Angiotensin II-induced Cardiac Hypertrophy Research Articles

Diacylglycerol-mediated Ca 2+ influx through TRPC3/6 is essential for angiotensin II-induced cardiac hypertrophy

Diacylglycerol-mediated Ca 2+ influx through TRPC3/6 is essential for angiotensin II-induced cardiac hypertrophy

Overexpression of angiotensinogen in the myocardium induces downregulation of the fatty acid oxidation pathway

Heart failure is associated with downregulation of the fatty acid oxidation pathway in the ventricular myocardium. Since angiotensin II plays a critical role in myocardial phenotypic changes associated with heart failure, we investigated the effect of chronic angiotensin II stimulation on the fatty acid oxidation pathway in transgenic (TG) mice with targeted overexpression of angiotensinogen in the myocardium (TG1306/1R mice). TG1306/R1 mice progressively developed left ventricular hypertrophy. After 12 months, approximately half of the mice exhibited signs of heart failure including increased lung weight index [> + 2 SD of age-matched wild-type (WT) mice] and 5-fold increase of myocardial brain natriuretic peptide expression. Myocardial mRNA and protein expression of peroxisome proliferator-activated receptor α (PPARα) progressively decreased in both WT and TG1306/R1 mice during the 12 months observation period, but much more pronounced in TG1306/R1 mice. Concomitantly, mRNA expression of enzymes of fatty acid oxidation (medium-chain acyl CoA dehydrogenase, MCAD; carnitine palmitoyl transferase I, CPT-I) was reduced in TG1306/R1 compared with age-matched WT mice. However, protein expression of MCAD and CPT-I was decreased concomitantly only in TG mice with criteria of heart failure. Correspondingly, myocardial oxidation of palmitate, measured during ex vivo working heart perfusion, was reduced by 25% in TG1306/R1 mice with heart failure. These results demonstrate that angiotensin II-induced cardiac hypertrophy is associated with reduction of PPARα and of mRNA expression of enzymes of fatty acid metabolism relative to age-matched WT mice. However, both protein expression of fatty acid oxidation enzymes and the rate of fatty acid oxidation remain unchanged unless heart failure occurs, suggesting the involvement of posttranscriptional mechanisms in the metabolic changes associated with heart failure.

Vascular Cell Locomotion

See related article, pages 1479–1489 Since the discovery of osteopontin (OPN) in the vasculature, vascular biologists have been intrigued by its potential role in vascular arteriosclerosis and vessel calcification during the aging process.1 Osteopontin is a phosphorylated acidic glycoprotein adhesion molecule, originally cloned from bone; and as in bone, its cardiovascular functions include cellular migration, adhesion, and spreading.2 The most salient features of this intriguing calcium-regulating molecule are its ability to interact with αvβ3 and other integrins on the surface of cells. Because this ligand–receptor complex is known to be involved in cell migration, it is not surprising that an antibody to the β3 subunit of this receptor effectively reduced restenosis in patients.3 Interestingly, angiotensin II and other growth factors, including platelet-derived growth factor and transforming growth factor-β, regulate OPN gene expression in vascular smooth muscle cell (VSMC) cultures and fibroblasts.1,4 Cardiac fibroblasts have been extensively reported to produce OPN in response to these growth factors, resulting in fibroblast proliferation. On the one hand, OPN is thought to cause vascular dystrophy by altering extracellular matrix formation; on the other hand, cellular motogenesis is a hallmark of this emerging vascular cytokine. Its cellular expression includes a variety of inflammatory cells, such as T cells and macrophages, as well as mesenchymal cells of the vasculature including adventitial myofibroblasts. Moreover, OPN has both pro- and antiinflammatory properties. As a proinflammatory agent it can attract and modulate the function of the above mentioned cell types. Of seemingly major importance, OPN interacts with intracellular signaling agents to promote cell migration and matrix metalloproteinases, both of which are required for cell tunneling through dense and elastin-rich vascular tissue. In fibroblasts these agents appear to include cell surface CD44 and ERM proteins located just below the plasma membrane …

HMG-CoA reductase inhibitor fluvastatin prevents angiotensin II-induced cardiac hypertrophy via Rho kinase and inhibition of cyclin D1

HMG-CoA reductase inhibitors, so called statins, decrease cardiac events. Previous studies have shown that HMG-CoA reductase inhibitors inhibit cardiomyocyte hypertrophy in vitro and in vivo by blocking Rho isoprenylation. We have shown that the G1 cell cycle regulatory proteins cyclin D1 and Cdk4 play important roles in cardiomyocyte hypertrophy. However, the relation between Rho and cyclin D1 in cardiomyocyte is unknown. To investigate whether HMG-CoA reductase inhibitors prevent cardiac hypertrophy through attenuation of Rho and cyclin D1, we studied the effect of fluvastatin on angiotensin II-induced cardiomyocyte hypertrophy in vitro and in vivo. Angiotensin II increased the cell surface area and [ 3H]leucine uptake of cultured neonatal rat cardiomyocytes and these changes were suppressed by fluvastatin treatment. Angiotensin II also induced activation of Rho kinase and increased cyclin D1, both of which were also significantly suppressed by fluvastatin. Specific Rho kinase inhibitor, Y-27632 inhibited angiotensin II-induced cardiomyocyte hypertrophy and increased cyclin D1. Overexpression of cyclin D1 by adenoviral gene transfer induced cardiomyocyte hypertrophy, as evidenced by increased cell size and increased protein synthesis; this hypertrophy was not diminished by concomitant treatment with fluvastatin. Infusion of angiotensin II to Wistar rats for 2 weeks induced hypertrophic changes in cardiomyocytes, and this hypertrophy was prevented by oral fluvastatin treatment. These results show that an HMG-CoA reductase inhibitor, fluvastatin, prevents angiotensin II-induced cardiomyocyte hypertrophy in part through inhibition of cyclin D1, which is linked to Rho kinase. This novel mechanism discovered for fluvastatin could be revealed how HMG-CoA reductase inhibitors are preventing cardiac hypertrophy.

Potential of Gene Therapy Strategy for the Treatment of Hypertension

Hypertension is one of the most important risk factors for cardiovascular diseases (CVDs). CVD extends across all populations and represents the leading cause of morbidity and mortality in industrialized countries. Hypertension increases the risk of peripheral arterial disease, cardiomyopathy, stroke, and renal failure. The disease affects &50 million Americans and goes undetected in at least one third of the population. In spite of the tremendous progress made by pharmacotherapy in the management and control of hypertension, there has been a steady escalation in its prevalence during the last decade. This has led many to conclude that traditional pharmacotherapy has reached an intellectual plateau and that novel and innovative approaches must be sought for the treatment, control, and possible cure of hypertension. As a result, efforts of our group and those of many others have been diverted to explore the use of gene transfer and gene therapy strategies for a long-term control of hypertension. We have argued that gene therapy offers potentially significant improvements and benefits over the use of traditional pharmacotherapy: (1) noncompliance by patients can be significantly reduced or even eliminated because of the fact that a single treatment involving gene transfer could remain effective for months or even years; (2) side effects associated with pharmacotherapy can be minimized as a result of specific targeting of a therapeutic gene in a given tissue and optimally influencing cardiovascular pathophysiology on an individual patient basis; and (3) with its potential to produce long-term beneficial outcomes in end-organ damage, the gene therapy strategy could lead to a cure of hypertension and its related pathophysiology. It is noteworthy to mention that current pharmacotherapies are often unable to reverse end-organ damage associated with hypertension. In order for the gene therapy for hypertension to be successful, one must provide conceptual support of its efficacy in …

Involvement of Reactive Oxygen Species in Angiotensin II-Induced Cardiac Hypertrophy in Neonatal Rat Ventricular Myocytes

Involvement of Reactive Oxygen Species in Angiotensin II-Induced Cardiac Hypertrophy in Neonatal Rat Ventricular Myocytes

Protection from angiotensin II‐induced cardiac hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats

Angiotensin converting enzyme 2 (ACE2), a newly discovered member of the renin-angiotensin system (RAS), is a potential therapeutic target for the control of cardiovascular disease owing to its key role in the formation of vasoprotective peptides from angiotensin II. The aim of the present study was to evaluate whether overexpression of ACE2 could protect the heart from angiotensin II-induced hypertrophy and fibrosis. Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in 5-day-old Sprague-Dawley rats. This resulted in expression of mACE2 in cardiac tissue for the duration of the study. Infusion of 200 ng kg-1 min-1 angiotensin II for 4 weeks resulted in an 80 mmHg increase in systolic blood pressure, a significant increase in the heart weight to body weight ratio (HW:BW), and marked myocardial fibrosis in control rats. Transduction with lenti-mACE2 resulted in significant attenuation of the increased HW:BW and myocardial fibrosis induced by angiotensin II infusion. These observations demonstrate that ACE2 overexpression results in protective effects on angiotensin II-induced cardiac hypertrophy and fibrosis.

Significance of the transcription factor KLF5 in cardiovascular remodeling.

Structural remodeling of the heart and blood vessels is an important pathologic process in the development of many cardiovascular diseases. However, transcriptional regulation of altered gene expression during cardiovascular remodeling is not well understood. We previously isolated KLF5/basic transcription element-binding (BTEB)2, a Krüppel-like factor, as a transcription factor that binds the promoter of the embryonic smooth muscle myosin heavy chain gene (SMemb). KLF5 activates many genes inducible during cardiovascular remodeling, such as platelet-derived growth factor (PDGF)-A/B, Egr-1, plasminogen activator inhibitor-1 (PAI-1), inducible nitric oxide synthase (iNOS), and vascular endothelial growth factor (VEGF) receptors. KLF5 is abundantly expressed in embryonic smooth muscles and is down-regulated with vascular development, but reinduced in proliferative neointimal smooth muscles in response to vascular injury. In KLF5 gene-targeted mice, homozygotes die at an early embryonic stage whereas heterozygotes are apparently normal. However, in response to external stress, arteries of heterozygotes exhibit diminished levels of smooth muscle and adventitial cell activation. Furthermore, angiotensin II-induced cardiac hypertrophy and fibrosis are attenuated in heterozygotes. KLF5 activities are regulated by many transcriptional regulators and nuclear receptors, such as retinoic acid receptor-alpha (RAR alpha), NF-kappaB, PPAR gamma, p300, and SET. Interestingly, RAR alpha agonist suppresses KLF5 and cardiovascular remodeling, whereas RAR alpha antagonist activates KLF5 and induces angiogenesis. These results indicate that KLF5 is an essential transcription factor in cardiovascular remodeling and a potential therapeutic target for cardiovascular disease.

Inhibition of Rho-kinase by fasudil attenuated angiotensin II-induced cardiac hypertrophy in apolipoprotein E deficient mice

Recent evidence indicates that the GTPase activated Rho/Rho-kinase pathway contributes angiotensin II-induced cardiac hypertrophy and vascular remodeling. We tested this hypothesis in vivo by determining the effects of fasudil, a Rho-kinase inhibitor, on angiotensin II-induced cardiac hypertrophy, coronary vascular remodeling, and ventricular dysfunction. Six-month-old apolipoprotein E deficient (apoE-KO) mice were subcutaneously infused with angiotensin II (1.44 mg/kg/day) using an osmotic mini-pump. Mice were randomly assigned to either vehicle or fasudil (136 or 213 mg/kg/day in drinking water) group. Infusion of angiotensin II for 4 weeks resulted in cardiac enlargement, myocyte hypertrophy, and myocardial interstitial and coronary artery perivascular fibrosis. These changes were accompanied by reduced aortic flow velocity and acceleration rate. Cardiac gene expression levels of atrial natriuretic peptide (ANP) and collagen type III detected by real-time reverse transcriptase polymerase chain reaction were significantly increased in angiotensin II-infused mice. Treatment with fasudil dose-dependently attenuated angiotensin II-induced cardiac hypertrophy, prevented perivascular fibrosis, blunted the increase in ANP and collagen type III expression, and improved cardiac function, without changing blood pressure. These data are consistent with a role for Rho-kinase activation in angiotensin II-induced cardiac remodeling and vascular wall fibrosis.

Issue Highlights

HomeCirculationVol. 111, No. 6Issue Highlights Free AccessIn BriefPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessIn BriefPDF/EPUBIssue Highlights Originally published15 Feb 2005https://doi.org/10.1161/circ.111.6.717Circulation. 2005;111:717TIMES TO TREATMENT IN TRANSFER PATIENTS UNDERGOING PRIMARY PERCUTANEOUS CORONARY INTERVENTION IN THE UNITED STATES: NATIONAL REGISTRY OF MYOCARDIAL INFARCTION (NRMI)-3/4 ANALYSIS, by Nallamothu et al.Primary percutaneous coronary angioplasty (PCI) has emerged as an attractive alternative reperfusion strategy for myocardial infarction (MI), and recent trials indicate it may be superior to fibrinolysis. However, PCI may necessitate transfer of MI patients to hospitals with such capabilities, and the inherent delay due to transfer may mitigate potential benefits. In this issue of Circulation, Nallamothu and colleagues analyze data from the National Registry of Myocardial Infarction to assess the time to PCI in more than 4000 patients treated at 419 hospitals in the United States. The investigators report that the “door-to-balloon” time was 180 minutes (twice the recommended standard) in 50 percent of the patients; fewer than 5 percent were treated within 90 minutes. Presence of comorbidity, nonclassical presentation, and rural location of the treating hospital were key correlates of longer time to PCI. The authors emphasize the need for improved process-of-care systems to maximize the therapeutic benefits of PCI in MI patients. See p 761.RISK OF RESTENOSIS AND HEALTH STATUS OUTCOMES FOR PATIENTS UNDERGOING PERCUTANEOUS CORONARY INTERVENTION VERSUS CORONARY ARTERY BYPASS GRAFT SURGERY, by Spertus et al.Most studies comparing bypass surgery (CABG) to percutaneous coronary intervention (PCI) have found similar outcomes with regard to death and myocardial infarction but more angina and need for repeat revascularization procedures after PCI, presumably because of restenosis. In this report, Spertus et al demonstrate a correlation between preprocedural restenosis risk (as measured by a scoring system they previously developed) and health outcome at follow-up. Administering the Seattle Anginal Questionnaire to 1469 patients undergoing CABG or PCI, they found no differences in 1-year angina or quality of life among the 37.4% of patients at low risk for restenosis, but a significant benefit for CABG when patients were at intermediate or high restenosis risk. This study provides the clinician with another useful tool when facing the complex choice between CABG and PCI. Also, because this study was performed in the bare metal stent era, it should encourage the use of drug-eluting stents, particularly in patients at increased risk for restenosis. See p 768.EARLY AND MID-TERM RESULTS OF DRUG-ELUTING STENT IMPLANTATION IN UNPROTECTED LEFT MAIN, by Chieffo et al.Recent advances in coronary stent design, together with the introduction of drug-eluting stents, have allowed percutaneous coronary intervention (PCI) to be offered as a revascularization strategy to high-risk patients, including those with unprotected left main coronary artery disease. Although the majority of patients with unprotected left main disease requiring revascularization are referred for coronary artery bypass grafting surgery, unprotected left main PCI and stent placement have been performed in selected patients. These patients warrant careful postprocedural surveillance for restenosis because the initial presenting symptom may be sudden death. Newer drug-eluting stents may have some utility in this setting inasmuch as they have markedly reduced the rates of restenosis in coronary vessels. In this issue of Circulation, Chieffo et al report their experience with drug-eluting stents in unprotected left main PCI. See p 791.Visit www.circ.ahajournals.org:Images in Cardiovascular MedicineAcute Pericarditis Caused by Acrylic Bone Cement After Percutaneous Vertebroplasty. See p e98.Radial Arteriovenous Fistula After Cardiac Catheterization. See p e99. Download figureDownload PowerPointCorrespondenceLetters Regarding Article by Hu et al, “Heme Oxygenase-1 Inhibits Angiotensin II-Induced Cardiac Hypertrophy In Vitro and In Vivo.” See p e100. Previous Back to top Next FiguresReferencesRelatedDetails February 15, 2005Vol 111, Issue 6 Advertisement Article InformationMetrics https://doi.org/10.1161/circ.111.6.717 Originally publishedFebruary 15, 2005 PDF download Advertisement

Letter Regarding Article by Hu et al, “Heme Oxygenase-1 Inhibits Angiotensin II-Induced Cardiac Hypertrophy In Vitro and In Vivo”

To the Editor: I read with great interest the work of Chien-Ming Hu et al,1 in which they suggest that heme oxygenase-1 (HO-1) attenuates angiotensin II (Ang II)-induced cardiac hypertrophy both in vitro and in vivo, and that this effect may be mediated, at least in part, by bilirubin via inhibition of reactive oxygen species production (ROS) after Ang II stimulation. I agree with the authors’ conclusions that HO-1-derived bilirubin may be partially responsible for the protective effect of the enzyme via ROS scavenging, which has been shown to play a key role in cardiac hypertrophy. Three points need to be raised, however, about alternative HO-protective pathways in Ang II-mediated hypertrophy. First, several lines of evidence suggest that p21, a well-known cell cycle inhibitor, plays an important role in the physiopathological process of Ang II-mediated cardiac …

Therapeutic Potential of Rho-Kinase Inhibitors in Cardiovascular Diseases

Rho-kinase is a signaling molecule that occurs downstream of the small GTPase Rho, which mediates various cellular functions. The Rho/Rho-kinase pathway plays an important role in pathophysiology and progression of various cardiovascular diseases such as hypertension, coronary vasospasm, angina pectoris, and restenosis after percutaneous coronary intervention, all of which are related to arteriosclerosis/atherosclerosis changes of the vasculature. Activation of the Rho/Rho-kinase pathway contributes to inflammatory and proliferative changes of the blood vessels and affects cardiac myocytes. Evidence from in vitro and in vivo studies suggests that Rho-kinase inhibitors have beneficial effects on cardiovascular diseases, particularly arteriosclerosis and coronary vasospasm. Furthermore, activation of the Rho/Rho-kinase pathway contributes to blood pressure regulation via the central sympathetic nervous system. There is evidence to suggest that Rho-kinase is involved in angiotensin II-induced cardiac hypertrophy and endothelial dysfunction, and preliminary data indicate that inhibition of Rho-kinase may be beneficial in vascular disorders such as pulmonary arterial hypertension and erectile dysfunction. Fasudil is currently the only Rho-kinase inhibitor available for clinical use and it is approved in Japan for the prevention of vasospasm in patients with subarachnoid hemorrhage. Emerging clinical data have shown that oral fasudil 80 mg three times daily is effective in preventing myocardial ischemia in patients with stable angina pectoris. Rho-kinase represents a new target for the management of cardiovascular diseases and further studies are needed to define the therapeutic potential of Rho-kinase inhibitors.

Evidence of a novel intracrine mechanism in angiotensin II-induced cardiac hypertrophy

Angiotensin II (Ang II) has a significant role in regulating cardiac homeostasis through humoral, autocrine and paracrine pathways, via binding to the plasma membrane AT 1 receptor. Recent literature has provided evidence for intracrine growth effects of Ang II in some cell lines, which does not involve interaction with the plasma membrane receptor. We hypothesized that such intracrine mechanisms are operative in the heart and likely participate in the cardiac hypertrophy induced by Ang II. Adenoviral and plasmid vectors were constructed to express Ang II peptide intracellularly. Neonatal rat ventricular myocytes (NRVMs) infected with the adenoviral vector showed significant hypertrophic growth as determined by cell size, protein synthesis and enhanced cytoskeletal arrangement. Adult mice injected with the plasmid vector developed significant cardiac hypertrophy after 48 h, without an increase in blood pressure or plasma Ang II levels. This was accompanied by increased transcription of transforming growth factor-β (TGF-β) and insulin-like growth factor-1 (IGF-1) genes. Losartan did not block the growth effects, excluding the involvement of extracellular Ang II and the plasma membrane AT 1 receptor. These data demonstrate a previously unknown growth mechanism of Ang II in the heart, which should be considered when designing therapeutic strategies to block Ang II actions.

Role of osteopontin in cardiac fibrosis and remodeling in angiotensin II-induced cardiac hypertrophy.

Osteopontin (OPN) is upregulated in several experimental models of cardiac fibrosis and remodeling. However, its direct effects remain unclear. We examined the hypothesis that OPN is important for the development of cardiac fibrosis and remodeling. Moreover, we examined whether the inhibitory effect of eplerenone (Ep), a novel aldosterone receptor antagonist, was mediated through the inhibition of OPN expression against cardiac fibrosis and remodeling. Wild-type (WT) and OPN-deficient mice were treated with angiotensin II (Ang II) for 4 weeks. WT mice receiving Ang II were divided into 2 groups: a control group and an Ep treatment group. Ang II treatment significantly elevated blood pressure and caused cardiac hypertrophy and fibrosis in WT mice. Ep treatment and OPN deficiency could reduce the Ang II-induced elevation of blood pressure and ameliorate the development of cardiac fibrosis, whereas Ep-only treatment abolished the development of cardiac hypertrophy. Most compelling, the reduction of cardiac fibrosis led to an impairment of cardiac systolic function and subsequent left ventricular dilatation in Ang II-treated OPN-deficient mice. These results suggest that OPN has a pivotal role in the development of Ang II-induced cardiac fibrosis and remodeling. Moreover, the effect of Ep on the prevention of cardiac fibrosis, but not cardiac hypertrophy, might be partially mediated through the inhibition of OPN expression.

KLF5/BTEB2, a Krüppel-like zinc-finger type transcription factor, mediates smooth muscle cell activation as well as cardiovascular remodeling

Phenotypic modulation of smooth muscle from the contractile to the synthetic type underlies the pathogenesis of atherosclerosis. We previously isolated a transcription factor, KLF5 (also known as BTEB2 and IKLF), to activate various gene promoters that are activated in phenotypically modulated smooth muscle cells, such as embryonic smooth muscle myosin heavy chain gene (SMemb), plasminogen activator inhibitor-1 (PAI-1), iNOS, PDGF-A, Egr-1 and VEGF receptors. KLF5 is downregulated with vascular development but upregulated in neointima. Chromatin immunoprecipitation assay showed KLF5 to be induced and to bind the promoter of the PDGF-A gene in response to angiotensin II stimulation. To define the role of KLF5 in cardiovascular remodeling, we targeted the KLF5 gene in mice. In response to external stress, arteries of heterozygotes exhibited diminished levels of smooth muscle and adventitial cell activation. We also found that RARα binds KLF5, and that Am80, a potent synthetic RAR agonist, inhibits angiotensin II-induced cardiac hypertrophy. These results indicate that KLF5 is an essential transcription factor that causes not only smooth muscle phenotypic modulation but also cardiac hypertrophy and fibrosis.

NADPH oxidase-derived superoxide anion mediates angiotensin II-induced cardiac hypertrophy

Cardiac hypertrophy is an adaptive response to increases in blood pressure. Recent studies indicate that the hypertrophic process is associated with increases in intracellular oxidative stress in cardiomyocytes. We hypothesize that superoxide anion mediates the hypertrophic response and that antioxidant therapy may be effective in attenuating cardiac hypertrophy. Neonatal rat cardiac myocytes were stimulated with angiotensin II (AngII, 1 μM) with and without various antioxidants. N-acetylcysteine (NAC, 10 mM) and probucol (50 μM), and to a lesser extent, vitamin C (500 μM) and reduced glutathione (1 mM), inhibited AngII-induced [ 3H]-leucine uptake and atrial natriuretic factor (ANF) promoter activity. The hypertrophic response is mediated by superoxide anion (O 2 –·) since cell-permeable polyethylene glycol (PEG)-conjugated superoxide dismutase (50 U/ml), but not PEG-catalase (500 U/ml), attenuated AngII-induced [ 3H]-leucine uptake and ANF promoter activity. Furthermore, NAC blocked AngII-induced increase in myocardial oxidative stress, decreased the expression of ANF and myosin light chain-2v, and inhibited the re-organization of cytoskeletal proteins, desmin and α-actinin. These effects of AngII were abolished by angiotensin type 1 receptor blocker, losartan, but not type 2 receptor blocker, PD123319. Indeed, co-administration of losartan (10 mg/kg/d, 14 d) or NAC (200 mg/kg/d, 14 d) inhibited AngII-induced O 2 –· production and cardiac hypertrophy in rats without affecting blood pressure. These findings indicate that the generation of O 2 –· contributes to oxidant-induced hypertrophic response and suggest that antioxidant therapy may have beneficial effects in cardiac hypertrophy.

Endothelin ETA receptor antagonism does not attenuate angiotensin II-induced cardiac hypertrophy in vivo in rats.

1. Angiotensin (Ang) II causes cardiac hypertrophy in vitro and in vivo. It also stimulates the release of endothelin (ET)-1. Endothelin-1 induces hypertrophy of cardiomyocytes in vitro. 2. In the present study, we examined whether the cardiac hypertrophic action of AngII in vivo was mediated by ET-1 via ETA receptors. We also determined whether arginine vasopressin (AVP), another ET-1 stimulator, could cause cardiac hypertrophy in vivo through an ET-1-dependent pathway. 3. In Sprague-Dawley rats (n = 8 per group), we determined whether the orally administered ETA receptor antagonist BMS 193884 could attenuate the cardiac hypertrophic effect of: (i) i.v. AngII infusion at either 100 or 200 ng/kg per min, i.v., for 1 week; (ii) AngII infusion at 100 ng/kg per min, i.v., for 2 weeks; and (iii) AVP infusion at either 2 or 10 ng/kg per min, i.v., for 1 week. Mean arterial pressure and heart rate were also measured. 4. Infusion with AngII for both 1 and 2 weeks increased left ventricular weight. Only AngII infusion at 200 ng/kg per min for 1 week increased blood pressure. Endothelin ETA receptor blockade did not attenuate the left ventricular hypertrophy, even though it reduced the hypertensive effect of AngII. Arginine vasopressin increased blood pressure, but did not cause cardiac hypertrophy. 5. We showed that AngII can cause cardiac hypertrophy through a direct, blood pressure-independent effect on the heart. Endothelin-1 did not mediate the cardiac hypertrophic effect of AngII through ETA receptors. This may indicate the involvement of ETB receptors in this model of cardiac hypertrophy. Arginine vasopressin did not cause cardiac hypertrophy in vivo.

Angiotensin II-Induced Ventricular Hypertrophy and Extracellular Signal-Regulated Kinase Activation Are Suppressed in Mice Overexpressing Brain Natriuretic Peptide in Circulation

Atrial and brain (B-type) natriuretic peptides (ANP and BNP, respectively) are known to exert various cardioprotective effects. For instance, knocking out the expression of ANP, BNP, or their receptor, guanylyl cyclase-A, induces cardiac hypertrophy and/or fibrosis. The cardiac effects of elevated circulating natriuretic peptides are less well understood, however. We therefore compared angiotensin (Ang) II-induced cardiac hypertrophy and fibrosis in BNP-transgenic (Tg) mice, in which circulating BNP levels were elevated by increased secretion from the liver, and their non-Tg littermates. Left ventricular expression of Ang II type 1a receptor was similar in BNP-Tg and non-Tg mice, and there was no significant difference in the elevation of blood pressure elicited by chronic infusion or acute injection of Ang II. Nevertheless, cardiac hypertrophy and fibrosis were significantly diminished in BNP-Tg mice chronically infused with Ang II. In addition, ventricular activation of extracellular signal-regulated kinase (ERK) induced by acute injection of Ang II was also diminished in BNP-Tg mice, as was activation of ERK kinase (MEK). Conversely, expression of mitogen-activated protein kinase phosphatase (MKP) was significantly increased in the ventricles of BNP-Tg mice. Based on these findings, we conclude that elevated circulating BNP exerts cardioprotective effects via inhibition of a ventricular ERK pathway. The mechanism responsible for this inhibition likely involves 1) increased ventricular MKP expression and 2) inhibition of transduction mediators situated upstream of ERK.

KLF5/BTEB2, a Krüppel-like zinc-finger type transcription factor, mediates both smooth muscle cell activation and cardiac hypertrophy.

Cardiac and vascular biology need to be approached interactively because they share many common biological features as seen in activation of the local renin-angiotensin system, angiogenesis, and extracellular matrix production. We previously reported KLF5/BTEB2, a Krüppel-like zinc-finger type transcription factor, to activate various gene promoters that are activated in phenotypically modulated smooth muscle cells, such as a nonmuscle type myosin heavy chain gene SMemb, plasminogen activator inhibitor-1 (PAI-1), iNOS, PDGF-A, Egr-1 and VEGF receptors at least in vitro. KLF5/BTEB2 mRNA levels are downregulated with vascular development but upregulated in neointima that is produced in response to vascular injury. Mitogenic stimulation activates KLF5/BTEB2 gene expression through MEK1 and Egr-1. Chromatin immunoprecipitation assay showed KLF5/BTEB2 to be induced and to bind the promoter of the PDGF-A gene in response to angiotensin II stimulation. In order to define the role of KLF5/BTEB2 in cardiovascular remodeling, we targeted the KLF5/BTEB2 gene in mice. Homozygous mice resulted in early embryonic lethality whereas heterozygous mice were apparently normal. However, in response to external stress, arteries of heterozygotes exhibited diminished levels of smooth muscle and adventitial cell activation. Furthermore, cardiac fibrosis and hypertrophy induced by continuous angiotensin II infusion. We also found that RARa binds KLF5/BTEB2, and that Am80, a potent synthetic RAR agonist, inhibits angiotensin II-induced cardiac hypertrophy. These results indicate that KLF5/BTEB2 is an essential transcription factor that causes not only smooth muscle phenotypic modulation but also cardiac hypertrophy and fibrosis.

Targeted disruption of NFATc3, but not NFATc4, reveals an intrinsic defect in calcineurin-mediated cardiac hypertrophic growth.

A calcineurin-nuclear factor of activated T cells (NFAT) regulatory pathway has been implicated in the control of cardiac hypertrophy, suggesting one mechanism whereby alterations in intracellular calcium handling are linked to the expression of hypertrophy-associated genes. Although recent studies have demonstrated a necessary role for calcineurin as a mediator of cardiac hypertrophy, the potential involvement of NFAT transcription factors as downstream effectors of calcineurin signaling has not been evaluated. Accordingly, mice with targeted disruptions in NFATc3 and NFATc4 genes were characterized. Whereas the loss of NFATc4 did not compromise the ability of the myocardium to undergo hypertrophic growth, NFATc3-null mice demonstrated a significant reduction in calcineurin transgene-induced cardiac hypertrophy at 19 days, 26 days, 6 weeks, 8 weeks, and 10 weeks of age. NFATc3-null mice also demonstrated attenuated pressure overload- and angiotensin II-induced cardiac hypertrophy. These results provide genetic evidence that calcineurin-regulated responses require NFAT effectors in vivo.