Transforming growth factor beta 1 and extracellular matrix gene expression in isoprenaline induced cardiac hypertrophy: effects of inhibition of the renin-angiotensin system

Defining the Cardiac Fibroblast Secretome in a Fibrotic Microenvironment

Background

Cardiac fibroblasts (CFs) have the ability to sense stiffness changes and respond to biochemical cues to modulate their states as either quiescent or activated myofibroblasts. Given the potential for secretion of bioactive molecules to modulate the cardiac microenvironment, we sought to determine how the CF secretome changes with matrix stiffness and biochemical cues and how this affects cardiac myocytes via paracrine signaling.

Methods and Results

Myofibroblast activation was modulated in vitro by combining stiffness cues with TGFβ1 (transforming growth factor β 1) treatment using engineered poly (ethylene glycol) hydrogels, and in vivo with isoproterenol treatment. Stiffness, TGFβ1, and isoproterenol treatment increased AKT (protein kinase B) phosphorylation, indicating that this pathway may be central to myofibroblast activation regardless of the treatment. Although activation of AKT was shared, different activating cues had distinct effects on downstream cytokine secretion, indicating that not all activated myofibroblasts share the same secretome. To test the effect of cytokines present in the CF secretome on paracrine signaling, neonatal rat ventricular cardiomyocytes were treated with CF conditioned media. Conditioned media from myofibroblasts cultured on stiff substrates and activated by TGFβ1 caused hypertrophy, and one of the cytokines in that media was insulin growth factor 1, which is a known mediator of cardiac myocyte hypertrophy.

Conclusions

Culturing CFs on stiff substrates, treating with TGFβ1, and in vivo treatment with isoproterenol all caused myofibroblast activation. Each cue had distinct effects on the secretome or genes encoding the secretome, but only the secretome of activated myofibroblasts on stiff substrates treated with TGFβ1 caused myocyte hypertrophy, most likely through insulin growth factor 1.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

microRNA expression changes after atrial fibrillation catheter ablation

Atrial fibrillation (AF) is most common arrhythmia in general population, with increasing trend in mortality and morbidity. Electrophysiological and structural abnormalities, promoting abnormal impulse formation and propagation, lead to this disease. AF catheter ablation is related to a not small percentage of nonresponder patients. microRNAs (miRs) have been used as AF fibrotic and electrical alterations biomarkers. miRs may differentiate responders patients to ablative approach. Selective miR target therapy, as upregulation by adenovirus transfection and/or miR downregulation by antagomiR, may be used to treat AF patients. Catheter ablation of triggering electrical pulmonary veins activity or fibrotic areas defragmentation may be upgraded by miR therapy to prevent cardiac electrical and fibrotic remodeling after AF ablation.

Early expression of monocyte chemoattractant protein-1 correlates with the onset of isoproterenol-induced cardiac fibrosis in rats with distinct angiotensin-converting enzyme polymorphism

INTRODUCTION

Isoproterenol treatment of Brown Norway and Lewis rats (high and low plasma angiotensin-I-converting enzyme activity, respectively) results in similar cardiac hypertrophy but higher cardiac fibrosis in Brown Norway rats.

MATERIALS AND METHODS

Rats were infused in vivo with isoproterenol for two or 10 days. Cardiac fibrosis and inflammation were evaluated histochemically. We measured the mRNAs of pro-fibrotic factors (transforming growth factor beta(1), endothelin-1) and pro-inflammatory factors (monocyte chemoattractant protein-1). In studies with cardiac fibroblasts incubated with isoproterenol in vitro , we measured cell proliferation, angiotensin-I-converting enzyme and matrix metalloprotease 2 activities and deposition of collagen type I and fibronectin.

RESULTS

After treatment with isoproterenol for two days, there were large areas of myocardial injury and numerous inflammatory foci in the left ventricle, these being greater in Brown-Norway than in Lewis rats. After treatment with isoproterenol for 10 days, there were large areas of damage with extensive collagen deposition only in the left ventricle; both strains exhibited this damage which was, however, more severe in Brown-Norway than in Lewis rats. After treatment with isoproterenol for two, but not 10, days, greater amounts of monocyte chemoattractant protein-1 mRNA were found in Brown Norway than in Lewis rats. Cell proliferation, activities of angiotensin-I-converting enzyme and matrix metalloprotease 2, amounts of collagen type I and fibronectin were similar in cardiac fibroblasts from both strains; changes after isoproterenol (10 microM) were also similar in both strains.

CONCLUSION

We conclude that the greater cardiac fibrosis in Brown Norway rats treated with isoproterenol correlates with the early and higher expression of proinflammatory factors.

Downregulation of miR-133 and miR-590 contributes to nicotine-induced atrial remodelling in canines

AIMS

The present study was designed to decipher molecular mechanisms underlying nicotine's promoting atrial fibrillation (AF) by inducing atrial structural remodelling.

METHODS AND RESULTS

The canine model of AF was successfully established by nicotine administration and rapid pacing. The atrial fibroblasts isolated from healthy dogs were treated with nicotine. The role of microRNAs (miRNAs) on the expression and regulation of transforming growth factor-beta1 (TGF-beta1), TGF-beta receptor type II (TGF-betaRII), and collagen production was evaluated in vivo and in vitro. Administration of nicotine for 30 days increased AF vulnerability by approximately eight- to 15-fold in dogs. Nicotine stimulated remarkable collagen production and atrial fibrosis both in vitro in cultured canine atrial fibroblasts and in vivo in atrial tissues. Nicotine produced significant upregulation of expression of TGF-beta1 and TGF-betaRII at the protein level, and a 60-70% decrease in the levels of miRNAs miR-133 and miR-590. This downregulation of miR-133 and miR-590 partly accounts for the upregulation of TGF-beta1 and TGF-betaRII, because our data established TGF-beta1 and TGF-betaRII as targets for miR-133 and miR-590 repression. Transfection of miR-133 or miR-590 into cultured atrial fibroblasts decreased TGF-beta1 and TGF-betaRII levels and collagen content. These effects were abolished by the antisense oligonucleotides against miR-133 or miR-590. The effects of nicotine were prevented by an alpha7 nicotinic acetylcholine receptor antagonist.

CONCLUSION

We conclude that the profibrotic response to nicotine in canine atrium is critically dependent upon downregulation of miR-133 and miR-590.

The involvement of transforming growth factor-β1 secretion in Urotensin II-induced collagen synthesis in neonatal cardiac fibroblasts

As the most potent vasoconstrictor in mammals, urotensin II (U II) has recently been demonstrated to play an important role in adverse cardiac remodeling and fibrosis. However, the mechanisms of U II-induced myocardial fibrosis remain to be clarified. We postulated that U II alters transforming growth factor-beta1 (TGF-beta1) expression, and thereby modulates cardiac fibroblast collagen metabolism. Experiments were conducted using cardiac fibroblast from neonatal Wistar rats to determine the expression of TGF-beta1, and the role of U II receptor UT in this process. The functional role of TGF-beta1 and UT in modulating U II effects on type I, III collagen mRNA expression and 3H-proline incorporation was also analyzed. TGF-beta1 gene and protein expression were consistently identified in quiescent cardiac fibroblasts. U II increased the expression of TGF-beta1 mRNA and protein in a time-dependent manner. This effect was UT mediated, because UT antagonist urantide abolished U II-induced TGF-beta1 expression. U II-induced increase in type I, III collagen mRNA expression and 3H-proline incorporation were both inhibited by a specific TGF-beta1 neutralizing antibody and UT receptor antagonist urantide. Hence, our results indicate that TGF-beta1 is upregulated in cardiac fibroblasts by U II via UT and modulates profibrotic effects of U II. These findings provide novel insights into U II-induced cardiac remodeling.

Cardiac hypertrophy induced by sustained β-adrenoreceptor activation: pathophysiological aspects

Cardiac hypertrophy is promoted by adrenergic over-activation and represents an independent risk factor for cardiovascular morbidity and mortality. The basic knowledge about mechanisms by which sustained adrenergic activation promotes myocardial growth, as well as understanding how structural changes in hypertrophied myocardium could affect myocardial function has been acquired from studies using an animal model of chronic systemic beta-adrenoreceptor agonist administration. Sustained beta-adrenoreceptor activation was shown to enhance the synthesis of myocardial proteins, an effect mediated via stimulation of myocardial growth factors, up-regulation of nuclear proto-oncogenes, induction of cardiac oxidative stress, as well as activation of mitogen-activated protein kinases and phosphatidylinositol 3-kinase. Sustained beta-adrenoreceptor activation contributes to impaired cardiac autonomic regulation as evidenced by blunted parasympathetically-mediated cardiovascular reflexes as well as abnormal storage of myocardial catecholamines. Catecholamine-induced cardiac hypertrophy is associated with reduced contractile responses to adrenergic agonists, an effect attributed to downregulation of myocardial beta-adrenoreceptors, uncoupling of beta-adrenoreceptors and adenylate cyclase, as well as modifications of downstream cAMP-mediated signaling. In compensated cardiac hypertrophy, these changes are associated with preserved or even enhanced basal ventricular systolic function due to increased sarcoplasmic reticulum Ca(2+) content and Ca(2+)-induced sarcoplasmic reticulum Ca(2+) release. The increased availability of Ca(2+) to maintain cardiomyocyte contraction is attributed to prolongation of the action potential due to inhibition of the transient outward potassium current as well as stimulation of the reverse mode of the Na(+)-Ca(2+) exchange. Further progression of cardiac hypertrophy towards heart failure is due to abnormalities in Ca(2+) handling, necrotic myocardial injury, and increased myocardial stiffness due to interstitial fibrosis.

Site specific differential activation of ras/raf/ERK signaling in rabbit isoproterenol-induced left ventricular hypertrophy

To understand better the mediating role of ras/raf/ERK signaling pathway in development of cardiac hypertrophy and cerebrovascular events in vivo, the molecular mechanism of the pathway in heart and cerebral arteries after isoproterenol (ISO) induced beta-adrenergic receptor (betaAR) stimulation was examined in rabbit as animal model. Compared with the heart, our findings indicate that ISO-stimulation results in increase in mRNA levels of ras, raf, and immediate-early genes in the cerebral arteries. Conversely, the ras and raf protein expression levels (determined by Western blot) and the ras-GTP level (determined by pull-down assay) in the heart, but not the cerebral arteries, are markedly elevated after treatment. In addition, despite constant ERK1/2 abundance, phosphorylated ERK (pERK) activity was elevated at both sites with prominent effect on heart following stimulation. Opposing to the PKA and PKC, as upstream contributors in the pathway, which seem to be similarly affected at both sites following ISO-stimulation, the results imply that the downstream candidates ras and raf, as well as immediate-early genes, have different responses at both sites post-stimulation. The results provide an evidence of site-dependent differential response of ras/raf/ERK pathway after cardiac hypertrophy-induced by ISO-stimulation. This varied response may account for underlying mechanisms of development of cardiac hypertrophy and cerebrovascular events in heart and cerebral arteries, respectively.

The influence of oestrogen-deficiency and ACE inhibition on the progression of myocardial hypertrophy in spontaneously hypertensive rats

BACKGROUND

ACE inhibitors are widely used to antagonize the biological activity of angiotensin II in hypertensive heart disease. Oestrogen reduces angiotensin type 1 receptor expression, and thereby modifies angiotensin signalling.

AIM

To investigate the interaction of oestrogen status and ACE inhibition on the development of left ventricular hypertrophy and expression of transforming growth factor (TGF)-beta(1) in female spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

Intact female SHR, ovariectomised SHR, and ovariectomised SHR with 17beta-oestradiol (E2) replacement therapy were either treated with placebo or the ACE inhibitor moexiprilat. Blood pressure, left ventricular hypertrophy, and expression of TGF-beta(1) and TGF-beta(1)-regulated genes were investigated. ACE inhibition reduced blood pressure in all groups. When normalised to blood pressure, a significant reduction in hypertrophy was found in ovariectomised animals receiving E2. Expression of TGF-beta(1) was increased in all three groups treated with the ACE inhibitor, with top levels in ovariectomised animals. Moreover, expression of ornithine decarboxylase (ODC), an adrenoceptor dependent gene, downstream of TGF-beta(1), was up-regulated upon ACE inhibition, except in animals which were ovariectomised and oestrogen supplemented. Parathyroid hormone-related peptide, a growth factor negatively regulated by TGF-beta(1), was down-regulated in all animals receiving the ACE inhibitor.

CONCLUSION

ACE inhibition modulated TGF-beta(1) and TGF-beta(1) dependent genes. Oestrogen deficiency alone did not influence the progression of cardiac hypertrophy in this model of female SHR.

Manipulation of the Renin Angiotensin System in Peripheral Arterial Disease

The Heart Outcomes Prevention Evaluation (HOPE) study has provided evidence for the use of ramipril for secondary cardiac prevention for patients with peripheral arterial disease. Despite this many vascular surgeons and general practitioners are reluctant to prescribe ACE inhibitors in a group of patients perceived to have a high incidence of renal artery stenosis. This review aims to review the pathophysiology of the renin-angiotensin system and make evidence based recommendations for commencing ACE inhibitors as part of a comprehensive delivery of best medical therapy to patients with peripheral arterial disease.

Concerted action of the renin-angiotensin system, mitochondria, and antioxidant defenses in aging

Angiotensin-converting enzyme inhibitors (ACEi) and AT-1 receptor blockers (ARB) are two types of drugs that inhibit the renin-angiotensin system (RAS), and can attenuate the progression to cardiac and/or renal functional impairment, secondary to diverse pathologies. Some of the beneficial effects of ACEi and ARB occur independently of the ability of these drugs to reduce arterial blood pressure. Both, in animals, and in humans, we observed an enhancement of antioxidant defenses that occurred after treatment with ACEi. Based on these results, we postulate that some of the beneficial health effects associated to RAS inhibition can be ascribed to the prevention of oxidant-mediated damage. Furthermore, considering that: (i). RAS inhibition attenuates certain age-associated degenerative changes; (ii). aging was postulated to result from the accumulation of oxidant-mediated damage; and (iii). mitochondria are a major source of oxidants, we studied potential associations among RAS inhibition, mitochondrial function and production of oxidants and nitric oxide, and aging. The results obtained suggest, that RAS inhibitors, i.e. enalapril and losartan, can protect against the effects of aging by attenuating oxidant damage to mitochondria, and in consequence, they preserve mitochondrial function. The mechanism(s) explaining such attenuation of oxidant damage can relay on a reduction of the ANG-II-dependent generation of superoxide and/or an increased detoxification of reactive nitrogen and oxygen species by recomposition of antioxidant defense levels.

Transforming growth factor beta in cardiovascular development and function

Transforming growth factor betas (TGFbetas) are pleiotropic cytokines involved in many biological processes. Genetic engineering and tissue explanation studies have revealed specific non-overlapping roles for TGFbeta ligands and their signaling molecules in development and in normal function of the cardiovascular system in the adult. In the embryo, TGFbetas appear to be involved in epithelial-mesenchymal transformations (EMT) during endocardial cushion formation, and in epicardial epithelial-mesenchymal transformations essential for coronary vasculature, ventricular myocardial development and compaction. In the adult, TGFbetas are involved in cardiac hypertrophy, vascular remodeling and regulation of the renal renin-angiotensin system. The evidence for TGFbeta activities during cardiovascular development and physiologic function will be given and areas which need further investigation will be discussed.

TGF-beta1 mediates the hypertrophic cardiomyocyte growth induced by angiotensin II

Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 gene expression. However, it is not known whether there is a causal relationship between increased levels of TGF-beta1 and cardiac hypertrophy. Echocardiographic analysis revealed that TGF-beta1-deficient mice subjected to chronic subpressor doses of Ang II had no significant change in left ventricular (LV) mass and percent fractional shortening during Ang II treatment. In contrast, Ang II-treated wild-type mice showed a >20% increase in LV mass and impaired cardiac function. Cardiomyocyte cross-sectional area was also markedly increased in Ang II-treated wild-type mice but unchanged in Ang II-treated TGF-beta1-deficient mice. No significant levels of fibrosis, mitotic growth, or cytokine infiltration were detected in Ang II-treated mice. Atrial natriuretic factor expression was approximately 6-fold elevated in Ang II-treated wild-type, but not TGF-beta1-deficient mice. However, the alpha- to beta-myosin heavy chain switch did not occur in Ang II-treated mice, indicating that isoform switching is not obligatorily coupled with hypertrophy or TGF-beta1. The Ang II effect on hypertrophy was shown not to result from stimulation of the endogenous renin-angiotensis system. These results indicate that TGF-beta1 is an important mediator of the hypertrophic growth response of the heart to Ang II.

In search of cardiovascular candidate genes: interactions between phenotypes and genotypes

Most cardiovascular traits of interest can be defined as "complex traits," with the first step in the identification of genetic factors affecting such traits being the detection of quantitative trait loci (QTLs). Animal models have proven particularly useful in this regard. However, only very few of the QTLs identified to date have led to the identification of candidate genes. We describe an example of our own work where the combination of anatomical and a biochemical intermediate phenotypes have led to the identification of the natriuretic peptide precursor A (Nppa) gene as a candidate gene for left ventricular hypertrophy (LVH). Combined with the power of comparative genetics, these strategies will continue to improve the chances of finding candidate genes for cardiovascular traits such as susceptibility to heart diseases, hypertension, and hypertension-induced end-organ damage.

Low-dose ACE with alpha- or beta-adrenergic receptor inhibitors have beneficial SHR cardiovascular effects

BACKGROUND

There are no data regarding the prolonged effect of alpha-1 adrenergic receptor antagonists on ventricular collagen content and coronary hemodynamics in spontaneously hypertensive rats (SHR). This study, therefore, was designed to determine the effects of chronic treatment with the alpha-1 adrenergic receptor inhibitor doxazosin on SHR systemic and regional (especially coronary) hemodynamics, cardiovascular mass, and ventricular collagen. The effects of the combination of doxazosin with low-dose angiotensin-converting enzyme inhibitor were studied versus the alpha-1 antagonist alone. These effects were compared with those of a beta-1 adrenergic receptor inhibitor.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular weight, hydroxyproline concentration, and aortic weight were measured at age 35 weeks. Doxazosin reduced arterial pressure and total peripheral resistance without changing left ventricular mass and collagen content, whereas monotherapies with the beta-1 antagonist metoprolol or a subdepressor dose of the ACE inhibitor enalapril were effective in reducing left ventricular mass and hydroxyproline without altering pressure. Doxazosin combined with the same low-dose ACE inhibitor reduced left ventricular mass and hydroxyproline without potentiating the hypotensive effect of doxazosin. By contrast, the combination of beta-1 antagonist with the low-dose ACE inhibitor reduced pressure, unlike either agent alone. Aortic weight index was significantly reduced only by doxazosin whether when used alone or with the ACE inhibitor. Low-dose ACE inhibitor with doxazosin or the beta-1 receptor antagonist as well as doxazosin alone decreased renal vascular resistance.

CONCLUSION

These data show that the low subdepressor dose ACE inhibitor with an alpha- or beta-adrenergic receptor antagonist provides beneficial cardiovascular effects in SHR.

Induction of cardiac fibrosis by transforming growth factor-beta(1)

The role of transforming growth factor-beta(1) (TGF-beta(1)) in the production and deposition of collagens and in the induction of gene expression in the myocardium in relation to the development of myocardial fibrosis will be discussed. Very low expression of TGF-beta(1) and collagen type I and III mRNA is seen in the normal rat heart. Both expressions are markedly increased in the infarcted heart and the levels of TGF-beta(1) mRNA precedes increases in mRNA levels for extracellular matrix (ECM) proteins, suggesting a possible role of TGF-beta(1) in remodeling processes in the myocardium. The TGF-beta(1) expression is normally only transient since continuous TGF-beta(1) overexpression seems to promote nonadaptive cardiac hypertrophy and myocardial fibrosis. In vitro, TGF-beta(1) induces an increase in collagen production and secretion and enhances the abundance of mRNA levels for collagen type I and III in rat cardiac fibroblasts in culture. TGF-beta(1) also stimulates in vivo the expression of ECM proteins and in vivo gene transfer of TGF-beta(1) can induce myocardial fibrosis. Increased myocardial TGF-beta(1) and ECM protein mRNA are found in myocardial fibrosis induced by angiotensin II infusion, by noradrenaline treatment, by isoprenaline infusion, and by long-term blockade of NO synthesis. In vivo antagonism of TGF-beta(1) by neutralizing anti-TGF-beta(1) antibodies or by proteoglycans prevents the increase in gene expression of ECM proteins and inhibits myocardial fibrosis, suggesting that the increases in matrix protein production and fibrosis are mediated by TGF-beta(1).

Beta-adrenergic agonist hyperplastic effect is associated with increased fibronectin gene expression and not mitogen-activated protein kinase modulation in C2C12 cells

Beta-adrenergic agonists (beta-AA) enhance protein accretion in skeletal muscles. This stimulation is characterized by increased protein synthesis, increased expression of myofibrillar protein genes and a depression in protein degradation in animals, and increased proliferation and DNA synthesis in muscle cells in vitro. The mechanism or signal path in muscle whereby beta-AA would elicit these physiological effects upon binding to the G protein-coupled beta-adrenergic receptor (beta-AR) is unclear. C2C12 myoblasts were used to determine beta-AR ligand binding characteristics, cyclic AMP synthesis in response to isoproterenol (ISO) stimulation, and effects of ISO on DNA synthesis, mitogen activated protein kinase (MAPK), and fibronectin (FN) gene expression. Results showed that C2C12 cells possess beta-AR which are specific, saturable, and of high affinity (Kd = 0.2 nM). Forskolin and ISO stimulated cAMP production by = 20-fold (P<0.001) and 17-fold (P<0.001), respectively. ISO and the cAMP analog, 8-bromo-cAMP (8-BC) stimulated DNA synthesis in proliferating cells by 150% (P<0.05) and 200% (P<0.01), respectively, without modulating MAPK activity, whereas addition of fetal bovine serum to culture resulted in a 500% increase (P<0.01) in DNA synthesis and MAPK activation. DNA synthesis in C2C12 cells treated with ISO, 8-BC, or FBS was abolished in the presence of 25 microM PD098059, an MAPK-kinase inhibitor, suggesting that an MAPK-dependent pathway is likely involved in C2C12 proliferation. During cAMP elevating agent stimulation, basal MAPK activity may be sufficient, in the presence of other putative signaling molecules, to support proliferation in these cells. ISO or 8-BC treatment increased FN mRNA by three- and seven-fold, respectively, in growing C2C12 cells implying a connection between increased DNA synthesis and FN gene expression.

Autocrine regulation of TGF beta expression in adult cardiomyocytes

As shown before, TGF beta acts in an autocrine manner on the induction of hypertrophic responsiveness to beta-adrenoceptor stimulation in cultured ventricular cardiomyocytes of adult rat. We now investigated how TGF beta expression and activation is regulated in these cultures and how beta-adrenoceptor stimulation influences TGF beta -mRNA expression. It was found that freshly isolated cardiomyocytes secrete latent TGF beta in the culture medium. Supplementation of the cultures with 20% FCS resulted in activation of the secreted TGF beta to 4.1+/-0.2 ng/ml active TGF beta after 6 days. Presence of the protease inhibitor aprotinin (50 microg/ml) reduced TGF beta activity by 44+/-5% (n=5, P<0.05). In cultures supplemented with 5% FCS, TGF beta was not activated. Active TGF beta downregulated its mRNA-expression: after 6 days TGF beta(1)-mRNA was reduced to 55.1+/-11.0%, TGF beta(2)-mRNA to 30.1+/-16.5%, and TGF beta(3)-mRNA to 0.3+/-0.4% in 20% FCS-cultures as compared to their expression in freshly isolated cells (n=4, P<0.05). TGF beta-mRNA expression did not change in cultures without active TGF beta. Isoprenaline (1 microm) increased TGF beta(1)-mRNA only in cultures which had been pre-exposed to active TGF beta. This effect was also seen when hearts from normal mice were compared with hearts from transgenic mice overexpressing TGF beta(1): only in hearts from transgenic animals perfusion with isoprenaline increased TGF beta(1)-mRNA. In conclusion, isolated cardiomyocytes release latent TGF beta, which is activated by external proteases. Active TGF beta downregulates its own mRNA expression. Preexposure to TGF beta is necessary for a beta-adrenoceptor-mediated increase in TGF beta(1)-mRNA in cardiomyocytes.

Increased JNK, AP-1 and NF-kappa B DNA binding activities in isoproterenol-induced cardiac remodeling

The in vivo signal transduction pathway, responsible for isoproterenol-induced cardiac hypertrophy or remodeling, remains to be clarified. The purpose of this study was to examine c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), activator protein-1 (AP-1) and nuclear factor-kappa B (NK-kappa B) DNA binding activity, which seem to be important in a signal transduction cascade upstream of the increased level of mRNA expression observed in isoproterenol-induced cardiac remodeling. Rats were continuously infused with saline and isoproterenol by intravenous injection (a short period; 0.5 microgram/kg/min) and an osmotic minipump (a long period; 0.5 or 3 mg/kg/day). Cardiac morphology was measured by echocardiography. JNK and ERK were measured by in gel kinase assay. AP-1 and NF-kappa B DNA binding activity was determined using an electrophoretic mobility shift assay. Echocardiogram showed that the thickness of the left ventricular anterior wall (AW) and left ventricular posterior wall (PW) increased at day 1 in low doses, and at day 1 in high doses. Isoproterenol significantly increased ERK and JNK activity at 15 min after intravenous infusion of 0.5 microgram/kg/min isoproterenol. At late phase about JNK and ERK activity, only a high dose of isoproterenol increased JNK. AP-1 DNA binding activities spurred by low or high doses of isoproterenol administration increased at 12 h, reached their peak of 24.1- and 37.1-fold (P < 0.01), respectively, at 24 h, and thereafter decreased. Although low doses of isoproterenol did not change the level of NF-kappa B DNA binding activities, high doses increased it to 10.9-fold (P < 0.01) at day 2. This study showed increased JNK, ERK, AP-1 and NF-kappa B DNA binding activities in isoproterenol-induced cardiac remodeling. AP-1 may contribute to the isoproterenol-induced cardiac remodeling, and JNK or NF-kappa B may also play some roles in it.

Overexpression of insulin-like growth factor-I in hearts of rats with isoproterenol-induced cardiac hypertrophy

Increased levels of plasma catecholamine lead to cardiac hypertrophy via the alpha-, beta-adrenergic receptors, and partially, type 1 angiotensin II (AT1) receptor. However, it remains unclear whether other factors are involved in catecholamine-induced cardiac hypertrophy. We investigated the expression of insulin-like growth factor (IGF)-I in hearts of male Wistar rats infused with a beta-adrenergic agent, isoproterenol (ISO) (3 mg/kg/day), with or without an AT1-receptor antagonist, TCV-116 (10 mg/kg/day). Cardiac myocytes became hypertrophied 1 day after the beginning of ISO administration. ISO induced a biphasic increase of cardiac myocytes positive for IGF-I protein in the early and late phases of the study period, whereas IGF-I gene expression was upregulated only in the late phase by ISO. TCV- 116 abolished the upregulation of IGF-I gene and protein expression in the late phase in association with the regression of cardiac hypertrophy. These results suggest that ISO-induced cardiac hypertrophy is mediated, at least in part, by IGF-I, the expression of which is upregulated through the activation of AT1 receptor.

Cosegregation analysis in genetic crosses suggests a protective role for atrial natriuretic factor against ventricular hypertrophy

In most rat models studied to date, increased ventricular mass is associated with high ventricular expression of the atrial natriuretic factor (ANF) gene. However, it is unknown whether ANF plays a beneficial or detrimental role in the course of left ventricular hypertrophy or whether ANF gene expression could be genetically linked to cardiac mass. To address such questions, we performed a cosegregation analysis in genetic crosses of inbred strains of rats. To select strains with the appropriate phenotypic characteristics, we first compared the ventricular abundance of ANF mRNA to ventricular mass (corrected for body weight) in 2 recombinant inbred strains derived from Wistar-Kyoto (WKY)/spontaneously hypertensive rat (SHR) hybrid crosses, ie, WKY-derived hyperactive (WKHA) and WKY-derived hypertensive (WKHT) rats, as well as in their parental inbred strains. In the 2 such strains that were normotensive, we observed that ventricular mass was higher in WKHA than in WKY rats, yet ventricular ANF mRNA was less abundant in WKHA than in WKY rats. Within a segregating population of F2 animals generated from a cross between WKY and WKHA genitors, the abundance of ventricular ANF mRNA and peptide correlated inversely with left ventricular mass, in contrast to the positive correlation observed with beta-myosin heavy chain mRNA. Finally, in the equally hypertensive SHR and WKHT strains, we found that ventricular mass was higher in SHR than in WKHT, yet ventricular ANF mRNA was less abundant in SHR than in WKHT. These results demonstrate for the first time that low ventricular ANF gene expression can be linked genetically to high cardiac mass independently of blood pressure and are consistent with a protective role for ANF against left ventricular hypertrophy.

Biphasic activation of the JAK/STAT pathway by angiotensin II in rat cardiomyocytes

This study was designed to demonstrate the characteristic pattern of angiotensin II-induced JAK/STAT (indicating just another kinase/signal transducer and activator of transcription) activation in cultured rat cardiomyocytes by comparing it with leukemia inhibitory factor (LIF)-induced activation. Angiotensin II (10(-7) mol/L) induced rapid phosphorylation of JAK2 and Tyk2, but not JAK1, and phosphorylated STAT1 and STAT2, but not STAT3, in the early stage up to 30 minutes. The time course of JAK/STAT activation by angiotensin II was apparently slower than that by LIF. Interestingly, angiotensin II phosphorylated STAT3 and rephosphorylated STAT1 in the late stage at 120 minutes. We also found that angiotensin II induced the formation of interferon-stimulating gene factor (ISGF) complexes biphasically, in the early stage at 15 to 30 minutes and in the late stage at 120 minutes, and that angiotensin II induced delayed activation of the sis-inducing factor (SIF) complex at 120 minutes. Formation of ISGF and SIF complexes in response to angiotensin II paralleled the phosphorylation pattern of STAT1 and STAT3 and was quite different from those obtained in response to LIF. The phosphorylation of STAT1 was suppressed by pretreatment with the angiotensin II type-1 (AT1) receptor antagonist CV11974, but the delayed addition of CV11974 failed to suppress phosphorylation of STAT3 at 120 minutes. In conclusion, angiotensin II-induced JAK/STAT activation in rat cardiomyocytes is biphasic and entirely different from LIF-induced activation.

Effect of manidipine hydrochloride, a calcium antagonist, on isoproterenol-induced left ventricular hypertrophy

We examined the effect of a calcium antagonist, manidipine hydrochloride, on cardiac hypertrophy and the expression of the atrial natriuretic peptide (ANP), transforming growth factor beta 1 (TGF-beta 1), and extracellular matrix protein genes in rats with isoproterenol-induced cardiac hypertrophy. Rats were continuously infused with saline or isoproterenol (0.5 mg/kg per day) for 7 days using an osmotic minipump. Treatment with manidipine hydrochloride (once a day at 3 mg/kg) began 1 day before minipump implantation and continued until the end of the experiments (each group; n = 6). After treatment, left ventricular weight was measured and mRNA was extracted and analyzed by Northern blot hybridization. Isoproterenol increased left ventricular weight (2.40 +/- 0.04 g/kg; p < 0.01) without increasing blood pressure. ANP, collagen type I and type III, and fibronectin mRNAs were increased 1.5-(p < 0.01), 1.9- (p < 0.01), 2.7- (p < 0.01), and 3.2-fold (p < 0.01), respectively, by isoproterenol infusion. However, TGF-beta 1, collagen type IV, and laminin B1 and B2 mRNA levels were unchanged by isoproterenol. Manidipine hydrochloride prevented isoproterenol-induced left ventricular hypertrophy (2.26 +/- 0.02 g/kg; p < 0.01) and expression of mRNA of ANP (0.9-fold of the control value; p < 0.01), collagen types I (1.1-fold; p < 0.01) and type III (1.6-fold; p < 0.01), and fibronectin (1.1-fold; p < 0.01). Thus, manidipine hydrochloride prevented cardiac hypertrophy and changes in the expression of genes for ANP and interstitial components of extracellular matrix induced by isoproterenol.

Effect of angiotensin II on myocardial collagen gene expression

Recent studies suggest that angiotensin II (angiotensin) may be involved in the regulation of metabolism of the cardiac extracellular matrix (ECM). Two major components of ECM are collagen types I and III which play an important role in maintaining the structure and function of the heart. Although the cellular metabolism of collagen is very complex (especially at the posttranslational level), we chose to address events that occur relatively early in the synthesis of cardiac collagen molecules. To gain an understanding of the role of angiotensin (12, 24, and 48 micrograms/kg/h) on adult heart and cultured neonatal cardiac fibroblasts. The steady-state mRNA abundance of collagen type I and III was monitored using Northern blot analysis in both left and right ventricular samples at day 3 of angiotensin infusion and in cultured cardiac fibroblasts stimulated with angiotensin. In all mRNA abundance studies, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) signal was used to normalize the data for possible differences in loading and/or transfer of total RNA. Both collagen types I/GAPDH and III/GAPDH mRNA signal ratios were increased significantly in left ventricle in all dose regimens used for angiotensin infusion. Only the collagen type I/GAPDH mRNA signal ratio was increased in right ventricle with angiotensin infusion. Angiotensin (10(-7)-10(-5) M) had no effect on the steady-state mRNA abundance of collagen genes in cultured neonatal cardiac fibroblasts after 24 h treatment in serum-free conditions. Our results confirm that infusion of angiotensin may upregulate steady-state collagen gene mRNA abundance in the heart. Angiotensin had no observable effect on collagen mRNA abundance in neonatal fibroblast culture. An explanation for the current results may be that angiotensin causes the release of undefined factors from cardiac myocytes, and that these secondary factors may be involved in either the activation of collagen gene transcription or in alteration of stability of collagen mRNA transcripts via a paracrine mechanism. Although our results indicate hemodynamic loading may potentiate the action of angiotensin, this scenario is unlikely as collagen type I gene expression was increased in the normotensive right ventricle.

Role of angiotensin-converting enzyme, adrenergic receptors, and blood pressure in cardiac gene expression of spontaneously hypertensive rats during development

We undertook this study to investigate the regulatory mechanism of cardiac gene expression in spontaneously hypertensive rats (SHR) during development. We measured cardiac mRNAs by Northern blot analysis. In 9-week-old SHR at the very early stage of cardiac hypertrophy, the expression of various cardiac genes related to the regulation of cardiac contraction and relaxation was already significantly changed compared with control Wistar-Kyoto rats, indicating that cardiac molecular changes are responsible for cardiac remodeling or the modulation of cardiac performance in SHR. We gave various types of antihypertensive drugs, at oral doses causing a mild and comparable hypotensive effect, to 27-week-old SHR to examine the effects on the altered cardiac gene expression. Imidapril, an angiotensin-converting enzyme inhibitor, normalized the increased gene expression of atrial natriuretic polypeptide and collagen types I and III and the decreased expression of alpha-myosin heavy chain in SHR heart. Atenolol (a beta 1-blocker) combined with doxazosin did not affect cardiac ANP and alpha-myosin heavy chain expression of SHR but normalized the increased collagen expression. In contrast, despite a hypotensive effect comparable to these two drug treatments, doxazosin (an alpha 1-blocker) alone or manidipine (a calcium antagonist) did not normalize these altered gene expressions of SHR. These results show that the cardiac renin-angiotensin system is involved in the altered cardiac gene expression in SHR. The beta 1- but not alpha 1-adrenergic receptor is also responsible for the increased cardiac collagen expression in SHR.