Molecular Mechanism of Cardiac Hypertrophy and Development

Large animal models of pressure overload-induced cardiac left ventricular hypertrophy to study remodelling of the human heart with aortic stenosis

Pathologic cardiac hypertrophy is a common consequence of many cardiovascular diseases, including aortic stenosis (AS). AS is known to increase the pressure load of the left ventricle, causing a compensative response of the cardiac muscle, which progressively will lead to dilation and heart failure. At a cellular level, this corresponds to a considerable increase in the size of cardiomyocytes, known as cardiomyocyte hypertrophy, while their proliferation capacity is attenuated upon the first developmental stages. Cardiomyocytes, in order to cope with the increased workload (overload), suffer alterations in their morphology, nuclear content, energy metabolism, intracellular homeostatic mechanisms, contractile activity, and cell death mechanisms. Moreover, modifications in the cardiomyocyte niche, involving inflammation, immune infiltration, fibrosis, and angiogenesis, contribute to the subsequent events of a pathologic hypertrophic response. Considering the emerging need for a better understanding of the condition and treatment improvement, as the only available treatment option of AS consists of surgical interventions at a late stage of the disease, when the cardiac muscle state is irreversible, large animal models have been developed to mimic the human condition, to the greatest extend. Smaller animal models lack physiological, cellular and molecular mechanisms that sufficiently resemblance humans and in vitro techniques yet fail to provide adequate complexity. Animals, such as the ferret (Mustello purtorius furo), lapine (rabbit, Oryctolagus cunigulus), feline (cat, Felis catus), canine (dog, Canis lupus familiaris), ovine (sheep, Ovis aries), and porcine (pig, Sus scrofa), have contributed to research by elucidating implicated cellular and molecular mechanisms of the condition. Essential discoveries of each model are reported and discussed briefly in this review. Results of large animal experimentation could further be interpreted aiming at prevention of the disease progress or, alternatively, at regression of the implicated pathologic mechanisms to a physiologic state. This review summarizes the important aspects of the pathophysiology of LV hypertrophy and the applied surgical large animal models that currently better mimic the condition.

Cardiovascular Diseases and Zinc

Zinc is structurally and functionally essential for more than 300 enzymes and 2000 transcription factors in human body. Intracellular labile zinc is the metabolically effective zinc and tiny changes in its concentrations significantly affect the intracellular signaling and enzymatic responses. Zinc is crucial for the embrionic and fetal development of heart. Therefore, it is shown to be related with a variety of congenital heart defects. It is involved in epithelial-to-mesenchymal transformation including endocardial cushion development, which is necessary for atrioventricular septation as well as the morphogenesis of heart valves. In atherosclerosis, monocyte endothelial adhesion, and diapedesis, activation and transformation into macrophages and forming foam cells by the ingestion of oxidized LDL are monocyte related steps which need zinc. Intracellular zinc increases intracellular calcium through a variety of pathways and furthermore, zinc itself can work as a second messenger as calcium. These demonstrate the significance of intracellular zinc in heart failure and arterial hypertension. However, extracellular zinc has an opposite effect by blocking calcium channels, explaining decreased serum zinc levels, contrary to the increased cardiomyocyte and erythrocyte zinc levels in hypertensive subjects. These and other data in the literature demonstrate that zinc has important roles in healthy and diseased cardiovascular system but zinc-cardiovascular system relationship is so complex that, it has not been explained in all means. In this article, we try to review some of the available knowledge about this complex relationship.

GCN5-mediated regulation of pathological cardiac hypertrophy via activation of the TAK1-JNK/p38 signaling pathway

Pathological cardiac hypertrophy is a process of abnormal remodeling of cardiomyocytes in response to pressure overload or other stress stimuli, resulting in myocardial injury, which is a major risk factor for heart failure, leading to increased morbidity and mortality. General control nonrepressed protein 5 (GCN5)/lysine acetyltransferase 2 A, a member of the histone acetyltransferase and lysine acetyltransferase families, regulates a variety of physiological and pathological events. However, the function of GCN5 in pathological cardiac hypertrophy remains unclear. This study aimed to explore the role of GCN5 in the development of pathological cardiac hypertrophy. GCN5 expression was increased in isolated neonatal rat cardiomyocytes (NRCMs) and mouse hearts of a hypertrophic mouse model. GCN5 overexpression aggravated the cardiac hypertrophy triggered by transverse aortic constriction surgery. In contrast, inhibition of GCN5 impairs the development of pathological cardiac hypertrophy. Similar results were obtained upon stimulation of NRCMs (having GCN5 overexpressed or knocked down) with phenylephrine. Mechanistically, our results indicate that GCN5 exacerbates cardiac hypertrophy via excessive activation of the transforming growth factor β-activated kinase 1 (TAK1)-c-Jun N-terminal kinase (JNK)/p38 signaling pathway. Using a TAK1-specific inhibitor in rescue experiments confirmed that the activation of TAK1 is essential for GCN5-mediated cardiac hypertrophy. In summary, the current study elucidated the role of GCN5 in promotion of cardiac hypertrophy, thereby implying it to be a potential target for treatment.

MEF2 in cardiac hypertrophy in response to hypertension

Hypertension is a globally prevalent pathological condition and an underlying risk factor for the development of cardiac hypertrophy leading to heart failure. Myocyte enhancer factor 2 (Mef2) has been identified as one of the primary effectors of morphological changes in the hypertensive heart, as part of a complex network of molecular signaling controlling cardiac gene expression. Experimental chronic pressure-overload models that mimic hypertension in the mammalian heart lead to the activation of various pathological mechanisms that result in structural changes leading to debilitating cardiac hypertrophy and ultimately heart failure. The purpose here is to survey the literature implicating Mef2 in hypertension induced cardiac hypertrophy, towards illuminating points of interest for understanding and potentially treating heart failure.

Pinocembrin Protects Cardiomyocytes Against Isoproterenol-Induced Hypertrophy

Cardiac hypertrophy is characterized by an increase in myocardial cell volume and extracellular matrix production. Persistent cardiac hypertrophy can cause dilated cardiomyopathy, heart failure, and even death. Pinocembrin (5,7-dihydroxyflavanone) is a type of flavonoid, extracted from propolis, that has antimicrobial, antioxidant, antiinflammatory, and anticancer properties. The results of the present study showed that pretreatment of isoproterenol (ISO)-treated H9c2 cardiomyocytes with pinocembrin reduced the messenger RNA levels of hypertrophic markers, including atrial natriuretic factor and βeta-myosin heavy chain, and inflammatory cytokines, such as tumor necrosis factor-α, interleukin-6, interleukin-1β, and interferon-γ, and also inhibited p65 phosphorylation and nuclear factor-kappa B (NF-κB) translocation. In addition, the activity of IκBα, an inhibitor of NF-κB, was increased while that of caspase-3 was reduced under these conditions. These results indicate that pinocembrin may inhibit ISO-induced myocardial hypertrophy by attenuating the NF-κB signaling pathway.

Histone deacetylases in modulating cardiac disease and their clinical translational and therapeutic implications

Cardiovascular diseases are the leading cause of mortality and morbidity worldwide. Histone deacetylases (HDACs) play an important role in the epigenetic regulation of genetic transcription in response to stress or pathological conditions. HDACs interact with a complex co-regulatory network of transcriptional regulators, deacetylate histones or non-histone proteins, and modulate gene expression in the heart. The selective HDAC inhibitors have been considered to be a critical target for the treatment of cardiac disease, especially for ameliorating cardiac dysfunction. In this review, we discuss our current knowledge of the cellular and molecular basis of HDACs in mediating cardiac development and hypertrophy and related pharmacologic interventions in heart disease.

The POU4F2/Brn-3b transcription factor is required for the hypertrophic response to angiotensin II in the heart

Adult hearts respond to increased workload such as prolonged stress or injury, by undergoing hypertrophic growth. During this process, the early adaptive responses are important for maintaining cardiac output whereas at later stages, pathological responses such as cardiomyocyte apoptosis and fibrosis cause adverse remodelling, that can progress to heart failure. Yet the factors that control transition from adaptive responses to pathological remodelling in the heart are not well understood. Here we describe the POU4F2/Brn-3b transcription factor (TF) as a novel regulator of adaptive hypertrophic responses in adult hearts since Brn-3b mRNA and protein are increased in angiotensin-II (AngII) treated mouse hearts with concomitant hypertrophic changes [increased heart weight:body weight (HW:BW) ratio]. These effects occur specifically in cardiomyocytes because Brn-3b expression is increased in AngII-treated primary cultures of neonatal rat ventricular myocytes (NRVM) or foetal heart-derived H9c2 cells, which undergo characteristic sarcomeric re-organisation seen in hypertrophic myocytes and express hypertrophic markers, ANP/βMHC. The Brn-3b promoter is activated by known hypertrophic signalling pathways e.g. p42/p44 mitogen-activated protein kinase (MAPK/ERK1/2) or calcineurin (via NFAT). Brn-3b target genes, e.g. cyclin D1, GLUT4 and Bax, are increased at different stages following AngII treatment, supporting distinct roles in cardiac responses to stress. Furthermore, hearts from male Brn-3b KO mutant mice display contractile dysfunction at baseline but also attenuated hypertrophic responses to AngII treatment. Hearts from AngII-treated male Brn-3b KO mice develop further contractile dysfunction linked to extensive fibrosis/remodelling. Moreover, known Brn-3b target genes, e.g. GLUT4, are reduced in AngII-treated Brn-3b KO hearts, suggesting that Brn-3b and its target genes are important in driving adaptive hypertrophic responses in stressed heart.

HMGB1 enhances mechanical stress-induced cardiomyocyte hypertrophy in vitro via the RAGE/ERK1/2 signaling pathway

Pressure overload-induced cardiac hypertrophy is associated with a complex spectrum of pathophysiological mechanisms, including the inflammation response. High mobility group box-1 (HMGB1), a pro-inflammatory cytokine, is not only increased in myocardium under pressure overload, but also exacerbates pressure overload-induced cardiac hypertrophy and dysfunction; however, the underlying mechanisms have remained elusive. In the present study, cultured cardiomyocytes were stimulated by mechanical stress and/or HMGB1 for various durations to examine the role of HMGB1 in cardiomyocyte hypertrophy, and to detect the expression of receptor for advanced glycation end products (RAGE), toll-like receptor 4 (TLR-4) and the activation status of mitogen-activated protein kinases (MAPKs) and Janus kinase 2 (JAK2)/STAT3. The results indicated that HMGB1 aggravated mechanical stress-induced cardiomyocyte hypertrophy. Furthermore, mechanical stress and HMGB1 stimulation activated extracellular signal-regulated kinase 1/2 (ERK1/2), P38 and JAK2/STAT3 signaling in cardiomyocytes, but an additive effect of the combined stimuli was only observed on the activation of ERK1/2. In addition, mechanical stress caused a prompt upregulation of the expression of RAGE and TLR-4 in cardiomyocytes, while the activation of ERK1/2 by HMGB1 was inhibited by blockage of RAGE, but not by blockage of TLR-4. In summary, the present results indicated that extracellular HMGB1 enhanced mechanical stress-induced cardiomyocyte hypertrophy in vitro, at least partially via the RAGE/ERK1/2 signaling pathway.

BAOXIN Granules Protected Mouse Model With Elevated Afterload From Cardiac Hypertrophy by Suppressing Both Inflammatory Reaction and Collagen Deposition

BAOXIN Pill was reported to be effective clinically for chronic heart failure based on the principles of traditional Chinese medicine (TCM), invigorating qi and activating blood. The present study evaluated preclinically the effects of the improved dosage form, BAOXIN Granules, on cardiac hypertrophy. Transverse aortic constriction (TAC) was performed in mice to model cardiac hypertrophy by aortic stenosis for 4 weeks. The sham and TAC group were intragastrically administrated with saline as the controls. Two treatment groups were administrated orally with 10 mg/kg⋅d Enalapril (positive control) or 0.77 g/kg⋅d BAOXIN Granules for 4 weeks respectively. The effects were evaluated by echocardiography, morphology, and biological markers for cardiac function. The specific genes involved in inflammation and fibrosis were also examined for their expressions to investigate the pathways involved in early heart failure. Just as Enalapril, BAOXIN Granules administration markedly attenuated left ventricular hypertrophy and improved heart function as evidenced by echo cardiography, morphology. Accordingly, the biomarkers of the early stage heart failure, ANP, BNP and β-MHC, were decreased in the two treatment groups. We also found that mRNA expressions of some inflammatory factors and fibrosis associated genes were down-regulated in the tissue of heart after treatment. BAOXIN Granules may protect the heart from myocardial hypertrophy caused by increasing left ventricular afterload. It can suppress both inflammatory reaction and collagen deposition during pressure overload. BAOXIN Granules is advised to be tested in clinical trials for heart failure in the future.

Emergence of Members of TRAF and DUB of Ubiquitin Proteasome System in the Regulation of Hypertrophic Cardiomyopathy

The ubiquitin proteasome system (UPS) plays an imperative role in many critical cellular processes, frequently by mediating the selective degradation of misfolded and damaged proteins and also by playing a non-degradative role especially important as in many signaling pathways. Over the last three decades, accumulated evidence indicated that UPS proteins are primal modulators of cell cycle progression, DNA replication, and repair, transcription, immune responses, and apoptosis. Comparatively, latest studies have demonstrated a substantial complexity by the UPS regulation in the heart. In addition, various UPS proteins especially ubiquitin ligases and proteasome have been identified to play a significant role in the cardiac development and dynamic physiology of cardiac pathologies such as ischemia/reperfusion injury, hypertrophy, and heart failure. However, our understanding of the contribution of UPS dysfunction in the plausible development of cardiac pathophysiology and the complete list of UPS proteins regulating these afflictions is still in infancy. The recent emergence of the roles of TNF receptor-associated factor (TRAFs) and deubiquitinating enzymes (DUBs) superfamily in hypertrophic cardiomyopathy has enhanced our knowledge. In this review, we have mainly compiled the TRAF superfamily of E3 ligases and few DUBs proteins with other well-documented E3 ligases such as MDM2, MuRF-1, Atrogin-I, and TRIM 32 that are specific to myocardial hypertrophy. In this review, we also aim to highlight their expression profile following physiological and pathological stimulation leading to the onset of hypertrophic phenotype in the heart that can serve as biomarkers and the opportunity for the development of novel therapies.

QiShenYiQi Pills, a compound in Chinese medicine, protects against pressure overload-induced cardiac hypertrophy through a multi-component and multi-target mode

The present study aimed to explore the holistic mechanism for the antihypertrophic effect of a compound in Chinese medicine, QiShenYiQi Pills (QSYQ) and the contributions of its components to the effect in rats with cardiac hypertrophy (CH). After induction of CH by ascending aortic stenosis, rats were treated with QSYQ, each identified active ingredient (astragaloside IV, 3, 4-dihydroxy-phenyl lactic acid or notoginsenoside R1) from its 3 major herb components or dalbergia odorifera, either alone or combinations, for 1 month. QSYQ markedly attenuated CH, as evidenced by echocardiography, morphology and biochemistry. Proteomic analysis and western blot showed that the majority of differentially expressed proteins in the heart of QSYQ-treated rats were associated with energy metabolism or oxidative stress. Each ingredient alone or their combinations exhibited similar effects as QSYQ but to a lesser extent and differently with astragaloside IV and notoginsenoside R1 being more effective for enhancing energy metabolism, 3, 4-dihydroxy-phenyl lactic acid more effective for counteracting oxidative stress while dalbergia odorifera having little effect on the variables evaluated. In conclusion, QSYQ exerts a more potent antihypertrophic effect than any of its ingredients or their combinations, due to the interaction of its active components through a multi-component and multi-target mode.

Anomalous left coronary artery from the right coronary cusp with gene positive apical hypertrophic cardiomyopathy: a case report and literature review

In the United States, hypertrophic cardiomyopathy and coronary artery anomalies account for the leading two causes of sudden death in athletes. We present a case of a patient with an anomalous origin of the left main from the right coronary sinus with associated gene-confirmed hypertrophic cardiomyopathy. The patient underwent surgical repair with unroofing of the intramural portion of the left main coronary artery with a good result. We also review the reported cases in the medical literature describing this uncommon association between anomalous coronary artery origin and hypertrophic cardiomyopathy.

Mutational screening of affected cardiac tissues and peripheral blood cells identified novel somatic mutations in GATA4 in patients with ventricular septal defect

The aim of this study was to examine how somatic mutations of the GATA4 gene contributed to the genesis of ventricular septal defect (VSD). The coding and intron-exon boundary regions of GATA4 were sequenced of DNA samples from peripheral blood cells and cardiac tissues of twenty surgically treated probands with VSD. Seven novel heterozygous variants were detected in cardiac tissues from VSD patients, but they were not detected in the peripheral blood cells of VSD patients or in 500 healthy control samples. We replicated 14 single nucleotide polymorphisms (SNPs) reported in NCBI. Bioinformatics analysis was performed to analyze the possible mechanism by which mutations were linked to VSD. Among those variants, c. 1004C>A (p.S335X) occurred in the highly conserved domain of GATA4 and generated a termination codon, which led to the production of truncated GATA4. The seven novel heterozygous GATA4 mutations were only identified in cardiac tissues with VSD, suggesting that they are of somatic origin. A higher mutation rate in cardiac tissues than in peripheral blood cells implies that the genetic contribution to VSD may have been underestimated.

Depletion of endogenous kallistatin exacerbates renal and cardiovascular oxidative stress, inflammation, and organ remodeling

Kallistatin (KS) levels are reduced in the kidney and blood vessels under oxidative stress conditions. To determine the function of endogenous KS in the renal and cardiovascular systems, KS levels were depleted by daily injection of anti-rat KS antibody into DOCA-salt hypertensive rats for 10 days. Administration of anti-KS antibody resulted in reduced KS levels in the circulation but increased levels of serum thiobarbituric acid reactive substances (an indicator of lipid peroxidation) as well as superoxide formation in the aorta. Moreover, anti-KS antibody injection resulted in increased NADH oxidase activity and superoxide production but decreased nitric oxide levels in the kidney and heart. Endogenous KS blockade aggravated renal dysfunction, damage, hypertrophy, inflammation, and fibrosis as evidenced by decreased creatinine clearance and increased serum creatinine, blood urea nitrogen and urinary protein levels, tubular dilation, protein cast formation, glomerulosclerosis, glomerular enlargement, inflammatory cell accumulation, and collagen deposition. In addition, rats receiving anti-KS antibody had enhanced cardiac injury as indicated by cardiomyocyte hypertrophy, inflammation, myofibroblast accumulation, and fibrosis. Renal and cardiac injury caused by endogenous KS depletion was accompanied by increases in the expression of the proinflammatory genes tumor necrosis factor-α and intercellular adhesion molecule-1 and the profibrotic genes collagen I and III, transforming growth factor-β, and tissue inhibitor of metalloproteinase-1. Taken together, these results implicate an important role for endogenous KS in protection against salt-induced renal and cardiovascular injury in rats by suppressing oxidative stress, inflammation, hypertrophy, and fibrosis.

The dynamics of fibroblast-myocyte-capillary interactions in the heart

In the heart, electrical, mechanical, and chemical signals create an environment essential for normal cellular responses to developmental and pathologic cues. Communication between fibroblasts, myocytes, and endothelial cells, as well as the extracellular matrix, are critical to fluctuations in heart composition and function during normal development and pathology. Recent evidence suggests that cytokines play a role in cell-cell signaling in the heart. Indeed, we find that interactions between myocytes and cardiac fibroblasts results in increased interleukin-6 and tumor necrosis factor-alpha secretion. We also used confocal and transmission electron microscopy to observe close relationships and possible direct communication between these cells in vivo. Our results highlight the importance of direct cell-cell communication in the heart, and indicate that interactions between fibroblasts, myocytes, and capillary endothelium results in differential cytokine expression. Studying these cell-cell interactions has many implications for the process of cardiac remodeling and overall heart function during development and cardiopathology.

Thyroid hormone-induced cardiac mechano growth factor expression depends on beating activity

The mechano growth factor (MGF), a splice variant of the IGF-I gene, was first discovered in mechanically overloaded skeletal muscle and was shown to play an important role in proliferation of muscle stem cells. Since then, the presence and effects of MGF have been demonstrated in other tissues. MGF has been shown to act neuroprotectively during brain ischemia, and pretreatment with MGF before myocardial infarction improves cardiac function. Because MGF plays a permissive role in exercise-induced skeletal muscle hypertrophy, we hypothesize that MGF is commonly involved in cardiac hypertrophy. To investigate the regulation of MGF expression in heart, mice were treated with thyroid hormone (T(3)) for 12 d to induce physiological cardiac hypertrophy. MGF mRNA expression was specifically increased in midregions of the septum and left ventricular wall. Interestingly, MGF expression strongly correlated with the increased or decreased beating frequency of hyperthyroid and hypothyroid hearts. To further investigate the mechanically dependent induction of MGF, neonatal rat cardiomyocytes were isolated and exposed to T(3). Upon T(3) treatment, cardiomyocytes increased both contractile activity measured as beats per minute and MGF as well as IGF-IEa mRNA expression. Importantly, when cardiomyocytes were contractile arrested by KCl, simultaneous exposure to T(3) prevented the up-regulation of MGF, whereas IGF-IEa was still induced. These studies demonstrated that MGF but not IGF-IEa expression is dependent on beating activity. These findings suggest that MGF is specifically stimulated by mechanical loading of the heart to mediate the hypertrophic response to thyroid hormone.

Exploiting cGMP-based therapies for the prevention of left ventricular hypertrophy: NO* and beyond

Left ventricular hypertrophy (LVH), an increased left ventricular (LV) mass, is common to many cardiovascular disorders, initially developing as an adaptive response to maintain myocardial function. In the longer term, this LV remodelling becomes maladaptive, with progressive decline in LV contractility and diastolic function. Indeed LVH is recognised as an important blood-pressure independent predictor of cardiovascular morbidity and mortality. The clinical efficacy of current treatments for LVH is reduced, however, by their tendency to slow disease progression rather than induce its reversal, and thus the development of new therapies for LVH is paramount. The signalling molecule cyclic guanosine-3',5'-monophosphate (cGMP), well-recognised for its role in regulating vascular tone, is now being increasingly identified as an important anti-hypertrophic mediator. This review is focused on the various means by which cGMP can be stimulated in the heart, such as via the natriuretic peptides, to exert anti-hypertrophic actions. In particular we address the limitations of traditional nitric oxide (NO*) donors in the face of the potential therapeutic advantages offered by novel alternatives; NO* siblings, ligands of the cGMP-generating enzymes, soluble (sGC) and particulate guanylyl cyclases (pGC), and phosphodiesterase inhibitors. Further impact of cGMP within the cardiovascular system is also discussed with a view to representing cGMP-based therapies as innovative pharmacotherapy, alone or concurrent with standard care, for the management of LVH.

Inhibition of farnesylpyrophosphate synthase prevents angiotensin II-induced hypertrophic responses in rat neonatal cardiomyocytes: involvement of the RhoA/Rho kinase pathway

The RhoA/Rho-kinase (ROCK) pathway is involved in angiotensin (Ang) II-induced cardiac hypertrophy. However, it is still unclear whether inhibition of farnesylpyrophosphate (FPP) synthase can attenuate Ang II-induced hypertrophic responses, and whether it involves the RhoA/ROCK pathway. The anti-hypertrophic effects of inhibition of FPP synthase with alendronate in Ang II-cultured neonatal cardiomyocytes were partially reversed by geranylgeranyol (GGOH) and were mimicked by GGTI-286, a geranylgeranyl transferase-I inhibitor, C3 exoenzyme, an inhibitor of Rho, or Y-27632, an inhibitor of ROCK. Pull-down assay showed alendronate reduced-active RhoA by Ang II was also partially antagonized by GGOH. This study revealed that the inhibition of FPP synthase by alendronate reduces RhoA activation by diminishing geranylgeranylation which prevents Ang II-induced hypertrophic responses in neonatal cardiomyocytes.

Selected zinc metabolism parameters and left ventricle mass in echocardiographic examination in primary arterial hypertension

The basal systolic and diastolic blood pressure, body mass index, left ventricular mass, serum and lymphocyte zinc levels, serum aldosterone, plasma rennin and angiotensin-converting enzyme activities, sodium and potassium levels, and the total and ouabain-dependent rate constants of zinc efflux from lymphocytes were measured in a group of 41 individuals of both sexes (overall age 46.3 +/- 11.4 years), of which 18 were women (48.5 +/- 7.1 years old) and 23 were men (44.7 +/- 13.8 years old). There were no significant differences between these parameters while dividing the subjects into groups according to sex, despite differences in weight, left ventricle mass, plasma rennin activity, and serum aldosterone content. Only the total and ouabain-dependent rate constants of zinc efflux from lymphocytes slightly negatively correlated to left ventricular mass, r = -0.30 to r = -0.36. This may constitute indirect evidence of zinc deficiency in cardiomyocytes of some hypertensive individuals with left ventricular hypertrophy.

Mechanisms of endothelin-1-induced decrease in contractility in adult mouse ventricular myocytes

BACKGROUND AND PURPOSE

The potent vasoconstrictor polypeptide endothelin-1 (ET-1) plays an important pathophysiological role in progression of cardiovascular diseases and elicits prominent effects on myocardial contractility. Although ET-1 produces a positive inotropy in cardiac muscle of most mammalian species, it induces a sustained negative inotropy in mice. This study was performed to gain an insight into the cellular mechanisms underlying the negative inotropy in adult mouse ventricular myocytes.

EXPERIMENTAL APPROACH

Cell shortening and Ca(2+) transients were simultaneously recorded from isolated mouse ventricular myocytes loaded with the Ca(2+)-sensitive fluorescent dye indo-1.

KEY RESULTS

ET-1 decreased cell shortening in a concentration-dependent manner (pD(2) value of 10.1). The ET-1-induced decrease in cell shortening was associated with a decrease in Ca(2+) transients. In addition, the Ca(2+) transient/cell-shortening relationship was shifted to the right by ET-1, indicating decreased myofilament Ca(2+) sensitivity. The instantaneous relationship of the rising phase of the Ca(2+) transient and cell shortening was shifted to the right by ET-1. Decreased Ca(2+) transients and cell shortening induced by ET-1 were markedly attenuated by the specific Na(+)/Ca(2+) exchange inhibitor SEA0400.

CONCLUSIONS AND IMPLICATIONS

ET-1-induced negative inotropy in mouse ventricular myocytes was mediated by decreased Ca(2+) transients and myofilament Ca(2+) sensitivity. These data are entirely consistent with the involvement of increased Ca(2+) extrusion via the Na(+)/Ca(2+) exchanger in the ET-1-mediated decrease in Ca(2+) transients. Decreased Ca(2+) sensitivity may be due to retardation of cell shortening in response to a rise in Ca(2+) transients.

Amelioration of hypertensive heart failure by amlodipine may occur via antioxidative effects

Although recent clinical studies have suggested that long-acting calcium channel blockers (CCBs) have beneficial effects on heart failure, the precise mechanism is unknown. In this study, Dahl salt-sensitive rats fed a high salt diet were treated with the long-acting CCB amlodipine, the low-molecular-weight membrane permeable superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (Tempol), or saline from 11 weeks after birth. The cardiac geometry and function, and gene expression profiles were determined at 17 weeks. Dahl salt-sensitive rats fed a high salt diet followed by saline as a non-treatment control (HS group) showed a marked increase in blood pressure and developed concentric hypertrophy at 11 weeks, followed by left ventricular (LV) dilation and congestive heart failure by 17 weeks. The treatment with amlodipine (AMLO group) or Tempol (TEMP group) significantly inhibited the development of LV hypertrophy and cardiac dysfunction. Analysis using an Affymetrix GeneChip U34 revealed that the expression levels of 195 genes were changed by the treatment with amlodipine. Among these 195 genes, 110 genes were increased in HS rats and decreased in AMLO rats. And of these 110 genes, 54 genes were also decreased in TEMP rats. In contrast, 85 genes were decreased in HS rats and increased in AMLO rats. Of these 85 genes, 38 genes were also increased in TEMP rats. Approximately 48% of the genes were changed in similar fashion in AMLO and TEMP rats, suggesting that amlodipine shows beneficial effects on heart failure mainly via antioxidative mechanisms.

Anomalous origin of the main stem of the left coronary artery from the pulmonary trunk presenting with left ventricular hypertrophy

Patients with anomalous origin of the left coronary artery from the pulmonary trunk may present with paroxysmal angina on exertion, congestive heart failure, dyspnoea, syncope or sudden death. The association of such anomalous origin of the left coronary artery from the pulmonary trunk with a hypertrophic left ventricle is extremely rare. In our cohort of patients with anomalous origin of the left coronary artery from the pulmonary trunk, two presented with a hypertrophic left ventricle. We discuss these cases, accompanied by a review of the English literature describing different morphological anomalies of the coronary arteries associated with left ventricular hypertrophy. Whether the hypertrophy is a result of the evolvement of the collateral coronary system, or due to an additional pathological gene for hypertrophic obstructive cardiomyopathy, remains an enigma. The hypertrophy may have served as a compensatory mechanism accounting for the atypical clinical presentation. We further discuss the possible factors associating the occurrence of anomalous origin of the left coronary artery from the pulmonary trunk and myohypertrophy, supported by the documentation of the regression of hypertrophy following surgical correction of the anomalous arterial origin as seen in our patients.

Effects of protein kinase inhibitors on thein vitrogrowth ofBabesia bovis

Staurosporine, Ro-31-7549, and KN-93, which are inhibitors of serine/threonine protein kinase, protein kinase C, and calcium-modulin kinase, respectively, were tested for their effects on thein vitrogrowth ofBabesia bovis. Staurosporine was the most effective inhibitor, completely clearing the parasitaemia as early as the first day of exposure at a concentration of 100 μM. Moreover, staurosporine caused a significant increase in the percentage of extracellular merozoites, most likely due to the inhibition of erythrocyte invasion by the parasite. Although 5 mMRo-31-7549 and KN-93 had a suppressive action, this was not enough to destroy the parasite. Interestingly, concentrations of 0·5 to 5 mMKN-93 influenced the parasitic development within the infected erythrocytes. The present study suggests thatB. bovisrequires, to a certain extent, the phosphorylations mediated by parasite- or host erythrocyte-protein kinases, in particular, for the processes of successful invasion of erythrocytes and intraerythrocytic development.

Balance between hypertrophic and hypoxic stimulus in caspase-3 activation during rat heart development

During heart development, cell hyperplasia and hypertrophy are the main mechanisms by which cardiac mass grows. Both these processes along with programmed cell death lead to complete growth and function. In addition, since the establishment of cardiac function depends on the relationship between oxygen supply and demand, we investigated some of the molecular mechanisms at the basis of rat myocardial cell response to hypoxic stress at different times of neonatal life. In particular, the role played by hypertrophic and survival factors like NF-kB and IAP-1 (Inhibiting Apoptosis Protein) and by death factors ASK-1 (Apoptosis Signal Regulating Kinase), JNK/SAPK (Jun-N-Terminal-Kinase/Stress-Activated Protein Kinase) pathways in regulating caspase-3 expression and activity has been evaluated by immunohistochemical and Western blotting analyses, respectively. Level of phosphorylation of IkBalpha and IAP-1 expression were substantial in 8-day-old hypoxic hearts, suggesting the persistence of NF-kB driven hypertrophic signal along with a rescue attempt against hypoxic stress. In contrast, ASK-1 mediated JNK/SAPK activation, regulating Bcl(2) levels, allows Bax homodimerization and caspase-3 activation in the same experimental conditions. Thus, a regulation carried out by NF-kB and JNK/SAPK pathways on caspase-3 activation at day 8 of neonatal life can be suggested as the main factor for the heart 'adaptive' response to hypoxia.

Differential gene expression of adrenomedullin receptors in pressure- and volume-overloaded heart--role of angiotensin II

Left ventricular (LV) adrenomedullin (AM) gene expression differs between pressure overload (POL) and volume overload (VOL) and angiotensin II could be a critical stimulator of AM gene expression in POL and VOL models. Calcitonin receptor-like receptor (CRLR) co-expressed with receptor activity modifying protein 2 (RAMP2) or RAMP3 functions as an AM receptor. Levels of CRLR, RAMP2 and RAMP3 mRNA that were significantly increased within 24 h returned to the basal level at 5 days after the imposition of POL in the present study. In contrast, mRNA levels of CRLR and RAMP2 gradually increased over 6 weeks after the imposition of VOL. Continuous infusion of angiotensin II stimulated LV AM gene and AM receptor gene expression independently of LV peak-systolic and LV end-diastolic pressure. The gene expression of LV AM receptors increased in different types of cardiac overload. The present study revealed an intimate association between the AM signaling system and angiotensin II.

Ca2+ dynamics of thrombin-stimulated rat heart-derived embryonic myocytes: relationship to protein synthesis and cell growth

Various cell types respond to the serum protease, thrombin, with increased proliferation rates. In non-dividing postnatal mammalian cardiomyocytes, however, thrombin induces cellular hypertrophy. Both growth responses are associated with early Ca2+ signaling. The present study was conducted to characterize Ca2+ dynamics in thrombin stimulated, dividing embryonic cardiomyocytes, and to ascertain whether such dynamics support hypertrophic or hyperplastic growth. H9c2 rat cardiomyoblasts responded to thrombin with immediate, large increments in free Ca2+ that arose principally from the release of S(E)R sequestered Ca2+ and that persisted for only a few min. Ca2+ stores were refilled within 1h. Thrombin also increased rates of overall protein synthesis for several hours. This translational up-regulation, which required gene transcription, was abolished if cells were incubated at low extracellular Ca2+ during the first hour with thrombin. The protease conferred protective effects against toxicity resulting from serum deprivation and doxorubicin treatment. However, thrombin induced neither cellular hypertrophy, as is seen with arginine vasopressin, nor hyperplasia, as is observed with platelet-derived growth factor (PDGF-BB), in H9c2 cardiomyocytes. In comparison with vasopressin or PDGF-BB, thrombin promoted brief Ca2+ signaling, little cation movement to the extracellular fluid, and more rapid refilling of the S(E)R. It is concluded that the Ca2+ signaling generated by thrombin and the translational stimulation shown in this report to depend on this Ca2+ signaling are insufficient to sustain a major growth response in these embryonic cardiomyocytes.

Left and right coronary circulation in left ventricular hypertrophy: effects of angiotensin converting enzyme inhibition

The circulation in the left and right coronary beds in pressure overload-induced left ventricular (LV) hypertrophy was studied in Wistar male rats (n=6/group) that were subjected to abdominal aortic constriction or to sham-operation. From 3 to 6 weeks after surgery, the animals with aortic constriction received vehicle or 0.01, 0.1, or 1 mg/kg per day po of the angiotensin converting enzyme (ACE) inhibitor, ramipril. At 6 weeks, after measuring blood pressure in the carotid artery in vivo, the hearts were isolated and the left and right coronary beds subjected to independent perfusion. Minimum coronary vascular resistance per unit heart weight (MCVR/g) was determined in both beds during simultaneous infusion of 10 micromol/L adenosine. Aortic constriction resulted in a significant increase in blood pressure, LV weight/body weight ratio, and bilateral MCVR/g. Ramipril lowered arterial pressure in a dose-dependent manner and reversed the increased right MCVR/g at the anti-hypertensive dose, but it did not affect LV mass or left MCVR/g. These results suggest that both coronary hypertension and myocardial hypertrophy contribute to the global impairment of coronary circulation in LV hypertrophy. ACE inhibitors may improve coronary circulation in LV hypertrophy when administrated at an appropriate dose and for a sufficient period.

Overexpression of endothelial nitric oxide synthase attenuates cardiac hypertrophy induced by chronic isoproterenol infusion

Endogenous nitric oxide (NO) inhibits the contractile response to beta-adrenergic stimulation, but its effect on cardiac hypertrophy mediated by beta-adrenoceptors remains unclear. The present study was designed to determine whether overproduction of endothelial NO synthase (eNOS) could inhibit cardiac hypertrophy induced by chronic isoproterenol (ISO) infusion (30mg/kg per day) using eNOS overexpressing (eNOS-Tg) mice and wild-type (WT) mice. In a separate group, WT mice were treated with ISO and hydralazine to decrease blood pressure to the same levels in eNOS-Tg mice. The eNOS expression, NOS activity, and cGMP levels in the heart were remarkably higher in eNOS-Tg mice than in WT mice. ISO increased both heart weight and the heart/body weight ratio, which were significantly attenuated in eNOS-Tg mice compared with WT or hydralazine-treated WT mice. Histological examination revealed that the extent of fibrosis was not significantly different among the 3 groups, and that the increase in myocyte size was more than 10% lower in eNOS-Tg than in the other groups. In addition, up-regulated expression of atrial natriuretic peptide mRNA associated with cardiac hypertrophy was significantly inhibited in eNOS-Tg mice during ISO infusion. These results indicate that endogenous NO might act as a negative modulator for the hypertrophic response to beta-adrenergic stimulation.

GRGDSP peptide-bound silicone membranes withstand mechanical flexing in vitro and display enhanced fibroblast adhesion

Mechanobiological studies of cardiac tissue require devices that allow forces to be exerted on cells in vitro. Silicone elastomer is often used in these devices because it is flexible and transparent, permitting optical imaging of the cells. However, native untreated silicone is hydrophobic and is unsuitable for cell culture. Peptides covalently bound to silicone surfaces are examined here for the enhancement of cellular adhesion during in vitro dynamic flexing. A procedure is described for the chemical modification of medical grade silicone membranes with covalently bound GRGDSP peptides. The conditions for mechanical studies of cardiac cell cultures are then duplicated and it is demonstrated that the peptide layers survive 48 h of mechanical flexing in vitro. Specifically, mechanical flexing in vitro of the 30 pmol/cm2 peptide-modified silicone membranes has no significant effect on the amount of peptides that remains bound to the surface. Cardiac fibroblasts display enhanced adhesion to these peptide-bound silicone membranes for at least 24 h of growth, compared with native silicone or tissue culture polystyrene. The effects of serum versus serum-free media on fibroblast growth are also examined.

Rapid increase in cardiac adrenomedullin gene expression caused by acute pressure overload: effect of the renin-angiotensin system on gene expression

To determine whether acute pressure overload (POL) can stimulate adrenomedullin (AM) production, the response of ventricular AM gene expression and plasma AM concentration to aortic banding was investigated in the rat. Furthermore, any link between AM expression and the renin-angiotensin system (RAS) enhanced by acute POL was examined using: a Ca channel blocker (manidipine), an angiotensin II type 1 receptor antagonist (candesartan), and an angiotensin-converting enzyme inhibitor (quinapril). Rats with acute POL produced by suprarenal aortic banding were studied 1, 5 and 14 days after surgery. Plasma AM concentrations in banded rats at day 1 increased 1.49-fold (p<0.01), then gradually declined to near the control level at day 14. Plasma AM concentrations correlated with plasma renin activity (PRA) (p<0.001). Adrenomedullin mRNA expression in the left ventricle (LV) increased 1.35-fold (p<0.05) at day 1. This increase was not significant at either 5 or 14 days after surgery. Adrenomedullin mRNA expression in the right ventricle on days 1 and 5 increased by 1.46-fold (p<0.05) and 1.52-fold (p<0.05), respectively. Candesartan, quinapril and manidipine reduced systolic blood pressure equally and activated PRA at day 1. However, augmented LV AM gene expression was suppressed completely by candesartan and quinapril, but remained unaffected by manidipine. In conclusion, POL induces a rapid increase in cardiac AM gene expression and in plasma AM concentrations. Cardiac AM transcription could therefore be partly regulated by RAS in suprarenal aortic banding rats.