) is a leading cause of morbidity and mortality in the United States. Despite a number of important therapeutic advances for the treatment of symptomatic HF,1 the prevalence, mortality, and cost associated with HF continue to grow in the United States and other developed countries. Given the aging of our population and the prevalence of diseases such as diabetes mellitus and hypertension that predispose patients to this syndrome, it is possible that HF prevalence will increase in the next decade. Current treatments primarily slow the progression of this syndrome, and there is a need to develop novel preventative and reparative therapies. Development of these novel HF therapies requires testing of the putative therapeutic strategies in appropriate HF animal models. The purposes of this scientific statement are to define the distinctive clinical features of the major causes of HF in humans and to recommend those distinctive pathological features of HF in humans that should be present in an animal model being used to identify fundamental causes of HF or to test preventative or reparative therapies that could reduce HF morbidity and mortality. HF is a clinical syndrome with primary symptoms including dyspnea, fatigue, exercise intolerance, and retention of fluid in the lungs and peripheral tissues. The causes of HF are myriad, but the common fundamental defect is a decreased ability of the heart to provide sufficient cardiac output to support the normal functions of the tissues because of impaired filling and/or ejection of blood. HF is a significant health burden in both the developed world and in emerging nations. In the United States, over a half million new diagnoses of HF occur each year, and the prevalence is 5.8 million individuals >20 years of age.1 HF has a substantial societal burden, with yearly costs in the United …

Adrenergic Nervous System in Heart Failure Pathophysiology and Therapy

Heart failure (HF), the leading cause of death in the western world, develops when a cardiac injury or insult impairs the ability of the heart to pump blood and maintain tissue perfusion. It is characterized by a complex interplay of several neurohormonal mechanisms that become activated in the syndrome to try and sustain cardiac output in the face of decompensating function. Perhaps the most prominent among these neurohormonal mechanisms is the adrenergic (or sympathetic) nervous system (ANS), whose activity and outflow are enormously elevated in HF. Acutely, and if the heart works properly, this activation of the ANS will promptly restore cardiac function. However, if the cardiac insult persists over time, chances are the ANS will not be able to maintain cardiac function, the heart will progress into a state of chronic decompensated HF, and the hyperactive ANS will continue to push the heart to work at a level much higher than the cardiac muscle can handle. From that point on, ANS hyperactivity becomes a major problem in HF, conferring significant toxicity to the failing heart and markedly increasing its morbidity and mortality. The present review discusses the role of the ANS in cardiac physiology and in HF pathophysiology, the mechanisms of regulation of ANS activity and how they go awry in chronic HF, methods of measuring ANS activity in HF, the molecular alterations in heart physiology that occur in HF, along with their pharmacological and therapeutic implications, and, finally, drugs and other therapeutic modalities used in HF treatment that target or affect the ANS and its effects on the failing heart.

Cardiac adenoviral S100A1 gene delivery rescues failing myocardium

Cardiac-restricted overexpression of the Ca2+-binding protein S100A1 has been shown to lead to increased myocardial contractile performance in vitro and in vivo. Since decreased cardiac expression of S100A1 is a characteristic of heart failure, we tested the hypothesis that S100A1 gene transfer could restore contractile function of failing myocardium. Adenoviral S100A1 gene delivery normalized S100A1 protein expression in a postinfarction rat heart failure model and reversed contractile dysfunction of failing myocardium in vivo and in vitro. S100A1 gene transfer to failing cardiomyocytes restored diminished intracellular Ca2+ transients and sarcoplasmic reticulum (SR) Ca2+ load mechanistically due to increased SR Ca2+ uptake and reduced SR Ca2+ leak. Moreover, S100A1 gene transfer decreased elevated intracellular Na+ concentrations to levels detected in nonfailing cardiomyocytes, reversed reactivated fetal gene expression, and restored energy supply in failing cardiomyocytes. Intracoronary adenovirus-mediated S100A1 gene delivery in vivo to the postinfarcted failing rat heart normalized myocardial contractile function and Ca2+ handling, which provided support in a physiological context for results found in myocytes. Thus, the present study demonstrates that restoration of S100A1 protein levels in failing myocardium by gene transfer may be a novel therapeutic strategy for the treatment of heart failure.

Alterations in cardiac adrenergic signaling and calcium cycling differentially affect the progression of cardiomyopathy.

The medical treatment of chronic heart failure has undergone a dramatic transition in the past decade. Short-term approaches for altering hemodynamics have given way to long-term, reparative strategies, including beta-adrenergic receptor (betaAR) blockade. This was once viewed as counterintuitive, because acute administration causes myocardial depression. Cardiac myocytes from failing hearts show changes in betaAR signaling and excitation-contraction coupling that can impair cardiac contractility, but the role of these abnormalities in the progression of heart failure is controversial. We therefore tested the impact of different manipulations that increase contractility on the progression of cardiac dysfunction in a mouse model of hypertrophic cardiomyopathy. High-level overexpression of the beta(2)AR caused rapidly progressive cardiac failure in this model. In contrast, phospholamban ablation prevented systolic dysfunction and exercise intolerance, but not hypertrophy, in hypertrophic cardiomyopathy mice. Cardiac expression of a peptide inhibitor of the betaAR kinase 1 not only prevented systolic dysfunction and exercise intolerance but also decreased cardiac remodeling and hypertrophic gene expression. These three manipulations of cardiac contractility had distinct effects on disease progression, suggesting that selective modulation of particular aspects of betaAR signaling or excitation-contraction coupling can provide therapeutic benefit.

G Protein–Coupled Receptor Kinase 2 Ablation in Cardiac Myocytes Before or After Myocardial Infarction Prevents Heart Failure

Myocardial G protein-coupled receptor kinase (GRK)2 is a critical regulator of cardiac &bgr;-adrenergic receptor (&bgr;AR) signaling and cardiac function. Its upregulation in heart failure may further depress cardiac function and contribute to mortality in this syndrome. Preventing GRK2 translocation to activated &bgr;AR with a GRK2-derived peptide that binds G&bgr;&ggr; (&bgr;ARKct) has benefited some models of heart failure, but the precise mechanism is uncertain, because GRK2 is still present and &bgr;ARKct has other potential effects. We generated mice in which cardiac myocyte GRK2 expression was normal during embryonic development but was ablated after birth (&agr;MHC-Cre×GRK2 fl/fl) or only after administration of tamoxifen (&agr;MHC-MerCreMer×GRK2 fl/fl) and examined the consequences of GRK2 ablation before and after surgical coronary artery ligation on cardiac adaptation after myocardial infarction. Absence of GRK2 before coronary artery ligation prevented maladaptive postinfarction remodeling and preserved &bgr;AR responsiveness. Strikingly, GRK2 ablation initiated 10 days after infarction increased survival, enhanced cardiac contractile performance, and halted ventricular remodeling. These results demonstrate a specific causal role for GRK2 in postinfarction cardiac remodeling and heart failure and support therapeutic approaches of targeting GRK2 or restoring &bgr;AR signaling by other means to improve outcomes in heart failure.

Embryonic Stem Cell-Derived Exosomes Promote Endogenous Repair Mechanisms and Enhance Cardiac Function Following Myocardial Infarction

RATIONALE Embryonic stem cells (ESCs) hold great promise for cardiac regeneration but are susceptible to various concerns. Recently, salutary effects of stem cells have been connected to exosome secretion. ESCs have the ability to produce exosomes, however, their effect in the context of the heart is unknown. OBJECTIVE Determine the effect of ESC-derived exosome for the repair of ischemic myocardium and whether c-kit(+) cardiac progenitor cells (CPCs) function can be enhanced with ESC exosomes. METHODS AND RESULTS This study demonstrates that mouse ESC-derived exosomes (mES Ex) possess ability to augment function in infarcted hearts. mES Ex enhanced neovascularization, cardiomyocyte survival, and reduced fibrosis post infarction consistent with resurgence of cardiac proliferative response. Importantly, mES Ex augmented CPC survival, proliferation, and cardiac commitment concurrent with increased c-kit(+) CPCs in vivo 8 weeks after in vivo transfer along with formation of bonafide new cardiomyocytes in the ischemic heart. miRNA array revealed significant enrichment of miR290-295 cluster and particularly miR-294 in ESC exosomes. The underlying basis for the beneficial effect of mES Ex was tied to delivery of ESC specific miR-294 to CPCs promoting increased survival, cell cycle progression, and proliferation. CONCLUSIONS mES Ex provide a novel cell-free system that uses the immense regenerative power of ES cells while avoiding the risks associated with direct ES or ES-derived cell transplantation and risk of teratomas. ESC exosomes possess cardiac regeneration ability and modulate both cardiomyocyte and CPC-based repair programs in the heart.