Molecular determinants of myocardial hypertrophy and failure: alternative pathways for beneficial and maladaptive hypertrophy

Daniel J. Lipsa, Leon J. deWindta, Dave J.W. van Kraaij and Pieter A. Doevendansb,c,*

a Department of Cardiology, Academic Hospital Maastricht, P. Debyelaan 25, 6202 AZ Maastricht, The Netherlands
b Interuniversity Cardiology Institute, The Netherlands
c Department of Cardiology, Heart Lung Center Utrecht, 3508 GA Utrecht, The Netherlands

* Corresponding author. Tel.: +31-30-3882100; fax: +31-30-25591111
E-mail address: p.doevendans{at}cardio.azm.nl

Received 8 November 2002; accepted 20 November 2002

Abstract

The implementation of molecular biological approaches has led to the discovery of single genetic variations that contribute to the development of cardiac failure. In the present review, the characteristics that are invariably associated with the development of failure in experimental animals and clinical studies are discussed, which may provide attractive biological targets in the treatment of human heart failure. Findings from the Framingham studies have provided evidence that the presence of left ventricular hypertrophy is the main risk factor for subsequent development of heart failure in man. Conventional views identify myocardial hypertrophy as a compensatory response to increased workload, prone to evoke disease. Recent findings in genetic models of myocardial hypertrophy and human studies have provided the molecular basis for a novel concept, which favours the existence of either compensatory or maladaptive forms of hypertrophy, of which only the latter leads the way to cardiac failure. Furthermore, the concept that hypertrophy compensates for augmented wall stress is probably outdated. In this article, we provide the molecular pathways that can distinguish beneficial from maladaptive hypertrophy.

Key Words: Hypertrophy • Heart failure • Gene-expression • Calcium handling • Apoptosis • Fibrosis

1. Introduction

Heart failure is associated with high morbidity and mortality rates in modern Western societies, and can be viewed upon as the end-stage of various forms of heart disease.1 The prognosis for patients with heart failure is poor and is in fact even worse than the survival chances in patients suffering fromvarious malignancies.2,3 In community studies, the annual mortality was found to be 10–20% in patients with mild–moderate symptoms requiring hospital admission and this figure can be as high as 40–60% in patients with severe heart failure.4 The single most powerful predictor for the development of heart failure is the presence of left ventricular hypertrophy.5 For this reason, much effort is currently undertaken to investigate the aetiology of hypertrophic mechanisms and to unravel the molecular pathways underlying this affliction. These efforts are part of ongoing research to find novel treatment modalities to prevent or even reverse human heart failure. Heart failure is one of the mostchallenging diseases of the future owing to the heterogeneous cardiac response, especially in its final stages. In addition, it is still under-represented in the public and political attention.

A powerful tool in the hands of cardiovascular researchers is the implementation of molecular biological approaches to investigate the role of single modifier genes on the development of cardiac disease. Accordingly, the number of transgenic and knockout models of hypertrophy and failure has grown exponentially in recent years, and this has provided us with novel genetic cues about the human aetiology of this affliction. The aim of the present review is to give a brief summary of the current status of our knowledge on cardiac hypertrophy and failure, and to discuss novel biological targets that have been demonstrated to be critical in the development of the disease in genetic models. These targets may become key players in future treatment of human heart failure.

2. Heart failure

Heart failure in humans is characterised by low cardiac output due to systolic and/or diastolicdysfunction.6 When depending on increased ventricular performance, for example during physical exercise, heart failure patients typically present with acute symptoms of clinical cardiac failure, e.g. fatigue, dyspnea and sometimes anginal pain, and palpitations (Table 1). For the diagnosis of heart failure, the clinical criteria from the European Society of Cardiology are being used.7 The diagnosis heart failure is made confidently in the presence of multiple symptoms and signs, combined with objective evidence of cardiac dysfunction, usually through echocardiography (Table 1). Echocardiography is essential for both systolic and diastolic failure.6 In cases where the diagnosis is in doubt, the diagnosis can be stated by an additional positive response to treatment directed towards heart failure. The degree of cardiovascular disability is distinguished by The New York Heart Association Functional Classification (classes I–IV) or the classification of symptoms in mild, moderate and severe. Both represent the degree of functional impairment in these patients.


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Table 1 Criteria for diagnosing human heart failurea

 
From a clinical point of view, three broad categories of heart failure have been proposed (see Table 1). In this view, heart failure can originate from: (1) increased hemodynamic burden, by far the most common cause; (2) inherited mutations in genes encoding structural components which affect contraction and relaxation; and (3) precipitating causes initiating episodes of clinical heart failure.8 A general misconception states that ischaemic heart disease (e.g. acute myocardial infarction (MI) or coronary artery disease) is the most common underlying and precipitating cause of heart failure in prevalence. Instead, heart failure in Western societies most often results from progressive hypertensive heart disease (Fig. 1).1 Patients who survived MI have, however, a significant higher relative risk to develop subsequent heart failure than patients with any other cardiac disease.1–3,5



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Fig. 1 Percentages of risk factors for male and female patients for the development of subsequent heart failure. The pie-diagrams are representative for Dutch males and females with a mean age of 69 years. The percentages of risk factors are rather similarly distributed between sexes, the percentage MIs being the only significant difference between males and females. High blood pressure is the by far most common risk factor for developing heart failure. (With permission from Mosterd et al. Prevalence of heart failure and left ventricular dysfunction in the general population: the Rotterdam study. Eur Heart J 1999;20(6):447–55.)

 
Multiple studies have described the contribution of several characteristic changes that are encountered in the end-stage failing heart, which distinguishes it from the non-diseased state. Thebest-documented characteristics on the intracellular, stromal or organ level are: (1) a genetic re-programming, which resembles the genetic-expression profile of the foetal heart; differing degrees of cardiomyocyte hypertrophy and concomitant activation of intracellular signallingmolecules, mitochondrial dysfunction, alterations at the level of the sarcomeric and cytoskeletal architecture, aberrant intracellular calcium handling, unfavourable myofibrillar architecture; (2) increased vulnerability or presence of necrotic or programmed cell death, excess extracellularmatrix formation; (3) a reduction of organ capillarisation and presence of regional ischaemia, evidence of systemic and myocardial (neuro)humoral stimulation, vulnerability to (supra)ventricular dysrrhythmias and, most notably, hemodynamic dysfunction at the systolic and/or diastolic level. Although each of these characteristic alterations appear to form independent entities, presence of any of the previously mentioned characteristics is sufficient, at least in experimental models, to set in motion a sequence of events invariably resulting in organ failure, characterised by a phenotype encompassing some or even all of the abnormalities formerly discussed.

3. Hypertrophy

Current conceptualisation states that the heart is able to augment output in the face of increased hemodynamic demands by means of growth ofcardiomyocytes. In that view, cardiac hypertrophy can be defined as the increase in myocardial mass in an effort to alleviate the elevation in wall stress, according to LaPlace's principle (Fig. 2).9 To execute this response, the myocardium is equipped with a host of conserved neurohumoral and intracellular reactive cascade systems. Since the proliferative capacity of the cardiac myocyte is absent or at best limited, the heart reduces wall stress by myocyte growth (hypertrophy), during which the nucleus of human cardiomyocytes undergoes polyploidy.10,11 The diploid set (2c) of the myocyte proliferates during this growth process to tetraploid (4c), octoploid (8c) sets of chromosomes, or even more. The polyploidisation probably enables the cardiomyocyte to hypertrophy without losing its normal cell volume/DNA content ratio, but the functional significance of this adaptation stillremains obscure. The myocardial cell-types that do respond with proliferation (hyperplasia) in response to mitogenic stimuli, are non-muscle cells, most notably fibroblasts, and this event does not lead to the required reduction of wall stress.



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Fig. 2 Morphology of the left ventricle: differences between normal and hypertrophic hearts. The schematic presentation of concentric and eccentric hypertrophy clearly shows the morphologic features, which generally are detected during echocardiographic analysis. (A) Also depicted are the elements, which determine circumferential wall stress (CWS) in the left ventricle, the strongest force generated within the ventricular wall. P indicates intraventricular pressure, a and b are the major and minor semi-axes and h is left ventricular wall thickness. These assumptions are only correct in those situations where left ventricular function is relatively uniform. (B) Wall stess ({sigma}) increases at any LV radius when LV pressure (e.g. afterload) rises, for example in case of systemic hypertension or aortic stenosis. Hypertrophy is thought to balance the augmented pressure by increasing wall thickness. (C) In dilated cardiomyopathy, the enlarged ventricular diameter results in a greater wall stress.

 
Data derived from mouse studies, however, cast doubt on the idea that a reduction of wall stress is required for preserving hemodynamic functioning during the development of hypertrophy.12 In gene-targeted mice, where Gqthe signalling pathway is genetically blocked, with blunted hypertrophy after experimentally pressure-overload, maintenance of cardiac function was observed, despite an inadequate normalisation of left ventricular wall stress. The mice with blunted hypertrophy fared better than their wild-type littermates in response to long-term load, as shown by the absence of progressive LV dilatation and dysfunction on serial echocardiography.12 The observation underscores the importance of preventing or inhibiting hypertrophic growth in the human heart as ventricular hypertrophy has been proven to be a risk factor for cardiovascular mortality in humans.13 Not only leads hypertrophic growth of the heart in time to increased morbidity and mortality, also the early correction of wall stress seems unnecessary to maintain cardiac function on the long-term. Therefore, a commonly accepted hypothesis should probably be re-considered.

Defined extrinsic hypertrophic stimuli consist of conditions of increased resistance to left ventricular afterload, resulting from outflow obstructions, such as aortic stenosis and systemic hypertension. These conditions produce a state of pressure-overload. The morphological adaptation to pressure-overload consists of concentric hypertrophy, characterised by thickening of the myocardial walls without a significant LV lumen dilation (Fig. 2). Other defined extrinsic stimuli include volume-overload, which occurs in the clinical setting of aortic valve regurgitation, mitral valve regurgitation, anaemia or other situations in which cardiac output is increased at normotensive pressures. Volume-overload specifically leads to eccentric hypertrophy defined by thickening of the free walls in conjunction with LV cavity diameter increase.14 Ischaemia, MI and episodes of atrial fibrillation also act as extrinsic hypertrophic stimuli.

Intrinsic stimuli involve genetic abnormalities (mutations) in sarcomeric motor protein genes or in genes that encode components of the cytoskeletal architecture and metabolic (mitochondrial) disorders.5,15 Mutations in sarcomeric proteins are the basis of congenital human heart disease such as hypertrophic cardiomyopathy (HCM), with a prevalence of 1 in 500 patients.5,16 Characteristic myocardial changes in HCM include a non-dilated left ventricular chamber with thickened walls, reminiscent of a concentric hypertrophy.5 HCM is a Mendelian trait with an autosomal dominant pattern of inheritance.5 Currently, mutations have been found in the human genes coding for ß-myosin heavy chain, cardiac troponin T, I, {alpha}-tropomyosin, myosin-binding protein C, myosin light chain 1 and 2, cardiac {alpha}-actin genes, titin and mitochondrial DNA.5,17–19 Mutated cytoskeletal genes are not able to handle the mechanical workload that is required, causing mechanical dysfunction of myocytes, thus provoking a hypertrophic response.

During both pressure and volume-overload defined systemic and local neurohumoral changes take place. The best-characterised example is the renin–angiotensin–aldosteron system (RAAS). Rise of systemic and myocardial angiotensin II (Ang II), acting through the angotensin (AT)-1 and AT-2 receptors, promotes fibroblast proliferation and collagen production, which is usually extensive enough to produce macroscopically visible fibrosis that contribute to increased left ventricular stiffness and reduced compliance.20 Independent of the systemic influences on vascular resistance and cardiac afterload, Ang II is prominently involved in promoting cardiomyocyte hypertrophy.20–25 Endothelin-1 (ET-1) is another humoral factor with systemic and local actions sufficient to induce a hypertrophic response in cardiomyocytes.23 ET-1 has been proven to be a local contributor to pressure-overload or mechanical-stretch induced hypertrophy.20,26,27 Finally, sympathetic activation is thought to be the cause of ß-adrenergic desensitisation in heart failure, a consequence of down-regulation of ß1-receptors and uncoupling of the ß2-receptors.28 The down-regulation and desensitisation of ß-adrenergic receptors is more prominent in failing then in hypertrophied myocardium.29 This uncoupling is thought to be caused by increased activity of a ß-adrenergic receptor kinase (ßARK) and an increase in inhibitory G-protein alpha subunits (Gi{alpha}), which depress adenylyl cyclase activity.30 The attenuation in adenylyl cyclase activity is thought to be a causal link in the transition from cardiac hypertrophy to cardiac failure.29,31

ACE-inhibition is currently accepted as a valuable therapeutic approach in the management of heart failure.32 Specific AT-1 antagonists overcome the potential limitations of the use of ACE-inhibitors, such as insufficient suppression of tissue ANG II production and bradykinin-related sideeffects.33

Numerous animal studies and clinical trials have convincingly demonstrated that beta-blockade improves functional capacity, ventricular function and decreases mortality in patients with heart failure of various aetiologies. Amongst the effects of beta-blockers are the improvement in function of failing myocardium, decrease in dilation and hypertrophy, and reduction in LV wall stress. Recent evidence indicates that beta-blockers can also inhibit the RAAS and in this role, limit progressive chamber stiffening, thereby attenuating chamber remodelling and diastolic dysfunction in heartfailure.34

Controversy exists as to whether LV hypertrophy should be considered as a pathological condition that invariably evokes disease by transforming in failure, or as fundamentally different forms of cardiomyocyte growth. For example, a profound increase in myocardial mass is observed shortly after birth due to hemodynamic demands on the neonatal heart. Also, increased demands for cardiac work, e.g. during athletic exercise or during pregnancy, evoke a considerable hypertrophic response, which is not associated with risk for the development of decompensation and failure. In view of the recent experimental observations and the distinctive phenotypic observations in humans, we rather favour a distinction between compensatory versus maladaptive forms of hypertrophy (Table 2). Since the morphological and hemodynamic characteristics associated with beneficial hypertrophic growth are fundamentally different from those following hypertension or MI, it seems feasible to reason that fundamentally different molecular programs underlie beneficial and maladaptive hypertrophy. In our view, maladaptive hypertrophy is invariably associated with activation of a molecular program involving persistent activation of unfavourable intracellular signalling modules, an increased rate of cardiomyocyte apoptosis, profound extracellular matrix deposition leading to reduced diastolic compliance and aberrant intracellular Ca2+handling. In the following sections these aspects are further delineated.


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Table 2 Characteristics of cardiac hypertrophy in transition to failurea

 
4. Current molecular investigations

In recent years, much research has focussed on the identification of intracellular signalling cascades, which mediate extrinsic and intrinsic growth signals into co-ordinated alterations of genetic profiles. In addition to causing changes in gene-expression, hypertrophic stimuli increase the overall rate of RNA transcription and protein synthesis, both leading to hypertrophic growth of cardiomyocytes. In the transition from compensating to decompensating hypertrophy, several intracellular molecules have found to be up- or down-regulated and, therefore, thought to be mediators of this pathologic process. Preventing the development of maladaptive hypertrophy is the ultimate goal of research into these molecules.

Hypertrophy is initiated and maintained in vitro and in vivo by several factors, such as vasoactive peptides, peptide growth factors, hormones and neurotransmitters (i.e. ET-1, {alpha}1-adrenergic agonists, Ang II, fibroblast growth factors (FGF), insulin-like growth factor (IGF)-1 and cardiotrophin (CT)-1).24,35–43 Estrogens on the other hand are believed to have hypertrophy reducing effects44–48, which are probably mediated via increased atrial natriuretic factor (ANF)-expression.49 The hypertrophic factors stimulate intracellular signalling cascades, which initiate a hypertrophic, foetal-like gene-programme. In pathological conditions ANF is produced by ventricular cells as part of the newly expressed ventricular foetal gene-programme. Theeffect of ANF on blood pressure, and also the direct cellular effects could explain the beneficial aspects of ANF.49,50

Most of the agonists bind to G protein coupled receptors, from whichGq/Glland Gi/Goare involved in the hypertrophic response.51–53 Protein kinases (PKs) are located downstream from these receptors, from which protein kinase C (PKC) is strongly implicated in hypertrophic signalling.35,54 The small GTP-binding proteins (Ras and Rho families) play important roles in the hypertrophic response through mediating the activation of the mitogen-activated protein kinase (MAPK) superfamily cascades following PKC activation.55,56 MAPKs are a widely distributed group of enzymes ending in three terminal MAPK branches (p38–MAPKs, the extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminalkinases (JNKs). Fig. 3). The family of MAPKs has been shown to play causal roles in the development of cardiac hypertrophy and the transition towards heart failure.54,57–59 Differential activation of single terminal branches of the MAPK families results in specific cardiac morphologic and functional phenotypes.57,60 For example, ERK1/2 MAPK activation leads to a concentric form of hypertrophy with enhanced cardiac function.57 In contrast, single activation of ERK5 MAPK leads to eccentric cardiac hypertrophy and rapid transition towards heart failure.60 Furthermore, p38–MAPK and JNK activation lead to maladaptive hypertrophy.61–65 Similar to ERK1/2 over-expression, another example of beneficial hypertrophic phenotypic alterations is observed upon activation of the phosphoinositide 3-kinase (PI3K), which lies downstream of many receptor tyrosine kinases. Furthermore, recent studies have indicated that pathways employing the gp130 receptor might be of benefit to the heart. Well-known intracellular mediators of gp130 signalling include the family of Janus kinase (JAK), which activate the family of the signal transducer and activator of transcription (STAT) proteins. The JAK/STAT pathway, which is activated by CT-1, leukaemia inhibitory factor (LIF) and Angiotensin II, is implicated in the hypertrophic response, but its role is still obscure.66–68



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Fig. 3 Simple presentation of the three kinase modules and MAPK subfamilies. The MAPK pathways consist of three separate terminal branches: the ERK, JNKs and the p38 MAPK pathways. These translocate to the nucleus after activation and set gene transcription. The MAPKs are activated by MAPK kinases (MAPKKs) upon extracellular stimulation. The MAPKK differ per kinase module. MEK1 and MEK2 MAPKKs activate ERK MAPKs; MKK7 and MKK4 activate JNK and MMK3/MKK6 are upstream of p38 MAPKs.

 
Because of these findings, it has been hypothesised that specific intracellular protein activation programmes lead to specific cardiac phenotypes. Similar results are presented in human studies.65 For example, involving the MAPK-family, the activation of JNK and p38–MAPKs are augmented in failing human hearts, while ERK activation remains on a physiologic level. This finding indicates an association between p38–MAPK, JNKs and a failing cardiac phenotype in human. Further understanding of the mechanisms, through which differential activation of MAPKs may lead to distinctive cardiac phenotypes, is essential for future clinical therapy.

5. Intracellular calcium handling

Intracellular Ca2+concentrations and handling are also involved in the hypertrophic response. The Ca2+/calmodulin-dependent PK II and the Ca2+/calmodulin-dependent protein phosphatase (calcineurin), in which the activity is Ca2+-dependent, are involved in the cardiac hypertrophic response.69–74 Activated calcineurin promotes the dephosphorylation of the transcription factor NF-AT3, which subsequently migrates into the nucleus and interacts with the transcription factor GATA4 to induce hypertrophic gene-programme expression.

In pressure-overload ventricular hypertrophy, after the early-response phase, reductions in the expression of sarcoplasmatic reticulum Ca2+ATPase (SERCA) mRNA and protein were shown (Fig. 4).75–81 This seems in contradiction with the situation in the early-response phase. During the catecholamine mediated early-response phase, the up-regulation of SERCA is needed to maintain cardiac output. The assumption is that when increased amounts of sarcomeric proteins start to stabilise cardiac function, SERCA is down-regulated. Within 72–96h, the SERCA-levels already return to baseline and they will decline even further in the progress of the hypertrophic process.82 The consequence is a down-regulated sarcoplasmic reticulum calcium uptake in the hypertrophic cardiomyocyte, resulting in a smaller amplitude and slower decline of the cellular [Ca2+]itransient.75–81 In dilated and failing human hearts, no differences in protein levels of SERCA, phospholamban and calsequestrin have been detected compared to the non-failing controls.83–87 Although no reduction in protein levels was detected, there were alterations found in the calcium handling, i.e. an attenuation in the sensitivity of SERCA develops.87 A possible explanation for the alterations in calcium handling is provided by the phospholamban–sarcoplasmic reticulum calcium pump interaction.59,88–92 The protein phospholamban is the inhibitor of SERCA in the reticular membrane.93–99 SERCA functions at the end of contraction of the heart. It pumps calcium out of the cytosol into the sarcoplasmic reticulum. During contraction, phospholamban is bound to SERCA, thereby decreasing the SERCA affinity for Ca2+.93 In this manner, phospholamban inhibits the function of SERCA. It is also possible to improve cardiac function by inhibiting phospholamban interaction with SERCA.98 An alternative mechanism was proposed by Esposito et al.,59 stating that the calcium homeostasis in the myocytes of diseased murine hearts is altered, leading to decreased intracellular [Ca2+] transients and contractile responses caused by a dysfunctional excitation–contraction coupling, identified as a decreased sensitivity of the SR Ca2+releasing mechanism to trigger Ca2+. The question remains as to which molecular process is essential in the transition from hypertrophy to failure. Nevertheless, the importance of the intracellular calcium milieu has been proven unequivocally.



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Fig. 4 The ß-adrenergic pathway leading to SR Ca2+uptake. Following ß-adrenergic stimulation of the adrenergic G-protein, coupled receptors, the Gs{alpha}- and Gsß{gamma}-subunits, detach from each other. The Gs{alpha}-subunit stimulates the membrane bound adenylcyclase to form cyclic AMP (cAMP) from ATP. The cAMP stimulates protein kinase A (PKA) to dephosphorylate the phospholamban protein (PLB) attached to the SERCA. Upon dephosphorylation, PLB looses its ability to bind SERCA. SERCA, without the PLB-binding, increases actively the sarcoplasmic reticulum Ca2+-uptake, which directly increases relaxation and indirectly increases contractility.

 
6. Apoptosis

The programmed cell death process (apoptosis) can be divided into several biochemical and morphological distinct phases.100 In the initiation phase, pro-apoptotic stimuli trigger the onset of molecular changes leading to apoptosis. The apoptotic process is working on its full capacity during the effector phase, in which nucleic acid degradation takes place. In the degradation phase, the hallmarks of apoptosis, such as membrane markers and morphologic changes, become evident. However, the point of no return occurs several hours before the appearance of the morphologic features.101 Some morphologic features are the shrinkage of the cell at the onset of apoptosis accompanied by nuclear chromatin condensation. The nucleus eventually breaks up, a process called karyorrhexis. The apoptotic cell detaches from neighbouring cells and surrounding extracellular matrix and forms extensions on its membrane. The extensions detach from the apoptotic cell (i.e. budding) and form apoptotic bodies. The bodies are rapidly phagocytosed by all sorts of neighbouring cells without associated inflammation, which could be the consequence of releasing intracellular contents in cardiac tissue.

The chronic exposure to catecholamines can exert a toxic effect on the myocardium by increasing the number of apoptotic myocytes mediated bythe beta1-adrenergic receptor. Furthermore, angiotensin II type 1 receptor pathways, nitric oxide and natriuretic peptides are involved in the induction of apoptosis in these cells, while alpha1- and beta2-adrenergic receptors, ET-1 receptor-type A pathways and gp130-activating cytokines are anti-apoptotic. The myocardial protection of the latter is mediated, at least in part, through MAPK-dependent pathways (especially ERK MAPK), consistent with the findings in other cell-types.57,102103 In contrast, in some cases, signalling pathways leading to apoptosis in cardiac myocytes are distinct from those in other cell-types. The cAMP/PKA pathway induces apoptosis in cardiac myocytes and blocks apoptosis in other cell-types. The p300 protein, a co-activator of p53, mediates apoptosis in fibroblasts, but appears to play a protective role in differentiated cardiac myocytes.104

Initiation of apoptosis is associated with activation of different cascades, including the release of cytochrome c and the apoptosis inducing factor (AIF) from mitochondria into the cytoplasm and the processing of proteolytic caspases.105–108 The activation of the caspases leads to fragmentation of various proteins, including cytoplasmic structural proteins, contractile proteins, proteins at the cell-to-cell and cell-to-matrix attachment sites and nuclear envelope proteins. At this time-point, apoptotic cells can be visualised by labelled Annexin-V in vivo.109,110 AIF, in contrast, translocates to the nucleus and initiates the fragmentation of nuclear DNA. This process results in the cleavage of chromatin into oligonucleosome-length DNA fragments, which is supported by endogenous DNA caspases, Dnases-like DNA fragmentation factor (DFF40) and caspase activated DNase (CAD). Caspases are cysteine proteases that cleave their substrate proteins specifically behind an aspartate residue.111 They are formed constitutively in the non-apoptotic cell and remain inactive by dimerisation with inhibitory proteins, DFF45 and inhibitor of CAD, until stimulation by one of two major pathways. The first pathway is initiated by ligation of the death receptors, Fas and TNF receptors.112 The other pathway is the mitochondrial pathway that integrates apoptotic signals. This pathway is regulated by the Bcl-2 protein family.113,114 When the mitochondrial pathway is activated, permeability transition associated pores in the outer membrane of the mitochondria are opened, and this enables cytochrome c and AIF to be released from the mitochondrial transmembrane space.115,116 In its turn, cytochrome c activates apoptosis protease-activating factor (Apaf-1) and dATP, which lead to caspase activation. DNases cut the internucleosomal regions into double-stranded DNA fragments of 180–200 base pairs (bp).100,117,118 This DNA fragmentation can be demonstrated by a characteristic laddering pattern on DNA agarose gel electrophoresis (DNA laddering) and terminal deoxynucleotidyltransferase-mediated dUTP nick end-labelling (TUNEL) assay. Formation of large size (50–300kbp) DNA fragments precedes internucleosomal fragmentation, which is dependent on AIF activity (Fig. 5).106–108



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Fig. 5 Apoptosis pathways in cardiomyocytes. Several pathways leading to apoptosis have been identified in cardiomyocytes. Cell shrinkage, membrane blebbing and DNA degradation are detected upon stimulation by death receptors, for instance Fas-receptors, or mitochondrial proteins, such as cytochrome-c and AIF. Fas-receptor activation leading to caspase 8 activation, which induces the activation of procaspase-3 to caspase-3, the critical caspase. Caspase can also be activated by cytochrome-c. Cytochrome c is normally present in the outer layer of the mitochondrial membranes in an inactive state. Upon stimulation, it travels through protein-pores into the sarcoplasm and simultaneously gets activated. In the sarcoplasm, cytochrome-c induces the activation of caspase-3, while AIF directly translocates to the nucleus and degrades the present DNA.

 
Apoptosis plays a role in the pathophysiology of several cardiac diseases, such as maladaptive hypertrophy and heart failure.105,119,120 Apoptosis is found to be increased in the remote myocardium after MI in animals and humans. Also, significantly more apoptotic cells are found in end-stage cardiomyopathy compared to control hearts. It has been proposed that ventricular dilatation and neurohumoral activation during heart failure lead to up-regulation of transcription factors and prepare the cell for re-entry into the cell cycle, which fails and induces apoptosis.105 The functional relevance of apoptosis though, is still obscure.

The question remains as to whether the frequency of apoptosis found in failing hearts issufficient to explain a deterioration of cardiac function. Also, whether apoptosis precedes the transition towards heart failure or only accompanies this process. Interpretation of the rate of apoptosis in diseased hearts is hampered by the fact that the time course of the apoptotic cascade in adult cardiomyocytes is unknown.121 Results from animal studies indicate tight regulation of the different steps of the apoptotic cascade, which are time-dependent.121 Furthermore, apoptosis seems to be a general muscular phenomenon.122 Myocyte apoptosis occurs also in the skeletal muscle of patients with chronic heart failure, and its magnitude is associated with the severity of exercise capacity limitation and the degree of muscle atrophy. Muscle atrophy contributes to the limitation of exercise capacity, together with the increased synthesis of fast, more fatigable myosin heavy chains.122

If apoptosis accompanies heart failure and could lead to deterioration of cardiac function, beneficial effects could be expected from blockade of the process. Although studies in rats revealed a reduction of apoptosis after caspase blockade, the rate of necrosis subsequently increased.121 This suggests that the cells are destined to die once the caspases are activated, for example by mitochondrial damage. Blockade of apoptosis would, therefore, not be beneficial, because necrosis is accompanied with secondary morbidity, i.e. inflammation and extensive fibrosis.

Myocyte replacement could explain the discrepancy between extensive collagen accumulation and the modest reduction in the number of ventricular myocytes and the occasional detection of nuclear mitotic divisions in the pathologic heart. These findings led to the suggestion that myocytes are not terminally differentiated and cell proliferation may be stimulated in cardiomyopathies. Recent data indicated an increase in myocytes in the diseased and decompensated human heart by myocyte division.123,124 Although these results appear very convincing, many cardiovascular researchers remain sceptic towards the rate and, therefore, the importance of cardiomyocyte division.

7. Fibrosis

Extracellular fibrillar collagen functions as scaffolding tissue to maintain cardiac structure and stiffness. An adverse accumulation of extracellular matrix structural protein compromises tissuestiffness and adversely affects myocardial viscoelasticity.125 Accumulation of fibrillar collagen leads to diastolic and systolic ventricular dysfunction. The increased amounts of myocardial fibrillar collagen in the setting of hypertrophy and heart failure are accompanied by elevated levels of circulating Ang II and aldosteron.125 There is sufficient evidence for a major role of the RAAS-system with autocrine and paracrine actions in the process mentioned. Augmented systemic and tissue angiotensin formation are observed in hypertrophy and heart failure, as already stated. These augmented hormone levels influence the progressive nature of heart failure. Normal cardiac tissue contains mineralocorticoid receptors (MR) and high affinity MR are localised on cardiomyocytes.126 High levels of aldosterone promote accumulation of interstitial collagen in the heart. This process is dependent on the salt status.126 Aldosterone promotes the re-absorption of sodium in the distal tubule of the nephrons, mostly in exchange for potassium and hydrogen excretion. The secretion of aldosterone in response to Ang IIis negatively controlled by salt-losing hormones as atrial natriuretic peptide and dopamine. Also, the adrenal response is enhanced following poor dietary sodium and potassium intake. The involvement of up-regulated AT-1 receptors for Ang II, which are targets for aldosterone, has been proposed.126,127 Ang II induces cardiac fibroblast proliferation, synthesis and secretion of adhesion molecules and extracellular matrix proteins, and expression of integrin adhesionreceptors.127,128 Ang II stimulates cardiac fibroblasts also to adhere more vigorously to defined matrixes.128 The ability of Ang II to induce collagen synthesis may be mediated by increased TGF-ß1 production, from which the expression is markedly increased in infarcted hearts and has shown to induce myocardial fibrosis.127,129 Either type I or type II Ang II receptor antagonists, or the competitive aldosterone antagonist spironolactone completely abolish the increased collagen deposition.130

The increased cardiac fibrosis in heart failure is not related to the augmented rates of apoptotic cell death, because dying myocytes are removed from the neighbouring cells in the absence of an inflammatory reaction and responsive fibrosis.131

The maladaptive fibrosis could be the target of pharmacologic intervention. Such cardioprotective strategies could be based on inhibiting the generation of these hormones or interfering with their receptor-ligand binding.125

Arrhythmias are common in heart failure and related to extensive cardiac fibrosis. In one half of heart failure patients, tachyarrhythmias lead to sudden death.132 Re-entrance mechanisms around scar tissue, after-depolarisations and the triggered activity due to changes in calcium metabolismsignificantly contribute to the aetiology ofarrhythmias.132

8. Conclusions

Causal factors for the transition from hypertrophy to heart failure detected in animal and human studies are: (1) the changes in cellular signalling molecules; (2) the increased degree of myocyte apoptosis; (3) the accelerated deposition of collagen; and (4) arrhythmogenicity, and the alterations in intracellular calcium handling and excitation contraction coupling are all contributing to this transition. However, the relative importance of the processes remains to be resolved. Certain is their relevance for the transition from hypertrophy to failure, and they explain largely the distinction between beneficial and maladaptive hypertrophy. Contributors to maladaptive hypertrophy lead to heart failure and eventually death. Our future challenge will be to allow compensatory hypertrophy and block maladaptive processes in the human heart.

References

  1. Mosterd A, Hoes AW, de Bruyne MC et al. Prevalence of heart failure and left ventricular dysfunction in the general population; The Rotterdam Study. Eur Heart J. 1999;20:447–455.[Abstract/Free Full Text]
  2. Murray CJ, Lopez AD. Global mortality, disability, and the contribution of risk factors: global burden of disease study. [see comments]Lancet. 1997;349:1436–1442.[CrossRef][Medline]
  3. Murray CJ, Lopez AD. Mortality by cause for eight regions of the world: global burden of disease study. [see comments]Lancet. 1997;349:1269–1276.[CrossRef][Medline]
  4. Dargie HJ, McMurray JJ, McDonagh TA. Heart failure—implications of the true size of the problem. J Intern Med. 1996;239:309–315.[CrossRef][Medline]
  5. Maron BJ. Hypertrophic cardiomyopathy. [published erratum appears in Lancet 1997 Nov 1;350(9087):1330]Lancet. 1997;350:127–133.[CrossRef][Medline]
  6. Van Kraaij D, Van Pol P, Ruiters AW et al. Diagnosing diastolic heart failure. Eur J Heart Fail. 2002;4:419–430.[CrossRef][Medline]
  7. Remme WJ, Swedberg K. Guidelines for the diagnosis and treatment of chronic heart failure. Eur Heart J. 2001;22:1527–1560.[Free Full Text]
  8. Braunwald E. Heart disease: a textbook of cardiovascular medicine. 5th ed. Philadelphia: WB Saunders; 1997. .
  9. James MA, Saadeh AM, Jones JV. Wall stress and hypertension. [in process citation]J Cardiovasc Risk. 2000;7:187–190.[Medline]
  10. Rockman HA, Ross RS, Harris AN et al. Segregation of atrial-specific and inducible expression of an atrial natriuretic factor transgene in an in vivo murine model of cardiac hypertrophy. [published erratum appears in Proc Natl Acad Sci U S A 1991 Nov 1;88(21):9907]Proc Natl Acad Sci U S A. 1991;88:8277–8281.[Abstract]
  11. Van der laarse ARC, Van Wamel JET, Van Gilst WH et al. Molecular aspects of cardiac hypertrophy and heart failure. Cardiologie. 1998;:.
  12. Esposito G, Rapacciuolo A, Prasad SV et al. Genetic alterations that inhibit in vivo pressure-overload hypertrophy prevent cardiac dysfunction despite increased wall stress. Circulation. 2002;105:85–92.[Abstract/Free Full Text]
  13. Matthew J, Sleight P, Lonn E et al. Reduction of cardiovascular risk by regression of electrocardiographic markers of left ventricular hypertrophy by the angiotensin-converting enzyme inhibitor ramipril. Circulation. 2001;104:1615–1621.[Abstract/Free Full Text]
  14. Lorell BH, Carabello BA. Left ventricular hypertrophy: pathogenesis, detection, and prognosis. Circulation. 2000;102:470–479.[Free Full Text]
  15. Obayashi T, Hattori K, Sugiyama S et al. Point mutations in mitochondrial DNA in patients with hypertrophic cardiomyopathy. Am Heart J. 1992;124:1263–1269.[Medline]
  16. Maron BJ, Gardin JM, Flack JM et al. Prevalence of hypertrophic cardiomyopathy in a general population of young adults. Echocardiographic analysis of 4111 subjects in the CARDIA study. Coronary artery risk development in (young) adults. [see comments]Circulation. 1995;92:785–789.[Abstract/Free Full Text]
  17. Olson TM, Michels VV, Thibodeau SN et al. Actin mutations in dilated cardiomyopathy, a heritable form of heart failure. Science. 1998;280:750–752.[Abstract/Free Full Text]
  18. Satoh M, Takahashi M, Sakamoto T et al. Structural analysis of the titin gene in hypertrophic cardiomyopathy: identification of a novel disease gene. Biochem Biophys Res Commun. 1999;262:411–417.[CrossRef][Medline]
  19. Watkins H, Seidman JG, Seidman CE. Familial hypertrophic cardiomyopathy: a genetic model of cardiac hypertrophy. Hum Mol Genet. 1995;4:1721–1727.[Abstract]
  20. Yamazaki T, Komuro I, Yazaki Y. Role of the renin–angiotensin system in cardiac hypertrophy. Am J Cardiol. 1999;83:53H–57H.[CrossRef][Medline]
  21. Baker KM, Chernin MI, Wixson SK et al. Renin–angiotensin system involvement in pressure-overload cardiac hypertrophy in rats. Am J Physiol. 1990;259:H324–H332.[Medline]
  22. Kijima K, Matsubara H, Murasawa S et al. Mechanical stretch induces enhanced of angiotensin II receptor subtypes in neonatal rat cardiac myocytes. Circ Res. 1996;79:887–897.[Abstract/Free Full Text]
  23. Mascareno E, Dhar M, Siddiqui MA. Signal transduction and activator of transcription (STAT) protein-dependent activation of angiotensinogen promoter: a cellular signal for hypertrophy in cardiac muscle. Proc Natl Acad Sci U S A. 1998;95:5590–5594.[Abstract/Free Full Text]
  24. Sadoshima J, Izumo S. Molecular characterization of angiotensin II-induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. Critical role of the AT1 receptor subtype. Circ Res. 1993;73:413–423.[Abstract]
  25. Sadoshima J, Xu Y, Slayter HS et al. Autocrine release of angiotensin II mediates stretch-induced hypertrophy of cardiac myocytes in vitro. Cell. 1993;75:977–984.[Medline]
  26. Arai M, Yoguchi A, Iso T et al. Endothelin-1 and its binding sites are upregulated in pressure overload cardiac hypertrophy. Am J Physiol. 1995;268:H2084–H2091.[Medline]
  27. Ito H, Hiroe M, Hirata Y et al. Endothelin ETA receptor antagonist blocks cardiac hypertrophy provoked by hemodynamic overload. Circulation. 1994;89:2198–2203.[Abstract]
  28. Murphree SS, Saffitz JE. Distribution of beta-adrenergic receptors in failing human myocardium. Implications for mechanisms of down-regulation. Circulation. 1989;79:1214–1225.[Abstract]
  29. Tse J, Huang MW, Leone RJ et al. Down regulation of myocardial beta1-adrenoceptor signal transduction system in pacing-induced failure in dogs with aortic stenosis-induced left ventricular hypertrophy. Mol Cell Biochem. 2000;205:67–73.[CrossRef][Medline]
  30. Rockman HA, Choi DJ, Akhter SA et al. Control of myocardial contractile function by the level of beta-adrenergic receptor kinase 1 in gene-targeted mice. J Biol Chem. 1998;273:18180–18184.[Abstract/Free Full Text]
  31. Bohm M, Flesch M, Schnabel P. Beta-adrenergic signal transduction in the failing and hypertrophied myocardium. J Mol Med. 1997;75:842–848.[CrossRef][Medline]
  32. Rush JE, Rajfer SI. Theoretical basis for the use of angiotensin II antagonists in the treatment of heart failure. J Hypertens Suppl. 1993;11:S69–S71.[Medline]
  33. Regitz-Zagrosek V, Neuss M, Fleck E. Effects of angiotensin receptor antagonists in heart failure: clinical and experimental aspects. Eur Heart J. 1995;16 Suppl N:86–91.[Medline]
  34. Senzaki H, Paolocci N, Gluzband YA et al. Beta-blockade prevents sustained metalloproteinase activation and diastolic stiffening induced by angiotensin II combined with evolving cardiac dysfunction. Circ Res. 2000;86:807–815.[Abstract/Free Full Text]
  35. Bogoyevitch MA, Glennon PE, Andersson MB et al. Endothelin-1 and fibroblast growth factors stimulate the mitogen-activated protein kinase signaling cascade in cardiac myocytes. The potential role of the cascade in the integration of two signaling pathways leading to myocyte hypertrophy. J Biol Chem. 1994;269:1110–1119.[Abstract/Free Full Text]
  36. Kaddoura S, Firth JD, Boheler KR et al. Endothelin-1 is involved in norepinephrine-induced ventricular hypertrophy in vivo. Acute effects of bosentan, an orally active, mixed endothelin ETA and ETB receptor antagonist. Circulation. 1996;93:2068–2079.[Abstract/Free Full Text]
  37. Pennica D, King KL, Shaw KJ et al. Expression cloning of cardiotrophin 1, a cytokine that induces cardiac myocyte hypertrophy. Proc Natl Acad Sci U S A. 1995;92:1142–1146.[Abstract]
  38. Parker TG, Chow KL, Schwartz RJ et al. Positive and negative control of the skeletal alpha-actin promoter in cardiac muscle. A proximal serum response element is sufficient for induction by basic fibroblast growth factor (FGF) but not for inhibition by acidic FGF. J Biol Chem. 1992;267:3343–3350.[Abstract/Free Full Text]
  39. Parker TG, Packer SE, Schneider MD. Peptide growth factors can provoke ‘fetal’ contractile protein gene expression in rat cardiac myocytes. J Clin Invest. 1990;85:507–514.[Medline]
  40. Ito H, Hiroe M, Hirata Y et al. Insulin-like growth factor-I induces hypertrophy with enhanced expression of muscle specific genes in cultured rat cardiomyocytes. Circulation. 1993;87:1715–1721.[Abstract]
  41. Ito H, Hirata Y, Adachi S et al. Endothelin-1 is an autocrine/paracrine factor in the mechanism of angiotensin II-induced hypertrophy in cultured rat cardiomyocytes. J Clin Invest. 1993;92:398–403.[Medline]
  42. Kim NN, Villarreal FJ, Printz MP et al. Trophic effects of angiotensin II on neonatal rat cardiac myocytes aremediated by cardiac fibroblasts. Am J Physiol. 1995;269:E426–E437.[Medline]
  43. Lavandero S, Foncea R, Perez V et al. Effect of inhibitors of signal transduction on IGF-1-induced protein synthesis associated with hypertrophy in cultured neonatal rat ventricular myocytes. FEBS Lett. 1998;422:193–196.[CrossRef][Medline]
  44. Van Eickels M, Grohe C, Cleutjens JPM et al. 17Beta-estradiol attenuates the development of pressure-overload hypertrophy. Circulation. 2001;104:1419–1423.[Abstract/Free Full Text]
  45. Hayward CS, Webb CM, Collins P. Effect of sex hormones on cardiac mass. Lancet. 2001;357:1354–1356.[CrossRef][Medline]
  46. Nuedling S, Kahlert S, Loebbert K et al. Differential effects of 17beta-estradiol on mitogen-activated protein kinase pathways in rat cardiomyocytes. FEBS Lett. 1999;454:271–276.[CrossRef][Medline]
  47. Grohe C, Kahlert S, Lobbert K et al. Expression of oestrogen receptor alpha and beta in rat heart: role of local oestrogen synthesis. J Endocrinol. 1998;156:R1–R7.[Abstract]
  48. Grohe C, Kahlert S, Lobbert K et al. Cardiac myocytes and fibroblasts contain functional estrogen receptors. FEBS Lett. 1997;416:107–112.[CrossRef][Medline]
  49. Babiker FA, De Windt LJ, Bronsaer RJP et al. Estrogen antagonizes cardiomyocyte hypertrophy by autocrine/paracrine stimulation of a guanyly cyclase-A receptor-cGMP-dependent protein kinase pathway. Circulation2001;104:77..
  50. Lin KF, Chao J, Chao L. Atrial natriuretic peptide gene delivery attenuates hypertension, cardiac hypertrophy, and renal injury in salt-sensitive rats. Hum Gene Ther. 1998;9:1429–1438.[Medline]
  51. Hilal-Dandan R, Ramirez MT, Villegas S et al. Endothelin ETA receptor regulates signaling and ANF gene expression via multiple G protein-linked pathways. Am J Physiol. 1997;272:H130–H137.[Medline]
  52. Milano CA, Dolber PC, Rockman HA et al. Myocardial expression of a constitutively active alpha 1B-adrenergic receptor in transgenic mice induces cardiac hypertrophy. Proc Natl Acad Sci U S A. 1994;91:10109–10113.[Abstract/Free Full Text]
  53. D'Angelo DD, Sakata Y, Lorenz JN et al. Transgenic Galphaq overexpression induces cardiac contractile failure in mice. Proc Natl Acad Sci U S A. 1997;94:8121–8126.[Abstract/Free Full Text]
  54. Clerk A, Bogoyevitch MA, Anderson MB et al. Differential activation of protein kinase C isoforms by endothelin-1 and phenylephrine and subsequent stimulation of p42 and p44 mitogen-activated protein kinases in ventricular myocytes cultured from neonatal rat hearts. J Biol Chem. 1994;269:32848–32857.[Abstract/Free Full Text]
  55. Denhardt DT. Signal-transducing protein phosphorylation cascades mediated by Ras/Rho proteins in the mammalian cell: the potential for multiplex signalling. Biochem J. 1996;318:729–747.[Medline]
  56. Thorburn J, Xu S, Thorburn A. MAP kinase- and Rho-dependent signals interact to regulate gene expression but not actin morphology in cardiac muscle cells. Embo J. 1997;16:1888–1900.[Abstract/Free Full Text]
  57. Bueno OF, De Windt LJ, Tymitz KM et al. The MEK1–ERK1/2 signaling pathway promotes compensated cardiac hypertrophy in transgenic mice. Embo J. 2000;19:6341–6350.[Abstract/Free Full Text]
  58. Bueno OF, De Windt LJ, Lim HW et al. The dual-specificity phosphatase MKP-1 limits the cardiac hypertrophic response in vitro and in vivo. Circ Res. 2001;88:88–96.[Abstract/Free Full Text]
  59. Esposito G, Santana LF, Dilly K et al. Cellular and functional defects in a mouse model of heart failure. [in process citation]Am J Physiol Heart Circ Physiol. 2000;279:H3101–H3112.[Abstract/Free Full Text]
  60. Nicol RL, Frey N, Pearson G et al. Activated MEK5 induces serial assembly of sarcomeres and eccentric cardiac hypertrophy. Embo J. 2001;20:2757–2767.[Abstract/Free Full Text]
  61. Zhang D, Gaussin V, Taffet GE et al. TAK1 is activated in the myocardium after pressure overload and is sufficient to provoke heart failure in transgenic mice. Nat Med. 2000;6:556–563.[CrossRef][Medline]
  62. Ng DC, Long CS, Bogoyevitch MA. A role for the ERK and p38 MAPKs in Interleukin-1beta-stimulated delayed STAT3 activation, ANF expression and cardiac myocyte morphology. J Biol Chem. 2001;29:29.
  63. Hayashida W, Kihara Y, Yasaka A et al. Stage-specific differential activation of mitogen-activated protein kinases in hypertrophied and failing rat hearts. J Mol Cell Cardiol. 2001;33:733–744.[CrossRef][Medline]
  64. Fischer TA, Ludwig S, Flory E et al. Activation of cardiac c-Jun NH(2)-terminal kinases and p38-mitogen-activated protein kinases with abrupt changes in hemodynamic load. Hypertension. 2001;37:1222–1228.[Abstract/Free Full Text]
  65. Cook SA, Sugden PH, Clerk A. Activation of c-Jun N-terminal kinases and p38-mitogen-activated protein kinases in human heart failure secondary to ischaemic heart disease. J Mol Cell Cardiol. 1999;31:1429–1434.[CrossRef][Medline]
  66. Sheng Z, Knowlton K, Chen J et al. Cardiotrophin 1 (CT-1) inhibition of cardiac myocyte apoptosis via a mitogen-activated protein kinase-dependent pathway. Divergence from downstream CT-1 signals for myocardial cell hypertrophy. J Biol Chem. 1997;272:5783–5791.[Abstract/Free Full Text]
  67. Kodama H, Fukuda K, Pan J et al. Biphasic activation of the JAK/STAT pathway by angiotensin II in rat cardiomyocytes. Circ Res. 1998;82:244–250.[Abstract/Free Full Text]
  68. Pan J, Fukuda K, Kodama H et al. Role of angiotensin II in activation of the JAK/STAT pathway induced by acute pressure overload in the rat heart. Circ Res. 1997;81:611–617.[Abstract/Free Full Text]
  69. De Windt LJ, Lim HW, Haq S et al. Calcineurin promotes protein kinase C and c-Jun NH2-terminal kinase activation in the heart. Cross-talk between cardiac hypertrophic signaling pathways. J Biol Chem. 2000;275:13571–13579.[Abstract/Free Full Text]
  70. De Windt LJ, Lim HW, Taigen T et al. Calcineurin-mediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: an apoptosis-independent model of dilated heart failure. Circ Res. 2000;86:255–263.[Abstract/Free Full Text]
  71. Lim HW, De Windt LJ, Steinberg L et al. Calcineurin expression, activation, and function in cardiac pressure-overload hypertrophy. Circulation. 2000;101:2431–2437.[Abstract/Free Full Text]
  72. Lim HW, De Windt LJ, Mante J et al. Reversal of cardiac hypertrophy in transgenic disease models by calcineurin inhibition. J Mol Cell Cardiol. 2000;32:697–709.[CrossRef][Medline]
  73. Ramirez MT, Zhao XL, Schulman H et al. The nuclear deltaB isoform of Ca2+/calmodulin-dependent protein kinase II regulates atrial natriuretic factor gene expression in ventricular myocytes. J Biol Chem. 1997;272:31203–31208.[Abstract/Free Full Text]
  74. Taigen T, De Windt LJ, Lim HW et al. Targeted inhibition of calcineurin prevents agonist-induced cardiomyocyte hypertrophy. Proc Natl Acad Sci U S A. 2000;97:1196–1201.[Abstract/Free Full Text]
  75. Maier LS, Brandes R, Pieske B et al. Effects of left ventricular hypertrophy on force and Ca2+handling in isolated rat myocardium. Am J Physiol. 1998;274:H1361–H1370.[Medline]
  76. Moore RL, Yelamarty RV, Misawa H et al. Altered Ca2+dynamics in single cardiac myocytes from renovascular hypertensive rats. Am J Physiol. 1991;260:C327–C337.[Medline]
  77. Qi M, Shannon TR, Euler DE et al. Downregulation of sarcoplasmic reticulum Ca(2+)-ATPase during progression of left ventricular hypertrophy. Am J Physiol. 1997;272:H2416–H2424.[Medline]
  78. Kiss E, Ball NA, Kranias EG et al. Differential changes in cardiac phospholamban and sarcoplasmic reticular Ca(2+)-ATPase protein levels. Effects on Ca2+ transport and mechanics in compensated pressure-overload hypertrophy and congestive heart failure. Circ Res. 1995;77:759–764.[Abstract/Free Full Text]
  79. de la Bastie D, Levitsky D, Rappaport L et al. Function of the sarcoplasmic reticulum and expression of its Ca2(+)-ATPase gene in pressure overload-induced cardiac hypertrophy in the rat. Circ Res. 1990;66:554–564.[Abstract]
  80. Bailey BA, Houser SR. Sarcoplasmic reticulum-related changes in cytosolic calcium in pressure overload-induced feline LV hypertrophy. Am J Physiol. 1993;265:H2009–H2016.[Medline]
  81. Arai M, Matsui H, Periasamy M. Sarcoplasmic reticulum gene expression in cardiac hypertrophy and heart failure. Circ Res. 1994;74:555–564.[Medline]
  82. Nediani C, Formigli L, Perna AM et al. Early changes induced in the left ventricle by pressure overload. An experimental study on swine heart. J Mol Cell Cardiol. 2000;32:131–142.[CrossRef][Medline]
  83. Movsesian MA, Schwinger RH. Calcium sequestration by the sarcoplasmic reticulum in heart failure. [see comments]Cardiovasc Res. 1998;37:352–359.[CrossRef][Medline]
  84. Munch G, Bolck B, Hoischen S et al. Unchanged protein expression of sarcoplasmic reticulum Ca2+-ATPase, phospholamban, and calsequestrin in terminally failing human myocardium. J Mol Med. 1998;76:434–441.[CrossRef][Medline]
  85. Schwinger RH, Bohm M, Schmidt U et al. Unchanged protein levels of SERCA II and phospholamban but reduced Ca2+ uptake and Ca(2+)-ATPase activity of cardiac sarcoplasmic reticulum from dilated cardiomyopathy patients compared with patients with nonfailing hearts. Circulation. 1995;92:3220–3228.[Abstract/Free Full Text]
  86. Schwinger RH, Bolck B, Munch G et al. cAMP-dependent protein kinase A-stimulated sarcoplasmic reticulum function in heart failure. Ann N Y Acad Sci. 1998;853:240–250.[Abstract/Free Full Text]
  87. Schwinger RH, Munch G, Bolck B et al. Reduced Ca(2+)-sensitivity of SERCA 2a in failing human myocardium due to reduced serin-16 phospholamban phosphorylation. J Mol Cell Cardiol. 1999;31:479–491.[CrossRef][Medline]
  88. Arber S, Halder G, Caroni P. Muscle LIM protein, a novel essential regulator of myogenesis, promotes myogenic differentiation. Cell. 1994;79:221–231.[Medline]
  89. Arber S, Caroni P. Specificity of single LIM motifs in targeting and LIM/LIM interactions in situ. Genes Dev. 1996;10:289–300.[Abstract]
  90. Arber S, Hunter JJ, Ross J Jr et al. MLP-deficient mice exhibit a disruption of cardiac cytoarchitectural organization, dilated cardiomyopathy, and heart failure. Cell. 1997;88:393–403.[Medline]
  91. Kong Y, Flick MJ, Kudla AJ et al. Muscle LIM protein promotes myogenesis by enhancing the activity of MyoD. Mol Cell Biol. 1997;17:4750–4760.[Abstract]
  92. Schneider AG, Sultan KR, Pette D. Muscle LIM protein: expressed in slow muscle and induced in fast muscle by enhanced contractile activity. Am J Physiol. 1999;276:C900–C906.[Medline]
  93. Mahaney JE, Autry JM, Jones LR. Kinetics studies of the cardiac Ca-ATPase expressed in Sf21 cells: new insights on Ca-ATPase regulation by phospholamban. Biophys J. 2000;78:1306–1323.[Abstract/Free Full Text]
  94. Luo W, Grupp IL, Harrer J et al. Targeted ablation of the phospholamban gene is associated with markedly enhanced myocardial contractility and loss of beta-agonist stimulation. Circ Res. 1994;75:401–409.[Abstract]
  95. Luo W, Chu G, Sato Y et al. Transgenic approaches to define the functional role of dual site phospholamban phosphorylation. J Biol Chem. 1998;273:4734–4739.[Abstract/Free Full Text]
  96. Hoit BD, Khoury SF, Kranias EG, Ball N, Walsh RA. In vivo echocardiographic detection of enhanced left ventricular function in gene-targeted mice with phospholamban deficiency. Circ Res. 1995;77:632–637.[Abstract/Free Full Text]
  97. Kadambi VJ, Ponniah S, Harrer JM, Hoit BD, Dorn GW 2nd, Walsh RA et al. Cardiac-specific overexpression of phospholamban alters calcium kinetics and resultant cardiomyocyte mechanics in transgenic mice. J Clin Invest. 1996;97:533–539.[Abstract/Free Full Text]
  98. Minamisawa S, Hoshijima M, Chu G et al. Chronic phospholamban-sarcoplasmic reticulum calcium ATPase interaction is the critical calcium cycling defect in dilated cardiomyopathy. Cell. 1999;99:313–322.[Medline]
  99. Schwinger RH, Brixius K, Savvidou-Zaroti P, Bolck B, Zobel C, Frank K et al. The enhanced contractility in phospholamban deficient mouse hearts is not associated with alterations in (Ca2+)-sensitivity or myosin ATPase-activity of the contractile proteins. Basic Res Cardiol. 2000;95:12–18.[CrossRef][Medline]
  100. Saraste A, Pulkki K. Morphologic and biochemical hallmarks of apoptosis. Cardiovasc Res. 2000;45:528–537.[CrossRef][Medline]
  101. Brunet CL, Gunby RH, Benson RS, Hickman JA, Watson AJ, Brady G. Commitment to cell death measured by loss of clonogenicity is separable from the appearance of apoptotic markers. Cell Death Differ. 1998;5:107–115.[CrossRef][Medline]
  102. Foncea R, Galvez A, Perez V et al. Extracellular regulated kinase, but not protein kinase C, is an antiapoptotic signal of insulin-like growth factor-1 on cultured cardiac myocytes. Biochem Biophys Res Commun. 2000;273:736–744.[CrossRef][Medline]
  103. Lips DJ, Bueno OF, Wilkins BJ et al. MEK1–ERK1/2-regulated signaling pathway plays a decisive cardioprotective role in ischemia-reperfusion injury. 2002 (submitted for publication)..
  104. Hasegawa K, Iwai-Kanai E, Sasayama S. Neurohormonal regulation of myocardial cell apoptosis during the development of heart failure. J Cell Physiol. 2001;186:11–18.[CrossRef][Medline]
  105. Narula J, Kolodgie FD, Virmani R. Apoptosis and cardiomyopathy. Curr Opin Cardiol. 2000;15:183–188.[CrossRef][Medline]
  106. Susin SA, Zamzami N, Castedo M et al. Bcl-2 inhibits the mitochondrial release of an apoptogenic protease. J Exp Med. 1996;184:1331–1341.[Abstract]
  107. Joza N, Susin SA, Daugas E et al. Essential role of the mitochondrial apoptosis-inducing factor in programmed cell death. Nature. 2001;410:549–554.[CrossRef][Medline]
  108. Hisatomi T, Sakamoto T, Murata T et al. Relocalization of apoptosis-inducing factor in photoreceptor apoptosis induced by retinal detachment in vivo. Am J Pathol. 2001;158:1271–1278.[Abstract/Free Full Text]
  109. Hofstra L, Liem IH, Dumont E et al. Visualisation of cell death in vivo in patients with acute myocardial infarction. Lancet. 2000;356:209–212.[CrossRef][Medline]
  110. Dumont E, Reutelingsperger CP, Smits JF et al. Real-time imaging of apoptotic cell-membrane changes at the single-cell level in the beating murine heart. Nat Med. 2001;7:1352–1355.[CrossRef][Medline]
  111. Thornberry NA, Lazebnik Y. Caspases: enemies within. Science. 1998;281:1312–1316.[Abstract/Free Full Text]
  112. Ashkenazi A, Dixit VM. Death receptors: signaling and modulation. Science. 1998;281:1305–1308.[Abstract/Free Full Text]
  113. Chen Z, Chua CC, Ho YS, Hamdy RC, Chua BH. Overexpression of Bcl-2 attenuates apoptosis and protects against myocardial I/R injury in transgenic mice. Am J Physiol Heart Circ Physiol. 2001;280:H2313–H2320.[Abstract/Free Full Text]
  114. Condorelli G, Morisco C, Stassi G et al. Increased cardiomyocyte apoptosis and changes in proapoptotic and antiapoptotic genes bax and bcl-2 during left ventricular adaptations to chronic pressure overload in the rat. Circulation. 1999;99:3071–3078.[Abstract/Free Full Text]
  115. Fearnhead HO, Rodriguez J, Govek EE et al. Oncogene-dependent apoptosis is mediated by caspase-9. Proc Natl Acad Sci U S A. 1998;95:13664–13669.[Abstract/Free Full Text]
  116. Soengas MS, Alarcon RM, Yoshida H et al. Apaf-1 and caspase-9 in p53-dependent apoptosis and tumor inhibition. Science. 1999;284:156–159.[Abstract/Free Full Text]
  117. Liu X, Li P, Widlak P et al. The 40-kDa subunit of DNA fragmentation factor induces DNA fragmentation and chromatin condensation during apoptosis. Proc Natl Acad Sci U S A. 1998;95:8461–8466.[Abstract/Free Full Text]
  118. Enari M, Sakahira H, Yokoyama H et al. A caspase-activated DNase that degrades DNA during apoptosis, and its inhibitor ICAD. Nature. 1998;391:43–50.[CrossRef][Medline]
  119. Narula J, Pandey P, Arbustini E et al. Apoptosis in heart failure: release of cytochrome c from mitochondria and activation of caspase-3 in human cardiomyopathy. Proc Natl Acad Sci U S A. 1999;96:8144–8149.[Abstract/Free Full Text]
  120. Narula J, Hajjar RJ, Dec GW. Apoptosis in the failing heart. Cardiol Clin. 1998;16:691–710.[Medline]
  121. Suzuki K, Kostin S, Person V, Elsasser A, Schaper J. Time course of the apoptotic cascade and effects of caspase inhibitors in adult rat ventricular cardiomyocytes. J Mol Cell Cardiol. 2001;33:983–994.[CrossRef][Medline]
  122. Vescovo G, Volterrani M, Zennaro R et al. Apoptosis in the skeletal muscle of patients with heart failure: investigation of clinical and biochemical changes. Heart. 2000;84:431–437.[Abstract/Free Full Text]
  123. Kajstura J, Leri A, Finato N et al. Myocyte proliferation in end-stage cardiac failure in humans. Proc Natl Acad Sci U S A. 1998;95:8801–8805.[Abstract/Free Full Text]
  124. Beltrami AP, Urbanek K, Kajstura J et al. Evidence that human cardiac myocytes divide after myocardial infarction. N Engl J Med. 2001;344:1750–1757.[Abstract/Free Full Text]
  125. Burlew BS, Weber KT. Connective tissue and the heart. Functional significance and regulatory mechanisms. Cardiol Clin. 2000;18:435–442.[Medline]
  126. Lijnen P, Petrov V. Induction of cardiac fibrosis by aldosterone. J Mol Cell Cardiol. 2000;32:865–879.[CrossRef][Medline]
  127. Lijnen PJ, Petrov VV, Fagard RH. Induction of cardiac fibrosis by angiotensin II. Methods Find Exp Clin Pharmacol. 2000;22:709–723.[Medline]
  128. Schnee JM, Hsueh WA. Angiotensin II adhesion, and cardiac fibrosis. Cardiovasc Res. 2000;46:264–268.[CrossRef][Medline]
  129. Lijnen PJ, Petrov VV, Fagard RH. Induction of cardiac fibrosis by transforming growth factor-beta(1). Mol Genet Metab. 2000;71:418–435.[CrossRef][Medline]
  130. Brilla CG, Zhou G, Matsubara L, Weber KT. Collagenmetabolism in cultured rat cardiac fibroblasts: response to angiotensin II and aldosterone. J Mol Cell Cardiol. 1994;26:809–820.[CrossRef][Medline]
  131. MacLellan WR, Schneider MD. Death by design. Programmed cell death in cardiovascular biology and disease. Circ Res. 1997;81:137–144.[Abstract/Free Full Text]
  132. Eckardt L, Haverkamp W, Johna R et al. Arrhythmias in heart failure: current concepts of mechanisms and therapy. J Cardiovasc Electrophysiol. 2000;11:106–117.[Medline]