Tomoko Minami

Cardiac-specific deletion of SOCS-3 prevents development of left ventricular remodeling after acute myocardial infarction.

OBJECTIVES The study investigated the role of myocardial suppressor of cytokine signaling-3 (SOCS3), an intrinsic negative feedback regulator of the janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling pathway, in the development of left ventricular (LV) remodeling after acute myocardial infarction (AMI). BACKGROUND LV remodeling after AMI results in poor cardiac performance leading to heart failure. Although it has been shown that JAK-STAT-activating cytokines prevent LV remodeling after AMI in animals, little is known about the role of SOCS3 in this process. METHODS Cardiac-specific SOCS3 knockout mice (SOCS3-CKO) were generated and subjected to AMI induced by permanent ligation of the left anterior descending coronary artery. RESULTS Although the initial infarct size after coronary occlusion measured by triphenyltetrazolium chloride staining was comparable between SOCS3-CKO and control mice, the infarct size 14 days after AMI was remarkably inhibited in SOCS3-CKO, indicating that progression of LV remodeling after AMI was prevented in SOCS3-CKO hearts. Prompt and marked up-regulations of multiple JAK-STAT-activating cytokines including leukemia inhibitory factor and granulocyte colony-stimulating factor (G-CSF) were observed within the heart following AMI. Cardiac-specific SOCS3 deletion enhanced multiple cardioprotective signaling pathways including STAT3, AKT, and extracellular signal-regulated kinase (ERK)-1/2, while inhibiting myocardial apoptosis and fibrosis as well as augmenting antioxidant expression. CONCLUSIONS Enhanced activation of cardioprotective signaling pathways by inhibiting myocardial SOCS3 expression prevented LV remodeling after AMI. Our data suggest that myocardial SOCS3 may be a key molecule in the development of LV remodeling after AMI.

Renal Nerve-Mediated Erythropoietin Release Confers Cardioprotection During Remote Ischemic Preconditioning

BACKGROUND Remote ischemic preconditioning (RIPC) induced by transient limb ischemia is a powerful innate mechanism of cardioprotection against ischemia. Several described mechanisms explain how RIPC may act through neural pathways or humoral factors; however, the mechanistic pathway linking the remote organ to the heart has not yet been fully elucidated. This study aimed to investigate the mechanisms underlying the RIPC-induced production of Janus kinase (JAK)-signal transducer and activator of the transcription (STAT)-activating cytokines and cardioprotection by using mouse and human models of RIPC. METHODS AND RESULTS Screened circulating cardioprotective JAK-STAT-activating cytokines in mice unexpectedly revealed increased serum erythropoietin (EPO) levels after RIP induced by transient ischemia. In mice, RIPC rapidly upregulated EPO mRNA and its main transcriptional factor, hypoxia-inducible factor-1α (HIF1α), in the kidney. Laser Doppler blood flowmetry revealed a prompt reduction of renal blood flow (RBF) after RIPC. RIPC activated cardioprotective signaling pathways and the anti-apoptotic Bcl-xL pathway in the heart, and reduced infarct size. In mice, these effects were abolished by administration of an EPO-neutralizing antibody. Renal nerve denervation also abolished RIPC-induced RBF reduction, EPO production, and cardioprotection. In humans, transient limb ischemia of the upper arm reduced RBF and increased serum EPO levels. CONCLUSIONS Based on the present data, we propose a novel RIPC mechanism in which inhibition of infarct size by RIPC is produced through the renal nerve-mediated reduction of RBF associated with activation of the HIF1α-EPO pathway.

Cardiomyocyte-specific transgenic expression of lysyl oxidase-like protein-1 induces cardiac hypertrophy in mice

Lysyl oxidase (LOX) and LOX-like protein-1 (LOXL-1) are extracellular matrix-embedded amine oxidases that have critical roles in the cross-linking of collagen and elastin. LOX family proteins are abundantly expressed in the remodeled heart of animals and humans and are implicated in cardiac fibrosis; however, their role in cardiac hypertrophy is unknown. In this study, in vitro stimulation with hypertrophic agonists significantly increased LOXL-1 expression, LOX enzyme activity and [3H] leucine incorporation in neonatal rat cardiomyocytes. A LOX inhibitor, beta-aminopropionitrile (BAPN), inhibited agonist-induced leucine incorporation in cardiomyocytes in vitro, suggesting the involvement of LOXL-1 in cardiomyocyte hypertrophy. Abdominal aortic constriction in rats produced left ventricular hypertrophy in parallel with LOXL-1 mRNA upregulation. And BAPN administration significantly inhibited angiotensin II-induced cardiac hypertrophy in vivo. These results suggest a role of LOXL-1 in cardiac hypertrophy in vivo. We generated transgenic mice with cardiomyocyte-specific expression of LOXL-1. LOXL-1 transgenic mice pups were born normally and grew to adulthood without increased mortality; these mice exhibited a greater left ventricle to body weight ratio, larger myocyte diameter, and more brain natriuretic peptide expression than their wild-type littermates. Echocardiography revealed that the LOXL-1 transgenic mice also had greater wall thickness with preserved cardiac contraction. Our results indicate a possible fundamental role of LOXL-1 in cardiac hypertrophy.

Disturbance of cardiac gene expression and cardiomyocyte structure predisposes Mecp2 -null mice to arrhythmias

Methyl-CpG-binding protein 2 (MeCP2) is an epigenetic regulator of gene expression that is essential for normal brain development. Mutations in MeCP2 lead to disrupted neuronal function and can cause Rett syndrome (RTT), a neurodevelopmental disorder. Previous studies reported cardiac dysfunction, including arrhythmias in both RTT patients and animal models of RTT. In addition, recent studies indicate that MeCP2 may be involved in cardiac development and dysfunction, but its role in the developing and adult heart remains unknown. In this study, we found that Mecp2-null ESCs could differentiate into cardiomyocytes, but the development and further differentiation of cardiovascular progenitors were significantly affected in MeCP2 deficiency. In addition, we revealed that loss of MeCP2 led to dysregulation of endogenous cardiac genes and myocardial structural alterations, although Mecp2-null mice did not exhibit obvious cardiac functional abnormalities. Furthermore, we detected methylation of the CpG islands in the Tbx5 locus, and showed that MeCP2 could target these sequences. Taken together, these results suggest that MeCP2 is an important regulator of the gene-expression program responsible for maintaining normal cardiac development and cardiomyocyte structure.

Cardiac-Specific SOCS3 Deletion Prevents In Vivo Myocardial Ischemia Reperfusion Injury through Sustained Activation of Cardioprotective Signaling Molecules.

Myocardial ischemia reperfusion injury (IRI) adversely affects cardiac performance and the prognosis of patients with acute myocardial infarction. Although myocardial signal transducer and activator of transcription (STAT) 3 is potently cardioprotective during IRI, the inhibitory mechanism responsible for its activation is largely unknown. The present study aimed to investigate the role of the myocardial suppressor of cytokine signaling (SOCS)-3, an intrinsic negative feedback regulator of the Janus kinase (JAK)-STAT signaling pathway, in the development of myocardial IRI. Myocardial IRI was induced in mice by ligating the left anterior descending coronary artery for 1 h, followed by different reperfusion times. One hour after reperfusion, the rapid expression of JAK-STAT–activating cytokines was observed. We precisely evaluated the phosphorylation of cardioprotective signaling molecules and the expression of SOCS3 during IRI and then induced myocardial IRI in wild-type and cardiac-specific SOCS3 knockout mice (SOCS3-CKO). The activation of STAT3, AKT, and ERK1/2 rapidly peaked and promptly decreased during IRI. This decrease correlated with the induction of SOCS3 expression up to 24 h after IRI in wild-type mice. The infarct size 24 h after reperfusion was significantly reduced in SOCS3-CKO compared with wild-type mice. In SOCS3-CKO mice, STAT3, AKT, and ERK1/2 phosphorylation was sustained, myocardial apoptosis was prevented, and the expression of anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) was augmented. Cardiac-specific SOCS3 deletion led to the sustained activation of cardioprotective signaling molecules including and prevented myocardial apoptosis and injury during IRI. Our findings suggest that SOCS3 may represent a key factor that exacerbates the development of myocardial IRI.

Screening for Fabry disease in patients with left ventricular hypertrophy

Kazutoshi Mawatari , Hideo Yasukawa ⁎, Toyoharu Oba , Takanobu Nagata , Tadayasu Togawa , Takahiro Tsukimura , Sachiko Kyogoku , Hideki Ohshima , Tomoko Minami , Yusuke Sugi , Hitoshi Sakuraba , Tsutomu Imaizumi a,b a Division of Cardiovascular Medicine, Department of Internal Medicine, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan b Cardiovascular Research Institute, Kurume University, 67 Asahi-machi, Kurume 830-0011, Japan c Department of Analytical Biochemistry, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan d Department of Clinical Genetics, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan