Essential role of sympathetic endothelin A receptors for adverse cardiac remodeling

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

The Microenvironment of the Pathogenesis of Cardiac Hypertrophy

Pathological cardiac hypertrophy is a key risk factor for the development of heart failure and predisposes individuals to cardiac arrhythmia and sudden death. While physiological cardiac hypertrophy is adaptive, hypertrophy resulting from conditions comprising hypertension, aortic stenosis, or genetic mutations, such as hypertrophic cardiomyopathy, is maladaptive. Here, we highlight the essential role and reciprocal interactions involving both cardiomyocytes and non-myocardial cells in response to pathological conditions. Prolonged cardiovascular stress causes cardiomyocytes and non-myocardial cells to enter an activated state releasing numerous pro-hypertrophic, pro-fibrotic, and pro-inflammatory mediators such as vasoactive hormones, growth factors, and cytokines, i.e., commencing signaling events that collectively cause cardiac hypertrophy. Fibrotic remodeling is mediated by cardiac fibroblasts as the central players, but also endothelial cells and resident and infiltrating immune cells enhance these processes. Many of these hypertrophic mediators are now being integrated into computational models that provide system-level insights and will help to translate our knowledge into new pharmacological targets. This perspective article summarizes the last decades' advances in cardiac hypertrophy research and discusses the herein-involved complex myocardial microenvironment and signaling components.

Calcineurin signaling promotes takotsubo syndrome

Takotsubo syndrome (TTS) is an acute heart failure syndrome that mimics the symptoms of acute myocardial infarction and is often preceded by emotional and/or physical stress. There is currently no treatment for TTS. Here we show that injection of 2.5 mg kg-1 of epinephrine (EPI) into mice recapitulates numerous features of human TTS, including increased myocardial damage and mortality in males. Gene set enrichment analysis of myocardial RNA sequencing after EPI injection revealed significant enrichment of calcineurin-dependent pro-inflammatory gene networks, which was more pronounced in male than in female mice, in agreement with observed sex discrepancies in the mouse phenotype. An increase in calcineurin activity was detected in the circulating cells of patients with TTS, suggesting a systemic nature of the syndrome. Preventive and therapeutic treatment of mice injected with EPI using calcineurin inhibitors cyclosporine and tacrolimus improved heart function and reduced myocardial injury. Our findings suggest that calcineurin inhibition could be a potential therapy for TTS.

Therapeutic Use and Molecular Aspects of Ivabradine in Cardiac Remodeling: A Review

Cardiac remodeling can cause ventricular dysfunction and progress to heart failure, a cardiovascular disease that claims many lives globally. Ivabradine, a funny channel (I_f) inhibitor, is used in patients with chronic heart failure as an adjunct to other heart failure medications. This review aims to gather updated information regarding the therapeutic use and mechanism of action of ivabradine in heart failure. The drug reduces elevated resting heart rate, which is linked to increased morbidity and mortality in patients with heart failure. Its use is associated with improved cardiac function, structure, and quality of life in the patients. Ivabradine exerts several pleiotropic effects, including an antiremodeling property, which are independent of its principal heart-rate-reducing effects. Its suppressive effects on cardiac remodeling have been demonstrated in animal models of cardiac remodeling and heart failure. It reduces myocardial fibrosis, apoptosis, inflammation, and oxidative stress as well as increases autophagy in the animals. It also modulates myocardial calcium homeostasis, neurohumoral systems, and energy metabolism. However, its role in improving heart failure remains unclear. Therefore, elucidating its molecular mechanisms is imperative and would aid in the design of future studies.

Delivery of miR-654-5p via SonoVue Microbubble Ultrasound Inhibits Proliferation, Migration, and Invasion of Vascular Smooth Muscle Cells and Arterial Thrombosis and Stenosis through Targeting TCF21

Background

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is an important cause of vascular stenosis. The study explored the mechanism of inhibition of vascular stenosis through the molecular mechanism of smooth muscle cell phenotype transformation.

Methods

Coronary heart disease-related genes were screened by bioinformatics, and the target genes of miR-654-5p were predicted by dual-luciferase method and immunofluorescence method. miR-654-5p mimic stimulation and transfection of TCF21 and MTAP into cells. SonoVue microbubble sonication was used to deliver miR-654-5p into cells. Cell proliferation, migration, and invasion were detected by CCK-8, wound scratch, and Transwell. HE and IHC staining were performed to study the effect of miR-654-5p delivery via SonoVue microbubble ultrasound on vessel stenosis in a model of arterial injury. Gene expression was determined by qRT-PCR and WB.

Results

TCF21 and MTAP were predicted as the target genes of miR-654-5p. Cytokines induced smooth muscle cell proliferation, migration, and invasion and promoted miR-654-5p downregulation; noticeably, downregulated miR-654-5p was positively associated with the cell proliferation and migration. Overexpression of TCF21 promoted proliferation, invasion, and migration, and mimic reversed such effects. miR-654-5p overexpression delivered by SonoVue microbubble ultrasound inhibited proliferation, migration, and invasion of cells. Moreover, in arterial injury model, we found that SonoVue microbubble ultrasound transmitted miR-654-5p into the arterial wall to inhibit arterial thrombosis and stenosis, while TCF21 was inhibited.

Conclusion

Ultrasound delivery of miR-654-5p via SonoVue microbubbles was able to inhibit arterial thrombosis and stenosis by targeting TCF21.

Signaling cascades in the failing heart and emerging therapeutic strategies

Chronic heart failure is the end stage of cardiac diseases. With a high prevalence and a high mortality rate worldwide, chronic heart failure is one of the heaviest health-related burdens. In addition to the standard neurohormonal blockade therapy, several medications have been developed for chronic heart failure treatment, but the population-wide improvement in chronic heart failure prognosis over time has been modest, and novel therapies are still needed. Mechanistic discovery and technical innovation are powerful driving forces for therapeutic development. On the one hand, the past decades have witnessed great progress in understanding the mechanism of chronic heart failure. It is now known that chronic heart failure is not only a matter involving cardiomyocytes. Instead, chronic heart failure involves numerous signaling pathways in noncardiomyocytes, including fibroblasts, immune cells, vascular cells, and lymphatic endothelial cells, and crosstalk among these cells. The complex regulatory network includes protein-protein, protein-RNA, and RNA-RNA interactions. These achievements in mechanistic studies provide novel insights for future therapeutic targets. On the other hand, with the development of modern biological techniques, targeting a protein pharmacologically is no longer the sole option for treating chronic heart failure. Gene therapy can directly manipulate the expression level of genes; gene editing techniques provide hope for curing hereditary cardiomyopathy; cell therapy aims to replace dysfunctional cardiomyocytes; and xenotransplantation may solve the problem of donor heart shortages. In this paper, we reviewed these two aspects in the field of failing heart signaling cascades and emerging therapeutic strategies based on modern biological techniques.

Ketone body oxidation increases cardiac endothelial cell proliferation

Blood vessel formation is dependent on metabolic adaption in endothelial cells. Glucose and fatty acids are essential substrates for ATP and biomass production; however, the metabolism of other substrates remains poorly understood. Ketone bodies are important nutrients for cardiomyocytes during starvation or consumption of carbohydrate‐restrictive diets. This raises the question whether cardiac endothelial cells would not only transport ketone bodies but also consume some of these to achieve their metabolic needs. Here, we report that cardiac endothelial cells are able to oxidize ketone bodies and that this enhances cell proliferation, migration, and vessel sprouting. Mechanistically, this requires succinyl‐CoA:3‐oxoacid‐CoA transferase, a key enzyme of ketone body oxidation. Targeted metabolite profiling revealed that carbon from ketone bodies got incorporated into tricarboxylic acid cycle intermediates as well as other metabolites fueling biomass production. Elevation of ketone body levels by a high‐fat, low‐carbohydrate ketogenic diet transiently increased endothelial cell proliferation in mouse hearts. Notably, in a mouse model of heart hypertrophy, ketogenic diet prevented blood vessel rarefication. This suggests a potential beneficial role of dietary intervention in heart diseases.

Pathophysiology of Takotsubo Syndrome - a joint scientific statement from the Heart Failure Association Takotsubo Syndrome Study Group and Myocardial Function Working Group of the European Society of Cardiology - Part 1: Overview and the central role for catecholamines and sympathetic nervous system

This is the first part of a scientific statement from the Heart Failure Association of the European Society of Cardiology focused upon the pathophysiology of Takotsubo syndrome and is complimentary to the previous HFA Position Statement on Takotsubo syndrome which focused upon clinical management. In part 1 we provide an overview of the pathophysiology of Takotsubo syndrome and fundamental questions to consider. We then review and discuss the central role of catecholamines and the sympathetic nervous system in the pathophysiology, and the direct effects of high surges in catecholamines upon myocardial biology including β-adrenergic receptor signaling, G protein coupled receptor kinases, cardiomyocyte calcium physiology, myofilament physiology, cardiomyocyte gene expression, myocardial electrophysiology and arrhythmogenicity, myocardial inflammation, metabolism and energetics. The integrated effects upon ventricular haemodynamics are discussed and integrated into the pathophysiological model. This article is protected by copyright. All rights reserved.

AAV-mediated expression of NFAT decoy oligonucleotides protects from cardiac hypertrophy and heart failure

Previous studies have underlined the substantial role of nuclear factor of activated T cells (NFAT) in hypertension-induced myocardial hypertrophy ultimately leading to heart failure. Here, we aimed at neutralizing four members of the NFAT family of transcription factors as a therapeutic strategy for myocardial hypertrophy transiting to heart failure through AAV-mediated cardiac expression of a RNA-based decoy oligonucleotide (dON) targeting NFATc1-c4. AAV-mediated dON expression markedly decreased endothelin-1 induced cardiomyocyte hypertrophy in vitro and resulted in efficient expression of these dONs in the heart of adult mice as evidenced by fluorescent in situ hybridization. Cardiomyocyte-specific dON expression both before and after induction of transverse aortic constriction protected mice from development of cardiac hypertrophy, cardiac remodeling, and heart failure. Singular systemic administration of AAVs enabling a cell-specific expression of dONs for selective neutralization of a given transcription factor may thus represent a novel and powerful therapeutic approach.

Sympathetic nervous system activation and heart failure: Current state of evidence and the pathophysiology in the light of novel biomarkers

Heart failure (HF) is a complex clinical syndrome characterized by the activation of at least several neurohumoral pathways that have a common role in maintaining cardiac output and adequate perfusion pressure of target organs and tissues. The sympathetic nervous system (SNS) is upregulated in HF as evident in dysfunctional baroreceptor and chemoreceptor reflexes, circulating and neuronal catecholamine spillover, attenuated parasympathetic response, and augmented sympathetic outflow to the heart, kidneys and skeletal muscles. When these sympathoexcitatory effects on the cardiovascular system are sustained chronically they initiate the vicious circle of HF progression and become associated with cardiomyocyte apoptosis, maladaptive ventricular and vascular remodeling, arrhythmogenesis, and poor prognosis in patients with HF. These detrimental effects of SNS activity on outcomes in HF warrant adequate diagnostic and treatment modalities. Therefore, this review summarizes basic physiological concepts about the interaction of SNS with the cardiovascular system and highlights key pathophysiological mechanisms of SNS derangement in HF. Finally, special emphasis in this review is placed on the integrative and up-to-date overview of diagnostic modalities such as SNS imaging methods and novel laboratory biomarkers that could aid in the assessment of the degree of SNS activation and provide reliable prognostic information among patients with HF.

Cardiac transcriptional and metabolic changes following thoracotomy

Non-cardiac surgery is associated with significant cardiovascular complications. Reported mortality rate ranges from 1.9% to 4% in unselected patients. A postoperative surge in pro-inflammatory cytokines is a well-known feature and putative contributor to these complications. Despite much clinical research, little is known about the biomolecular changes in cardiac tissue following non-cardiac surgery. In order to increase our understanding, we analyzed whole-transcriptional and metabolic profiling data sets from hearts of mice harvested two, four, and six weeks following isolated thoracotomy. Hearts from healthy litter-mates served as controls. Functional network enrichment analyses showed a distinct impact on cardiac transcription two weeks after surgery characterized by a downregulation of mitochondrial pathways in the absence of significant metabolic alterations. Transcriptional changes were not detectable four and six weeks following surgery. Our study shows distinct and reversible transcriptional changes within the first two weeks following isolated thoracotomy. This coincides with a time period, in which most cardiovascular events happen.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

The lipid droplet-associated protein ABHD5 protects the heart through proteolysis of HDAC4

Catecholamines stimulate the first step of lipolysis by PKA-dependent release of the lipid droplet-associated protein ABHD5 from perilipin to co-activate the lipase ATGL. Here, we unmask a yet unrecognized proteolytic and cardioprotective function of ABHD5. ABHD5 acts in vivo and in vitro as a serine protease cleaving HDAC4. Through the production of an N-terminal polypeptide of HDAC4 (HDAC4-NT), ABHD5 inhibits MEF2-dependent gene expression and thereby controls glucose handling. ABHD5-deficiency leads to neutral lipid storage disease in mice. Cardiac-specific gene therapy of HDAC4-NT does not protect from intra-cardiomyocyte lipid accumulation but strikingly from heart failure, thereby challenging the concept of lipotoxicity-induced heart failure. ABHD5 levels are reduced in failing human hearts and murine transgenic ABHD5 expression protects from pressure-overload induced heart failure. These findings represent a conceptual advance by connecting lipid with glucose metabolism through HDAC4 proteolysis and enable new translational approaches to treat cardiometabolic disease.

Induction of cardiomyocyte proliferation and angiogenesis protects neonatal mice from pressure overload-associated maladaptation

Cardiac pressure overload (for example due to aortic stenosis) induces irreversible myocardial dysfunction, cardiomyocyte hypertrophy and interstitial fibrosis in patients. In contrast to adult, neonatal mice can efficiently regenerate the heart after injury in the first week after birth. To decipher whether insufficient cardiac regeneration contributes to the progression of pressure overload dependent disease, we established a transverse aortic constriction protocol in neonatal mice (nTAC). nTAC in the non-regenerative stage (at postnatal day P7) induced cardiac dysfunction, myocardial fibrosis and cardiomyocyte hypertrophy. In contrast, nTAC in the regenerative stage (at P1) largely prevented these maladaptive responses and was in particular associated with enhanced myocardial angiogenesis and increased cardiomyocyte proliferation, which both supported adaptation during nTAC. A comparative transcriptomic analysis between hearts after regenerative versus non-regenerative nTAC suggested the transcription factor GATA4 as master regulator of the regenerative gene-program. Indeed, cardiomyocyte specific deletion of GATA4 converted the regenerative nTAC into a non-regenerative, maladaptive response. Our new nTAC model can be used to identify mediators of adaptation during pressure overload and to discover novel potential therapeutic strategies.

Epigenetic regulation of intercellular communication in the heart

The myocardium is a highly structured tissue consisting of different cell types including cardiomyocytes, endothelial cells, fibroblasts, smooth muscle cells, inflammatory cells, and stem cells. Microvascular endothelial cells are the most abundant cell type in the myocardium and play crucial roles during cardiac development, in normal adult myocardium, and during myocardial diseases such as heart failure. In the last decade, epigenetic changes have been described regulating cellular function in almost every cell type in the organism. Here, we review recent evidence on different epigenetic changes that regulate intercellular communication in normal myocardium and during myocardial diseases, including cardiac remodeling. Epigenetic changes influence many intercellular communication signaling systems, including the nitric oxide, angiotensin, and endothelin signaling systems. In this review, we go beyond discussing classic endothelial function (for instance nitric oxide secretion) and will discuss epigenetic regulation of intercellular communication.

Interaction between Endothelin-1 and Left Stellate Ganglion Activation: A Potential Mechanism of Malignant Ventricular Arrhythmia during Myocardial Ischemia

Endothelin-1 (ET-1) is synthesized primarily by endothelial cells. ET-1 administration in vivo enhances the cardiac sympathetic afferent reflex and sympathetic activity. Previous studies have shown that sympathetic hyperactivity promotes malignant ventricular arrhythmia (VA). The aim of this study was to investigate whether ET-1 could activate the left stellate ganglion (LSG) and promote malignant VA. Twelve male beagle dogs who received local microinjections of saline (control, n = 6) and ET-1 into the LSG (n = 6) were included. The ventricular effective refractory period (ERP), LSG function, and LSG activity were measured at different time points. VA was continuously recorded for 1 h after left anterior descending occlusion (LADO), and LSG tissues were then collected for molecular detection. Compared to that of the control group, local ET-1 microinjection significantly decreased the ERP and increased the occurrence of VA. In addition, local microinjection of ET-1 increased the function and activity of the LSG in the normal and ischemic hearts. The expression levels of proinflammatory cytokines and the protein expression of c-fos and nerve growth factor (NGF) in the LSG were also increased. More importantly, endothelin A receptor (ETA-R) expression was found in the LSG, and its signaling was significantly activated in the ET-1 group. LSG activation induced by local ET-1 microinjection aggravates LADO-induced VA. Activated ETA-R signaling and the upregulation of proinflammatory cytokines in the LSG may be responsible for these effects.

Endothelial mineralocorticoid receptor contributes to systolic dysfunction induced by pressure overload without modulating cardiac hypertrophy or inflammation

Heart Failure (HF) is associated with increased circulating levels of aldosterone and systemic inflammation. Mineralocorticoid receptor (MR) antagonists block aldosterone action and decrease mortality in patients with congestive HF. However, the molecular mechanisms underlying the therapeutic benefits of MR antagonists remain unclear. MR is expressed in all cell types in the heart, including the endothelial cells (EC), in which aldosterone induces the expression of intercellular adhesion molecule 1 (ICAM‐1). Recently, we reported that ICAM‐1 regulates cardiac inflammation and cardiac function in mice subjected to transverse aortic constriction (TAC). Whether MR specifically in endothelial cells (EC) contributes to the several mechanisms of pathological cardiac remodeling and cardiac dysfunction remains unclear. Basal cardiac function and LV dimensions were comparable in mice with MR selectively deleted from ECs (EC‐MR^−/−) and wild‐type littermate controls (EC‐MR^+/+). MR was specifically deleted in heart EC, and in EC‐containing tissues, but not in leukocytes of TAC EC‐MR^−/− mice. While EC‐MR^−/−TAC mice showed preserved systolic function and some alterations in the expression of fetal genes, the proinflammatory cytokine TNFα and the endothelin receptors in the LV as compared to EC‐MR^+/+TAC mice, no difference was observed between both TAC groups in overall cardiac hypertrophy, ICAM‐1 LV expression and leukocyte infiltration, cardiac fibrosis or capillary rarefaction, all hallmarks of pathological cardiac remodeling. Our data indicate that EC‐MR contributes to the transition of cardiac hypertrophy to systolic dysfunction independently of other maladaptive changes induced by LV pressure overload.

Inhibition of Endothelial Notch Signaling Impairs Fatty Acid Transport and Leads to Metabolic and Vascular Remodeling of the Adult Heart

BACKGROUND

Nutrients are transported through endothelial cells before being metabolized in muscle cells. However, little is known about the regulation of endothelial transport processes. Notch signaling is a critical regulator of metabolism and angiogenesis during development. Here, we studied how genetic and pharmacological manipulation of endothelial Notch signaling in adult mice affects endothelial fatty acid transport, cardiac angiogenesis, and heart function.

METHODS

Endothelial-specific Notch inhibition was achieved by conditional genetic inactivation of Rbp-jκ in adult mice to analyze fatty acid metabolism and heart function. Wild-type mice were treated with neutralizing antibodies against the Notch ligand Delta-like 4. Fatty acid transport was studied in cultured endothelial cells and transgenic mice.

RESULTS

Treatment of wild-type mice with Delta-like 4 neutralizing antibodies for 8 weeks impaired fractional shortening and ejection fraction in the majority of mice. Inhibition of Notch signaling specifically in the endothelium of adult mice by genetic ablation of Rbp-jκ caused heart hypertrophy and failure. Impaired heart function was preceded by alterations in fatty acid metabolism and an increase in cardiac blood vessel density. Endothelial Notch signaling controlled the expression of endothelial lipase, Angptl4, CD36, and Fabp4, which are all needed for fatty acid transport across the vessel wall. In endothelial-specific Rbp-jκ-mutant mice, lipase activity and transendothelial transport of long-chain fatty acids to muscle cells were impaired. In turn, lipids accumulated in the plasma and liver. The attenuated supply of cardiomyocytes with long-chain fatty acids was accompanied by higher glucose uptake, increased concentration of glycolysis intermediates, and mTOR-S6K signaling. Treatment with the mTOR inhibitor rapamycin or displacing glucose as cardiac substrate by feeding a ketogenic diet prolonged the survival of endothelial-specific Rbp-jκ-deficient mice.

CONCLUSIONS

This study identifies Notch signaling as a novel regulator of fatty acid transport across the endothelium and as an essential repressor of angiogenesis in the adult heart. The data imply that the endothelium controls cardiomyocyte metabolism and function.

Involvement of the metabolic sensor GPR81 in cardiovascular control

GPR81 is a receptor for the metabolic intermediate lactate with an established role in regulating adipocyte lipolysis. Potentially novel GPR81 agonists were identified that suppressed fasting plasma free fatty acid levels in rodents and in addition improved insulin sensitivity in mouse models of insulin resistance and diabetes. Unexpectedly, the agonists simultaneously induced hypertension in rodents, including wild-type, but not GPR81-deficient mice. Detailed cardiovascular studies in anesthetized dogs showed that the pressor effect was associated with heterogenous effects on vascular resistance among the measured tissues: increasing in the kidney while remaining unchanged in hindlimb and heart. Studies in rats revealed that the pressor effect could be blocked, and the renal resistance effect at least partially blocked, with pharmacological antagonism of endothelin receptors. In situ hybridization localized GPR81 to the microcirculation, notably afferent arterioles of the kidney. In conclusion, these results provide evidence for a potentially novel role of GPR81 agonism in blood pressure control and regulation of renal vascular resistance including modulation of a known vasoeffector mechanism, the endothelin system. In addition, support is provided for the concept of fatty acid lowering as a means of improving insulin sensitivity.

Plasma endothelin-1 levels in patients with resistant hypertension: effects of renal sympathetic denervation

INTRODUCTION

Resistant arterial hypertension (RHT) is defined as poor controlled blood pressure (BP) despite optimal doses of three or more antihypertensive agents, including a diuretic. In the development of RHT, hyperactivity of sympathetic (SNS) and renin-angiotensin-aldosterone (SRAA) systems are involved, and SNS is a potent stimulator of vasoactive endothelin-1 (ET-1) peptide. Renal sympathetic denervation (RSD) through disrupting renal afferent and efferent nerves attenuates SNS activity.

MATERIAL AND METHODS

We carried out pilot study investigating the effect of RSD on BP and plasma ET-1 levels in consecutive 9 RHT patients (7 male and 2 female, mean age of 56 ± 13.3).

RESULTS

After 12 months of the RSD, we observed a significant reduction of BP office, 24-h ambulatory BP monitoring (ABPM) (p < 0.05, respectively), and "non-dipping" pattern (from 55% to 35%) (p < 0.05). Moreover, RSD significantly decreased plasma ET-1 levels in both renal artery (at right from 21.8 ± 4.1 to 16.8 ± 2.9 pg/ml; p = 0.004; at left from 22.1 ± 3.7 to 18.9 ± 3.3 pg/ml; p = 0.02). We observed positive correlations between plasma renal arteries ET-1 levels and systolic BP values at ABPM [Global-SBP (r = 0.58; p < 0.01), Diurnal-SBP (r = 0.51; p < 0.03) and Nocturnal-SBP (r = 0.58; p < 0.01), respectively].

DISCUSSION

Our data confirmed the positive effects of RSD on BP values in patients with RHT, and showed a possible physio-pathological role of ET-1. KEY MESSAGES RSD is associated to a significant reduction of plasma ET-1 levels, representing an useful tool into reduction of BP in RHT patients.

Depletion of cardiac catecholamine stores impairs cardiac norepinephrine re-uptake by downregulation of the norepinephrine transporter

In heart failure (HF), a disturbed cardiac norepinephrine (NE) homeostasis is characterized by depleted cardiac NE stores, impairment of the cardiac NE re-uptake by the neuronal norepinephrine transporter (NET) and enhanced cardiac NE net release. Reduced cardiac NE content appears to be caused by enhanced cardiac NE net release from sympathetic neurons in HF, triggered by neurohumoral activation. However, it remains unclear whether reduced NE itself has an impact on cardiac NE re-uptake, independent of neurohumoral activation. Here, we evaluated whether depletion of cardiac NE stores alone can regulate cardiac NE re-uptake. Treatment of Wistar rats with reserpine (5 mg/kg/d) for one (1d) or five days (5d) resulted in markedly reduced cardiac NE content, comparable to NE stores in experimental HF due to pressure overload. In order to assess cardiac NE re-uptake, the specific cardiac [³H]-NE uptake via the NET in a Langendorff preparation was measured. Reserpine treatment led to decreased NE re-uptake at 1d and 5d compared to saline treatment. Expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of the NE synthesis, was elevated in left stellate ganglia after reserpine. Mechanistically, measurement of NET mRNA expression in left stellate ganglia and myocardial NET density revealed a post-transcriptional downregulation of the NET by reserpine. In summary, present data demonstrate that depletion of cardiac NE stores alone is sufficient to impair cardiac NE re-uptake via downregulation of the NET, independent of systemic neurohumoral activation. Knowledge about the regulation of the cardiac NE homeostasis may offer novel therapeutic strategies in HF.

Bisoprolol in idiopathic pulmonary arterial hypertension: an explorative study

While beta-blockers are considered contraindicated in pulmonary arterial hypertension (PAH), the prognostic significance of sympathetic nervous system over-activity suggests a potential benefit of beta-blocker therapy. The aim of this randomised, placebo-controlled, crossover, single centre study was to determine the effects of bisoprolol on right ventricular ejection fraction (RVEF) in idiopathic PAH (iPAH) patients. Additional efficacy and safety parameters were explored.Patients with optimally treated, stable iPAH (New York Heart Association functional class II/III) were randomised to placebo or bisoprolol. Imaging and functional measurements were performed at baseline, crossover and end of study.18 iPAH patients were included, because inclusion faltered before enrolment of the targeted 25 patients. 17 patients completed 6 months of bisoprolol, 15 tolerated bisoprolol, one patient required intravenous diuretics. Bisoprolol was associated with a lower heart rate (17 beats per minute, p=0.0001) but RVEF remained unchanged. A drop in cardiac index (0.5 L·min(-1)·m(-2), p=0.015) was observed, along with a trend towards a decreased 6-min walking distance (6MWD).Although careful up-titration of bisoprolol was tolerated by most patients and resulted in a decreased heart rate, no benefit of bisoprolol in iPAH was demonstrated. Decreases in cardiac index and 6MWD suggest a deteriorated cardiac function. The results do not favour the use of bisoprolol in iPAH patients.

Evidence for biased agonists and antagonists at the endothelin receptors

Biased ligands represent a new strategy for the development of more effective and better tolerated drugs. To date there has been a paucity of research exploring the potential of ligands that exhibit either G protein or β-arrestin pathway selectivity at the endothelin receptors. Re-analysis of data may allow researchers to determine whether there is existing evidence that the endogenous ET peptides or currently available agonists and antagonists exhibit pathway bias in a particular physiological or disease setting and this is explored in the review. An alternative to molecules that bind at the orthosteric site of the ET receptors are cell penetrating peptides that interact with a segment of an intracellular loop of the receptor to modify signalling behaviour. One such peptide IC2B has been shown to have efficacy in a model of pulmonary arterial hypertension. Finally, understanding the molecular pathways that contribute to disease is critical to determining whether biased ligands will provide clinical benefit. The role of ET_A signalling in ovarian cancer has been delineated in some detail and this has led to the suggestion that the development of ET_A G protein biased agonists or β-arrestin biased antagonists should be explored.

Roles and post-translational regulation of cardiac class IIa histone deacetylase isoforms

Cardiomyocyte hypertrophy is an integral component of pathological cardiac remodelling in response to mechanical and chemical stresses in settings such as chronic hypertension or myocardial infarction. For hypertrophy to ensue, the pertinent mechanical and chemical signals need to be transmitted from membrane sensors (such as receptors for neurohormonal mediators) to the cardiomyocyte nucleus, leading to altered transcription of the genes that regulate cell growth. In recent years, nuclear histone deacetylases (HDACs) have attracted considerable attention as signal-responsive, distal regulators of the transcriptional reprogramming that in turn precipitates cardiomyocyte hypertrophy, with particular focus on the role of members of the class IIa family, such as HDAC4 and HDAC5. These histone deacetylase isoforms appear to repress cardiomyocyte hypertrophy through mechanisms that involve protein interactions in the cardiomyocyte nucleus, particularly with pro-hypertrophic transcription factors, rather than via histone deacetylation. In contrast, evidence indicates that class I HDACs promote cardiomyocyte hypertrophy through mechanisms that are dependent on their enzymatic activity and thus sensitive to pharmacological HDAC inhibitors. Although considerable progress has been made in understanding the roles of post-translational modifications (PTMs) such as phosphorylation, oxidation and proteolytic cleavage in regulating class IIa HDAC localisation and function, more work is required to explore the contributions of other PTMs, such as ubiquitination and sumoylation, as well as potential cross-regulatory interactions between distinct PTMs and between class IIa and class I HDAC isoforms.

Endothelin XIII

Twenty-five years ago, a groundbreaking paper from Tsukuba University in Japan was published, identifying the sequence of the endothelin gene and peptide (Nature 332, 411-415, 1988). This work opened the way for the discovery of the endothelin receptors and the development of orally active endothelin receptor antagonists (ERAs). Today, ERAs are part of medical therapy of patients around the world for the treatment of pulmonary arterial hypertension. Since the discovery of endothelin, about 1000 papers per year have been published, with more than 27,000 articles available today. Many important and break-through findings presented in the endothelin conferences have been published in the conferences' proceedings. Endothelin XIII is the proceedings of the Thirteenth International Conference on Endothelin, held at Tokyo Campus of Tsukuba University, Japan, in September 2013. At the conference, the 25th anniversary of endothelin's discovery was celebrated and articles produced from data presented at the conference are compiled in this Special Issue of Life Sciences. Endothelin XIII includes more than fifty articles, including review articles by experts in the field and numerous original research articles. As the Editors of this special issue, we are proud to present Endothelin XIII and wish the field continued growth for the benefit of patients and for the advancement of biomedical science.