Beta-adrenoceptors in cardiac disease

Functional-Molecular Mechanisms of Sympathetic-Parasympathetic Dysfunction in PVC-Induced Cardiomyopathy Revealed by Dual Stressor PVC-Exercise Challenge

BACKGROUND

The significance of autonomic dysfunction in premature ventricular contraction-induced cardiomyopathy (PVC-CM) remain unknown.

OBJECTIVE

Utilizing a novel "dual stressor" provocative challenge combining exercise with premature ventricular contraction (PVCs), the authors characterized the functional and molecular mechanisms of cardiac autonomic (cardiac autonomic nervous system) remodeling in a PVC-CM animal model.

METHODS

In 15 canines (8 experimental, 7 sham), we implanted pacemakers and neurotelemetry devices and subjected animals to 12 weeks of bigeminal PVCs to induce PVC-CM. Sympathetic nerve activity (SNA), vagal nerve activity (VNA), and heart rate were continuously recorded before, during, and after treadmill exercise challenge with and without PVCs, at baseline and after development of PVC-CM. Western blot and enzyme-linked immunosorbent assay were used to evaluate molecular markers of neural remodeling.

RESULTS

Exercise triggered an increase in both SNA and VNA followed by late VNA withdrawal. With PVCs, the degree of exercise-induced SNA augmentation was magnified, whereas late VNA withdrawal became blunted. After PVC-CM development, SNA was increased at rest but failed to adequately augment during exercise, especially with PVCs, coupled with impaired VNA and heart rate recovery after exercise. In the remodeled cardiac autonomic nervous system, there was widespread sympathetic hyperinnervation and elevated transcardiac norepinephrine levels but unchanged parasympathetic innervation, indicating sympathetic overload. However, cardiac nerve growth factor was paradoxically downregulated, suggesting an antineurotrophic counteradaptive response to PVC-triggered sympathetic overload.

CONCLUSIONS

Sympathetic overload, sympathetic dysfunction, and parasympathetic dysfunction in PVC-CM are unmasked by combined exercise and PVC challenge. Reduced cardiac neurotrophic factor might underlie the mechanisms of this dysfunction. Neuromodulation therapies to restore autonomic function could constitute a novel therapeutic approach for PVC-CM.

α7 nicotinic receptors play a role in regulation of cardiac hemodynamics

The α7 nicotinic receptors (NR) have been confirmed in the heart but their role in cardiac functions has been contradictory. To address these contradictory findings, we analyzed cardiac functions in α7 NR knockout mice (α7-/-) in vivo and ex vivo in isolated hearts. A standard limb leads electrocardiogram was used, and the pressure curves were recorded in vivo, in Arteria carotis and in the left ventricle, or ex vivo, in the left ventricle of the spontaneously beating isolated hearts perfused following Langedorff's method. Experiments were performed under basic conditions, hypercholinergic conditions, and adrenergic stress. The relative expression levels of α and β NR subunits, muscarinic receptors, β1 adrenergic receptors, and acetylcholine life cycle markers were determined using RT-qPCR. Our results revealed a prolonged QT interval in α7-/- mice. All in vivo hemodynamic parameters were preserved under all studied conditions. The only difference in ex vivo heart rate between genotypes was the loss of bradycardia in prolonged incubation of isoproterenol-pretreated hearts with high doses of acetylcholine. In contrast, left ventricular systolic pressure was lower under basal conditions and showed a significantly higher increase during adrenergic stimulation. No changes in mRNA expression were observed. In conclusion, α7 NR has no major effect on heart rate, except when stressed hearts are exposed to a prolonged hypercholinergic state, suggesting a role in acetylcholine spillover control. In the absence of extracardiac regulatory mechanisms, left ventricular systolic impairment is revealed.

Relation of Plasma Catecholamine Concentrations and Myocardial Mitochondrial Respiratory Activity in Anesthetized and Mechanically Ventilated, Cardiovascular Healthy Swine

Chronic heart failure is associated with reduced myocardial β-adrenergic receptor expression and mitochondrial function. Since these data coincide with increased plasma catecholamine levels, we investigated the relation between myocardial β-receptor expression and mitochondrial respiratory activity under conditions of physiological catecholamine concentrations. This post hoc analysis used material of a prospective randomized, controlled study on 12 sexually mature (age 20-24 weeks) Early Life Stress or control pigs (weaning at day 21 and 28-35 after birth, respectively) of either sex. Measurements in anesthetized, mechanically ventilated, and instrumented animals comprised serum catecholamine (liquid-chromatography/tandem-mass-spectrometry) and 8-isoprostane levels, whole blood superoxide anion concentrations (electron spin resonance), oxidative DNA strand breaks (tail moment in the "comet assay"), post mortem cardiac tissue mitochondrial respiration, and immunohistochemistry (β2-adrenoreceptor, mitochondrial respiration complex, and nitrotyrosine expression). Catecholamine concentrations were inversely related to myocardial mitochondrial respiratory activity and β2-adrenoceptor expression, whereas there was no relation to mitochondrial respiratory complex expression. Except for a significant, direct, non-linear relation between DNA damage and noradrenaline levels, catecholamine concentrations were unrelated to markers of oxidative stress. The present study suggests that physiological variations of the plasma catecholamine concentrations, e.g., due to physical and/or psychological stress, may affect cardiac β2-adrenoceptor expression and mitochondrial respiration.

Microtubule-Mediated Regulation of β2AR Translation and Function in Failing Hearts

BACKGROUND

β1AR (beta-1 adrenergic receptor) and β2AR (beta-2 adrenergic receptor)-mediated cyclic adenosine monophosphate signaling has distinct effects on cardiac function and heart failure progression. However, the mechanism regulating spatial localization and functional compartmentation of cardiac β-ARs remains elusive. Emerging evidence suggests that microtubule-dependent trafficking of mRNP (messenger ribonucleoprotein) and localized protein translation modulates protein compartmentation in cardiomyocytes. We hypothesized that β-AR compartmentation in cardiomyocytes is accomplished by selective trafficking of its mRNAs and localized translation.

METHODS

The localization pattern of β-AR mRNA was investigated using single molecule fluorescence in situ hybridization and subcellular nanobiopsy in rat cardiomyocytes. The role of microtubule on β-AR mRNA localization was studied using vinblastine, and its effect on receptor localization and function was evaluated with immunofluorescent and high-throughput Förster resonance energy transfer microscopy. An mRNA protein co-detection assay identified plausible β-AR translation sites in cardiomyocytes. The mechanism by which β-AR mRNA is redistributed post-heart failure was elucidated by single molecule fluorescence in situ hybridization, nanobiopsy, and high-throughput Förster resonance energy transfer microscopy on 16 weeks post-myocardial infarction and detubulated cardiomyocytes.

RESULTS

β1AR and β2AR mRNAs show differential localization in cardiomyocytes, with β1AR found in the perinuclear region and β2AR showing diffuse distribution throughout the cell. Disruption of microtubules induces a shift of β2AR transcripts toward the perinuclear region. The close proximity between β2AR transcripts and translated proteins suggests that the translation process occurs in specialized, precisely defined cellular compartments. Redistribution of β2AR transcripts is microtubule-dependent, as microtubule depolymerization markedly reduces the number of functional receptors on the membrane. In failing hearts, both β1AR and β2AR mRNAs are redistributed toward the cell periphery, similar to what is seen in cardiomyocytes undergoing drug-induced detubulation. This suggests that t-tubule remodeling contributes to β-AR mRNA redistribution and impaired β2AR function in failing hearts.

CONCLUSIONS

Asymmetrical microtubule-dependent trafficking dictates differential β1AR and β2AR localization in healthy cardiomyocyte microtubules, underlying the distinctive compartmentation of the 2 β-ARs on the plasma membrane. The localization pattern is altered post-myocardial infarction, resulting from transverse tubule remodeling, leading to distorted β2AR-mediated cyclic adenosine monophosphate signaling.

The Sympathetic Nervous System in Hypertensive Heart Failure with Preserved LVEF

The neurohormonal model of heart failure (HF) pathogenesis states that a reduction in cardiac output caused by cardiac injury results in sympathetic nervous system (SNS) activation, that is adaptive in the short-term and maladaptive in the long-term. This model has proved extremely valid and has been applied in HF with a reduced left ventricular (LV) ejection fraction (LVEF). In contrast, it has been undermined in HF with preserved LVEF (HFpEF), which is due to hypertension (HTN) in the vast majority of the cases. Erroneously, HTN, which is the leading cause of cardiovascular disease and premature death worldwide and is present in more than 90% of HF patients, is tightly linked with SNS overactivity. In this paper we provide a contemporary overview of the contribution of SNS overactivity to the development and progression of hypertensive HF (HHF) as well as the clinical implications resulting from therapeutic interventions modifying SNS activity. Throughout the manuscript the terms HHF with preserved LVEF and HfpEF will be used interchangeably, considering that the findings in most HFpEF studies are driven by HTN.

Beta-Blockers and Their Current Role in Maternal and Neonatal Health: A Narrative Review of the Literature

Beta-blockers are a class of medications that act on beta-adrenergic receptors and are categorized as cardio-selective and non-selective. They are principally used to treat cardiovascular conditions such as hypertension and arrhythmias. Beta-blockers have also been used to treat non-cardiogenic indications in non-pregnant individuals and the pediatric population. In pregnancy, labetalol is the mainstay treatment for hypertension and other cardiovascular indications. However, contraindications to certain sub-types of beta-blockers include bradycardia, heart failure, obstructive lung diseases, and hemodynamic instability. There is conflicting evidence of the adverse effects on fetal and neonatal health due to a scarce safety and efficacy profile, and further studies are necessary to understand the pharmacokinetics of the different classes of beta-blockers in pregnancy and fetal health. Understanding the hemodynamic changes during the stages of pregnancy is important to target a more beneficial therapy for both mother and fetus as well as better neonatal outcomes. Beta-blocker use in the pediatric population is less documented in studies but does have the potential to treat various cardiogenic and non-cardiogenic conditions. Future comprehensive studies would further benefit the direction of beta-blocker treatment during pregnancy in neonates and pediatrics.

Cardiac PDGFRα+ interstitial cells generate spontaneous inward currents that contribute to excitability in the heart

The cell types and conductance that contribute to normal cardiac functions remain under investigation. We used mice that express an enhanced green fluorescent protein (eGFP)-histone 2B fusion protein driven off the cell-specific endogenous promoter for Pdgfra to investigate the distribution and functional role of PDGFRα+ cells in the heart. Cardiac PDGFRα+ cells were widely distributed within the endomysium of atria, ventricle, and sino-atrial node (SAN) tissues. PDGFRα+ cells formed a discrete network of cells, lying in close apposition to neighboring cardiac myocytes in mouse and Cynomolgus monkey (Macaca fascicularis) hearts. Expression of eGFP in nuclei allowed unequivocal identification of these cells following enzymatic dispersion of muscle tissues. FACS purification of PDGFRα+ cells from the SAN and analysis of gene transcripts by qPCR revealed that they were a distinct population of cells that expressed gap junction transcripts, Gja1 and Gjc1. Cardiac PDGFRα+ cells generated spontaneous transient inward currents (STICs) and spontaneous transient depolarizations (STDs) that reversed at 0 mV. Reversal potential was maintained when ECl  = -40 mV. [Na+ ]o replacement and FTY720 abolished STICs, suggesting they were due to a non-selective cation conductance (NSCC) carried by TRPM7. PDGFRα+ cells also express β2 -adrenoceptor gene transcripts, Adrb2. Zinterol, a selective β2 -receptor agonist, increased the amplitude and frequency of STICs, suggesting these cells could contribute to adrenergic regulation of cardiac excitability. PDGFRα+ cells in cardiac muscles generate inward currents via an NSCC. STICs generated by these cells may contribute to the integrated membrane potentials of cardiac muscles, possibly affecting the frequency of pacemaker activity.

Beta-blockers in cardiac arrhythmias-Clinical pharmacologist's point of view

β-blockers is a vast group of antiarrhythmic drugs which differ in their pharmacokinetic and chemical properties. Some of them block β-adrenergic receptors selectively while the others work non-selectively. Consequently, they reduce the influence of the sympathetic nervous system on the heart, acting negatively inotropic, chronotropic, bathmotropic and dromotropic. Although they have been present in medicine since the beginning of the 1960s, they still play a crucial role in the treatment of cardiac arrhythmias. They are also first-line group of drugs used to control the ventricular rate in patients with the most common arrhythmia-atrial fibrillation. Previous reports indicate that infection with SARS-CoV-2 virus may constitute an additional risk factor for arrhythmia. Due to the aging of the population in developed countries and the increase in the number of patients with cardiac burden, the number of people suffering from cardiac arrhythmias will increase in the upcoming years. As a result the role of above-mentioned beta-blockers will remain significant. Particularly noteworthy is propranolol-the oldest beta adrenergic antagonist, which in recent years has found additional applications due to its unique properties. In this article, we reviewed the accessible literature and summarized the current guidelines on the use of beta-blockers in the treatment of cardiac arrhythmias.

Autonomic Nervous System Regulation of Epicardial Adipose Tissue: Potential Roles for Regulator of G Protein Signaling-4

The epicardial adipose tissue (EAT) or epicardial fat is a visceral fat depot in the heart that contains intrinsic adrenergic and cholinergic nerves, through which it interacts with the cardiac sympathetic (adrenergic) and parasympathetic (cholinergic) nervous systems. These EAT nerves represent a significant source of several adipokines and other bioactive molecules, including norepinephrine, epinephrine, and free fatty acids. The production of these molecules is biologically relevant for the heart, since abnormalities in EAT secretion are implicated in the development of pathological conditions, including coronary atherosclerosis, atrial fibrillation, and heart failure. Sympathetic hyperactivity and parasympathetic (cholinergic) derangement are associated with EAT dysfunction, leading to a variety of adverse cardiac conditions, such as heart failure, diastolic dysfunction, atrial fibrillation, etc.; therefore, several studies have focused on exploring the autonomic regulation of EAT as it pertains to heart disease pathogenesis and progression. In addition, Regulator of G protein Signaling (RGS)-4 is a protein with significant regulatory roles in both adrenergic and muscarinic receptor signaling in the heart. In this review, we provide an overview of the autonomic regulation of EAT, with a specific focus on cardiac RGS4 and the potential roles this protein plays in this regulation.

Flavonoid Extract from Propolis Provides Cardioprotection following Myocardial Infarction by Activating PPAR-γ

We have previously reported that flavonoid extract from propolis (FP) can improve cardiac function in rats following myocardial infarction (MI). However, the mechanisms responsible for the cardioprotective effects of FP have not been fully elucidated. In the current study, we explored whether FP can reduce inflammatory cytokines and attenuate sympathetic nerve system activity and antiendoplasmic reticulum (ER) stress and whether the cardioprotective effects are related to peroxisome proliferator-activated receptor gamma (PPAR-γ) activation. Sprague Dawley rats were randomly divided into six groups: Sham group received the surgical procedure but no artery was ligated; MI group received ligation of the left anterior descending (LAD) branch of the coronary artery; MI + FP group received FP (12.5 mg/kg/d, intragastrically) seven days prior to LAD ligation; FP group (Sham group + 12.5 mg/kg/d, intragastrically); MI + FP + GW9662 group received FP prior to LAD ligation with the addition of a specific PPAR-γ inhibitor (GW9662), 1 mg/kg/d, orally); and MI + GW9662 group received the PPAR-γ inhibitor and LAD ligation. The results demonstrated that the following inflammatory markers were significantly elevated following MI as compared with expression in sham animals: IL-1β, TNF-α, CRP; markers of sympathetic activation: plasma norepinephrine, epinephrine and GAP43, nerve growth factor, thyroid hormone; and ER stress response markers GRP78 and CHOP. Notably, the above changes were attenuated by FP, and GW9662 was able to alleviate the effect of FP. In conclusion, FP induces a cardioprotective effect following myocardial infarction by activating PPAR-γ, leading to less inflammation, cardiac sympathetic activity, and ER stress.

C-Reactive Protein (CRP) Blocks the Desensitization of Agonistic Stimulated G Protein Coupled Receptors (GPCRs) in Neonatal Rat Cardiomyocytes

Recently, C-reactive protein (CRP) was shown to affect intracellular calcium signaling and blood pressure in vitro and in vivo, respectively. The aim of the present study was to further investigate if a direct effect on G-protein coupled receptor (GPCR) signaling by CRP can be observed by using CRP in combination with different GPCR agonists on spontaneously beating cultured neonatal rat cardiomyocytes. All used agonists (isoprenaline, clenbuterol, phenylephrine, angiotensin II and endothelin 1) affected the beat rate of cardiomyocytes significantly and after washing them out and re-stimulation the cells developed a pronounced desensitization of the corresponding receptors. CRP did not affect the basal beating-rate nor the initial increase/decrease in beat-rate triggered by different agonists. However, CRP co-incubated cells did not exhibit desensitization of the respective GPCRs after the stimulation with the different agonists. This lack of desensitization was independent of the GPCR type, but it was dependent on the CRP concentration. Therefore, CRP interferes with the desensitization of GPCRs and has to be considered as a novel regulator of adrenergic, angiotensin-1 and endothelin receptors.

Comparative characterization of β-adrenoceptors in the bladder, heart, and lungs of rats: Alterations in spontaneously hypertensive rats

The present study aimed to characterize and compare β-adrenoceptors in the rat bladder with those in the heart and lungs of SD rats (8-10 weeks old) using subtype-selective agonists and antagonists in a radioligand binding assay with (-)-[125I]cyanopindolol ([125I]CYP), and also to clarify alterations in β-adrenoceptors in the bladder of spontaneously hypertensive rats (SHR) at 14 weeks old, from those of Wistar-Kyoto rats (WKY) and Wistar rats at the same age. A radioligand binding assay with [125I]CYP was used to measure β-adrenoceptor binding activity in rat tissues. Metoprolol exhibited the highest affinity to specific binding sites of [125I]CYP in the rat heart, indicating the dominance of β1-adrenoceptors. β3-selective agonists (BRL37344 and CL316243) and antagonist (SR59230A) exhibited higher affinity to specific binding sites of [125I]CYP in the bladder than in the heart and lungs. Furthermore, the binding affinity of the β2-selective antagonist, ICI118551 was the highest in the bladder. The Bmax of specific [125]CYP binding in the bladder was significantly lower in WKY and SHR than in Wistar rats. The present study provides further evidence for the coexistence of β2-and β3-adrenoceptors in the rat bladder, and indicates that β-adrenoceptor density is lower in the bladders of WKY and SHR.

Electrophysiological Remodeling: Cardiac T-Tubules and ß-Adrenoceptors

Beta-adrenoceptors (βAR) are often viewed as archetypal G-protein coupled receptors. Over the past fifteen years, investigations in cardiovascular biology have provided remarkable insights into this receptor family. These studies have shifted pharmacological dogma, from one which centralized the receptor to a new focus on structural micro-domains such as caveolae and t-tubules. Important studies have examined, separately, the structural compartmentation of ion channels and βAR. Despite links being assumed, relatively few studies have specifically examined the direct link between structural remodeling and electrical remodeling with a focus on βAR. In this review, we will examine the nature of receptor and ion channel dysfunction on a substrate of cardiomyocyte microdomain remodeling, as well as the likely ramifications for cardiac electrophysiology. We will then discuss the advances in methodologies in this area with a specific focus on super-resolution microscopy, fluorescent imaging, and new approaches involving microdomain specific, polymer-based agonists. The advent of powerful computational modelling approaches has allowed the science to shift from purely empirical work, and may allow future investigations based on prediction. Issues such as the cross-reactivity of receptors and cellular heterogeneity will also be discussed. Finally, we will speculate as to the potential developments within this field over the next ten years.

The Use of β-Blockers in Heart Failure with Reduced Ejection Fraction

Treatment with β-blockers is the main strategy for managing patients with heart failure and reduced ejection fraction because of their ability to reverse the neurohumoral effects of the sympathetic nervous system, with consequent prognostic and symptomatic benefits. However, to date, they are underused, mainly because of the misconception that hypotension and bradycardia may worsen the haemodynamic status of patients with HFrEF and because of the presence of comorbidities falsely believed to be absolute contraindications to their use. To promote proper use of β-blockers in this article, we review the clinical pharmacology of β-blockers, the evidence of the beneficial effects of these drugs in heart failure with reduced ejection fraction, and the current guidelines for their use in clinical practice and in the presence of comorbidities (e.g., pulmonary disease, diabetes, atrial fibrillation, peripheral arterial disease, etc.). It is hoped that the practical approach discussed in this review will allow for a proper diffusion of knowledge about the correct use of β-blockers and the drug-disease interactions to achieve their increased use and titration, as well as for the selection of a specific agent with a view to a properly tailored approach for HFrEF patients.

Xiao-Qing-Long-Tang Maintains Cardiac Function during Heart Failure with Reduced Ejection Fraction in Salt-Sensitive Rats by Regulating the Imbalance of Cardiac Sympathetic Innervation

Objective

The anatomical and functional imbalances of sympathetic nerves are associated with cardiovascular disease progression. Xiao-Qing-Long-Tang (XQLT), an ancient Chinese herbal formula, has been used to treat cardiovascular diseases in eastern Asia for thousands of years. We determined the effect of XQLT in maintaining cardiac function during heart failure with reduced ejection fraction (HFrEF) with respect to its neurobiological effects in salt-sensitive rats.

Methods

Dahl salt-sensitive (DS) rats were fed a high-salt diet to establish an HFrEF model and were divided into model (DS, administered normal saline) and XQL groups (administrated XQLT) randomly, with SS-13BN rats being used as the control. The bodyweight and blood pressure of rats were observed regularly. Electrocardiogram, echocardiography, and plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) were determined to assess cardiac function. The sympathetic tune and myocardial morphological changes were evaluated. Western blot and qRT-PCR were used to assay the expression of the nerve growth factor (NGF) and leukemia inhibitory factor (LIF). Tyrosine hydroxylase (TH), choline acetyltransferase (CHAT), and growth-associated protein 43 (GAP43) were assayed to confirm sympathetic remodeling. The micromorphological changes in cardiac sympathetic nerve endings were observed by transmission electron microscopy.

Results

Four weeks after XQLT treatment, cardiac function and bodyweight were higher and blood pressure was lower than that of the DS group. Myocardial noradrenaline (NA) increased, while the plasma NA level decreased significantly. The morphology demonstrated that XQLT significantly alleviated myocardial damage. XQLT decreased the expression of LIF, increased the expression of NGF, enhanced the TH+/GAP43+ and TH+/CHAT + positive nerve fiber density, and improved the TH and GAP43 protein expression, but had no effect on CHAT. Moreover, XQLT improved the micromorphology of sympathetic nerve endings in the myocardium.

Conclusion

XQLT maintains cardiac function during HFrEF in salt-sensitive rats, in part, by regulating the imbalance of cardiac sympathetic innervation.

β-Arrestin as a Therapeutic Target in Heart Failure

Heart failure is a major source of morbidity and mortality, driven, in part, by maladaptive sympathetic hyperactivity in response to poor cardiac output. Current therapies target β-adrenergic and angiotensin II G protein-coupled receptors to reduce adverse cardiac remodeling and improve clinical outcomes; however, there is a pressing need for new therapeutic approaches to preserve cardiac function. β-arrestin is a multifunctional protein which has come under analysis in recent years as a key player in G protein-coupled receptor signal transduction and a potential therapeutic target in heart failure. β-arrestin attenuates β-adrenergic and angiotensin II receptor signaling to limit the deleterious response to excessive sympathetic stimulation while simultaneously transactivating cardioprotective signaling cascades that preserve cardiac structure and function in response to injury. β-arrestin signaling may provide unique advantages compared to classic heart failure treatment approaches, but a number of challenges currently limit clinical applications. In this review, we discuss the role and functions of β-arrestin and the current attempts to develop G protein-coupled receptor agonists biased towards β-arrestin activation. Furthermore, we examine the functional diversity of cardiac β-arrestin isotypes to explore key considerations in the promise of β-arrestin as a pharmacotherapeutic target in heart failure.

Adrenergic Downregulation in Critical Care: Molecular Mechanisms and Therapeutic Evidence

Catecholamines remain the mainstay of therapy for acute cardiovascular dysfunction. However, adrenergic receptors quickly undergo desensitization and downregulation after prolonged stimulation. Moreover, prolonged exposure to high circulating catecholamines levels is associated with several adverse effects on different organ systems. Unfortunately, in critically ill patients, adrenergic downregulation translates into progressive reduction of cardiovascular response to exogenous catecholamine administration, leading to refractory shock. Accordingly, there has been a growing interest in recent years toward use of noncatecholaminergic inotropes and vasopressors. Several studies investigating a wide variety of catecholamine-sparing strategies (eg, levosimendan, vasopressin, β-blockers, steroids, and use of mechanical circulatory support) have been published recently. Use of these agents was associated with improvement in hemodynamics and decreased catecholamine use but without a clear beneficial effect on major clinical outcomes. Accordingly, additional research is needed to define the optimal management of catecholamine-resistant shock.

Adrenoceptor regulation of the mechanistic target of rapamycin in muscle and adipose tissue

A vital role of adrenoceptors in metabolism and energy balance has been well documented in the heart, skeletal muscle, and adipose tissue. It has been only recently demonstrated, however, that activation of the mechanistic target of rapamycin (mTOR) makes a significant contribution to various metabolic and physiological responses to adrenoceptor agonists. mTOR exists as two distinct complexes named mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) and has been shown to play a critical role in protein synthesis, cell proliferation, hypertrophy, mitochondrial function, and glucose uptake. This review will describe the physiological significance of mTORC1 and 2 as a novel paradigm of adrenoceptor signalling in the heart, skeletal muscle, and adipose tissue. Understanding the detailed signalling cascades of adrenoceptors and how they regulate physiological responses is important for identifying new therapeutic targets and identifying novel therapeutic interventions. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Detailed insight on β-adrenoceptors as therapeutic targets

Human G protein-coupled receptors (GPCRs), especially adrenoceptors, play a crucial role in maintaining important physiological activities including cardiovascular and pulmonary functions. Among all adrenoceptors, β-adrenoceptors are the best characterized GPCRs and possess distinctive features as drug targets. Similarly, ligands that activate/deactivate β-adrenoceptors also hold a significant position in the field of biomarker identification and drug discovery. Several studies regarding molecular characterization of the β-adrenoceptor ligands have revealed that ligands with abilities to inhibit basal or intrinsic receptor activity or prevent receptor desensitization are particularly important to efficiently manage detrimental health conditions, including chronic heart failure, asthma, chronic obstructive pulmonary disease, obesity, and diabetes. Given the importance of β-adrenoceptors as molecular targets for many pathological conditions, this review aims to provide a detailed insight on the structural and functional aspects of β-adrenoceptors, with a particular emphasis on their importance as biomarkers and therapeutic targets.

β-Adrenergic Receptor Signaling and Heart Failure: From Bench to Bedside

Despite improvements in management and therapeutic approach in the last decades, heart failure is still associated with high mortality rates. The sustained enhancement in the sympathetic nervous system tone, observed in patients with heart failure, causes alteration in β-adrenergic receptor signaling and function. This latter phenomenon is the result of several heart failure-related molecular abnormalities involving adrenergic receptors, G-protein-coupled receptor kinases, and β-arrestins. This article summarizes novel encouraging preclinical strategies to reactivate β-adrenergic receptor signaling in heart failure, including pharmacologic and gene therapy approaches, and attempts to translate acquired notions into the clinical setting.

GRK2 and GRK5 as therapeutic targets and their role in maladaptive and pathological cardiac hypertrophy

INTRODUCTION

One in every four deaths in the United States is attributed to cardiovascular disease, hence the development and employment of novel and effective therapeutics are necessary to improve the quality of life and survival of affected patient. Pathological hypertrophy is a maladaptive response by the heart to relieve wall stress that could result from cardiovascular disease. Maladaptive hypertrophy can lead to further disease progression and complications such as heart failure; hence, efforts to target hypertrophy to prevent and treat further morbidity and mortality are necessary. Areas covered: This review summarizes the compelling literature that describes the mechanistic role of GRK2 and GRK5 in maladaptive cardiac hypertrophy; it examines the approaches to inhibit these kinases in hypertrophic animal models and furthermore, it assesses the potential of GRK2 and GRK5 as therapeutic targets for hypertrophy. Expert opinion: GRK2 and GRK5 are novel therapeutic targets for pathological hypertrophy and may have added benefits of ameliorating morbidity and mortality. Despite the lesser researched role of GRK2 in cardiac hypertrophy, it may be the advantageous strategy for treating cardiac hypertrophy because of its role in other maladaptive pathways. Anti-GRK2 therapy optimization and the discovery and development of specific GRK2 and GRK5 small-molecule inhibitors is necessary for the eventual application of successful, effective therapeutics.

Therapeutic Targets for Treatment of Heart Failure: Focus on GRKs and β-Arrestins Affecting βAR Signaling

Heart failure (HF) is a heart disease that is classified into two main types: HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). Both types of HF lead to significant risk of mortality and morbidity. Pharmacological treatment with β-adrenergic receptor (βAR) antagonists (also called β-blockers) has been shown to reduce the overall hospitalization and mortality rates and improve the clinical outcomes in HF patients with HFrEF but not HFpEF. Although, the survival rate of patients suffering from HF continues to drop, the management of HF still faces several limitations and discrepancies highlighting the need to develop new treatment strategies. Overstimulation of the sympathetic nervous system is an adaptive neurohormonal response to acute myocardial injury and heart damage, whereas prolonged exposure to catecholamines causes defects in βAR regulation, including a reduction in the amount of βARs and an increase in βAR desensitization due to the upregulation of G protein-coupled receptor kinases (GRKs) in the heart, contributing in turn to the progression of HF. Several studies show that myocardial GRK2 activity and expression are raised in the failing heart. Furthermore, β-arrestins play a pivotal role in βAR desensitization and, interestingly, can mediate their own signal transduction without any G protein-dependent pathway involved. In this review, we provide new insight into the role of GRKs and β-arrestins on how they affect βAR signaling regarding the molecular and cellular pathophysiology of HF. Additionally, we discuss the therapeutic potential of targeting GRKs and β-arrestins for the treatment of HF.

Stimulation of the Beta2 Adrenergic Receptor at Reperfusion Limits Myocardial Reperfusion Injury via an Interleukin-10-Dependent Anti-Inflammatory Pathway in the Spleen

BACKGROUND

In addition to the airway-relaxing effects, β₂ adrenergic receptor (β₂AR) agonists are also found to have broad anti-inflammatory effects. The current study was conducted to define the role of β₂AR agonists in limiting myocardial ischemia/reperfusion injury (IRI). Methods and Results: Adult male wild-type (WT) and interleukin (IL)-10 knockout (KO) mice underwent a 40-min left coronary artery ligation and 60-min reperfusion. A selective β₂AR agonist, Clenbuterol, at doses of 0.1 μg or 1 μg/g weight i.v. 5 min before reperfusion, significantly reduced myocardial infarct size (IS) by 28% and 39% (vs. control, P<0.05) in WT mice respectively, but had no protective effect in IL-10 KO mice. Inhalational therapy with nebulized Clenbuterol, Albuterol, Salmeterol or Arformoterol immediately before ischemia significantly reduced IS (P<0.05) in WT mice. Splenectomy similarly reduced IS as Clenbuterol-treated mice, but intravenous Clenbuterol did not further reduce IS in splenectomized mice. In splenectomized WT mice, acute transfer of isolated splenocytes, not the Clenbuterol-pretreated splenocytes, restored the myocardial IS to the level of intact mice. Intravenous Clenbuterol significantly increased splenic protein levels of β₂AR, phosphorylated Akt and IL-10 and plasma IL-10, and inhibited the expression of pro-inflammatory mRNAs.

CONCLUSIONS

Both intravenous and inhalational β₂AR agonists exert a cardioprotective effect against IRI by activating the anti-inflammatory β₂AR-IL-10 pathway.

Novel Paradigms Governing β1-Adrenergic Receptor Trafficking in Primary Adult Rat Cardiac Myocytes

The β₁-adrenergic receptor (β₁-AR) is a major cardiac G protein-coupled receptor, which mediates cardiac actions of catecholamines and is involved in genesis and treatment of numerous cardiovascular disorders. In mammalian cells, catecholamines induce the internalization of the β₁-AR into endosomes and their removal promotes the recycling of the endosomal β₁-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the β₁-AR in response to β-agonists and antagonists was determined by confocal microscopy in primary adult rat ventricular myocytes (ARVMs), which are terminally differentiated myocytes with unique structures such as transverse tubules (T-tubules) and contractile sarcomeres. In unstimulated ARVMs, the fluorescently labeled β₁-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface β₁-ARs into small (∼225-250 nm) regularly spaced internal punctate structures that overlapped with puncta stained by Di-8 ANEPPS, a membrane-impermeant T-tubule-specific dye. Replacing the β-agonist with the β-blocker alprenolol, induced the translocation of the wild-type β₁-AR from these punctate structures back to the plasma membrane. This step was dependent on two barcodes, namely, the type-1 PDZ binding motif and serine at position 312 of the β₁-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the β₁-AR. These data show that redistribution of the β₁-AR in ARVMs from internal structures back to the plasma membrane was mediated by a novel sorting mechanism, which might explain unique aspects of cardiac β₁-AR signaling under normal or pathologic conditions.

Cross-Talk Between Insulin Signaling and G Protein-Coupled Receptors

Diabetes is a major risk factor for the development of heart failure. One of the hallmarks of diabetes is insulin resistance associated with hyperinsulinemia. The literature shows that insulin and adrenergic signaling is intimately linked to each other; however, whether and how insulin may modulate cardiac adrenergic signaling and cardiac function remains unknown. Notably, recent studies have revealed that insulin receptor and β2 adrenergic receptor (β2AR) forms a membrane complex in animal hearts, bringing together the direct contact between 2 receptor signaling systems, and forming an integrated and dynamic network. Moreover, insulin can drive cardiac adrenergic desensitization via protein kinase A and G protein-receptor kinases phosphorylation of the β2AR, which compromises adrenergic regulation of cardiac contractile function. In this review, we will explore the current state of knowledge linking insulin and G protein-coupled receptor signaling, especially β-adrenergic receptor signaling in the heart, with emphasis on molecular insights regarding its role in diabetic cardiomyopathy.

Mechanisms of Cardiovascular Protection Associated with Intermittent Hypobaric Hypoxia Exposure in a Rat Model: Role of Oxidative Stress

More than 140 million people live and works (in a chronic or intermittent form) above 2500 m worldwide and 35 million live in the Andean Mountains. Furthermore, in Chile, it is estimated that 55,000 persons work in high altitude shifts, where stays at lowlands and interspersed with working stays at highlands. Acute exposure to high altitude has been shown to induce oxidative stress in healthy human lowlanders, due to an increase in free radical formation and a decrease in antioxidant capacity. However, in animal models, intermittent hypoxia (IH) induce preconditioning, like responses and cardioprotection. Here, we aimed to describe in a rat model the responses on cardiac and vascular function to 4 cycles of intermittent hypobaric hypoxia (IHH). Twelve adult Wistar rats were randomly divided into two equal groups, a four-cycle of IHH, and a normobaric hypoxic control. Intermittent hypoxia was induced in a hypobaric chamber in four continuous cycles (1 cycle = 4 days hypoxia + 4 days normoxia), reaching a barometric pressure equivalent to 4600 m of altitude (428 Torr). At the end of the first and fourth cycle, cardiac structural, and functional variables were determined by echocardiography. Thereafter, ex vivo vascular function and biomechanical properties were determined in femoral arteries by wire myography. We further measured cardiac oxidative stress biomarkers (4-Hydroxy-nonenal, HNE; nytrotirosine, NT), reactive oxygen species (ROS) sources (NADPH and mitochondrial), and antioxidant enzymes activity (catalase, CAT; glutathione peroxidase, GPx, and superoxide dismutase, SOD). Our results show a higher ejection and shortening fraction of the left ventricle function by the end of the 4th cycle. Further, femoral vessels showed an improvement of vasodilator capacity and diminished stiffening. Cardiac tissue presented a higher expression of antioxidant enzymes and mitochondrial ROS formation in IHH, as compared with normobaric hypoxic controls. IHH exposure determines a preconditioning effect on the heart and femoral artery, both at structural and functional levels, associated with the induction of antioxidant defence mechanisms. However, mitochondrial ROS generation was increased in cardiac tissue. These findings suggest that initial states of IHH are beneficial for cardiovascular function and protection.

Onset of decreased heart work is correlated with increased heart rate and shortened QT interval in high-carbohydrate fed overweight rats

Mechanical activity of the heart is adversely affected in metabolic syndrome (MetS) characterized by increased body mass and marked insulin resistance. Herein, we examined the effects of high carbohydrate intake on cardiac function abnormalities by evaluating in situ heart work, heart rate, and electrocardiograms (ECGs) in rats. MetS was induced in male Wistar rats by adding 32% sucrose to drinking water for 22–24 weeks and was confirmed by insulin resistance, increased body weight, increased blood glucose and serum insulin, and increased systolic and diastolic blood pressures in addition to significant loss of left ventricular integrity and increased connective tissue around myofibrils. Analysis of in situ ECG recordings showed a markedly shortened QT interval and decreased QRS amplitude with increased heart rate. We also observed increased oxidative stress and decreased antioxidant defense characterized by decreases in serum total thiol level and attenuated paraoxonase and arylesterase activities. Our data indicate that increased heart rate and a shortened QT interval concomitant with higher left ventricular developed pressure in response to β-adrenoreceptor stimulation as a result of less cyclic AMP release could be regarded as a natural compensation mechanism in overweight rats with MetS. In addition to the persistent insulin resistance and obesity associated with MetS, one should consider the decreased heart work, increased heart rate, and shortened QT interval associated with high carbohydrate intake, which may have more deleterious effects on the mammalian heart.

Visualization and quantification of GPCR trafficking in mammalian cells by confocal microscopy

G protein-coupled receptors (GPCRs) are recognized as one of the most fruitful group of therapeutic targets, accounting for more than 40% of all approved pharmaceuticals on the market. Therefore, the search for selective agents that affect GPCR function is of major interest to the pharmaceutical industry. This chapter describes methods for measuring agonist-promoted GPCR trafficking, which involves the internalization of the GPCR and its subsequent recycling back to the plasma membrane or retention and eventual degradation. These pathways will be analyzed by confocal cellular imaging, using the β₁-adrenergic receptor (β₁-AR) as a primary model. A major problem encountered in studying GPCR trafficking is the unavailability of antibodies that would recognize the native receptor in cells or tissues. Therefore, wild-type, point mutants, and β₁-AR chimeras are generated as epitope-tagged proteins, which are stably- or transiently expressed in mammalian cells. GPCR are labeled with a fluorophore-conjugated antibody directed against the N-terminal epitope tag. The trafficking of the fluorophore-tagged GPCR between divergent trafficking pathways that result in retention and eventual degradation or recycling and reinsertion into the plasma membrane can be followed by confocal immunofluorescence microscopy techniques outlined in this review.

Barcoding of GPCR trafficking and signaling through the various trafficking roadmaps by compartmentalized signaling networks

Proper signaling by G protein coupled receptors (GPCR) is dependent on the specific repertoire of transducing, enzymatic and regulatory kinases and phosphatases that shape its signaling output. Activation and signaling of the GPCR through its cognate G protein is impacted by G protein-coupled receptor kinase (GRK)-imprinted "barcodes" that recruit β-arrestins to regulate subsequent desensitization, biased signaling and endocytosis of the GPCR. The outcome of agonist-internalized GPCR in endosomes is also regulated by sequence motifs or "barcodes" within the GPCR that mediate its recycling to the plasma membrane or retention and eventual degradation as well as its subsequent signaling in endosomes. Given the vast number of diverse sequences in GPCR, several trafficking mechanisms for endosomal GPCR have been described. The majority of recycling GPCR, are sorted out of endosomes in a "sequence-dependent pathway" anchored around a type-1 PDZ-binding module found in their C-tails. For a subset of these GPCR, a second "barcode" imprinted onto specific GPCR serine/threonine residues by compartmentalized kinase networks was required for their efficient recycling through the "sequence-dependent pathway". Mutating the serine/threonine residues involved, produced dramatic effects on GPCR trafficking, indicating that they played a major role in setting the trafficking itinerary of these GPCR. While endosomal SNX27, retromer/WASH complexes and actin were required for efficient sorting and budding of all these GPCR, additional proteins were required for GPCR sorting via the second "barcode". Here we will review recent developments in GPCR trafficking in general and the human β1-adrenergic receptor in particular across the various trafficking roadmaps. In addition, we will discuss the role of GPCR trafficking in regulating endosomal GPCR signaling, which promote biochemical and physiological effects that are distinct from those generated by the GPCR signal transduction pathway in membranes.

New and Emerging Therapies and Targets: Beta-3 Agonists

While crucial for the acute physiologic response to stress, the adrenergic system may become maladaptive upon prolonged stimulation in the course of development of heart failure. This has been the basis for the development of beta-blocking therapies, targeting mainly beta1-2 adrenoreceptors (B1-2AR). The third isotype, B3AR, was more recently identified in cardiac myocytes and endothelial cells from human (and many other animal species), where its distinctive coupling to nitric oxide and antioxidant pathways suggested potential protective properties that were unexploited so far. The observation of beneficial effects of B3AR expression/activation on myocardial remodeling and the availability of specific agonists for clinical use now open the way for directly testing the hypothesis in heart failure patients. We will briefly review the specificities of B3AR signaling in the context of the cardiovascular adrenergic system, the evidence supporting its beneficial effects and outline an ongoing clinical trial using the B3AR agonist, mirabegron in patients with/at risk of developing heart failure with preserved ejection fraction (HFpEF).

T-Tubular Electrical Defects Contribute to Blunted β-Adrenergic Response in Heart Failure

Alterations of the β-adrenergic signalling, structural remodelling, and electrical failure of T-tubules are hallmarks of heart failure (HF). Here, we assess the effect of β-adrenoceptor activation on local Ca²⁺ release in electrically coupled and uncoupled T-tubules in ventricular myocytes from HF rats. We employ an ultrafast random access multi-photon (RAMP) microscope to simultaneously record action potentials and Ca²⁺ transients from multiple T-tubules in ventricular cardiomyocytes from a HF rat model of coronary ligation compared to sham-operated rats as a control. We confirmed that β-adrenergic stimulation increases the frequency of Ca²⁺ sparks, reduces Ca²⁺ transient variability, and hastens the decay of Ca²⁺ transients: all these effects are similarly exerted by β-adrenergic stimulation in control and HF cardiomyocytes. Conversely, β-adrenergic stimulation in HF cells accelerates a Ca²⁺ rise exclusively in the proximity of T-tubules that regularly conduct the action potential. The delayed Ca²⁺ rise found at T-tubules that fail to conduct the action potential is instead not affected by β-adrenergic signalling. Taken together, these findings indicate that HF cells globally respond to β-adrenergic stimulation, except at T-tubules that fail to conduct action potentials, where the blunted effect of the β-adrenergic signalling may be directly caused by the lack of electrical activity.

Differences in the control of basal L-type Ca(2+) current by the cyclic AMP signaling cascade in frog, rat, and human cardiac myocytes

β-adrenergic receptors (β-ARs) mediate the positive inotropic effects of catecholamines by cAMP-dependent phosphorylation of the L-type Ca(2+) channels (LTCCs), which provide Ca(2+) for the initiation and regulation of cell contraction. The overall effect of cAMP-modulating agents on cardiac calcium current (I Ca,L) and contraction depends on the basal activity of LTCCs which, in turn, depends on the basal activities of key enzymes involved in the cAMP signaling cascade. Our current work is a comparative study demonstrating the differences in the basal activities of β-ARs, adenylyl cyclase, phosphodiesterases, phosphatases, and LTCCs in the frog and rat ventricular and human atrial myocytes. The main conclusion is that the basal I Ca,L, and consequently the contractile function of the heart, is secured from unnecessary elevation of its activity and energy consumption at the several "checking-points" of cAMP-dependent signaling cascade and the loading of these "checking-points" may vary in different species and tissues.

Adeno-associated virus-mediated gene therapy in cardiovascular disease

PURPOSE OF REVIEW

The use of adeno-associated virus (AAV) as an efficient, cardiotropic, and safe vector, coupled with the identification of key molecular targets, has placed gene-based therapies within reach of cardiovascular diseases. The purpose of this review is to provide a focused update on the current advances related to AAV-mediated gene therapy in cardiovascular diseases, and particularly in heart failure (HF), wherein gene therapy has recently made important progress.

RECENT FINDINGS

Multiple successful preclinical studies suggest a potential utility of AAV gene therapy for arrhythmias and biological heart pacing, as well as RNA overexpression. Moreover, AAV-mediated overexpression of several molecular targets involved in HF has demonstrated promising results in clinically relevant large animal models. In humans, a safe and successful completion of a phase 2 clinical trial targeting the sarcoplasmic reticulum calcium ATPase pump with AAV has been reported. Serial studies are ongoing to further prove the efficacy of AAV-mediated sarcoplasmic reticulum calcium ATPase pump gene transfer in human HF.

SUMMARY

Significant progress in clinical translation of AAV-mediated cardiac gene therapy has been achieved in recent years. This will prompt further clinical trials, and positive results could open a new era for cardiac gene therapy.

Cardiac cAMP: production, hydrolysis, modulation and detection

Cyclic adenosine 3′,5′-monophosphate (cAMP) modulates a broad range of biological processes including the regulation of cardiac myocyte contractile function where it constitutes the main second messenger for β-adrenergic receptors' signaling to fulfill positive chronotropic, inotropic and lusitropic effects. A growing number of studies pinpoint the role of spatial organization of the cAMP signaling as an essential mechanism to regulate cAMP outcomes in cardiac physiology. Here, we will briefly discuss the complexity of cAMP synthesis and degradation in the cardiac context, describe the way to detect it and review the main pharmacological arsenal to modulate its availability.

Vascular nitric oxide: Beyond eNOS

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

Cardiac Dysfunction Induced by Obesity Is Not Related to β-Adrenergic System Impairment at the Receptor-Signalling Pathway

Obesity has been shown to impair myocardial performance. Some factors have been suggested as responsible for possible cardiac abnormalities in models of obesity, among them beta-adrenergic (βA) system, an important mechanism of regulation of myocardial contraction and relaxation. The objective of present study was to evaluate the involvement of βA system components in myocardial dysfunction induced by obesity. Thirty-day-old male Wistar rats were distributed in control (C, n = 25) and obese (Ob, n = 25) groups. The C group was fed a standard diet and Ob group was fed four unsaturated high-fat diets for 15 weeks. Cardiac function was evaluated by isolated papillary muscle preparation and βA system evaluated by using cumulative concentrations of isoproterenol and Western blot. After 15 weeks, the Ob rats developed higher adiposity index than C rats and several comorbidities; however, were not associated with changes in systolic blood pressure. Obesity caused structural changes and the myocardial responsiveness to post-rest contraction stimulus and increased extracellular calcium (Ca²⁺) was compromised. There were no changes in cardiac function between groups after βA stimulation. The obesity was not accompanied by changes in protein expression of G protein subunit alpha (Gsα) and βA receptors (β₁AR and β₂AR). In conclusion, the myocardial dysfunction caused by unsaturated high-fat diet-induced obesity, after 15 weeks, is not related to βAR system impairment at the receptor-signalling pathway.

Gene therapy for cardiovascular disease: advances in vector development, targeting, and delivery for clinical translation

Gene therapy is a promising modality for the treatment of inherited and acquired cardiovascular diseases. The identification of the molecular pathways involved in the pathophysiology of heart failure and other associated cardiac diseases led to encouraging preclinical gene therapy studies in small and large animal models. However, the initial clinical results yielded only modest or no improvement in clinical endpoints. The presence of neutralizing antibodies and cellular immune responses directed against the viral vector and/or the gene-modified cells, the insufficient gene expression levels, and the limited gene transduction efficiencies accounted for the overall limited clinical improvements. Nevertheless, further improvements of the gene delivery technology and a better understanding of the underlying biology fostered renewed interest in gene therapy for heart failure. In particular, improved vectors based on emerging cardiotropic serotypes of the adeno-associated viral vector (AAV) are particularly well suited to coax expression of therapeutic genes in the heart. This led to new clinical trials based on the delivery of the sarcoplasmic reticulum Ca²⁺-ATPase protein (SERCA2a). Though the first clinical results were encouraging, a recent Phase IIb trial did not confirm the beneficial clinical outcomes that were initially reported. New approaches based on S100A1 and adenylate cyclase 6 are also being considered for clinical applications. Emerging paradigms based on the use of miRNA regulation or CRISPR/Cas9-based genome engineering open new therapeutic perspectives for treating cardiovascular diseases by gene therapy. Nevertheless, the continuous improvement of cardiac gene delivery is needed to allow the use of safer and more effective vector doses, ultimately bringing gene therapy for heart failure one step closer to reality.

Studying GPCR/cAMP pharmacology from the perspective of cellular structure

Signal transduction via G-protein coupled receptors (GPCRs) relies upon the production of cAMP and other signaling cascades. A given receptor and agonist pair, produce multiple effects upon cellular physiology which can be opposite in different cell types. The production of variable cellular effects via the signaling of the same GPCR in different cell types is a result of signal organization in space and time (compartmentation). This organization is usually based upon the physical and chemical properties of the membranes in which the GPCRs reside and the repertoire of downstream effectors and co-factors that are available at that location. In this review we explore mechanisms of GPCR signal compartmentation and broadly review the state-of-the-art methodologies which can be utilized to study them. We provide a clear rationale for a “localized” approach to the study of the pharmacology and physiology of GPCRs and particularly the secondary messenger cAMP.

Pharmacogenomics of cardiovascular complications in diabetes and obesity

Heart disease is a major cause of death in US and worldwide. The complex interplay of the mechanisms between diabetes, obesity and inflammation raises concerns for therapeutic understanding and developing treatment options for patients. Recent advances utilizing pharmacogenomics has helped researchers to probe in to disease pathophysiology and physicians to detect and, diagnose the disease in patients. The understanding developed in the area primarily addresses the issue focusing on the nature and asks the question 'Why' some individuals respond to the standard medication regimen and others do not. The central idea that genomics play a vital part in how the healthcare providers: physician, pharmacist, and nurse provide treatment utilizing the best practices available for maximum benefits. Pharmacogenomics is the scientific basis which offers the fundamental understanding for diseases, based on which therapeutic approaches can be designed and delivered. The discovery that not all humans respond to the drug in the same way is a 'paradigm shift' in how current therapies are offered. The area of pharmacogenomics at its core is linked to the genetic basis for the disease and the response to treatment. Given that diabetes and obesity are major metabolic ailments globally wherein patients also often suffer from cardiac disorders, a comprehensive genetic and pharmacogenomic understanding of these conditions enable the development of effective therapeutic strategies. In this review, we discuss various pharmacogenomic approaches with special emphasis on heart disease as it relates to diabetes and obesity. Recent information in regard to relevant patents in this topic are also discussed.

Molecular imaging to predict ventricular arrhythmia in heart failure

Ventricular tachycardia (VT) is a major cause of sudden cardiac death (SCD) in patients with heart failure (HF). Left ventricular ejection fraction (LVEF) and heart failure class according to the New York Heart association (NYHA) are in most common use to identify patients that may benefit from implantable cardioverter defibrillator (ICD) therapy. But during 3 years of follow up only 35% of patients receive appropriate ICD action. Therefore, there is a continued need for refinement of selection criteria for ICD implantation. In this regard, molecular imaging of the autonomic nervous system, which plays a central role in HF progression and cardiac electro-mechanical regulation, can make a substantial contribution. This article reviews the currently available literature concerning the value of molecular neuronal cardiac imaging for prediction of ventricular arrhythmias in HF patients.

Pharmacogenetics of cardiac inotropy

The ability to stimulate cardiac contractility is known as positive inotropy. Endogenous hormones, such as adrenaline and several natural or synthetic compounds possess this biological property, which is invaluable in the modern cardiovascular therapy setting, especially in acute heart failure or in cardiogenic shock. A number of proteins inside the cardiac myocyte participate in the molecular pathways that translate the initial stimulus, that is, the hormone or drug, into the effect of increased contractility (positive inotropy). Genetic variations (polymorphisms) in several genes encoding these proteins have been identified and characterized in humans with potentially significant consequences on cardiac inotropic function. The present review discusses these polymorphisms and their effects on cardiac inotropy, along with the individual pharmacogenomics of the most important positive inotropic agents in clinical use today. Important areas for future investigations in the field are also highlighted.

The autonomic nervous system and heart failure

The pathophysiology of heart failure (HF) is characterized by hemodynamic abnormalities that result in neurohormonal activation and autonomic imbalance with increase in sympathetic activity and withdrawal of vagal activity. Alterations in receptor activation from this autonomic imbalance may have profound effects on cardiac function and structure. Inhibition of the sympathetic drive to the heart through β-receptor blockade has become a standard component of therapy for HF with a dilated left ventricle because of its effectiveness in inhibiting the ventricular structural remodeling process and in prolonging life. Several devices for selective modulation of sympathetic and vagal activity have recently been developed in an attempt to alter the natural history of HF. The optimal counteraction of the excessive sympathetic activity is still unclear. A profound decrease in adrenergic support with excessive blockade of the sympathetic nervous system may result in adverse outcomes in clinical HF. In this review, we analyze the data supporting a contributory role of the autonomic functional alterations on the course of HF, the techniques used to assess autonomic nervous system activity, the evidence for clinical effectiveness of pharmacological and device interventions, and the potential future role of autonomic nervous system modifiers in the management of this syndrome.

The Autonomic Nervous System and Hypertension

Physiological studies have long documented the key role played by the autonomic nervous system in modulating cardiovascular functions and in controlling blood pressure values, both at rest and in response to environmental stimuli. Experimental and clinical investigations have tested the hypothesis that the origin, progression, and outcome of human hypertension are related to dysfunctional autonomic cardiovascular control and especially to abnormal activation of the sympathetic division. Here, we review the recent literature on the adrenergic and vagal abnormalities that have been reported in essential hypertension, with emphasis on their role as promoters and as amplifiers of the high blood pressure state. We also discuss the possible mechanisms underlying these abnormalities and their importance in the development and progression of the structural and functional cardiovascular damage that characterizes hypertension. Finally, we examine the modifications of sympathetic and vagal cardiovascular influences induced by current nonpharmacological and pharmacological interventions aimed at correcting elevations in blood pressure and restoring the normotensive state.

Gene therapy for heart disease: molecular targets, vectors and modes of delivery to myocardium

Despite the numerous hurdles that gene therapy has encountered along the way, clinical trials over the last few years are showing promising results in many fields of medicine, including cardiology, where many targets are moving toward clinical development. In this review, the authors discuss the current state of the art in terms of clinical and preclinical development. They also examine vector technology and available vector-delivery strategies.

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Cardiovascular gene therapy for myocardial infarction

INTRODUCTION

Cardiovascular gene therapy is the third most popular application for gene therapy, representing 8.4% of all gene therapy trials as reported in 2012 estimates. Gene therapy in cardiovascular disease is aiming to treat heart failure from ischemic and non-ischemic causes, peripheral artery disease, venous ulcer, pulmonary hypertension, atherosclerosis and monogenic diseases, such as Fabry disease.

AREAS COVERED

In this review, we will focus on elucidating current molecular targets for the treatment of ventricular dysfunction following myocardial infarction (MI). In particular, we will focus on the treatment of i) the clinical consequences of it, such as heart failure and residual myocardial ischemia and ii) etiological causes of MI (coronary vessels atherosclerosis, bypass venous graft disease, in-stent restenosis).

EXPERT OPINION

We summarise the scheme of the review and the molecular targets either already at the gene therapy clinical trial phase or in the pipeline. These targets will be discussed below. Following this, we will focus on what we believe are the 4 prerequisites of success of any gene target therapy: safety, expression, specificity and efficacy (SESE).

Negative impact of β-arrestin-1 on post-myocardial infarction heart failure via cardiac and adrenal-dependent neurohormonal mechanisms

β-Arrestin (βarr)-1 and β-arrestin-2 (βarrs) are universal G-protein-coupled receptor adapter proteins that negatively regulate cardiac β-adrenergic receptor (βAR) function via βAR desensitization and downregulation. In addition, they mediate G-protein-independent βAR signaling, which might be beneficial, for example, antiapoptotic, for the heart. However, the specific role(s) of each βarr isoform in cardiac βAR dysfunction, the molecular hallmark of chronic heart failure (HF), remains unknown. Furthermore, adrenal βarr1 exacerbates HF by chronically enhancing adrenal production and hence circulating levels of aldosterone and catecholamines. Herein, we sought to delineate specific roles of βarr1 in post-myocardial infarction (MI) HF by testing the effects of βarr1 genetic deletion on normal and post-MI cardiac function and morphology. We studied βarr1 knockout (βarr1KO) mice alongside wild-type controls under normal conditions and after surgical MI. Normal (sham-operated) βarr1KO mice display enhanced βAR-dependent contractility and post-MI βarr1KO mice enhanced overall cardiac function (and βAR-dependent contractility) compared with wild type. Post-MI βarr1KO mice also show increased survival and decreased cardiac infarct size, apoptosis, and adverse remodeling, as well as circulating catecholamines and aldosterone, compared with post-MI wild type. The underlying mechanisms, on one hand, improved cardiac βAR signaling and function, as evidenced by increased βAR density and procontractile signaling, via reduced cardiac βAR desensitization because of cardiac βarr1 absence, and, on the other hand, decreased production leading to lower circulating levels of catecholamines and aldosterone because of adrenal βarr1 absence. Thus, βarr1, via both cardiac and adrenal effects, is detrimental for cardiac structure and function and significantly exacerbates post-MI HF.

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.