Teruki Sato

Apelin is a positive regulator of ACE2 in failing hearts

Angiotensin converting enzyme 2 (ACE2) is a negative regulator of the renin-angiotensin system (RAS), catalyzing the conversion of Angiotensin II to Angiotensin 1-7. Apelin is a second catalytic substrate for ACE2 and functions as an inotropic and cardioprotective peptide. While an antagonistic relationship between the RAS and apelin has been proposed, such functional interplay remains elusive. Here we found that ACE2 was downregulated in apelin-deficient mice. Pharmacological or genetic inhibition of angiotensin II type 1 receptor (AT1R) rescued the impaired contractility and hypertrophy of apelin mutant mice, which was accompanied by restored ACE2 levels. Importantly, treatment with angiotensin 1-7 rescued hypertrophy and heart dysfunctions of apelin-knockout mice. Moreover, apelin, via activation of its receptor, APJ, increased ACE2 promoter activity in vitro and upregulated ACE2 expression in failing hearts in vivo. Apelin treatment also increased cardiac contractility and ACE2 levels in AT1R-deficient mice. These data demonstrate that ACE2 couples the RAS to the apelin system, adding a conceptual framework for the apelin-ACE2-angiotensin 1-7 axis as a therapeutic target for cardiovascular diseases.

ELABELA-APJ axis protects from pressure overload heart failure and angiotensin II-induced cardiac damage

Aims Elabela/Toddler/Apela (ELA) has been identified as a novel endogenous peptide ligand for APJ/Apelin receptor/Aplnr. ELA plays a crucial role in early cardiac development of zebrafish as well as in maintenance of self-renewal of human embryonic stem cells. Apelin was the first identified APJ ligand, and exerts positive inotropic heart effects and regulates the renin-angiotensin system. The aim of this study was to investigate the biological effects of ELA in the cardiovascular system. Methods and results Continuous infusion of ELA peptide significantly suppressed pressure overload-induced cardiac hypertrophy, fibrosis and impaired contractility in mice. ELA treatment reduced mRNA expression levels of genes associated with heart failure and fibrosis. The cardioprotective effects of ELA were diminished in APJ knockout mice, indicating that APJ is the key receptor for ELA in the adult heart. Mechanistically, ELA downregulated angiotensin-converting enzyme (ACE) expression in the stressed hearts, whereas it showed little effects on angiotensin-converting enzyme 2 (ACE2) expression, which are distinct from the effects of Apelin. FoxM1 transcription factor, which induces ACE expression in the stressed hearts, was downregulated by ELA but not by Apelin. ELA antagonized angiotensin II-induced hypertension, cardiac hypertrophy, and fibrosis in mice. Conclusion The ELA-APJ axis protects from pressure overload-induced heart failure possibly via suppression of ACE expression and pathogenic angiotensin II signalling. The different effects of ELA and Apelin on the expression of ACE and ACE2 implicate fine-tuned mechanisms for a ligand-induced APJ activation and downstream signalling.

Contralateral Pulmonary Embolism Caused by Pulmonary Artery Stump Thrombosis After Pneumonectomy

A 73-year-old man with atrial fibrillation and previous left pneumonectomy was admitted with pleural effusion. Anticoagulant therapy was discontinued because of chest tube drainage. Six days later, the patient experienced chest discomfort. Echocardiography showed a pedunculated thrombus with swaying motion in the left pulmonary artery (PA) stump. Contrast-enhanced computed tomography of the chest revealed filling defects in not only the left PA stump but also the right PA, implying contralateral pulmonary embolism. Anticoagulants were resumed, and thrombolysis was successful 3 days later. Patients undergoing pneumonectomy in whom anticoagulant therapy is discontinued should be recognized as being at high risk for PA stump thrombosis and subsequent contralateral pulmonary embolism.

The CCR4-NOT deadenylase complex controls Atg7-dependent cell death and heart function

Destabilization of Atg7 mRNA by the CCR4-NOT complex prevents p53-dependent cell death in the heart. Protecting the heart by destabilizing mRNA The removal of polyadenylate tails from mRNAs by the CCR4-NOT complex marks these mRNAs for degradation. Yamaguchi et al. (see also the Focus by Das) found that this activity of this complex was required to prevent cell death in the heart. Mice deficient in a component of this complex suffered from cardiac dysfunction and died of heart failure due to cardiomyocyte death. The CCR4-NOT complex deadenylated Atg7 mRNA, which encodes a protein required for autophagy, a process by which cellular constituents and organelles are digested. The increase in Atg7 in the mutant mice resulted in activation of cell death–associated genes by the transcription factor p53. Drugs that increase autophagy have been explored for the treatment of various diseases, but the authors note that their results raise the possibility of cardiovascular side effects for such drugs. Shortening and removal of the polyadenylate [poly(A)] tail of mRNA, a process called deadenylation, is a key step in mRNA decay that is mediated through the CCR4-NOT (carbon catabolite repression 4–negative on TATA-less) complex. In our investigation of the regulation of mRNA deadenylation in the heart, we found that this complex was required to prevent cell death. Conditional deletion of the CCR4-NOT complex components Cnot1 or Cnot3 resulted in the formation of autophagic vacuoles and cardiomyocyte death, leading to lethal heart failure accompanied by long QT intervals. Cnot3 bound to and shortened the poly(A) tail of the mRNA encoding the key autophagy regulator Atg7. In Cnot3-depleted hearts, Atg7 expression was posttranscriptionally increased. Genetic ablation of Atg7, but not Atg5, increased survival and partially restored cardiac function of Cnot1 or Cnot3 knockout mice. We further showed that in Cnot3-depleted hearts, Atg7 interacted with p53 and modulated p53 activity to induce the expression of genes encoding cell death–promoting factors in cardiomyocytes, indicating that defects in deadenylation in the heart aberrantly activated Atg7 and p53 to promote cell death. Thus, mRNA deadenylation mediated by the CCR4-NOT complex is crucial to prevent Atg7-induced cell death and heart failure, suggesting a role for mRNA deadenylation in targeting autophagy genes to maintain normal cardiac homeostasis.

Right Atrial Giant Myxoma Occupying the Right Ventricular Cavity

We report a case of a giant right atrial myxoma mimicking the right ventricular tumor. The 75-year-old patient underwent cardiac surgery, and the tumor was excised along with the stalk. Tricuspid valve annuloplasty was performed before closure of the right atriotomy. The tumor may have caused intraventricular stenosis, hepatic dysfunction, and progressive fatigue as a result of low cardiac output. This case is of special interest because the myxoma was very large compared with those ever reported, and a right atrial myxoma occupying the right ventricular cavity is rare.

Apelin and Elabela/Toddler; double ligands for APJ/Apelin receptor in heart development, physiology, and pathology

Apelin is an endogenous peptide ligand for the G protein-coupled receptor APJ/AGTRL1/APLNR and is widely expressed throughout human body. In adult hearts Apelin-APJ/Apelin receptor axis is potently inotropic, vasodilatory, and pro-angiogenic and thereby contributes to maintaining homeostasis in normal and pathological hearts. Apelin-APJ/Apelin receptor is also involved in heart development including endoderm differentiation, heart morphogenesis, and coronary vascular formation. APJ/Apelin receptor had been originally identified as an orphan receptor for its sequence similarity to Angiotensin II type 1 receptor, and it was later deorphanized by identification of Apelin in 1998. Both Apelin and Angiotensin II are substrates for Angiotensin converting enzyme 2 (ACE2), which degrades the peptides and thus negatively regulates their agonistic activities. Elabela/Toddler, which shares little sequence homology with Apelin, has been recently identified as a second endogenous APJ ligand. Elabela plays crucial roles in heart development and disease conditions presumably at time points or at areas of the heart different from Apelin. Apelin and Elabela seem to constitute a spatiotemporal double ligand system to control APJ/Apelin receptor signaling in the heart. These expanding knowledges of Apelin systems would further encourage therapeutic applications of Apelin, Elabela, or their synthetic derivatives for cardiovascular diseases.

Isolated Atrial Septal Defect Complicated by Tricuspid Valve Infective Endocarditis

Infective endocarditis (IE) associated with atrial septal defect (ASD) is extremely rare. However, tricuspid regurgitation (TR) secondary to right ventricular overload is a potential cause of IE, and once it occurs, the development of a paradoxical embolism may lead to fatal complications. We herein report the case of a 50-year-old woman who was admitted due to a persistent fever resistant to antibiotics. Echocardiography showed secundum ASD, moderate TR and a mobile vegetation measuring 15×10 mm attached to the tricuspid valve. Given the risk of developing a paradoxical embolism, urgent surgery was successfully performed.

Position-Dependent Right-to-Left Shunt Causing a Brain Abscess

A 50-year-old man suffering from generalized convulsions and right quadrantic hemianopia was admitted to the hospital. Contrast-enhanced magnetic resonance imaging showed an enhanced ring in the left parieto-occipital lobe, suggesting a brain abscess (Figure 1). The patient underwent an immediate craniotomy and drainage. Culture of pus yielded α-hemolytic streptococci. Brain abscesses are often caused by hematogenous spread of bacteria from a primary source. Although much effort was expended seeking the primary infection, the origin of the brain abscess in this patient remained unclear. After almost complete relief of his neurological symptoms, the patient was referred for further diagnostic workup in our hospital. Chest contrast-enhanced computed tomography in the arterial phase revealed an anomalous vessel bridging from …