Xiangru Lu

Development of Heart Failure and Congenital Septal Defects in Mice Lacking Endothelial Nitric Oxide Synthase

Background—Nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays an important role in the regulation of cell growth, apoptosis, and tissue perfusion. Recent studies showed that mice deficient in eNOS developed abnormal aortic bicuspid valves. The aim of the present study was to additionally investigate the role of eNOS in heart development. Methods and Results—We examined postnatal mortality, cardiac function, and septum defects in eNOS−/−, eNOS+/−, and wild-type mice. Postnatal mortality was significantly increased in eNOS−/− (85.1%) and eNOS+/− (38.3%) compared with wild-type mice (13.3%, P <0.001). Postmortem examination found severe pulmonary congestion with focal alveolar edema in mice deficient in eNOS. Heart shortening determined by ultrasound crystals was significantly decreased in eNOS−/− compared with wild-type mice (P <0.05). Congenital atrial and ventricular septal defects were found in neonatal hearts. The incidence of atrial or ventricular septal defects was significantly increased in eNOS−/− (75%) and eNOS+/− (32.4%) neonates compared with those of the wild-type mice (4.9%). At embryonic days 12.5 and 15.5, cardiomyocyte apoptosis and myocardial caspase-3 activity were increased in the myocardium of eNOS−/− compared with wild-type embryos (P <0.01), and increases in apoptosis persisted to neonatal stage in eNOS−/− mice. Conclusions—Deficiency in eNOS results in heart failure and congenital septal defects during cardiac development, which is associated with increases in cardiomyocyte apoptosis. Our data demonstrate that eNOS plays an important role in normal heart development.

Pivotal Role of gp91phox-Containing NADH Oxidase in Lipopolysaccharide-Induced Tumor Necrosis Factor-α Expression and Myocardial Depression

Background—Lipopolysaccharide (LPS) induces cardiomyocyte tumor necrosis factor-α (TNF-α) production, which is responsible for myocardial depression during sepsis. The aim of this study was to investigate the role of gp91phox-containing NADH oxidase signaling in cardiomyocyte TNF-α expression and myocardial dysfunction induced by LPS. Methods and Results—In cultured mouse neonatal cardiomyocytes, LPS increased NADH oxidase (gp91phox subunit) expression and superoxide generation. Deficiency of gp91phox or inhibition of NADH oxidase blocked TNF-α expression stimulated by LPS. TNF-α induction was also inhibited by tempol, N-acetylcysteine, or 1,3-dimethyl-2-thiourea. NADH oxidase activation by LPS increased ERK1/2 and p38 phosphorylation, and inhibition of ERK1/2 and p38 phosphorylation blocked the effect of NADH oxidase on TNF-α expression. Isolated mouse hearts were perfused with LPS (5 μg/mL) alone or in the presence of apocynin for 1 hour. Myocardial TNF-α production was decreased in gp91phox-deficient or apocynin-treated hearts compared with those of wild type (P<0.05). To investigate the role of gp91phox-containing NADH oxidase in endotoxemia, mice were treated with LPS (4 mg/kg IP) for 4 and 24 hours, and their heart function was measured with a Langendorff system. Deficiency of gp91phox significantly attenuated LPS-induced myocardial depression (P<0.05). Conclusions—gp91phox-Containing NADH oxidase is pivotal in LPS-induced TNF-α expression and cardiac depression. Effects of NADH oxidase activation are mediated by ERK1/2 and p38 MAPK pathway. The present results suggest that gp91phox-containing NADH oxidase may represent a potential therapeutic target for myocardial dysfunction in sepsis.

Fasudil, a Rho-Kinase Inhibitor, Attenuates Angiotensin II–Induced Abdominal Aortic Aneurysm in Apolipoprotein E–Deficient Mice by Inhibiting Apoptosis and Proteolysis

Background—Angiotensin II (Ang II) accelerates atherosclerosis and induces abdominal aortic aneurysm (AAA) in an experimental mouse model. Agonism of a G protein–coupled receptor by Ang II activates Rho-kinase and other signaling pathways and results in activation of proteolysis and apoptosis. Enhanced proteolysis and smooth muscle cell apoptosis are important mechanisms associated with AAA. In this study, we tested the hypothesis that fasudil, a Rho-kinase inhibitor, could attenuate Ang II–induced AAA formation by inhibiting vascular wall apoptosis and extracellular matrix proteolysis. Methods and Results—Six-month-old apolipoprotein E–deficient mice were infused with Ang II (1.44 mg · kg−1 · d−1) for 1 month. Animals were randomly assigned to treatment with fasudil (136 or 213 mg · kg−1 · d−1 in drinking water) or tap water. Ang II infusion induced AAA formation in 75% of the mice, which was accompanied by an increase in proteolysis detected by zymographic analysis and quantified by active matrix metalloproteinase-2 activity, as well as apoptosis detected by terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling and quantified by both caspase-3 activity and histone-associated DNA fragmentation. The level of DNA fragmentation in the suprarenal aorta correlated with AAA diameter. Ang II also increased atherosclerotic lesion area and blood pressure. Fasudil treatment resulted in a dose-dependent reduction in both the incidence and severity of AAA. At the higher dose, fasudil decreased AAA by 45% while significantly inhibiting both apoptosis and proteolysis, without affecting atherosclerosis or blood pressure. Conclusions—These data demonstrate that inhibition of Rho-kinase by fasudil attenuated Ang II–induced AAA through inhibition of both apoptosis and proteolysis pathways.

Neuronal Nitric Oxide Synthase Protects Against Myocardial Infarction-Induced Ventricular Arrhythmia and Mortality in Mice

Background— Neuronal nitric oxide synthase (nNOS) is expressed in cardiomyocytes and plays a role in regulating cardiac function and Ca2+ homeostasis. However, the role of nNOS in cardiac electrophysiology after myocardial infarction (MI) is unclear. We hypothesized that nNOS deficiency increases ventricular arrhythmia and mortality after MI. Methods and Results— MI was induced in wild-type (WT) or nNOS−/− mice by ligation of the left coronary artery. Thirty-day mortality was significantly higher in nNOS−/− compared with WT mice. Additionally, nNOS−/− mice had impaired cardiac function 2 days after MI. Telemetric ECG monitoring showed that compared with WT, nNOS−/− mice had significantly more ventricular arrhythmias and were more likely to develop ventricular fibrillation after MI. Treatment with the L-type Ca2+ channel blocker verapamil reduced the incidence of arrhythmia and ventricular fibrillation in nNOS−/− mice after MI. To assess the role of nNOS in Ca2+ handling, patch-clamp and Ca2+ fluorescence techniques were used. Ca2+ transients and L-type Ca2+ currents were higher in nNOS−/− compared with WT cardiomyocytes. Additionally, nNOS−/− cardiomyocytes exhibited significantly higher systolic and diastolic Ca2+ over a range of pacing frequencies. Treatment with the NO donor S-nitroso N-acetyl-penicillamine decreased Ca2+ transients and L-type Ca2+ current in both nNOS−/− and WT cardiomyocytes. Furthermore, S-nitrosylation of Ca2+ handling proteins was significantly decreased in nNOS−/− myocardium after MI. Conclusions— Deficiency in nNOS increases ventricular arrhythmia and mortality after MI in mice. The antiarrhythmic effect of nNOS involves inhibition of L-type Ca2+ channel activity and regulation of Ca2+ handling proteins via S-nitrosylation.

Inhibition of p38 MAPK decreases myocardial TNF-alpha expression and improves myocardial function and survival in endotoxemia

OBJECTIVES The role of p38 mitogen-activated protein kinase (MAPK) activation in lipopolysaccharide (LPS)-induced myocardial dysfunction has not been clearly defined. Our aim was to investigate the contribution of p38 MAPK in myocardial tumor necrosis factor-alpha (TNF-alpha) expression, cardiac function and survival during acute endotoxemia in mice. METHODS Acute endotoxemia was induced by LPS (10 mg/kg, i.p.) in mice. Two hours after LPS treatment, left ventricular (LV) function was assessed. Phosphorylation of p38 MAPK was measured by Western blotting. TNF-alpha mRNA and protein levels were determined by semi-quantitative reverse-transcriptase polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS LPS rapidly increased phosphorylation of p38 MAPK, followed by TNF-alpha mRNA expression and protein expression in the LV myocardium. Pre-treatment of the p38 MAPK inhibitor SB202190 (2 mg/kg, i.p.) decreased TNF-alpha mRNA and protein by 65 and 36%, respectively (P<0.05). Immunohistochemical staining confirmed that cardiomyocytes were the major source of TNF-alpha production in the myocardium and blocking p38 MAPK activation inhibited TNF-alpha expression in response to LPS. Pre-treatment of SB202190 or a TNF-alpha antagonist etanercept (2 mg/kg, i.p) significantly reversed LPS-induced LV depression (P<0.05). LPS (20 mg/kg, i.p.) induced 94% mortality in mice within 72 h and pre-treatment with SB202190 and etanercept decreased LPS-induced mortality to 65 and 40%, respectively (P<0.01). CONCLUSION p38 MAPK activation represents an important mechanism leading to myocardial TNF-alpha production and cardiac dysfunction during acute endotoxemia in mice. Our data suggest that p38 MAPK is a potential therapeutic target of endotoxemia.

Endothelial Nitric Oxide Synthase Promotes Bone Marrow Stromal Cell Migration to the Ischemic Myocardium via Upregulation of Stromal Cell‐Derived Factor‐1α

The aim of this study was to investigate the role of endothelial nitric oxide synthase (eNOS) in the host myocardium on bone marrow mesenchymal stromal cells (MSC) migration to the ischemic myocardium and whether stromal cell‐derived factor‐1α (SDF‐1α) contributes to eNOS‐mediated MSC migration. MSCs and coronary microvascular endothelial cells were isolated from adult wild‐type (WT) mouse bone marrow and hearts, respectively. Cultured neonatal cardiomyocytes from WT, eNOS−/−, and eNOS overexpressing transgenic (Tg) mice were subjected to anoxia and reoxygenation (A/R), and the conditioned medium was used as a chemoattractant for in vitro transendothelial migration assay. MSC migration was decreased in the presence of conditioned medium derived from eNOS−/− cardiomyocytes but increased in the presence of eNOS‐Tg conditioned medium. SDF‐1α expression was decreased in eNOS−/− but increased in eNOS‐Tg cardiomyocytes following A/R and in the myocardium following ischemia/reperfusion (I/R). SDF‐1α expression was cGMP‐dependent as inhibition of soluble guanylyl cyclase decreased SDF‐1α expression in WT cardiomyocytes. MSCs expressed very low levels of eNOS proteins compared with the adult myocardium. To examine MSC migration in vivo, MSCs derived from mice expressing enhanced green fluorescence protein (EGFP+) were intravenously administered to WT mice subjected to myocardial I/R. EGFP+ cells in the ischemic region were decreased in eNOS−/− but increased in eNOS‐Tg compared with WT hearts. MSC treatment improved cardiac function following I/R in WT but not in eNOS−/− mice. In conclusion, eNOS in the host myocardium promotes MSC migration to the ischemic myocardium and improves cardiac function through cGMP‐dependent increases in SDF‐1α expression. STEM CELLS 2009;27:961–970

NOX2 Deficiency Protects Against Streptozotocin-Induced β-Cell Destruction and Development of Diabetes in Mice

OBJECTIVE The role of NOX2-containing NADPH oxidase in the development of diabetes is not fully understood. We hypothesized that NOX2 deficiency decreases reactive oxygen species (ROS) production and immune response and protects against streptozotocin (STZ)-induced β-cell destruction and development of diabetes in mice. RESEARCH DESIGN AND METHODS Five groups of mice—wild-type (WT), NOX2−/−, WT treated with apocynin, and WT adoptively transferred with NOX2−/− or WT splenocytes—were treated with multiple-low-dose STZ. Blood glucose and insulin levels were monitored, and an intraperitoneal glucose tolerance test was performed. Isolated WT and NOX2−/− pancreatic islets were treated with cytokines for 48 h. RESULTS Significantly lower blood glucose levels, higher insulin levels, and better glucose tolerance was observed in NOX2−/− mice and in WT mice adoptively transferred with NOX2−/− splenocytes compared with the respective control groups after STZ treatment. Compared with WT, β-cell apoptosis, as determined by TUNEL staining, and insulitis were significantly decreased, whereas β-cell mass was significantly increased in NOX2−/− mice. In response to cytokine stimulation, ROS production was significantly decreased, and insulin secretion was preserved in NOX2−/− compared with WT islets. Furthermore, proinflammatory cytokine release induced by concanavalin A was significantly decreased in NOX2−/− compared with WT splenocytes. CONCLUSIONS NOX2 deficiency decreases β-cell destruction and preserves islet function in STZ-induced diabetes by reducing ROS production, immune response, and β-cell apoptosis.

Cardiomyocyte-Specific Overexpression of Human Stem Cell Factor Improves Cardiac Function and Survival After Myocardial Infarction in Mice

Background— Soluble stem cell factor (SCF) has been shown to mobilize bone marrow stem cells and improve cardiac repair after myocardial infarction (MI). However, the effect of membrane-associated SCF on cardiac remodeling after MI is not known. The present study investigated the effects of cardiomyocyte-specific overexpression of the membrane-associated isoform of human SCF (hSCF) on cardiac function after MI. Methods and Results— A novel mouse model with tetracycline-inducible and cardiac-specific overexpression of membrane-associated hSCF was generated. MI was induced by left coronary artery ligation. Thirty-day mortality after MI was decreased in hSCF/tetracycline transactivator (tTA) compared with wild-type mice. In vivo cardiac function was significantly improved in hSCF/tTA mice at 5 and 30 days after MI compared with wild-type mice. Endothelial progenitor cell recruitment and capillary density were increased and myocardial apoptosis was decreased in the peri-infarct area of hSCF/tTA mice. Myocyte size was decreased in hSCF/tTA mice 30 days after MI compared with WT mice. Furthermore, hSCF overexpression promoted de novo angiogenesis as assessed by matrigel implantation into the left ventricular myocardium. Conclusions— Cardiomyocyte-specific overexpression of hSCF improves myocardial function and survival after MI. These beneficial effects of hSCF may result from increases in endothelial progenitor cell recruitment and neovascularization and decreases in myocardial apoptosis and cardiac remodeling.

Role of heme oxygenase-1 in the cardioprotective effects of erythropoietin during myocardial ischemia and reperfusion.

We have recently demonstrated that erythropoietin (EPO) protects cardiomyocytes from apoptosis during myocardial ischemia-reperfusion (I/R). The objective of the present study was to investigate the role of heme oxygenase (HO)-1 in the antiapoptotic effects of EPO. Primary cultures of neonatal mouse cardiomyocytes were subjected to anoxia-reoxygenation (A/R). Pretreatment with EPO significantly reduced apoptosis in A/R-treated cells. This reduction in apoptosis was preceded by an increase in the mRNA and protein expression of HO-1. Selective inhibition of HO-1 using chromium mesoporphyrin (CrMP) significantly diminished the ability of EPO to inhibit apoptosis. Cotreatment of EPO with SB-202190, an inhibitor of p38 activation, blocked the EPO-mediated HO-1 expression and antiapoptotic effects, suggesting a p38-dependent mechanism. The in vivo significance of p38 and HO-1 as mediators of EPOs cardioprotection was investigated in mice subjected to myocardial I/R. Pretreatment with EPO decreased infarct size as well as I/R-induced apoptosis in wild-type mice. However, these effects were significantly diminished in HO-1(-/-) mice. Furthermore, EPO given during ischemia reduced infarct size in mice subjected to I/R, and this effect was blocked by CrMP treatment in wild-type mice. Moreover, inhibition of p38 diminished the cardioprotective effects of EPO. We conclude that upregulation of HO-1 expression via p38 signaling contributes to EPO-mediated cardioprotection during myocardial I/R.

JNK1/c-fos inhibits cardiomyocyte TNF-a expression via a negative crosstalk with ERK and p38 MAPK in endotoxaemia

AIMS Myocardial tumour necrosis factor-alpha (TNF-alpha) production plays an important role in cardiac dysfunction during sepsis. The aim of this study was to investigate the role of c-Jun NH2-terminal kinases (JNK) signalling in cardiomyocyte TNF-alpha expression during lipopolysaccharide (LPS) stimulation and myocardial function in endotoxaemic mice. METHODS AND RESULTS In cultured neonatal mouse cardiomyocytes, deficiency of JNK1 or selective inhibition of JNK1 signalling by over-expression of a dominant negative mutant of JNK1 enhanced LPS-induced TNF-alpha expression, which was associated with elevations in phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK). At the organ level, LPS-induced TNF-alpha expression was significantly increased in JNK1(-/-) compared with wild-type hearts. JNK1 activation by LPS also induced immediate c-fos expression in cardiomyocytes, which was blocked by inhibition of JNK1 signalling. The role of c-fos expression in LPS-induced TNF-alpha expression was investigated in both cultured c-fos(-/-) cardiomyocytes and isolated c-fos(-/-) hearts. Deficiency of c-fos significantly enhanced LPS-induced TNF-alpha expression in cardiomyocytes and isolated hearts. Over-expression of c-fos decreased TNF-alpha expression in LPS-stimulated cardiomyocytes, which was associated with a decrease in phosphorylation of ERK1/2 and p38. In mice with endotoxaemia, deficiency of either JNK1 or c-fos further decreased cardiac function compared with corresponding wild-type controls. CONCLUSION JNK1/c-fos inhibits ERK1/2 and p38 MAPK signalling, leading to decreased cardiomyocyte TNF-alpha expression and improvements in cardiac function during endotoxaemia.