Expression of A-, B-, and C-type natriuretic peptide genes in failing and developing human ventricles. Correlation with expression of the Ca(2+)-ATPase gene

Myocardial SERCA2 Protects Against Cardiac Damage and Dysfunction Caused by Inhaled Bromine

Myocardial sarcoendoplasmic reticulum calcium ATPase 2 (SERCA2) activity is critical for heart function. We have demonstrated that inhaled halogen (chlorine or bromine) gases inactivate SERCA2, impair calcium homeostasis, increase proteolysis, and damage the myocardium ultimately leading to cardiac dysfunction. To further elucidate the mechanistic role of SERCA2 in halogen-induced myocardial damage, we used bromine-exposed cardiac-specific SERCA2 knockout (KO) mice [tamoxifen-administered SERCA2 (flox/flox) Tg (αMHC-MerCreMer) mice] and compared them to the oil-administered controls. We performed echocardiography and hemodynamic analysis to investigate cardiac function 24 hours after bromine (600 ppm for 30 minutes) exposure and measured cardiac injury markers in plasma and proteolytic activity in cardiac tissue and performed electron microscopy of the left ventricle (LV). Cardiac-specific SERCA2 knockout mice demonstrated enhanced toxicity to bromine. Bromine exposure increased ultrastructural damage, perturbed LV shape geometry, and demonstrated acutely increased phosphorylation of phospholamban in the KO mice. Bromine-exposed KO mice revealed significantly enhanced mean arterial pressure and sphericity index and decreased LV end diastolic diameter and LV end systolic pressure when compared with the bromine-exposed control FF mice. Strain analysis showed loss of synchronicity, evidenced by an irregular endocardial shape in systole and irregular vector orientation of contractile motion across different segments of the LV in KO mice, both at baseline and after bromine exposure. These studies underscore the critical role of myocardial SERCA2 in preserving cardiac ultrastructure and function during toxic halogen gas exposures. SIGNIFICANCE STATEMENT: Due to their increased industrial production and transportation, halogens such as chlorine and bromine pose an enhanced risk of exposure to the public. Our studies have demonstrated that inhalation of these halogens leads to the inactivation of cardiopulmonary SERCA2 and results in calcium overload. Using cardiac-specific SERCA2 KO mice, these studies further validated the role of SERCA2 in bromine-induced myocardial injury. These studies highlight the increased susceptibility of individuals with pathological loss of cardiac SERCA2 to the effects of bromine.

Transcriptional Targeting Approaches in Cardiac Gene Transfer Using AAV Vectors

Cardiac-targeted transgene delivery offers new treatment opportunities for cardiovascular diseases, which massively contribute to global mortality. Restricted gene transfer to cardiac tissue might protect extracardiac organs from potential side-effects. This could be mediated by using cis-regulatory elements, including promoters and enhancers that act on the transcriptional level. Here, we discuss examples of tissue-specific promoters for targeted transcription in myocytes, cardiomyocytes, and chamber-specific cardiomyocytes. Some promotors are induced at pathological states, suggesting a potential use as "induction-by-disease switches" in gene therapy. Recent developments have resulted in the identification of novel enhancer-elements that could further pave the way for future refinement of transcriptional targeting, for example, into the cardiac conduction system.

Mitochondrial Calcium Overload Plays a Causal Role in Oxidative Stress in the Failing Heart

Heart failure is a serious global health challenge, affecting more than 6.2 million people in the United States and is projected to reach over 8 million by 2030. Independent of etiology, failing hearts share common features, including defective calcium (Ca2+) handling, mitochondrial Ca2+ overload, and oxidative stress. In cardiomyocytes, Ca2+ not only regulates excitation-contraction coupling, but also mitochondrial metabolism and oxidative stress signaling, thereby controlling the function and actual destiny of the cell. Understanding the mechanisms of mitochondrial Ca2+ uptake and the molecular pathways involved in the regulation of increased mitochondrial Ca2+ influx is an ongoing challenge in order to identify novel therapeutic targets to alleviate the burden of heart failure. In this review, we discuss the mechanisms underlying altered mitochondrial Ca2+ handling in heart failure and the potential therapeutic strategies.

Targeting calcium regulators as therapy for heart failure: focus on the sarcoplasmic reticulum Ca-ATPase pump

Impaired myocardial Ca2+ cycling is a critical contributor to the development of heart failure (HF), causing changes in the contractile function and structure remodeling of the heart. Within cardiomyocytes, the regulation of sarcoplasmic reticulum (SR) Ca2+ storage and release is largely dependent on Ca2+ handling proteins, such as the SR Ca2+ ATPase (SERCA2a) pump. During the relaxation phase of the cardiac cycle (diastole), SERCA2a plays a critical role in transporting cytosolic Ca2+ back to the SR, which helps to restore both cytosolic Ca2+ levels to their resting state and SR Ca2+ content for the next contraction. However, decreased SERCA2a expression and/or pump activity are key features in HF. As a result, there is a growing interest in developing therapeutic approaches to target SERCA2a. This review provides an overview of the regulatory mechanisms of the SERCA2a pump and explores potential strategies for SERCA2a-targeted therapy, which are being investigated in both preclinical and clinical studies.

CNP, the Third Natriuretic Peptide: Its Biology and Significance to the Cardiovascular System

Simple Summary

CNP is the third natriuretic peptide to be isolated and is widely expressed in the central nervous system, osteochondral system, and vascular system. The receptor that is mainly targeted by CNP is GC-B, which differs from GC-A, the receptor targeted by the other two natriuretic peptides, ANP and BNP. Consequently, the actions of CNP differ somewhat from those of ANP and BNP. Research into the actions of CNP has shown that CNP attenuates cardiac remodeling in animal models of cardiac hypertrophy, myocardial infarction, and myocarditis. Studies examining CNP/GC-B signaling showed that it contributes to the prevention of cardiac stiffness. Endogenous CNP, perhaps acting in part through CNP/NPR-C signaling, contributes to the regulation of vascular function and blood pressure. CNP regulates vascular remodeling and angiogenesis via CNP/GC-B/CGK signaling. CNP attenuates interstitial fibrosis and fibrosis-related gene expression in pressure overload and myocardial infarction models. The clinical application of CNP as a therapeutic agent for cardiovascular diseases is anticipated.

Abstract

The natriuretic peptide family consists of three biologically active peptides: ANP, BNP, and CNP. CNP is more widely expressed than the other two peptides, with significant levels in the central nervous system, osteochondral system, and vascular system. The receptor that is mainly targeted by CNP is GC-B, which differs from GC-A, the receptor targeted by ANP and BNP. Consequently, the actions of CNP differ somewhat from those of ANP and BNP. CNP knockout leads to severe dwarfism, and there has been important research into the role of CNP in the osteochondral system. As a result, a CNP analog is now available for clinical use in patients with achondroplasia. In the cardiovascular system, CNP and its downstream signaling are involved in the regulatory mechanisms underlying myocardial remodeling, cardiac function, vascular tone, angiogenesis, and fibrosis, among others. This review focuses on the roles of CNP in the cardiovascular system and considers its potential for clinical application in the treatment of cardiovascular diseases.

Physiological and Pathophysiological Effects of C-Type Natriuretic Peptide on the Heart

Simple Summary

C-type natriuretic peptide (CNP) is the third member of the natriuretic peptide family. Unlike atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), CNP was not previously regarded as an important cardiac modulator. However, recent studies have revealed the physiological and pathophysiological importance of CNP in the heart; in concert with its cognate natriuretic peptide receptor-B (NPR-B), CNP has come to be regarded as the major heart-protective natriuretic peptide in the failed heart. In this review, I introduce the history of research on CNP in the cardiac field.

Abstract

C-type natriuretic peptide (CNP) is the third member of the natriuretic peptide family. Unlike other members, i.e., atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), which are cardiac hormones secreted from the atrium and ventricle of the heart, respectively, CNP is regarded as an autocrine/paracrine regulator with broad expression in the body. Because of its low expression levels compared to ANP and BNP, early studies failed to show its existence and role in the heart. However, recent studies have revealed the physiological and pathophysiological importance of CNP in the heart; in concert with the distribution of its specific natriuretic peptide receptor-B (NPR-B), CNP has come to be regarded as the major heart-protective natriuretic peptide in the failed heart. NPR-B generates intracellular cyclic guanosine 3′,5′-monophosphate (cGMP) upon CNP binding, followed by various molecular effects including the activation of cGMP-dependent protein kinases, which generates diverse cytoprotective actions in cardiomyocytes, as well as in cardiac fibroblasts. CNP exerts negative inotropic and positive lusitropic responses in both normal and failing heart models. Furthermore, osteocrin, the intrinsic and specific ligand for the clearance receptor for natriuretic peptides, can augment the effects of CNP and may supply a novel therapeutic strategy for cardiac protection.

The Significance of The Detection of Serum Lactate Dehydrogenase, Hypersensitive C-Reactive Protein, and N-Terminal Pro-Brain Natriuretic Peptide for the Evaluation of the Severity and Progression of Pediatric Patients with Traumatic Brain Injury

OBJECTIVE

This study aimed to investigate changes in the levels of serum lactate dehydrogenase (LDH), hypersensitive C-reactive protein (hs-CRP), and N-terminal pro-brain natriuretic peptide (NT-proBNP) in pediatric patients with traumatic brain injury and the clinical significance of detecting these changes for the evaluation of injury severity and patient progress.

METHODS

A retrospective study was conducted on 40 pediatric patients admitted to the Tongren Hospital of China Capital Medical University with traumatic brain injury between January 2018 and December 2019. Immunoturbidimetric assay and electrochemiluminescence were used to detect the serum levels of LDH, hs-CRP, and NT-proBNP. Correlation analysis was used to determine the degree of association between the indicators and the sensitivity and specificity of each indicator.

RESULTS

The serum levels of LDH, hs-CRP, and NT-proBNP in the poor-prognosis group were higher than those in the good-prognosis group, and the differences were statistically significant (P < 0.05).

CONCLUSION

The detection of serum LDH, hs-CRP, and NT-proBNP might be of great significance for the evaluation of the severity of a traumatic brain injury, disease progression, and the prognosis of pediatric patients with traumatic brain injury. The combined detection of the relevant indicators could provide more effective sensitivity and specificity and therefore offer better guidance and assistance in clinical practice.

Beta-blocker/ACE inhibitor therapy differentially impacts the steady state signaling landscape of failing and non-failing hearts

Heart failure is a multifactorial disease that affects an estimated 38 million people worldwide. Current pharmacotherapy of heart failure with reduced ejection fraction (HFrEF) includes combination therapy with angiotensin-converting enzyme inhibitors (ACEi) and β-adrenergic receptor blockers (β-AR blockers), a therapy also used as treatment for non-cardiac conditions. Our knowledge of the molecular changes accompanying treatment with ACEi and β-AR blockers is limited. Here, we applied proteomics and phosphoproteomics approaches to profile the global changes in protein abundance and phosphorylation state in cardiac left ventricles consequent to combination therapy of β-AR blocker and ACE inhibitor in HFrEF and control hearts. The phosphorylation changes induced by treatment were profoundly different for failing than for non-failing hearts. HFrEF was characterized by profound downregulation of mitochondrial proteins coupled with derangement of β-adrenergic and pyruvate dehydrogenase signaling. Upon treatment, phosphorylation changes consequent to HFrEF were reversed. In control hearts, treatment mainly led to downregulation of canonical PKA signaling. The observation of divergent signaling outcomes depending on disease state underscores the importance of evaluating drug effects within the context of the specific conditions present in the recipient heart.

BNP and NT-proBNP Concentrations in Paired cerebrospinal Fluid and Plasma Samples of Patients with Traumatic Brain Injury

BACKGROUND

The aim of this study was to investigate the secretion patterns of brain natriuretic peptide (BNP) and N-terminal-proBNP (NT-proBNP) after traumatic brain injury (TBI) and to analyze the source of them in cerebrospinal fluid (CSF).

MATERIALS AND METHODS

We synchronously measured BNP and NT-proBNP concentrations in paired CSF and plasma samples from 22 moderate to severe TBI patients and 40 healthy control patients. The CSF and/or plasma ratio of albumin (Q_Albumin) was calculated daily. The BNP and NT-proBNP levels of CSF and plasma were compared between TBI patients and control patients.

RESULTS

CSF BNP and NT-proBNP levels peaked on day 3 after injury, as did the plasma BNP and NT-proBNP levels. The CSF BNP and NT-proBNP levels in TBI patients were elevated from day 1, which was significantly higher than control group (P < 0.05 and P < 0.01, respectively). However, in plasma, only NT-proBNP levels were significantly higher than in the control group from day 2 (P < 0.05). In addition, Q_BNP, defined as CSF BNP concentration and/or plasma BNP concentration, was significantly higher in TBI patients than in the control group (P < 0.01). However, Q_Albumin remained within ranges of a mild to moderate dysfunction of blood-brain-barrier in TBI patients.

CONCLUSIONS

CSF BNP concentrations are elevated and peak on day 3 after moderate to severe TBI. CSF BNP may originate from the brain and may be a potential biomarker of TBI.

The structural reconformation of peptides in enhancing functional and therapeutic properties: Insights into their solid state crystallizations

Therapeutic peptides derived proteins with alpha-reconformation states like antibody shape have shown potential effects in combating terrible diseases linked with earlier signs of angiogensis, mutagenesis and transgenesis. Alpha reconformation in material design refers to the folding of the peptide chains and their transitions under reversible chemical bonds of disulfide chemical bridges and further non-covalence lesions. Thus, the rational design of signal peptides into alpha-helix is intended in increasing the defending effects of peptides into cores like adjuvant antibiotic and/or vaccines. Thereby, the signal peptides are able in displaying multiple eradicating regions by changing crystal-depositions and deviation angles. These types of molecular structures could have multiple advantages in tracing disease syndromes and impurities by increasing the host defense against the fates of pathogens and viruses, eventually leading to the loss in signaling by increasing peptide susceptibility levels to folding and unfolding and therefore, formation of transgenic peptide models. Alpha reconformation peptides is aimed in triggering as well as other regulatory functions such as remodulating metabolic chain disorders of lipolysis and glucolysis by increasing the insulin and leptin resistance for best lipid storages and lipoprotein density distributions.

Hypertrophic signaling compensates for contractile and metabolic consequences of DNA methyltransferase 3A loss in human cardiomyocytes

The role of DNA methylation in cardiomyocyte physiology and cardiac disease remains a matter of controversy. We have recently provided evidence for an important role of DNMT3A in human cardiomyocyte cell homeostasis and metabolism, using engineered heart tissue (EHT) generated from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes carrying a knockout of the de novo DNA methyltransferase DNMT3A. Unlike isogenic control EHT, knockout EHT displayed morphological abnormalities such as lipid accumulations inside cardiomyocytes associated with impaired mitochondrial metabolism, as well as functional defects and impaired glucose metabolism. Here, we analyzed the role of DNMT3A in the setting of cardiac hypertrophy. We induced hypertrophic signaling by treatment with 50 nM endothelin-1 and 20 μM phenylephrine for one week and assessed EHT contractility, morphology, DNA methylation, and gene expression. While both knockout EHTs and isogenic controls showed the expected activation of the hypertrophic gene program, knockout EHTs were protected from hypertrophy-related functional impairment. Conversely, hypertrophic treatment prevented the metabolic consequences of a loss of DNMT3A, i.e. abolished lipid accumulation in cardiomyocytes likely by partial normalization of mitochondrial metabolism and restored glucose metabolism and metabolism-related gene expression of knockout EHT. Together, these data suggest an important role of DNA methylation not only for cardiomyocyte physiology, but also in the setting of cardiac disease.

Circulating products of C-type natriuretic peptide and links with organ function in health and disease

Paracrine actions of CNP and rapid degradation at source severely limit study of CNP's many roles in vivo. However provided sensitive and validated assays are used, there is increasing evidence that low concentrations of bioactive CNP in plasma, and the readily detectable concentrations of the bio-inactive processed product of proCNP (aminoterminal proCNP), can be used to advance understanding of the hormone's role in pathophysiology. Provided renal function is normal, concordant changes in both CNP and NTproCNP reflect change in tissue production of proCNP whereas change in CNP alone results from altered rates of bioactive CNP degradation and are reflected in the ratio of NTproCNP to CNP. As already shown in juveniles, where plasma concentration of CNP products are higher and are associated with concurrent endochondral bone growth, measurements of plasma CNP products in mature adults have potential to clarify organ response to stress and injury. Excepting the role of CNP in fetal-maternal welfare, this review examines evidence linking plasma CNP products with function of a wide range of tissues in adults, including the impact of extraneous factors such as nutrients, hormone therapy and exercise.

An Important Role for DNMT3A-Mediated DNA Methylation in Cardiomyocyte Metabolism and Contractility

Supplemental Digital Content is available in the text.

Background:

DNA methylation acts as a mechanism of gene transcription regulation. It has recently gained attention as a possible therapeutic target in cardiac hypertrophy and heart failure. However, its exact role in cardiomyocytes remains controversial. Thus, we knocked out the main de novo DNA methyltransferase in cardiomyocytes, DNMT3A, in human induced pluripotent stem cells. Functional consequences of DNA methylation-deficiency under control and stress conditions were then assessed in human engineered heart tissue from knockout human induced pluripotent stem cell–derived cardiomyocytes.

Methods:

DNMT3A was knocked out in human induced pluripotent stem cells by CRISPR/Cas9gene editing. Fibrin-based engineered heart tissue was generated from knockout and control human induced pluripotent stem cell–derived cardiomyocytes. Development and baseline contractility were analyzed by video-optical recording. Engineered heart tissue was subjected to different stress protocols, including serum starvation, serum variation, and restrictive feeding. Molecular, histological, and ultrastructural analyses were performed afterward.

Results:

Knockout of DNMT3A in human cardiomyocytes had three main consequences for cardiomyocyte morphology and function: (1) Gene expression changes of contractile proteins such as higher atrial gene expression and lower MYH7/MYH6 ratio correlated with different contraction kinetics in knockout versus wild-type; (2) Aberrant activation of the glucose/lipid metabolism regulator peroxisome proliferator-activated receptor gamma was associated with accumulation of lipid vacuoles within knockout cardiomyocytes; (3) Hypoxia-inducible factor 1α protein instability was associated with impaired glucose metabolism and lower glycolytic enzyme expression, rendering knockout-engineered heart tissue sensitive to metabolic stress such as serum withdrawal and restrictive feeding.

Conclusion:

The results suggest an important role of DNA methylation in the normal homeostasis of cardiomyocytes and during cardiac stress, which could make it an interesting target for cardiac therapy.

B-type natriuretic peptide and its role in altering Ca2+-regulatory proteins in heart failure-mechanistic insights

Heart failure (HF) is a worldwide disease with high levels of morbidity and mortality. The pathogenesis of HF is complicated and involves imbalances in hormone and electrolyte. B-type natriuretic peptide (BNP) has served as a biomarker of HF severity, and in recent years, it has been used to treat the disease, thanks to its cardio-protective effects, such as diuresis, natriuresis, and vasodilatation. In stage C/D HF, symptoms are severe despite elevated BNP. Disturbances in Ca²⁺ homeostasis are often a dominating feature of the disease, causing Ca²⁺-regulatory protein dysfunction, including reduced expression and activity of sarcoplasmic reticulum Ca²⁺-ATPase2a (SERCA2a), impaired ryanodine receptors (RYRs) function, intensive Na⁺-Ca²⁺ exchanger (NCX), and downregulation of S100A1. The relationship between natriuretic peptides (NPs) and Ca²⁺-regulatory proteins has been widely studied and represents important mechanisms in the etiology of HF. In this review, we present evidence that BNP may regulate Ca²⁺-regulatory proteins, in particular, suppressing SERCA2a and S100A1 expression. However, relationships between BNP and other Ca²⁺-regulatory proteins remain vague.

Impact of oxidative posttranslational modifications of SERCA2 on heart failure exacerbation in young patients with non-ischemic cardiomyopathy: A pilot study

Background

Oxidative posttranslational modifications (OPTM) impair the function of Sarcoplasmic/endoplasmic reticulum (SR) calcium (Ca²⁺) ATPase (SERCA) 2 and trigger cytosolic Ca²⁺ dysregulation. We investigated the extent of OPTM of SERCA2 in patients with non-ischemic cardiomyopathy (NICM).

Methods and results

Endomyocardial biopsy (EMB) was obtained in 40 consecutive patients with NICM. Total expression and OPTM of SERCA2, including sulfonylation at cysteine-674 (S-SERCA2) and nitration at tyrosine-294/295 (N-SERCA2), were examined by immunohistochemical analysis. S-SERCA2 increased in the presence of late gadolinium enhancement on cardiac magnetic resonance imaging. S-SERCA2/SERCA2 and N-SERCA2/SERCA2 correlated with cardiac fibrosis evaluated by Masson’s trichrome staining of EMB. SERCA2 expression modestly increased in parallel with an upward trend in OPTM of SERCA2 with aging. This tendency became prominent only in patients aged >65 years. OPTM of SERCA2 positively correlated with brain natriuretic peptide (BNP) values only in patients aged ≤65 years. Composite major adverse cardiac events (MACE) increased more in the high OPTM group of younger patients; however, MACE-free survival was similar irrespective of the extent of OPTM in older patients.

Conclusions

OPTM of SERCA2 correlate with myocardial fibrosis in NICM. In younger patients, OPTM of SERCA2 correlate with elevated BNP and increased composite MACE.

Immunolocalization of natriuretic peptides and their receptors in goat (Capra hircus) heart

Natriuretic peptides are structurally similar, but genetically distinct, hormones that participate in cardiovascular homeostasis by regulating blood and extracellular fluid volume and blood pressure. We investigated the distribution of natriuretic peptides and their receptors in goat (Capra hircus) heart tissue using the peroxidase-anti-peroxidase (PAP) immunohistochemical method. Strong staining of atrial natriuretic peptide (ANP) was observed in atrial cardiomyocytes, while strong staining for brain natriuretic peptide (BNP) was observed in ventricular cardiomyocytes. Slightly stronger cytoplasmic C-type natriuretic peptide (CNP) immunostaining was detected in the ventricles compared to the atria. Natriuretic peptide receptor-A (NPR-A) immunoreactivity was more prominent in the atria, while natriuretic peptide receptor-B (NPR-B) immunoreactivity was stronger in the ventricles. Cytoplasmic natriuretic peptide receptor-C (NPR-C) immunoreactivity was observed in both the atria and ventricles, although staining was more prominent in the ventricles. ANP immunoreactivity ranged from weak to strong in endothelial and vascular smooth muscle cells. Endothelial cells exhibited moderate to strong BNP immunoreactivity, while vascular smooth cells displayed weak to strong staining. Endothelial cells exhibited weak to strong cytoplasmic CNP immunoreactivity. Vascular smooth muscle cells were labeled moderately to strongly for CNP. Weak to strong cytoplasmic NPR-A immunoreactivity was found in the endothelial cells and vascular smooth muscle cells stained weakly to moderately for NPR-A. Endothelial and vascular smooth cells exhibited weak to strong cytoplasmic NPR-B immunoreactivity. Moderate to strong NPR-C immunoreactivity was observed in the endothelial and smooth muscle cells. Small gender differences in the immunohistochemical distribution of natriuretic peptides and receptors were observed. Our findings suggest that endothelial cells, vascular smooth cells and cardiomyocytes express both natriuretic peptides and their receptors.

Genetics of guanylyl cyclase pathways in the cochlea and their influence on hearing

Although hearing loss is the most common sensory deficit in Western societies, there are no successful pharmacological treatments for this disorder. Recent experiments have demonstrated that manipulation of intracellular cyclic guanosine monophosphate (cGMP) concentrations can have both beneficial and harmful effects on hearing. In this review, we will examine the role of cGMP as a key second messenger involved in many aspects of cochlear function and discuss the known functions of downstream effectors of cGMP in sound processing. The nitric oxide-stimulated soluble guanylyl cyclase system (sGC) and the two natriuretic peptide-stimulated particulate GCs (pGCs) will be more extensively covered because they have been studied most thoroughly. The cochlear GC systems are attractive targets for medical interventions that improve hearing while simultaneously representing an under investigated source of sensorineural hearing loss.

Non-adrenergic control of lipolysis and thermogenesis in adipose tissues

The enormous plasticity of adipose tissues, to rapidly adapt to altered physiological states of energy demand, is under neuronal and endocrine control. In energy balance, lipolysis of triacylglycerols and re-esterification of free fatty acids are opposing processes operating in parallel at identical rates, thus allowing a more dynamic transition from anabolism to catabolism, and vice versa. In response to alterations in the state of energy balance, one of the two processes predominates, enabling the efficient mobilization or storage of energy in a negative or positive energy balance, respectively. The release of noradrenaline from the sympathetic nervous system activates lipolysis in a depot-specific manner by initiating the canonical adrenergic receptor-G_s-protein-adenylyl cyclase-cyclic adenosine monophosphate-protein kinase A pathway, targeting proteins of the lipolytic machinery associated with the interface of the lipid droplets. In brown and brite adipocytes, lipolysis stimulated by this signaling pathway is a prerequisite for the activation of non-shivering thermogenesis. Free fatty acids released by lipolysis are direct activators of uncoupling protein 1-mediated leak respiration. Thus, pro- and anti-lipolytic mediators are bona fide modulators of thermogenesis in brown and brite adipocytes. In this Review, we discuss adrenergic and non-adrenergic mechanisms controlling lipolysis and thermogenesis and provide a comprehensive overview of pro- and anti-lipolytic mediators.

New insights into SERCA2a gene therapy in heart failure: pay attention to the negative effects of B-type natriuretic peptides

Sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a) is a target of interest in gene therapy for heart failure with reduced ejection fraction (HFrEF). However, the results of an important clinical study, the Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID) trial, were controversial. Promising results were observed in the CUPID 1 trial, but the results of the CUPID 2 trial were negative. The factors that caused the controversial results remain unclear. Importantly, enrolled patients were required to have a higher plasma level of B-type natriuretic peptide (BNP) in the CUPID 2 trial. Moreover, BNP was shown to inhibit SERCA2a expression. Therefore, it is possible that high BNP levels interact with treatment effects of SERCA2a gene transfer and accordingly lead to negative results of CUPID 2 trial. From this point of view, effects of SERCA2a gene therapy should be explored in heart failure with preserved ejection fraction, which is characterised by lower BNP levels compared with HFrEF. In this review, we summarise the current knowledge of SERCA2a gene therapy for heart failure, analyse potential interaction between BNP levels and therapeutic effects of SERCA2a gene transfer and provide directions for future research to solve the identified problems.

Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues

Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.

Importance of Endogenous Atrial and Brain Natriuretic Peptides in Murine Embryonic Vascular and Organ Development

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) bind to the receptor guanylyl cyclase (GC)-A, leading to diuresis, natriuresis, and blood vessel dilation. In addition, ANP and BNP have various angiogenic properties in ischemic tissue. When breeding mice devoid of GC-A, we noted significant skewing of the Mendelian ratio in the offspring, suggesting embryonic lethality due to knockout of GC-A. Consequently, we here investigated the roles of endogenous ANP and BNP in embryonic neovascularization and organ morphogenesis. Embryos resulting from GC-A(-/-) × GC-A(+/-) crosses developed hydrops fetalis (HF) beginning at embryonic day (E)14.5. All embryos with HF had the genotype GC-A(-/-). At E17.5, 33.3% (12 of 36) of GC-A(-/-) embryos had HF, and all GC-A(-/-) embryos with HF were dead. Beginning at E16.0, HF-GC-A(-/-) embryos demonstrated poorly developed superficial vascular vessels and sc hemorrhage, the fetal side of the placenta appeared ischemic, and vitelline vessels on the yolk sac were poorly developed. Furthermore, HF-GC-A(-/-) embryos also showed abnormal constriction of umbilical cord vascular vessels, few cardiac trabeculae and a thin compact zone, hepatic hemorrhage, and poor bone development. Electron microscopy of E16.5 HF-GC-A(-/-) embryos revealed severe vacuolar degeneration in endothelial cells, and the expected 3-layer structure of the smooth muscle wall of the umbilical artery was indistinct. These data demonstrate the importance of the endogenous ANP/BNP-GC-A system not only in the neovascularization of ischemic tissues but also in embryonic vascular development and organ morphogenesis.

Systemic, but not cardiomyocyte-specific, deletion of the natriuretic peptide receptor guanylyl cyclase A increases cardiomyocyte number in neonatal mice

Guanylyl cyclase A (GC-A), the receptor for atrial and B-type natriuretic peptides, is implicated in the regulation of blood pressure and cardiac growth. We used design-based stereological methods to examine the effect of GC-A inactivation on cardiomyocyte volume, number and subcellular composition in postnatal mice at day P2. In mice with global, systemic GC-A deletion, the cardiomyocyte number was significantly increased, demonstrating that hyperplasia is the main cause for the increase in ventricle weight in these early postnatal animals. In contrast, conditional, cardiomyocyte-restricted inactivation of GC-A had no significant effect on ventricle weight or cardiomyocyte number. The mean volume of cardiomyocytes and the myocyte-related volumes of the four major cell organelles (myofibrils, mitochondria, nuclei and sarcoplasm) were similar between genotypes. Taken together, systemic GC-A deficiency induces cardiac enlargement based on a higher number of normally composed and sized cardiomyocytes early after birth, whereas cardiomyocyte-specific GC-A abrogation is not sufficient to induce cardiac enlargement and has no effect on number, size and composition of cardiomyocytes. We conclude that postnatal cardiac hyperplasia in mice with global GC-A inactivation is provoked by systemic alterations, e.g., arterial hypertension. Direct GC-A-mediated effects in cardiomyocytes seem not to be involved in the regulation of myocyte proliferation at this early stage.

Plasma brain-type natriuretic Peptide level following seizure and syncope: pilot study

Background and Purpose:

To explore the clinical feasibility of plasma brain-type natriuretic peptide (proBNP) level to differentiate the two major causes of transient unconsciousness, seizure and vasovagal syncope (VVS) in adult patients.

Methods:

ProBNP levels were evaluated within 24 hours following attack in patients who had experienced a transient episode of unconsciousness. For confirmatory diagnosis, clinical history was reviewed thoroughly and several work-ups including electroencephalography and cerebral imaging and tilt-table test, were performed in cases of putative VVS, as a part of routine clinical approaches.

Results:

According to various relevant evaluations, 15 patients were diagnosed as seizure (age, 40.3±13.8 years) and 12 patients were VVS (age, 38.1±17.1 years). Plasma concentrations of pro-BNP were not different between two groups (p=0.714). Median level was 34.3 pg/mL (interquartile range: 12.9–91.1) in post-seizure group and 32.3 pg/mL (interquartile range 8.9–77.4) in post-VVS group. Additionally, it was not correlated with the sampling times within 24 hours after the episodes.

Conclusions:

The plasma level of pro-BNP has a limited clinical value in differentiating seizure and vasovagal syncope in adults. However, the more validated results with a large population should be sought in the future studies to confirm its value.

Natriuretic peptides in cardiometabolic regulation and disease

In the 30 years since the identification of the natriuretic peptides, their involvement in regulating fluid and blood pressure has become firmly established. Data indicating a role for these hormones in lifestyle-related metabolic and cardiovascular disorders have also accumulated over the past decade. Dysregulation of the natriuretic peptide system has been associated with obesity, glucose intolerance, type 2 diabetes mellitus, and essential hypertension. Moreover, the natriuretic peptides have been implicated in the protection against atherosclerosis, thrombosis, and myocardial ischaemia. All these conditions can coexist and potentially lead to heart failure, a syndrome associated with a functional natriuretic peptide deficiency despite high circulating concentrations of immunoreactive peptides. Therefore, dysregulation of the natriuretic peptide system, a 'natriuretic handicap', might be an important factor in the initiation and progression of metabolic dysfunction and its accompanying cardiovascular complications. This Review provides a summary of the natriuretic peptide system and its involvement in these cardiometabolic conditions. We propose that these peptides might have an integrating role in lifestyle-related metabolic and cardiovascular disorders.

RNA sequencing analysis and atrial natriuretic peptide production in patients with dilated and ischemic cardiomyopathy

BACKGROUND

The atrium is the major site of ANP synthesis, which has been said to increase in heart failure as a result of increased production in the left ventricular (LV) myocardium. This is a key issue related to its diagnostic and prognostic capabilities. We aimed to evaluate protein levels of proANP and ANP and the enzymes that cleave the natriuretic peptides, corin and furin, in the LV tissue of heart transplant patients with dilated (DCM) and ischemic (ICM) cardiomyopathy compared with control donors (CNT). We also evaluate mRNA levels of ANP gene (NPPA) by RNA sequencing in the same tissue.

METHODS AND RESULTS

Seventy-three human LV tissue samples from ICM (n=30) and DCM (n=33) patients and CNT (n=10) were analyzed by Western blot and RNA sequencing. Comparing protein levels according to etiology, neither DCM nor ICM showed levels of proANP or ANP different from those of CNT. However, NPPA was increased in both groups compared to CNT (DCM 32 fold, p<0.0001; ICM 10 fold, p<0.0001). Corin (but not furin) was elevated in the ICM group compared to CNT (112 ± 24 vs. 100 ± 7, p<0.05), and its level was inversely related with LV ejection fraction (LVEF) (r=-0.399, p<0.05).

CONCLUSIONS

Patients present with elevated levels of NPPA but not of proANP or ANP proteins in LV tissue, which may be due to posttranscripcional regulation of NPPA or different pathways for ANP secretion between the atrium and ventricle. Moreover, there are differences between DCM and ICM in corin levels, indicating that a different molecular mechanism may exist that converge in this syndrome. Further, LV concentration of corin is inversely related to LVEF in ICM.

The heart as an endocrine organ

The concept of the heart as an endocrine organ arises from the observation that the atrial cardiomyocytes in the mammalian heart display a phenotype that is partly that of endocrine cells. Investigations carried out between 1971 and 1983 characterised, by virtue of its natriuretic properties, a polypeptide referred to atrial natriuretic factor (ANF). Another polypeptide isolated from brain in 1988, brain natriuretic peptide (BNP), was subsequently characterised as a second hormone produced by the mammalian heart atria. These peptides were associated with the maintenance of extracellular fluid volume and blood pressure. Later work demonstrated a plethora of other properties for ANF and BNP, now designated cardiac natriuretic peptides (cNPs). In addition to the cNPs, other polypeptide hormones are expressed in the heart that likely act upon the myocardium in a paracrine or autocrine fashion. These include the C-type natriuretic peptide, adrenomedullin, proadrenomedullin N-terminal peptide and endothelin-1. Expression and secretion of ANF and BNP are increased in various cardiovascular pathologies and their levels in blood are used in the diagnosis and prognosis of cardiovascular disease. In addition, therapeutic uses for these peptides or related substances have been found. In all, the discovery of the endocrine heart provided a shift from the classical functional paradigm of the heart that regarded this organ solely as a blood pump to one that regards this organ as self-regulating its workload humorally and that also influences the function of several other organs that control cardiovascular function.

Depletion of extracellular signal-regulated kinase 1 in mice with cardiomyopathy caused by lamin A/C gene mutation partially prevents pathology before isoenzyme activation

Mutations in the lamin A/C gene (LMNA) encoding A-type nuclear lamins cause dilated cardiomyopathy with variable muscular dystrophy. These mutations enhance mitogen-activated protein kinase signaling in the heart and pharmacological inhibition of extracellular signal-regulated kinase (ERK) 1 and 2 improves cardiac function in Lmna(H222P/H222P) mice. In the current study, we crossed mice lacking ERK1 to Lmna(H222P/H222P) mice and examined cardiac performance and survival. Male Lmna(H222P/H222P)/Erk1(-/-) mice lacking ERK1 had smaller left ventricular end systolic diameters and increased fractional shortening (FS) at 16 weeks of age than Lmna(H222P/H222P/)Erk1(+/+) mice. Their mean survival was also significantly longer. However, the improved cardiac function was abrogated at 20 weeks of age concurrent with an increased activity of ERK2. Lmna(H222P/H222P)/Erk1(-/-) mice treated with an inhibitor of ERK1/2 activation had smaller left ventricular diameters and increased FS at 20 weeks of age. These results provide genetic evidence that ERK1 and ERK2 contribute to the development of cardiomyopathy caused by LMNA mutations and reveal interplay between these isoenzymes in maintaining a combined pathological activity in heart.

C-type natriuretic peptide: a new cardiac mediator

Natriuretic peptides are endogenous hormones released by the heart in response to myocardial stretch and overload. While atrial and brain natriuretic peptides (ANP, BNP) were immediately considered cardiac hormones and their role was well-characterized and defined in predicting risk in cardiovascular disease, evidence indicating the role of C-type natriuretic peptide (CNP) in cardiovascular regulation was slow to emerge until about 8 years ago. Since then, considerable literature on CNP and the cardiovascular system has been published; the aim of this review is to examine current literature relating to CNP and cardiovascular disease, in particular its role in heart failure (HF) and myocardial infarction (MI). This review retraces the fundamental steps in research that led understanding the role of CNP in HF and MI; from increased CNP mRNA expression and plasmatic concentrations in humans and in animal models, to detection of CNP expression in cardiomyocytes, to its evaluation in human leukocytes. The traditional view of CNP as an endothelial peptide has been surpassed by the results of many studies published in recent years, and while its physiological role is still under investigation, information is now available regarding its contribution to cardiovascular function. Taken together, these observations suggest that CNP and its specific receptor, NPR-B, can play a very important role in regulating cardiac hypertrophy and remodeling, indicating NPR-B as a new potential drug target for the treatment of cardiovascular disease.

Different roles of the cardiac Na+/Ca2+-exchanger in ouabain-induced inotropy, cell signaling, and hypertrophy

Previous studies have shown that digitalis drugs, acting as specific inhibitors of cardiac Na(+)/K(+)-ATPase, not only cause positive inotropic effects, but also activate cell signaling pathways that lead to cardiac myocyte hypertrophy. A major aim of this work was to assess the role of Na(+)/Ca(2+)-exchanger, NCX1, in the above two seemingly related drug effects. Using a mouse with ventricular-specific knockout (KO) of NCX1, ouabain-induced positive inotropy that was evident in isolated wild-type (Wt) hearts was clearly reduced in KO hearts. Ouabain also increased Ca(2+) transient amplitudes in Wt myocytes, but not in KO myocytes. Ouabain-induced activations of ERK 1/2 were noted in Wt myocytes, but not in KO myocytes; however, ouabain activated PI3K1A and Akt in both Wt and KO myocytes. Protein synthesis rate, as a measure of hypertrophy, was increased by ouabain in Wt and KO myocytes; these drug effects were prevented by a PI3K inhibitor but not by a MEK/ERK inhibitor. Hypertrophy caused by ET-1, but not that induced by ouabain, was accompanied by upregulation of BNP gene in Wt and KO myocytes. The findings indicate 1) the necessity of NCX1 for positive inotropic action of ouabain; 2) the irrelevance of NCX1 and ERK 1/2 activation to ouabain-induced hypertrophy; and 3) that hypertrophy caused by ouabain through the activation of PI3K1A/Akt pathway is likely to be beneficial to the heart.

Functional evidence for an active role of B-type natriuretic peptide in cardiac remodelling and pro-arrhythmogenicity

AIMS

During heart failure (HF), the left ventricle (LV) releases B-type natriuretic peptide (BNP), possibly contributing to adverse cardiovascular events including ventricular arrhythmias (VAs) and LV remodelling. We investigated the cardiac effects of chronic BNP elevation in healthy mice and compared the results with a model of HF after myocardial infarction (PMI mice).

METHODS AND RESULTS

Healthy mice were exposed to circulating BNP levels (BNP-Sham) similar to those measured in PMI mice. Telemetric surface electrocardiograms showed that in contrast with fibrotic PMI mice, electrical conduction was not affected in BNP-Sham mice. VAs were observed in both BNP-Sham and PMI but not in Sham mice. Analysis of heart rate variability indicated that chronic BNP infusion increased cardiac sympathetic tone. At the cellular level, BNP reduced Ca(2+) transients and impaired Ca(2+) reuptake in the sarcoplasmic reticulum, in line with blunted SR Ca(2+) ATPase 2a and S100A1 expression. BNP increased Ca(2+) spark frequency, reflecting Ca(2+) leak through ryanodine receptors, elevated diastolic Ca(2+), and promoted spontaneous Ca(2+) waves. Similar effects were observed in PMI mice. Most of these effects were reduced in BNP-Sham and PMI mice by the selective β1-adrenergic blocker metoprolol.

CONCLUSION

Elevated BNP levels, by inducing sympathetic overdrive and altering Ca(2+) handling, promote adverse cardiac remodelling and VAs, which could account in part for the progression of HF after MI. The early use of β-blockers to prevent the deleterious effects of chronic BNP exposure may be beneficial in HF.

M-CAT element mediates mechanical stretch-activated transcription of B-type natriuretic peptide via ERK activation

The muscle-CAT (M-CAT) promoter element is found on promoters of most muscle-specific cardiac genes, but its role in cardiac pathology is poorly understood. Here we studied whether the M-CAT element is involved in hypertrophic process activated by mechanical stretch, and identified the intracellular pathways mediating the response. When an in vitro stretch model of cultured neonatal rat cardiomyocytes and luciferase reporter construct driven by rat B-type natriuretic peptide (BNP) promoter were used, mutation of M-CAT element inhibited not only the basal reporter activity (88%), but also the stretch-activated BNP transcription (58%, p < 0.001). Stretch-induced BNP promoter activation was associated with an increase in transcriptional enhancer factor-1 (TEF-1) binding activity after 24 h mechanical stretch (p < 0.05). Inhibition of mitogen-activated protein kinases ERK, JNK, or p38 attenuated stretch-induced BNP activation. Interestingly, as opposed to p38 and JNK, inhibition of ERK had no additional effect on transcriptional activity of BNP promoter harboring the M-CAT mutation, suggesting a pivotal role for ERK in regulating stretch-induced BNP transcription via M-CAT binding site. Finally, immunoprecipitation studies showed that mechanical stretch induced myocyte enhancer factor-2 (MEF-2) binding to TEF-1. These data suggest a central role for M-CAT element in regulation of mechanical stretch-induced hypertrophic response via ERK activation.

Expression of C-type natriuretic peptide and its receptor NPR-B in cardiomyocytes

C-type natriuretic peptide (CNP) was recently found in myocardium at the mRNA and protein levels, but it is not known whether cardiomyocytes are able to produce CNP. The aim of this study was to determine the expression of CNP and its specific receptor NPR-B in cardiac cells, both in vitro and ex vivo. CNP, brain natriuretic peptide (BNP) and natriuretic peptide receptor (NPR)-B mRNA expression were examined by RT-PCR in the H9c2 rat cardiac myoblast cell line, in neonatal rat primary cardiomyocytes and in human umbilical vein endothelial cells (HUVECs) as control. CNP protein expression was probed in cardiac tissue sections obtained from adult male minipigs by immunohistochemistry, and in H9c2 cells both by immunocytochemistry and by specific radioimmunoassay. The results showed that cardiac cells as well as endothelial cells were able to produce CNP. Unlike cardiomyocytes, as expected, in endothelial cells expression of BNP was not detected. NPR-B mRNA expression was found in both cell types. Production of CNP in the heart muscle cells at protein level was confirmed by radioimmunological determination (H9c2: CNP=0.86 ± 0.083 pg/mg) and by immunocytochemistry studies. By immunostaining of tissue sections, CNP was detected in both endothelium and cardiomyocytes. Expression of CNP in cardiac cells at gene and protein levels suggests that the heart is actively involved in the production of CNP.

Mitogen-activated protein kinase inhibitors improve heart function and prevent fibrosis in cardiomyopathy caused by mutation in lamin A/C gene

BACKGROUND

Mutations in the lamin A/C gene, LMNA, can cause dilated cardiomyopathy. We have shown abnormal activation of the extracellular signal-regulated kinase (ERK) and the c-jun N-terminal kinase (JNK) branches of the mitogen-activated protein kinase signaling cascade in hearts from Lmna(H222P/H222P) mice that develop dilated cardiomyopathy. We recently showed that partial inhibition of ERK and JNK signaling before the onset of cardiomyopathy in Lmna(H222P/H222P) mice prevented the development of left ventricle dilatation and decreased cardiac ejection fraction at a time when they occurred in untreated mice.

METHODS AND RESULTS

To determine whether pharmacological inhibitors of ERK and JNK signaling could be clinically useful to treat cardiomyopathy caused by LMNA mutation, we administered them to Lmna(H222P/H222P) mice after they developed left ventricular dilatation and decreased ejection fraction. Lmna(H222P/H222P) mice were treated with ERK and JNK signaling inhibitors from 16 to 20 or, in pilot experiments, 19 to 24 weeks of age. The inhibitors blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere architecture that occurred in placebo-treated mice. Echocardiography and histological analysis demonstrated that treatment prevented left ventricular end-systolic dilatation, increased ejection fraction, and decreased myocardial fibrosis.

CONCLUSION

Inhibitors of ERK and JNK signaling could potentially be used to treat humans with cardiomyopathy caused by LMNA mutations.

Relation of smoking status to serum levels of N-terminal pro-brain natriuretic peptide in middle-aged men without overt cardiovascular disease

Cigarette smoking impairs arterial function and promotes atherosclerosis. However, whether smoking status is associated with cardiac overload has not yet been fully examined, particularly from an epidemiologic viewpoint. The present study examined the relation of smoking status to serum levels of N-terminal pro-brain natriuretic peptide (NT-pro-BNP), a marker of cardiac overload, in middle-aged men without overt cardiovascular disease. Serum NT-pro-BNP levels were measured in a work-site based population of 969 men (mean age 44 ± 6 years) who did not have any history or presence of cardiovascular disease. Smoking status was evaluated by self-reported questionnaire. Four hundred fifty-nine, 222, and 288 subjects were never, former, and current smokers, respectively. NT-pro-BNP levels were significantly higher in current smokers (21.7 ± 2.3 pg/ml) than in never smokers (17.9 ± 2.1 pg/ml, p <0.001). This significant difference was maintained even after adjusting for age, obesity, heart rate, hypertension, dyslipidemia, impaired fasting glucose/diabetes mellitus, left ventricular hypertrophy, estimated glomerular filtration rate, high-sensitivity C-reactive protein, alcohol consumption, and regular exercise. Current smokers had an increased odds ratio (3.04, 95% confidence interval 1.64 to 5.61, p <0.001) for elevated NT-pro-BNP (>54.5 pg/ml) compared to never smokers, even after adjusting for the studied variables. In contrast, former smokers did not show a significantly increased odds ratio for elevated NT-pro-BNP. NT-pro-BNP levels showed a weak, but significant negative correlation with duration of smoking cessation (partial r = -0.15, p = 0.034) in former smokers. In conclusion, these results suggest that cigarette smoking increases cardiac overload, whereas smoking cessation ameliorates these conditions.

Practical application of natriuretic peptides in paediatric cardiology

It is still uncertain if cardiac natriuretic peptides are useful biomarkers in paediatric cardiology. In this review we identify four clinical scenarios in paediatric cardiology, where clinical decision-making can be difficult, and where we feel the paediatric cardiologists need additional diagnostic tools. Natriuretic peptide measurements could be that extra tool. We discuss and suggest N-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide reference intervals for children without cardiovascular disease and cut-off points for the four specific paediatric heart conditions. We conclude that in premature neonates with persistent arterial ducts; in teenagers with tetralogy of Fallot and pulmonary regurgitation; and in children with heart transplants and potential allograft rejection cardiac peptides can provide the clinician with additional information, but in children with atrial septal defects the peptides are not helpful in guiding treatment or follow-up.

Efficacy and safety of nesiritide in patients with acute decompensated heart failure

Acute decompensated heart failure is a common clinical problem with associated poor outcomes. Over the last decade, attention to this area has greatly increased, with a focus on medical therapies that may safely offer improvement in acute symptoms and early outcomes. Previous therapies that focused on increased inotropy have generally failed to improve symptoms without adverse consequences. Thus, attention towards vasodilators and natriuretic peptides, such as nesiritide, has increased owing to nesiritide's symptomatic improvement and unique mechanism of improvement in hemodynamics. However, the pathophysiology of acute decompensated heart failure is complex and the impact of nesiritide on important clinical end points, beyond symptomatic and hemodynamic improvement, is unknown.

Biodesign of a renal-protective peptide based on alternative splicing of B-type natriuretic peptide

Alternative RNA splicing may provide unique opportunities to identify drug targets and therapeutics. We identified an alternative spliced transcript for B-type natriuretic peptide (BNP) resulting from intronic retention. This transcript is present in failing human hearts and is reduced following mechanical unloading. The intron-retained transcript would generate a unique 34 amino acid (aa) carboxyl terminus while maintaining the remaining structure of native BNP. We generated antisera to this carboxyl terminus and identified immunoreactivity in failing human heart tissue. The alternatively spliced peptide (ASBNP) was synthesized and unlike BNP, failed to stimulate cGMP in vascular cells or vasorelax preconstricted arterial rings. This suggests that ASBNP may lack the dose-limiting effects of recombinant BNP. Given structural considerations, a carboxyl-terminal truncated form of ASBNP was generated (ASBNP.1) and was determined to retain the ability of BNP to stimulate cGMP in canine glomerular isolates and cultured human mesangial cells but lacked similar effects in vascular cells. In a canine-pacing model of heart failure, systemic infusion of ASBNP.1 did not alter mean arterial pressure but increased the glomerular filtration rate (GFR), suppressed plasma renin and angiotensin, while inducing natriuresis and diuresis. Consistent with its distinct in vivo effects, the activity of ASBNP.1 may not be explained through binding and activation of NPR-A or NPR-B. Thus, the biodesigner peptide ASBNP.1 enhances GFR associated with heart failure while lacking the vasoactive properties of BNP. These findings demonstrate that peptides with unique properties may be designed based on products of alternatively splicing.

The effects of norepinephrine on myocardial biology: implications for the therapy of heart failure

Increased sympathetic nervous system (SNS) activity in patients with heart failure may help to support cardiovascular function. However, increased SNS activity, particularly if prolonged, may exert deleterious effects on cardiovascular structure and function by stimulating pathologic myocardial remodeling. In vitro, norepinephrine mimics many features of myocardial remodeling, including hypertrophy of individual myocytes and reinduction of fetal genes. Furthermore, stimulation of the beta-adrenergic pathway has been shown to stimulate apoptosis of cardiac myocytes in vitro, in rats infused with isoproterenol, and in mice that overexpress the stimulatory G-protein, Gs. Thus, increased SNS activity, acting via beta-adrenergic receptors, may play an important role in the progression of myocardial failure by acting directly on myocytes and other cell types in the heart to regulate fundamental biologic properties such as growth, apoptosis, and the composition of the extracellular matrix. This thesis provides a mechanism by which beta-adrenergic antagonists may inhibit or reverse pathologic remodeling, improve myocardial structure and function, and prolong patient survival.

Left Atrial Size by Planimetry is Superior to M-mode Diameter: Biochemical Calibration by Atrial and Brain Natriuretic Peptide

BACKGROUND

Left atrial (LA) size is routinely assessed by M-mode on echocardiography. Recently, a superiority of apical measures of LA size has been suggested, but no biochemical calibration has been attempted yet. The aim of the current study was to compare echocardiographic parameters of LA size through biochemical calibration with the natriuretic peptides atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP).

METHODS

A total of 610 middle-aged (50-67 years) subjects from a population-based sample (MONICA Augsburg, Germany) were characterized with respect to LA area and volume from the apical two-chamber (2C) and four-chamber (4C) views in addition to M-mode echocardiography. ANP and BNP concentrations were determined by radioimmunoassay.

RESULTS

A significant correlation to ANP and BNP was present with all measures on LA size. The univariate correlation was lowest with M-mode diameter (r = 0.11 with ANP; r = 0.09 with BNP, both P < .03), whereas 2C volume displayed the closest correlation (r = 0.20 with ANP and r = 0.28 with BNP, both P < .001) and even slightly exceeded 2C area, 4C volume, and 4C area. 2C volume further displaced LV systolic function, mass index, and heart rate as statistically significant predictors of ANP (P < .001) and BNP (P < .001) on adjusted regression analysis, whereas M-mode diameter was displaced as a significant predictor of ANP and BNP (P = not significant).

CONCLUSIONS

The current population-based echocardiographic study allows new insight into the value of different measures of LA size. The closer association between natriuretic peptide concentrations and parameters derived from planimetry and volumetry suggests a superiority of these parameters LA diameter. LA volumetry should be included in routine echocardiography for optimized assessment of LA size.

Altered expression of connexin43 contributes to the arrhythmogenic substrate during the development of heart failure in cardiomyopathic hamster

Heart failure is known to predispose to life-threatening ventricular tachyarrhythmias even before compromising the systemic circulation, but the underlying mechanism is not well understood. The aim of this study was to clarify the connexin43 (Cx43) gap junction remodeling and its potential role in the pathogenesis of arrhythmias during the development of heart failure. We investigated stage-dependent changes in Cx43 expression in UM-X7.1 cardiomyopathic hamster hearts and associated alterations in the electrophysiological properties using a high-resolution optical mapping system. UM-X7.1 hamsters developed left ventricular (LV) hypertrophy by ages 6∼10 wk and showed a moderate reduction in LV contractility at age 20 wk. Appreciable interstitial fibrosis was recognized at these stages. LV mRNA and protein levels of Cx43 in UM-X7.1 were unaffected at age 10 wk but significantly reduced at 20 wk. The expression level of Ser255-phosphorylated Cx43 in UM-X7.1 at age 20 wk was significantly greater than that in control golden hamsters at the same age. In UM-X7.1 at age 10 wk, almost normal LV conduction was preserved, whereas the dispersion of action potential duration was significantly increased. UM-X7.1 at age 20 wk showed significant reduction of cardiac space constant, significant decrease in conduction velocity, marked distortion of activation fronts, and pronounced increase in action potential duration dispersion. Programmed stimulation resulted in sustained ventricular tachycardia or fibrillation in UM-X7.1. LV activation during polymorphic ventricular tachycardia was characterized by multiple phase singularities or wavebreaks. During the development of heart failure in the cardiomyopathic hamster, alterations of Cx43 expression and phosphorylation in concert with interstitial fibrosis may create serious arrhythmogenic substrate through an inhibition of cell-to-cell coupling.

A double-blind randomized multicentre clinical trial to evaluate the efficacy and safety of two doses of etomoxir in comparison with placebo in patients with moderate congestive heart failure: the ERGO (etomoxir for the recovery of glucose oxidation) study

Etomoxir is an inhibitor of mitochondrial CPT1 (carnitine palmitoyltransferase 1) and thereby switches energy metabolism from fatty acids to glucose oxidation. Such a metabolic change may be beneficial in CHF (congestive heart failure). The ERGO (etomoxir for the recovery of glucose oxidation) study was designed in which etomoxir was tested at a dose of 80 and 40 mg compared with placebo for a period of 6 months in patients with CHF. As the principle measure of efficacy, a maximal exercise tolerance test and a submaximal 6-min corridor walk test were used. Secondary end points were echocardiographical dimensions and quality-of-life assessment scores. A total of 350 patients were planned to be screened, with the expectation that end point data would be available from approx. 260 patients. However, the study had to be stopped prematurely, because unacceptably high liver transaminase levels were detected in four patients taking etomoxir. At the termination of the study, 121 patients were randomized to placebo, 118 to 40 mg of etomoxir and 108 to 80 mg of etomoxir. At that time, 21 patients in the placebo group, 16 in the 40 mg of etomoxir group and 14 patients in the 80 mg of etomoxir group had completed the study. The mean increases in exercise time were 3.3, 10.2 and 19.4 s for the placebo, 40 mg of etomoxir and 80 mg of etomoxir groups respectively (P value was not significant). No changes were obvious in the 6-min corridor walk test or in echocardiographical parameters from baseline. The number of patients that completed the study was too small to demonstrate significant effects on exercise time, although there was a tendency towards an increase in exercise time. Therefore, before rejecting the hypothesis that inhibition of fatty acid oxidation might be beneficial in CHF, similar studies have to be performed using different inhibitors of fatty acid oxidation targeting CPT1 and other enzymes in this metabolic pathway.

Activation of MAPK pathways links LMNA mutations to cardiomyopathy in Emery-Dreifuss muscular dystrophy

Mutations in LMNA, which encodes nuclear Lamins A and C cause diseases affecting various organs, including the heart. We have determined the effects of an Lmna H222P mutation on signaling pathways involved in the development of cardiomyopathy in a knockin mouse model of autosomal dominant Emery-Dreifuss muscular dystrophy. Analysis of genome-wide expression profiles in hearts using Affymetrix GeneChips showed statistically significant differences in expression of genes in the MAPK pathways at the incipience of the development of clinical disease. Using real-time PCR, we showed that activation of MAPK pathways preceded clinical signs or detectable molecular markers of cardiomyopathy. In heart tissue and isolated cardiomyocytes, there was activation of MAPK cascades and downstream targets, implicated previously in the pathogenesis of cardiomyopathy. Expression of H222P Lamin A in cultured cells activated MAPKs and downstream target genes. Activation of MAPK signaling by mutant A-type lamins could be a cornerstone in the development of heart disease in autosomal dominant Emery-Dreifuss muscular dystrophy.