Controversies in ventricular remodelling

Valvular heart disease: a primer for the clinical pharmacist

Valvular heart disease is a commonly encountered clinical condition that is not taught in most undergraduate and graduate pharmacy programs, leaving the practicing pharmacist without basic knowledge to expand on and subsequently apply to direct patient care. Unlike other areas of cardiology in which thousands of patients are recruited in many well-designed randomized clinical trials, data assessing treatments for valvular heart disease are limited and often consist of retrospective case series or observations. Our goal is to provide a basic overview of chronic valvular heart disease, with emphasis on describing the common conditions requiring surgery and the available options, as well as common pharmacologic therapies used in this patient population. Anomalies in valves can be broadly classified as stenosis and regurgitation. Depending on the valve and the type of anomaly, the impact on the cardiovascular system will vary. Understanding the hemodynamic consequences of aortic stenosis, aortic regurgitation, mitral stenosis, and mitral regurgitation is imperative to effectively counsel patients surrounding disease progression and self-monitoring, use of vasodilators, and prophylaxis for endocarditis and rheumatic fever. Further, patient characteristics factored into the choice of implanting either a bioprosthetic (tissue) or prosthetic (metal) valve encompass patient choice, life expectancy, and willingness or ability to accept lifelong anticoagulation therapy. The evolution of metal valves has resulted in newer generations under clinical study that have more laminar flow (minimizing interaction with blood products) and improved pyrolytic carbon (minimizing infection and interaction with blood products). Although antithrombotic therapy with warfarin is now mandatory in North America for all patients receiving metal valves, research is ongoing to assess the need with the most recent generation of valves.

Cardiac imaging after myocardial infarction

After myocardial infarction, optimal clinical management depends critically on cardiac imaging. Remodelling and heart failure, presence of inducible ischaemia, presence of dysfunctional viable myocardium, future risk of adverse events including risk of ventricular arrhythmias, need for anticoagulation, and other questions should be addressed by cardiac imaging. Strengths and weaknesses, recent developments, choice, and timing of the different non-invasive techniques are reviewed for this frequent clinical scenario.

Proteomic analysis of myocardial tissue from the border zone during early stage post-infarct remodelling in rats

AIMS

Long-term outcome of patients after myocardial infarction (MI) largely depends on the extent of post-infarct remodelling. To explore the molecular mechanism of remodelling, comparative proteomic analysis was undertaken to identify differential myocardial proteome profiles expressed in the border zone of the post-MI heart.

METHODS AND RESULTS

Two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry were used to identify the differential protein profiles expressed in the border zone at specific time points (Days 0, 1, 4, and 10 post-infarction) in a permanent rat MI model. We identified 96 differential protein spots, corresponding to 69 proteins. Cluster analysis exhibited five main temporal expression patterns corresponding to the three phases of early stage remodelling. The alteration in expression was supported by reverse transcription-polymerase chain reaction, western blotting, and immunohistochemical analysis of three selected proteins. Bioinformatics analysis revealed that the proteins in each pattern were functionally related to specific cell processes in remodelling, such as ischaemia, inflammation, and proliferation.

CONCLUSION

A differential myocardial proteome profile was identified in the border zone during early stage post-infarct remodelling. Bioinformatics analysis indicated a possible role of these proteins in remodelling. Proteomics data provided the basis for further functional study of these proteins and for identifying potential molecular targets with therapeutic anti-remodelling effects.

Heart failure with preserved left ventricular ejection fraction: concepts, misconceptions and future directions

Heart failure with preserved left ventricular ejection fraction (HFPEF) represents a huge medical problem, especially in light of an increasing elderly population. Dysfunction of both left ventricular filling and ejection, combined with adverse loading conditions related to advanced age, arterial hypertension, diabetes mellitus, obesity and atrial fibrillation are fundamental pathophysiological mechanisms. Hypertension is probably the most important modifiable risk factor. The diagnosis has largely been based on signs of increased left ventricular filling pressure. Additional matters of debate are the interpretation of left ventricular ejection fraction in concentric remodelling and the cut-off used for the definition of HFPEF, as well as inconsistencies related to prevalence and prognosis, and lack of benefit of drugs in randomized trials.

Extracellular signal-regulated kinases 1 and 2 regulate the balance between eccentric and concentric cardiac growth

RATIONALE

An increase in cardiac afterload typically produces concentric hypertrophy characterized by an increase in cardiomyocyte width, whereas volume overload or exercise results in eccentric growth characterized by cellular elongation and addition of sarcomeres in series. The signaling pathways that control eccentric versus concentric heart growth are not well understood.

OBJECTIVE

To determine the role of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in regulating the cardiac hypertrophic response.

METHODS AND RESULTS

Here, we used mice lacking all ERK1/2 protein in the heart (Erk1(-/-) Erk2(fl/fl-Cre)) and mice expressing activated mitogen-activated protein kinase kinase (Mek)1 in the heart to induce ERK1/2 signaling, as well as mechanistic experiments in cultured myocytes to assess cellular growth characteristics associated with this signaling pathway. Although genetic deletion of all ERK1/2 from the mouse heart did not block the cardiac hypertrophic response per se, meaning that the heart still increased in weight with both aging and pathological stress stimulation, it did dramatically alter how the heart grew. For example, adult myocytes from hearts of Erk1(-/-) Erk2(fl/fl-Cre) mice showed preferential eccentric growth (lengthening), whereas myocytes from Mek1 transgenic hearts showed concentric growth (width increase). Isolated adult myocytes acutely inhibited for ERK1/2 signaling by adenoviral gene transfer showed spontaneous lengthening, whereas infection with an activated Mek1 adenovirus promoted constitutive ERK1/2 signaling and increased myocyte thickness. A similar effect was observed in engineered heart tissue under cyclic stretching, where ERK1/2 inhibition led to preferential lengthening.

CONCLUSIONS

Taken together, these data demonstrate that the ERK1/2 signaling pathway uniquely regulates the balance between eccentric and concentric growth of the heart.

Distribution of active fiber stress at the beginning of ejection depends on left-ventricular shape

Left-ventricular shape is an important determinant of regional wall mechanics during passive filling. To examine the influence of left-ventricular shape for the ejection phase, the distribution of active fiber stress at the beginning of ejection was calculated in a finite element study. Hereto, finite element models were constructed with varying left-ventricular shapes, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity and wall volume constant. A realistic transmural gradient in fiber orientation was assumed. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. The activation of the left-ventricular wall was governed by the eikonal-diffusion equation. Active contraction was incorporated using a Hill-like model. For each left-ventricular shape, a simulation was performed in which passive filling was followed by isovolumic contraction. It was found that the transmural gradient of active fiber stress at the beginning of ejection steepens at the mid-height level when the left ventricle becomes more spherical, which was also obtained previously for end-diastolic passive fiber stress and strain.

Transforming growth factor beta 1 (TGF-beta 1) in atrial fibrillation and acute congestive heart failure

PURPOSE

Atrial fibrillation (AF) and acute congestive heart failure (aCHF) are characterized by an adverse cardiac remodeling. Arrhythmogenic or structural remodeling can be caused by interstitial fibrosis. Transforming growth factor beta 1 (TGF-beta 1) represents a central regulator of cardiac fibrosis. This study investigates serum levels of TGF-beta 1 in patients with AF and aCHF.

METHODS

401 patients presenting with symptoms of dyspnea or peripheral edema were prospectively enrolled. Blood samples for measurement of TGF-beta 1 (R&D Systems, Inc.) and amino-terminal pro-brain natriuretic peptide (NT-proBNP) (DadeBehring ltd.) were collected after the initial clinical evaluation.

RESULTS

Median TGF-beta 1 levels were lower in patients with AF (21.0 ng/ml, interquartile range (IR) 15.4-27.6 ng/ml, n = 107) compared to those without (25.0 ng/ml, IR 18.5-31.6 ng/ml, n = 294) (p = 0.009). Patients with aCHF had lower TGF-beta 1 levels (median 22.0 ng/ml, IR 15.6-27.1 ng/ml, n = 122) than those without (median 24.9 ng/ml, IR 18.1-31.9 ng/ml, n = 279) (p = 0.0005). In logistic regression models TGF-beta 1 was still associated with AF (odds ratio (OR) 3.00, 95% CI 1.37-6.61, p = 0.0001) and aCHF (OR 3.98, 95% CI 1.55-10.19, p = 0.004). TGF-beta 1 inversely correlated with left atrial diameter (r = -0.30, p = 0.007) and NT-proBNP (r = -0.14, p = 0.007).

CONCLUSIONS

Low serum levels of TGF-beta 1 are associated with AF and aCHF. This decrease may result from a higher consumption of TGF-beta 1 within the impaired myocardium or antifibrotic functions of natriuretic peptides.

Surgical ventricular restoration: an operation to reverse remodeling - the basic science (part I)

Congestive heart failure as a consequence of ischemic heart disease is an increasing medical problem. Notwithstanding the huge advances in the medical and conventional surgical management of heart failure, eventual outcomes remain suboptimal. This 2 part article outlines the magnitude of the problem, the limitations of conventional therapies as they exist, and the use of newer procedures that directly address the restoration of ventricular pump function.

The first part of the article deals with the pathology of different facets of the remodeling process, and the unique anatomy, geometry and flow dynamics as they pertain to ventricular function in the normal as well as the failing heart. It then details the limitations of conventional therapy, thereby laying the basis for the need and evolution of newer surgical procedures and ends with the selection of patients for ventricular restoration procedures and the pitfalls in the choice of patients for such newer techniques.

Regulation of myocardial fibrosis by MicroRNAs

Interstitial and perivascular fibrosis is a hallmark of adverse cardiac remodeling in response to stress such as hypertension, valve disease, or myocardial infarction. The cross talk between fibroblasts and cardiomyocytes seems to be a major determinant of the hypertrophic response, and fibroblasts may prove to be essential regulators of cardiac remodeling. The present review summarizes current knowledge on the modulation of myocardial fibrosis by microRNAs (miRNAs), single-stranded molecules consisting of approximately 22 noncoding nucleotides that regulate a variety of target genes involved in cardiovascular (patho)physiology. Dissection of miRNA-mediated mechanisms on myocardial and cellular and subcellular levels will provide insights into the impact of miRNAs for cardiac structural changes induced by different stressors and also expand our understanding of the interdependence of different cell types in the heart with regard to extracellular matrix formation during healing and remodeling after myocardial infarction or in response to pressure overload. The first successful treatment of fibrosis and failure in a murine pressure overload model by application of miRNA antagonists such as antagomirs in vivo raises the hope that manipulating miRNAs may emerge as a novel treatment strategy for fibrotic changes not only in the heart but also in other organs.

Influence of different doses of retinoic acid on cardiac remodeling

OBJECTIVE

The role of retinoic acid in promoting postnatal heart alterations is still unclear. The aim of this study was to evaluate whether the cardiac alterations caused by all-trans- retinoic acid (ATRA) in normal adult rat hearts are physiologic or pathologic and if these alterations are dose-dependent.

METHODS

Rats were allocated into a control group that received a diet without ATRA (n=16), a group that received 0.3 mg of ATRA/kg of diet (n=17), a group that received a diet containing 10 mg of ATRA/kg (n=18), or a group that received 50 mg of ATRA/kg in the diet (n=18). After 4 wk, the animals were evaluated echocardiographically, morphologically, and biochemically.

RESULTS

The 50-mg ATRA group presented cardiac hypertrophy with maintenance of cardiac geometry and increased systolic function, whereas diastolic function was similar to that of the control group. In addition, progressive increases in the ATRA dose resulted in gradual augmentations of left atrial diameter, left ventricular diastolic and systolic diameters, left ventricular mass index, cardiac output, cardiac index, and aortic velocity. The ATRA did not produce alterations in interferon-γ and tumor necrosis factor-α cardiac levels, interstitial collagen volume fraction, or the intensity and localization of connexin-43. In addition, no alteration was observed in β-hydroxyacyl coenzyme A dehydrogenase, lactate dehydrogenase, or citrate synthase, suggesting that cardiac energetic metabolism was preserved with ATRA.

CONCLUSION

These results suggest that ATRA produced dose-dependent effects and cardiac remodeling that is more compatible with a physiologic response.

Relations of biomarkers of extracellular matrix remodeling to incident cardiovascular events and mortality

OBJECTIVE

To evaluate if biomarkers reflecting left ventricular/vascular extracellular matrix remodeling are associated with cardiovascular disease (CVD) and death in the community.

METHODS AND RESULTS

In 922 Framingham Study participants (mean age, 58 years; 56% women), we related circulating concentrations of matrix metalloproteinase-9 (binary variable: detectable versus undetectable), log of tissue inhibitor of matrix metalloproteinase-1, and log of procollagen type III aminoterminal peptide (PIIINP) to incident CVD and death. On follow-up (mean, 9.9 years), 51 deaths and 81 CVD events occurred. Each SD increment of log of tissue inhibitor of matrix metalloproteinase-1 and log-PIIINP was associated with multivariable-adjusted hazards ratios of 1.72 (95% CI, 1.30 to 2.27) and 1.47 (95% CI, 1.11 to 1.96), respectively, for mortality risk. Log-PIIINP concentrations were also associated with CVD risk (hazard ratio [95% CI] per SD, 1.35 [1.05 to 1.74]). Death and CVD incidence rates were 2-fold higher in participants with both biomarkers higher than the median (corresponding hazard ratio [95% CI], 2.78 [1.43 to 5.40] and 1.77 [1.04 to 3.03], respectively) compared with those with either or both less than the median. The inclusion of both biomarkers improved the C-statistic (for predicting mortality) from 0.78 to 0.82 (P=0.03). Matrix metalloproteinase-9 was unrelated to either outcome.

CONCLUSIONS

Higher circulating tissue inhibitor of matrix metalloproteinase-1 and PIIINP concentrations are associated with mortality, and higher PIIINP is associated with incident CVD, in the community.

Differential cardiac remodeling in preload versus afterload

BACKGROUND

Hemodynamic load regulates myocardial function and gene expression. We tested the hypothesis that afterload and preload, despite similar average load, result in different phenotypes.

METHODS AND RESULTS

Afterload and preload were compared in mice with transverse aortic constriction (TAC) and aortocaval shunt (shunt). Compared with sham mice, 6 hours after surgery, systolic wall stress (afterload) was increased in TAC mice (+40%; P<0.05), diastolic wall stress (preload) was increased in shunt (+277%; P<0.05) and TAC mice (+74%; P<0.05), and mean total wall stress was similarly increased in TAC (69%) and shunt mice (67%) (P=NS, TAC versus shunt; each P<0.05 versus sham). At 1 week, left ventricular weight/tibia length was significantly increased by 22% in TAC and 29% in shunt mice (P=NS, TAC versus shunt). After 24 hours and 1 week, calcium/calmodulin-dependent protein kinase II signaling was increased in TAC. This resulted in altered calcium cycling, including increased L-type calcium current, calcium transients, fractional sarcoplasmic reticulum calcium release, and calcium spark frequency. In shunt mice, Akt phosphorylation was increased. TAC was associated with inflammation, fibrosis, and cardiomyocyte apoptosis. The latter was significantly reduced in calcium/calmodulin-dependent protein kinase IIdelta-knockout TAC mice. A total of 157 mRNAs and 13 microRNAs were differentially regulated in TAC versus shunt mice. After 8 weeks, fractional shortening was lower and mortality was higher in TAC versus shunt mice.

CONCLUSIONS

Afterload results in maladaptive fibrotic hypertrophy with calcium/calmodulin-dependent protein kinase II-dependent altered calcium cycling and apoptosis. Preload is associated with Akt activation without fibrosis, little apoptosis, better function, and lower mortality. This indicates that different loads result in distinct phenotype differences that may require specific pharmacological interventions.

The effect of feto-maternal size and childhood growth on left ventricular mass and arterial stiffness in Afro-Caribbean children

We hypothesized that maternal size, fetal size and childhood growth are associated with childhood blood pressure, left ventricular mass (LVM) and arterial stiffness. The Vulnerable Windows Cohort is a longitudinal study of 569 mothers and their offspring. Anthropometry was measured on each child at birth, at 6 weeks, once in 3 months upto 2 years and then every 6 months. Blood pressure and body composition were assessed in 185 children (age 11.5 years) and echocardiography performed. LVM was not associated with maternal size after adjustment for child's weight. LVM was significantly associated with faster growth in childhood and with current weight, fat mass and lean mass. Systolic blood pressure was not related to maternal, fetal or newborn anthropometry, but was positively associated with infant and childhood growth, as well as current body size and fat mass. The pulse pressure/stroke volume ratio (an index of arterial stiffness) was inversely associated with maternal size, placental volume at 20 weeks, fetal size at 35 weeks and childhood growth even after adjustment for current weight. In conclusion, LVM in childhood is positively associated with maternal height, child's current size and rate of growth. Arterial stiffness is inversely related to maternal, fetal and placental size as well as growth throughout childhood.

Increasing cardiac contractility after myocardial infarction exacerbates cardiac injury and pump dysfunction

RATIONALE

Myocardial infarction (MI) leads to heart failure (HF) and premature death. The respective roles of myocyte death and depressed myocyte contractility in the induction of HF after MI have not been clearly defined and are the focus of this study.

OBJECTIVES

We developed a mouse model in which we could prevent depressed myocyte contractility after MI and used it to test the idea that preventing depression of myocyte Ca(2+)-handling defects could avert post-MI cardiac pump dysfunction.

METHODS AND RESULTS

MI was produced in mice with inducible, cardiac-specific expression of the β2a subunit of the L-type Ca(2+) channel. Myocyte and cardiac function were compared in control and β2a animals before and after MI. β2a myocytes had increased Ca(2+) current; sarcoplasmic reticulum Ca(2+) load, contraction and Ca(2+) transients (versus controls), and β2a hearts had increased performance before MI. After MI, cardiac function decreased. However, ventricular dilation, myocyte hypertrophy and death, and depressed cardiac pump function were greater in β2a versus control hearts after MI. β2a animals also had poorer survival after MI. Myocytes isolated from β2a hearts after MI did not develop depressed Ca(2+) handling, and Ca(2+) current, contractions, and Ca(2+) transients were still above control levels (before MI).

CONCLUSIONS

Maintaining myocyte contractility after MI, by increasing Ca(2+) influx, depresses rather than improves cardiac pump function after MI by reducing myocyte number.

Temporal evaluation of cardiac myocyte hypertrophy and hyperplasia in male rats secondary to chronic volume overload

The temporal myocardial remodeling induced by chronic ventricular volume overload in male rats was examined. Specifically, left ventricular (LV) cardiomyocyte length and width, sarcomere length, and number of nuclei were measured in male rats (n = 8 to 17) at 1, 3, 5, 7, 21, 35, and 56 days after creation of an infrarenal aortocaval fistula. In contrast to previously published reports of progressive increases in cardiomyocyte length and cross-sectional area at 5 days post-fistula and beyond in female hearts, cardiomyocyte length and width did not increase significantly in males during the first 35 days of volume overload. Furthermore, a significant decrease in cardiomyocyte length relative to age-matched controls, together with a reduced number of sarcomeres per cell, was noted in male hearts at 5 days post-fistula. There was a concurrent increase in the percentage of mononucleated cardiomyocytes from 11.6% to 18% at 5 days post-fistula. These initial differences could not be attributed to cardiomyocyte proliferation, and treatment with a microtubule stabilizing agent prevented them from occurring. The subsequent significant increase in LV weight without corresponding increases in cardiomyocyte dimensions is indicative of hyperplasia. Thus, these findings indicate hyperplasia resulting from cytokinesis of cardiomyocytes is a key mechanism, independent of hypertrophy, that contributes to the significant increase in LV mass in male hearts subjected to chronic volume overload.

Lack of uniform progression of endocardial scar in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy and ventricular tachycardia

BACKGROUND

The endocardial substrate for ventricular arrhythmias in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is thought to be caused by a progressive degenerative process. Many clinical decisions and treatment plans are guided by this pathophysiologic assumption, but the extent of progression of macroscopic endocardial scar and right ventricular (RV) dilatation have not been assessed.

METHODS AND RESULTS

Eleven patients with ARVD/C and ventricular tachycardia had 2 detailed sinus rhythm electroanatomic endocardial voltage maps (average, 291+/-122 points per map; range, 114 to 558 points) performed a mean of 57 months apart (minimum, 9 months) as part of ventricular tachycardia ablation procedures. Voltage-defined scar (<1.5 mV) and RV volume were measured by area and volume measurement software and compared. Two of the 11 patients had a clear increase in scar area (47 cm(2); 32 cm(2)) confirmed by visual inspection. The remaining 9 (81%; 95% CI, 48% to 98%) patients had no increase (<10-cm(2) difference) in scar area between studies. In contrast, 10 of the 11 patients had a significant increase in RV volume, with an average increase of 24% (212+/-67 mL to 263+/-52 mL; P< or =0.01).

CONCLUSIONS

In patients with ARVD/C and ventricular tachycardia, progressive RV dilatation is the rule, and rapid progression of significant macroscopic endocardial scar occurs in only a subset of patients. These results have important management implications, suggesting that efforts to prevent RV dilatation in this population are needed and that an aggressive substrate-based ablation strategy offers the potential to provide long-term ventricular tachycardia control.

Defects in ryanodine receptor function are associated with systolic dysfunction in rats subjected to volume overload

Cardiac hypertrophy is the compensatory enlargement of the heart aimed at reducing stress induced by either pressure overload or volume overload (VO); however, sustained hypertrophy leads to cardiac dysfunction. We hypothesize that cardiac dysfunction which develops due to VO will be associated with abnormalities in sarcoplasmic reticulum (SR) function. Volume overload was induced in rats by aortocaval shunt surgery ('VO rats'). Echocardiographic measurements were used to compare cardiac structure and function in control and VO rats. The SR was isolated from left ventricular tissue. Sarcoplasmic reticulum Ca(2+) uptake and SR Ca(2+) release were examined by the filtration method. The expression levels of SR proteins were assessed by Western immunoblotting. Rats subjected to VO developed eccentric hypertrophy. Diastolic function in VO rats was improved at all time points and was associated with elevated SR Ca(2+) uptake at 16 and 28 weeks. Sarcoendoplasmic reticulum ATPase 2a protein level was increased at 16 weeks but normalized at 28 weeks; Amounts of phospholamban protein were unaltered, but Serine16 phospholamban and Threonine17 phospholamban were reduced at 28 weeks. Systolic function was impaired in the VO rats at 16 and 28 weeks and was associated with reduced Ca(2+) release at the 28 week time point. The ryanodine receptor 2 (RyR2) protein level was reduced at 28 weeks; RyR2 phosphorylation status and the amount of FK-binding protein 12.6 were increased at 28 weeks. On the basis of the results, we conclude that the progression of hypertrophy due to VO in rats is accompanied by the impairment of systolic function, which in turn is associated with defects in RyR2 expression and function.

MicroRNAs--regulators of signaling networks in dilated cardiomyopathy

MicroRNAs (miRNAs) are endogenous small non-coding ribonucleotides that regulate expression of target genes governing diverse biological functions. Mechanistically, miRNA binding to the target complimentary sequences on the mRNA results in degradation or inhibition of protein translation. The short guiding and binding sequence of miRNA allows them to target a large repertoire of transcripts altering expression of many proteins. These miRNA targets are not restricted to specific signaling pathways but to a diverse group of transcripts, which harbor the target complimentary sequence. miRNA targeting of these diverse transcripts result in regulation of multiple signaling pathways establishing miRNAs as regulators of systems biomolecular networks. Accumulating evidence shows that miRNAs play an important role in cardiac development, hypertrophy, and failure, thereby are integral to regulating adaptive and maladaptive remodeling. Since cardiac remodeling and failure is a complex phenotype, it is apparent that global biomolecular networks and miRNAs profiles would be altered. Indeed, the miRNA profiles are varied with different etiologies of heart failure indicating that miRNAs could be the global regulators. Although the idea of miRNA being global regulators is not new, we believe that the time is ripe to discuss the role of miRNAs in regulating biomolecular networks. We discuss in the review, the use of Ingenuity Pathways Analysis algorithms with predicted targets of altered miRNA in dilated cardiomyopathy to computationally determine the alterations in canonical functional pathways and to generate biomolecular networks.

Resveratrol arrests and regresses the development of pressure overload- but not volume overload-induced cardiac hypertrophy in rats

Cardiac hypertrophy is a compensatory enlargement of the heart due to either volume overload (VO) and/or pressure overload (PO) that develops into heart failure if left untreated. The polyphenol resveratrol has been reported to regress PO-induced cardiac hypertrophy in rats. Our aim in this study was to assess the effectiveness of resveratrol on VO-induced cardiac hypertrophy. Sprague Dawley rats were subjected to aortocaval shunt and abdominal aortic banding surgeries to create VO and PO, respectively; sham-operated rats served as controls. To arrest the development of cardiac hypertrophy, daily resveratrol treatment (2.5 mg/kg body weight) was started 2 d postsurgery for 26 d and assessed by echocardiography at 2, 14, and 28 d postsurgery. Similarly, to regress cardiac hypertrophy resveratrol treatment was started after structural and functional abnormalities developed (14 d postsurgery) for 14 d and assessed by echocardiography at 14 and 28 d postsurgery. VO surgeries induced eccentric hypertrophy characterized by increased left ventricle internal dimensions (LVID) without wall thickening. Conversely, PO induced concentric hypertrophy with increased wall thickness without change in LVID. Lipid peroxidation, a marker for oxidative stress, was significantly elevated in both PO and VO rats. Resveratrol treatment arrested the development and regressed abnormalities in cardiac structure and function in PO but not VO rats. Treatment with resveratrol also significantly reduced oxidative stress in cardiac tissue of PO and VO rats. The results on cardiac structure and function demonstrate a potential for resveratrol in the treatment of cardiac hypertrophy due to PO but not VO.

Female sex and estrogen receptor-beta attenuate cardiac remodeling and apoptosis in pressure overload

We investigated sex differences and the role of estrogen receptor-beta (ERbeta) on myocardial hypertrophy in a mouse model of pressure overload. We performed transverse aortic constriction (TAC) or sham surgery in male and female wild-type (WT) and ERbeta knockout (ERbeta(-/-)) mice. All mice were characterized by echocardiography and hemodynamic measurements and were killed 9 wk after surgery. Left ventricular (LV) samples were analyzed by microarray profiling, real-time RT-PCR, and histology. After 9 wk, WT males showed more hypertrophy and heart failure signs than WT females. Notably, WT females developed a concentric form of hypertrophy, while males developed eccentric hypertrophy. ERbeta deletion augmented the TAC-induced increase in cardiomyocyte diameter in both sexes. Gene expression profiling revealed that WT male hearts had a stronger induction of matrix-related genes and a stronger repression of mitochondrial genes than WT female hearts. ERbeta(-/-) mice exhibited a different transcriptional response. ERbeta(-/-)/TAC mice of both sexes exhibited induction of proapoptotic genes with a stronger expression in ERbeta(-/-) males. Cardiac fibrosis was more pronounced in male WT/TAC than in female mice. This difference was abolished in ERbeta(-/-) mice. The number of apoptotic nuclei was increased in both sexes of ERbeta(-/-)/TAC mice, most prominent in males. Female sex offers protection against ventricular chamber dilation in the TAC model. Both female sex and ERbeta attenuate the development of fibrosis and apoptosis, thus slowing the progression to heart failure.

ERK1/2 signaling dominates over RhoA signaling in regulating early changes in RNA expression induced by endothelin-1 in neonatal rat cardiomyocytes

Background

Cardiomyocyte hypertrophy is associated with changes in gene expression. Extracellular signal-regulated kinases 1/2 (ERK1/2) and RhoA [activated by hypertrophic agonists (e.g. endothelin-1)] regulate gene expression and are implicated in the response, but their relative significance in regulating the cardiomyocyte transcriptome is unknown. Our aim was to establish the significance of ERK1/2 and/or RhoA in the early cardiomyocyte transcriptomic response to endothelin-1.

Methods/Principal Findings

Cardiomyocytes were exposed to endothelin-1 (1 h) with/without PD184352 (to inhibit ERK1/2) or C3 transferase (C3T, to inhibit RhoA). RNA expression was analyzed using microarrays and qPCR. ERK1/2 signaling positively regulated ∼65% of the early gene expression response to ET-1 with a small (∼2%) negative effect, whereas RhoA signaling positively regulated ∼10% of the early gene expression response to ET-1 with a greater (∼14%) negative contribution. Of RNAs non-responsive to endothelin-1, 66 or 448 were regulated by PD184352 or C3T, respectively, indicating that RhoA had a more significant effect on baseline RNA expression. mRNAs upregulated by endothelin-1 encoded a number of receptor ligands (e.g. Ereg, Areg, Hbegf) and transcription factors (e.g. Abra/Srf) that potentially propagate the response.

Conclusions/Significance

ERK1/2 dominates over RhoA in the early transcriptomic response to endothelin-1. RhoA plays a major role in maintaining baseline RNA expression but, with upregulation of Abra/Srf by endothelin-1, RhoA may regulate changes in RNA expression over longer times. Our data identify ERK1/2 as a more significant node than RhoA in regulating the early stages of cardiomyocyte hypertrophy.

The influence of left-ventricular shape on end-diastolic fiber stress and strain

Passive filling is a major determinant for the pump performance of the left ventricle and is determined by the filling pressure and the ventricular compliance. We quantified the influence of left-ventricular shape on the overall compliance and the distribution of passive fiber stress and strain during the filling period in normal myocardium. Hereto, fiber stress and strain were calculated in a finite element analysis during the inflation of left ventricles of different shape, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity and wall volume constant. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. A realistic transmural gradient in fiber orientation was assumed. While compliance was not altered, the transmural distribution of both passive fiber stress and strain was highly dependent on ventricular shape, where more spherical ventricles exhibited a higher subendocardial gradient in both quantities.

Influence of left-ventricular shape on passive filling properties and end-diastolic fiber stress and strain

Passive filling is a major determinant for the pump performance of the left ventricle and is determined by the filling pressure and the ventricular compliance. In the quantification of the passive mechanical behaviour of the left ventricle and its compliance, focus has been mainly on fiber orientation and constitutive parameters. Although it has been shown that the left-ventricular shape plays an important role in cardiac (patho-)physiology, the dependency on left-ventricular shape has never been studied in detail. Therefore, we have quantified the influence of left-ventricular shape on the overall compliance and the intramyocardial distribution of passive fiber stress and strain during the passive filling period. Hereto, fiber stress and strain were calculated in a finite element analysis of passive inflation of left ventricles with different shapes, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity volume constant. For each shape, the wall volume was varied to obtain ventricles with different wall thickness. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. A realistic transmural distribution in fiber orientation was assumed. We found that compliance was not altered substantially, but the transmural distribution of both passive fiber stress and strain was highly dependent on regional wall curvature and thickness. A low curvature wall was characterized by a maximum in the transmural fiber stress and strain in the mid-wall region, while a steep subendocardial transmural gradient was present in a high curvature wall. The transmural fiber stress and strain gradients in a low and high curvature wall were, respectively, flattened and steepened by an increase in wall thickness.

Myeloid differentiation factor-88 contributes to TLR9-mediated modulation of acute coxsackievirus B3-induced myocarditis in vivo

Toll-like receptor 9 (TLR9) is a member of the innate immune system and has been shown to influence myocardial function, but its role in myocarditis is hitherto unknown. We therefore investigated whether or not TLR9 plays a role in this disease in coxsackievirus B3 (CVB3)-induced myocarditis in mice. Left ventricular (LV) function, cardiac immune cell infiltration, virus mRNA, and components of the TLR9 downstream pathway were investigated in TLR9-deficient [knockout (KO)] and wild-type (WT) mice after infection with CVB3. Murine cardiac TLR9 expression was significantly increased in WT mice with acute CVB3 infection but not in WT mice with chronic myocarditis. Furthermore, in the acute phase of CVB3-induced myocarditis, CVB3-infected KO mice displayed improved LV function associated with reduced cardiac inflammation indexed by reduced amounts of immune cells compared with CVB3-infected WT mice. In contrast, in the chronic phase, LV function and inflammation were not seen to differ among the infected groups. The cardioprotective effects due to TLR9 deficiency were associated with suppression of the TLR9 downstream pathway as indexed by reduced cardiac levels of the adapter protein myeloid differentiation factor (MyD)-88 and the proinflammatory cytokine TNF-alpha. In addition, TLR9 deficiency led to an activation of the antiviral cytokine interferon-beta in the heart as a result from viral infection. In conclusion, the MyD88/TNF-alpha axis due to TLR9 activation in the heart contributes the development of acute myocarditis but not of chronic myocarditis.

SHP2 mediates gp130-dependent cardiomyocyte hypertrophy via negative regulation of skeletal alpha-actin gene

Morphological and biochemical phenotypes of cardiomyocyte hypertrophy are determined by neurohumoral factors. Stimulation of G protein-coupled receptor (GPCR) results in uniform cell enlargement in all directions with an increase in skeletal alpha-actin (alpha-SKA) gene expression, while stimulation of gp130 receptor by interleukin-6 (IL-6)-related cytokines induces longitudinal elongation with no increase in alpha-SKA gene expression. Thus, alpha-SKA is a discriminating marker for hypertrophic phenotypes; however, regulatory mechanisms of alpha-SKA gene expression remain unknown. Here, we clarified the role of SH2-containing protein tyrosine phosphatase 2 (SHP2) in alpha-SKA gene expression. In neonatal rat cardiomyocytes, endothelin-1 (ET-1), a GPCR agonist, but not leukemia inhibitory factor (LIF), an IL-6-related cytokine, induced RhoA activation and promotes alpha-SKA gene expression via RhoA. In contrast, LIF, but not ET-1, induced activation of SHP2 in cardiomyocytes, suggesting that SHP2 might negatively regulate alpha-SKA gene expression downstream of gp130. Therefore, we examined the effect of adenovirus-mediated overexpression of wild-type SHP2 (SHP2(WT)), dominant-negative SHP2 (SHP2(C/S)), or beta-galactosidase (beta-gal), on alpha-SKA gene expression. LIF did not upregulate alpha-SKA mRNA in cardiomyocytes overexpressing either beta-gal or SHP2(WT). In cardiomyocytes overexpressing SHP2(C/S), LIF induced upregulation of alpha-SKA mRNA, which was abrogated by concomitant overexpression of either C3-toxin or dominant-negative RhoA. RhoA was activated after LIF stimulation in the cardiomyocytes overexpressing SHP2(C/S), but not in myocytes overexpressing beta-gal. Furthermore, SHP2 mediates LIF-induced longitudinal elongation of cardiomyocytes via ERK5 activation. Collectively, these findings indicate that SHP2 negatively regulates alpha-SKA expression via RhoA inactivation and suggest that SHP2 implicates ERK5 in cardiomyocyte elongation downstream of gp130.

Size, shape, and stamina: the impact of left ventricular geometry on exercise capacity

Although several studies have examined the cardiac functional determinants of exercise capacity, few have investigated the effects of structural remodeling. The current study evaluated the association between cardiac geometry and exercise capacity. Subjects with ejection fraction > or = 50% and no valvular disease, myocardial ischemia, or arrhythmias were identified from a large prospective exercise echocardiography database. Left ventricular mass index and relative wall thickness were used to classify geometry into normal, concentric remodeling, eccentric hypertrophy, and concentric hypertrophy. All of the subjects underwent symptom-limited treadmill exercise according to standard Bruce protocol. Maximal exercise tolerance was measured in metabolic equivalents. Of 366 (60+/-14 years; 57% male) subjects, 166 (45%) had normal geometry, 106 (29%) had concentric remodeling, 40 (11%) had eccentric hypertrophy, and 54 (15%) had concentric hypertrophy. Geometry was related to exercise capacity: in descending order, the maximum achieved metabolic equivalents were 9.9+/-2.8 in normal, 8.9+/-2.6 in concentric remodeling, 8.6+/-3.1 in eccentric hypertrophy, and 8.0+/-2.7 in concentric hypertrophy (all P<0.02 versus normal). Left ventricular mass index and relative wall thickness were negatively correlated with exercise tolerance in metabolic equivalents (r=-0.14; P=0.009 and r=-0.21; P<0.001, respectively). Augmentation of heart rate and ejection fraction with exercise were blunted in concentric hypertrophy compared with normal, even after adjusting for medications. In conclusion, the pattern of ventricular remodeling is related to exercise capacity among low-risk adults. Subjects with concentric hypertrophy display the greatest limitation, and this is related to reduced systolic and chronotropic reserve. Reverse remodeling strategies may prevent or treat functional decline in patients with structural heart disease.

TEAD-1 overexpression in the mouse heart promotes an age-dependent heart dysfunction

TEA domain transcription factor-1 (TEAD-1) is essential for proper heart development and is implicated in cardiac specific gene expression and the hypertrophic response of primary cardiomyocytes to hormonal and mechanical stimuli, and its activity increases in the pressure-overloaded hypertrophied rat heart. To investigate whether TEAD-1 is an in vivo modulator of cardiac specific gene expression and hypertrophy, we developed transgenic mice expressing hemagglutinin-tagged TEAD-1 under the control of the muscle creatine kinase promoter. We show that a sustained increase in TEAD-1 protein leads to an age-dependent dysfunction. Magnetic resonance imaging revealed decreases in cardiac output, stroke volume, ejection fraction, and fractional shortening. Isolated TEAD-1 hearts revealed decreased left ventricular power output that correlated with increased betaMyHC protein. Histological analysis showed altered alignment of cardiomyocytes, septal wall thickening, and fibrosis, although electrocardiography displayed a left axis shift of mean electrical axis. Transcripts representing most members of the fetal heart gene program remained elevated from fetal to adult life. Western blot analyses revealed decreases in p-phospholamban, SERCA2a, p-CX43, p-GSK-3alpha/beta, nuclear beta-catenin, GATA4, NFATc3/c4, and increased NCX1, nuclear DYKR1A, and Pur alpha/beta protein. TEAD-1 mice did not display cardiac hypertrophy. TEAD-1 mice do not tolerate stress as they die over a 4-day period after surgical induction of pressure overload. These data provide the first in vivo evidence that increased TEAD-1 can induce characteristics of cardiac remodeling associated with cardiomyopathy and heart failure.

Long-term outcome after thrombectomy in acute myocardial infarction

BACKGROUND

Current data appear in favour of thrombectomy for ST-elevation myocardial infarction (STEMI). However, information on long-term outcome after thrombectomy is limited. We performed a retrospective long-term study to assess the risk of cardiac re-hospitalizations and survival after discharge from the index hospitalization for STEMI.

METHODS

Patients originally randomized to percutaneous coronary intervention (PCI) with thrombectomy vs. standard PCI were included in a retrospective long-term observational study. The primary study endpoint was the combined risk for all-cause death or cardiac re-hospitalization after index discharge under optimal medical therapy. The cumulative number of cardiac hospitalization days and ventricular remodelling assessed by echocardiography and plasma biomarkers were secondary endpoints.

RESULTS

Of 94 STEMI patients who had been randomized between 11/2000 and 03/2003, 89 patients consented to long-term follow-up. A total of 43 patients had been allocated to thrombectomy and 46 to standard primary PCI. The minimum follow-up time was 1115 days. There was a significantly lower risk for death or cardiac re-hospitalization for patients of the thrombectomy group (hazard ratio = 0.69, 95% CI: 0.49-0.98, P = 0.036). The incidence of recurrent myocardial infarction was not different (P = 0.343). No differences in cardiac remodelling were detected by echocardiography, with the exception that heart-type fatty acid binding protein at 53.2 +/- 17 months was lower in the thrombectomy group (P = 0.045).

CONCLUSION

Thrombectomy in STEMI may decrease the long-term risk for death or cardiac re-hospitalization.

Resveratrol prevents the development of pathological cardiac hypertrophy and contractile dysfunction in the SHR without lowering blood pressure

BACKGROUND

Cardiac hypertrophy is a compensatory enlargement of the heart in response to stress such as hypertension. It is beneficial in reducing stress placed on the heart. However, when the stress is of a chronic nature, it becomes pathological and leads to cardiac dysfunction and heart failure. Current treatments for hypertension and heart failure have proven beneficial but are not highly specific and associated with side effects. Accordingly, there is an important need for alternative strategies to provide safe and effective treatment.

METHODS

Ten-week-old male spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats were treated with resveratrol (2.5 mg/kg/day) for a period of 10 weeks. Systolic blood pressure, and cardiac structure and function were measured in all groups at different time points of resveratrol treatment. Oxidative stress was also determined in all groups after 10 weeks of resveratrol treatment.

RESULTS

SHRs were characterized with high blood pressure and concentric hypertrophy from 15 weeks of age. Cardiac functional abnormalities were also evident in SHR from 15 weeks onwards. Resveratrol treatment significantly prevented the development of concentric hypertrophy, and systolic and diastolic dysfunction in SHR without lowering blood pressure. Resveratrol also significantly reduced the oxidative stress levels of cardiac tissue in SHR.

CONCLUSIONS

Resveratrol treatment was beneficial in preventing the development of concentric hypertrophy and cardiac dysfunction in SHR. The cardioprotective effect of resveratrol in SHR may be partially mediated by a reduction in oxidative stress. Thus, resveratrol may have potential in preventing cardiac impairment in patients with essential hypertension.

Oral levosimendan prevents postinfarct heart failure and cardiac remodeling in diabetic Goto-Kakizaki rats

BACKGROUND

Diabetes increases the risk for fatal myocardial infarction and development of heart failure. Levosimendan, an inodilator acting both via calcium sensitization and opening of ATP-dependent potassium channels, is used intravenously for acute decompensated heart failure. The long-term effects of oral levosimendan on postinfarct heart failure are largely unknown.

OBJECTIVE

To examine whether oral treatment with levosimendan could improve cardiac functions and prevent cardiac remodeling after myocardial infarction in a rodent model of type 2 diabetes, the Goto-Kakizaki rat.

METHODS

Myocardial infarction (MI) was induced to diabetic Goto-Kakizaki and nondiabetic Wistar rats by coronary ligation. Twenty-four hours after surgery, Goto-Kakizaki and Wistar rats were randomized into four groups: MI group without treatment, MI group with levosimendan for 12 weeks (1 mg/kg per day), sham-operated group, sham-operated group with levosimendan. Blood pressure, cardiac functions as wells as markers of cardiac remodeling were determined.

RESULTS

In Goto-Kakizaki rats, MI induced systolic heart failure, pronounced cardiac hypertrophy in the remote area, and sustained cardiomyocyte apoptosis. Postinfarct cardiac remodeling was associated with increased atrial natriuretic peptide, interleukin-6 and connective tissue growth factor mRNA expressions, as well as three-fold increased cardiomyocyte senescence, measured as cardiac p16 mRNA expression. Levosimendan improved cardiac function and prevented postinfarct cardiomyocyte hypertrophy, cardiomyocyte apoptosis, and cellular senescence. Levosimendan also ameliorated MI-induced atrial natriuretic peptide, IL-6, and connective tissue growth factor overexpression as well as MI-induced disturbances in calcium-handling proteins (SERCA2, Na-Ca exchanger) without changes in diabetic status or systemic blood pressure. In nondiabetic Wistar rats, MI induced systolic heart failure; however, the postinfarct cardiac remodeling was associated with less pronounced cardiac hypertrophy, cardiomyocyte apoptosis, inflammatory reaction, and induction of cellular senescence. Levosimendan only partially prevented postinfarct heart failure and cardiac remodeling in Wistar rats.

CONCLUSION

Our findings suggest a therapeutic role for oral levosimendan in prevention of postinfarct heart failure and cardiac remodeling in type 2 diabetes and underscore the importance of sustained cardiomyocyte apoptosis and induction of cellular senescence in the pathogenesis.

Sirtuin1-p53, forkhead box O3a, p38 and post-infarct cardiac remodeling in the spontaneously diabetic Goto-Kakizaki rat

Background

Diabetes is associated with changes in myocardial stress-response pathways and is recognized as an independent risk factor for cardiac remodeling. Using spontaneously diabetic Goto Kakizaki rats as a model of type 2 DM we investigated whether post-translational modifications in the Akt - FOXO3a pathway, Sirt1 - p53 pathway and the mitogen activated protein kinase p38 regulator are involved in post-infarct cardiac remodeling

Methods

Experimental myocardial infarction (MI) was induced by left anterior descending coronary artery ligation in spontaneously diabetic Goto-Kakizaki rats and non-diabetic Wistar controls. Cardiac function was studied by echocardiography. Myocardial hypertrophy, cardiomyocyte apoptosis and cardiac fibrosis were determined histologically 12 weeks post MI or Sham operation. Western blotting was used to study Caspase-3, Bax, Sirt1, acetylation of p53 and phosphorylation of p38, Akt and FOXO3a. Electrophoretic mobility shift assay was used to assess FOXO3a activity and its nuclear localization.

Results

Post-infarct heart failure in diabetic GK rats was associated with pronounced cardiomyocyte hypertrophy, increased interstitial fibrosis and sustained cardiomyocyte apoptosis as compared with their non-diabetic Wistar controls. In the GK rat myocardium, Akt- and FOXO3a-phosphorylation was decreased and nuclear localization of FOXO3a was increased concomitantly with increased PTEN protein expression. Furthermore, increased Sirt1 protein expression was associated with decreased p53 acetylation, and phosphorylation of p38 was increased in diabetic rats with MI.

Conclusions

Post-infarct heart failure in diabetic GK rats was associated with more pronounced cardiac hypertrophy, interstitial fibrosis and sustained cardiomyocyte apoptosis as compared to their non-diabetic controls. The present study suggests important roles for Akt-FOXO3a, Sirt1 - p53 and p38 MAPK in the regulation of post-infarct cardiac remodeling in type 2 diabetes.

Induction of Mitogen-Activated Protein Kinases Is Proportional to the Amount of Pressure Overload

Pressure overload has been shown to induce mitogen activated protein kinases (MAPKs) and reactivate the atrial natriuretic factor in the heart. To test the sensitivity of these signals to pressure overload, we assayed the activity of MAPKs extracellular signal–regulated kinase, c-Jun N-terminal kinase 1, and p38 in protein lysates from the left ventricle (LV) or white blood cells (WBC) isolated from aortic banded mice with varying levels of pressure overload. In separated mice we measured atrial natriuretic factor mRNA levels by Northern blotting. As expected, a significant induction of atrial natriuretic factor mRNA levels was observed after aortic banding, and it significantly correlated with the trans -stenotic systolic pressure gradient but not with the LV weight:body weight ratio. In contrast, a significant correlation with systolic pressure gradient or LV weight:body weight ratio was observed for all of the MAPK activity detected in LV samples or WBCs. Importantly, LV activation of MAPKs significantly correlated with their activation in WBCs from the same animal. To test whether MAPK activation in WBCs might reflect uncontrolled blood pressure levels in humans, we assayed extracellular signal–regulated kinase, c-Jun N-terminal kinase 1, and p38 activation in WBCs isolated from normotensive volunteers, hypertensive patients with controlled blood pressure values, or hypertensive patients with uncontrolled blood pressure values. Interestingly, in hypertensive patients with controlled blood pressure values, LV mass and extracellular signal–regulated kinase phosphorylation were significantly reduced compared with those in hypertensive patients with uncontrolled blood pressure values. These results suggest that MAPKs are sensors of pressure overload and that extracellular signal–regulated kinase activation in WBCs might be used as a novel surrogate biomarker of uncontrolled human hypertension.

MEF2C silencing attenuates load-induced left ventricular hypertrophy by modulating mTOR/S6K pathway in mice

Background

The activation of the members of the myocyte enhancer factor-2 family (MEF2A, B, C and D) of transcription factors promotes cardiac hypertrophy and failure. However, the role of its individual components in the pathogenesis of cardiac hypertrophy remains unclear.

Methodology/Principal Findings

In this study, we investigated whether MEF2C plays a role in mediating the left ventricular hypertrophy by pressure overload in mice. The knockdown of myocardial MEF2C induced by specific small interfering RNA (siRNA) has been shown to attenuate hypertrophy, interstitial fibrosis and the rise of ANP levels in aortic banded mice. We detected that the depletion of MEF2C also results in lowered levels of both PGC-1α and mitochondrial DNA in the overloaded left ventricle, associated with enhanced AMP:ATP ratio. Additionally, MEF2C depletion was accompanied by defective activation of S6K in response to pressure overload. Treatment with the amino acid leucine stimulated S6K and suppressed the attenuation of left ventricular hypertrophy and fibrosis in the aforementioned aortic banded mice.

Conclusion/Significance

These findings represent new evidences that MEF2C depletion attenuates the hypertrophic responses to mechanical stress and highlight the potential of MEF2C to be a target for new therapies to cardiac hypertrophy and failure.

Early exercise training after myocardial infarction prevents contractile but not electrical remodelling or hypertrophy

AIMS

Exercise started early after myocardial infarction (MI) improves in vivo cardiac function and myofilament responsiveness to Ca(2+). We investigated whether this represents partial or complete reversal of cellular remodelling.

METHODS AND RESULTS

Mice with MI following left coronary ligation were given free access to a running wheel (MI(EXE), N = 22) or housed sedentary (MI(SED), N = 18) for 8 weeks and compared with sedentary sham-operated animals (SHAM, N = 11). Myocytes were enzymatically isolated from the non-infarcted left ventricle. Myocytes in MI were significantly longer and even more so with exercise (165 +/- 3 microm in MI(EXE) vs. 148 +/- 3 microm in MI(SED) and 136 +/- 2 microm in SHAM; P < 0.05, mean +/- SEM); cell width was not different. Contraction was measured during electrical field stimulation at 1, 2, and 4 Hz. Unloaded cell shortening was significantly reduced in MI(SED) (at 1 Hz, L/L(0)=4.4 +/- 0.3% vs. 6.7 +/- 0.4% in SHAM; P < 0.05, also at 2 and 4 Hz). Exercise restored cell shortening to SHAM values (MI(EXE), L/L(0)=6.4 +/- 0.5%). Membrane currents and [Ca(2+)](i) were measured via whole-cell patch clamping, with Fluo-3 as Ca(2+) indicator, all at 30 degrees C. Ca(2+) transient amplitude, I(CaL) and sarcoplasmic reticulum Ca(2+) content were not different between the three groups. Diastolic Ca(2+) levels at 4 Hz were significantly elevated in MI(SED) only, with a trend to increased spontaneous Ca(2+) release events (sparks). Action potential duration was increased and transient outward K(+) currents significantly reduced after MI; this was unaffected by exercise.

CONCLUSIONS

Early voluntary exercise training after MI restores cell contraction to normal values predominantly because of changes in the myofilament Ca(2+) response and has a beneficial effect on diastolic Ca(2+) handling. However, the beneficial effect is not a complete reversal of remodelling as hypertrophy and loss of repolarizing K(+) currents are not affected.

Feasibility of left ventricular shape analysis from transthoracic real-time 3-D echocardiographic images

Despite the potential ability of left ventricular (LV) shape analysis to provide independent information complementary to ventricular size and function, in clinical practice only ejection fraction (EF) is currently assessed while LV shape is not routinely quantified. Moreover, geometric assumptions in the computation of EF from multiple two-dimensional (2-D) cut-planes by disc summation or area-length methods, introduce inaccuracies in the estimates. Also, previous approaches for the quantification of LV shape were based on geometric modeling and, as a result, proved inaccurate. Our aims were (1) to develop and test a three-dimensional (3-D) technique for direct quantification of LV shape from real-time 3-D echocardiographic (RT3DE) images without the need for geometric modeling using a new class of LV shape indices; and (2) to study the relationship between these indices and ventricular size and function in normal and abnormal ventricles. Spherical (S), ellipsoidal (E) and conical (C) shape indices were calculated using custom software for analysis of transthoracic RT3DE images on both global and regional levels and initially tested on computer simulated objects of different shapes. The feasibility of using these indices to differentiate between normal and abnormal ventricles was tested in three groups of patients: normal volunteers (NL, n=9), dilated cardiomyopathy (DCM, n=9) and coronary artery disease with apical regional wall motion abnormalities (RWMA, n=9). Computer simulation demonstrated that these shape indices are size-independent and can correctly classify the simulated objects. In human ventricles, both S and C but not E correlated well with LV volumes and EF. Also, S and C changed throughout the cardiac cycle while E remained almost constant. In addition, both regional and global S and C were able to identify differences between NL and abnormal ventricles: normal ventricles were less spherical and more conical than those of patients with DCM at both end-systole and end-diastole (p<0.05) both globally and regionally. In contrast, in patients with RWMA, similar differences were noted only at end-systole, both on a global level and in the apical region. In this study, we demonstrated the feasibility of quantifying LV shape from transthoracic RT3DE images at both global and regional levels. Potentially, such 3-D shape analysis could be combined with conventional evaluation of LV volume and function to provide a more comprehensive assessment of left ventricular performance.

Immunosuppression with an interleukin-2 fusion protein leads to improved LV function in experimental ischemic cardiomyopathy

Several cytokines are activated in chronic heart failure (CHF), including interleukin-2 (IL-2). IL-2 is important for the survival of regulatory T cells, as well as for the function of activated T cells. Its role in ischemic cardiomyopathy has not yet been investigated. We therefore studied left ventricular (LV) performance and remodeling in a rat model of myocardial infarction (MI) after treatment with an IL-2IgG2b fusion protein to stimulate IL-2 signaling. Spraque-Dawley rats (SD) were submitted to permanent ligation of the left descending artery (LAD) to induce a MI or to a sham operation. Twenty-four hours, 6 days and 3 weeks after MI, LV function was determined in vivo using a tip catheter. Cardiac IL-2 and IL-1beta content was measured by immunohistochemical staining on cryo-fixed heart cross sections at 24h and 6 days post MI. Total collagen content of the LV was determined by Sirius red stained formalin-stored sections under circularly polarized light 3 weeks post MI. Compared to sham-operated animals, IL-2 content was increased 13-fold (P<0.01) 24h post MI and 16-fold (P<0.01) 6 days post MI in the infarction area as well as 2-fold (P<0.05) 6 days post MI in the non-infarction area. Despite similar infarct sizes, LV function and remodeling were ameliorated in IL-2 fusion protein-treated ischemic rats, indicated by improved LV pressure (LVP), contractility (LVdP/dt(max)) and relaxation (LVdP/dt(min)) at all three time points. LV collagen content as a surrogate parameter for remodeling and IL-1beta expression as a marker for myocardial inflammation were reduced in the non-infarcted LV, but not in the LV infarction area compared to vehicle-treated controls. LV contractile dysfunction after experimental MI is improved after treatment with an IL-2-IgG2b fusion protein.

Modulation of interleukin signalling and gene expression in cardiac myocytes by endothelin-1

The related inflammatory cytokines, interleukin- (IL-) 1beta and IL-33, are both implicated in the response of the heart to injury. They also activate mitogen-activated protein kinases (MAPKs) in cardiac myocytes. The hypertrophic Gq protein-coupled receptor agonist endothelin-1 is a potentially cardioprotective peptide and may modulate the inflammatory response. Endothelin-1 also stimulates (MAPKs) in cardiac myocytes and promotes rapid changes in expression of mRNAs encoding intercellular and intracellular signalling components including receptors for IL-33 (ST2) and phosphoprotein phosphatases. Prior exposure to endothelin-1 may specifically modulate the response to IL-33 and, more globally, influence MAPK activation by different stimuli. Neonatal rat ventricular myocytes were exposed to IL-1beta or IL-33 with or without pre-exposure to endothelin-1 (5h) and MAPK activation assessed. IL-33 activated ERK1/2, JNKs and p38-MAPK, but to a lesser degree than IL-1beta. Endothelin-1 increased expression of soluble IL-33 receptors (sST2 receptors) which may prevent binding of IL-33 to the cell-surface receptors. However, pretreatment with endothelin-1 only inhibited activation of p38-MAPK by IL-33 with no significant influence on ERK1/2 and a small increase in activation of JNKs. Inhibition of p38-MAPK signalling following pretreatment with endothelin-1 was also detected with IL-1beta, H(2)O(2) or tumour necrosis factor alpha (TNFalpha) indicating an effect intrinsic to the signalling pathway. Endothelin-1 pretreatment suppressed the increase in expression of IL-6 mRNA induced by IL-1beta and decreased the duration of expression of TNFalpha mRNA. Coupled with the general decrease in p38-MAPK signalling, we conclude that endothelin-1 attenuates the cardiac myocyte inflammatory response, potentially to confer cardioprotection.

Activation of MTK1/MEKK4 induces cardiomyocyte death and heart failure

MTK1 (MEKK4) is a mitogen-activated protein kinase kinase kinase that regulates the activity of its downstream mitogen-activated kinases, p38, and c-Jun N-terminal kinase (JNK). However, the physiological function of MTK1 in the heart remains to be determined. Here, we attempted to elucidate the function of MTK1 in the heart using in vitro and in vivo models. MTK1 was activated in the hearts of mice subjected to pressure overload-induced heart failure. Overexpression of a constitutively active mutant of MTK1 (MTK1DeltaN) induced apoptosis in isolated neonatal rat cardiomyocytes, whereas a kinase domain-deleted form of MTK1 attenuated H(2)O(2)-induced apoptosis. Specific inhibitors of p38 or JNK effectively protected cardiomyocytes from MTK1DeltaN-induced cell death. In mice, cardiac-specific overexpression of MTK1DeltaN resulted in early mortality compared with the lifespan of littermate controls. Echocardiographic analysis revealed increases in end-diastolic and end-systolic left ventricular internal dimensions and a decrease in fractional shortening in MTK1DeltaN transgenic mice. In addition, the mice showed characteristic phenotypes of heart failure such as an increase in lung weight. The number of TUNEL-positive myocytes and the level of cleaved caspase 3 protein were both increased in MTK1DeltaN transgenic mice. Thus, MTK1 plays an important role in the regulation of cell death and is also involved in the pathogenesis of heart failure.