Embryonic atrial function is essential for mouse embryogenesis, cardiac morphogenesis and angiogenesis

The requirement for atrial function in developing heart is unknown. To address this question, we have generated mice deficient in atrial myosin light chain 2 (MLC2a), a major structural component of the atrial myofibrillar apparatus. Inactivation of the Mlc2a gene resulted in severely diminished atrial contraction and consequent embryonic lethality at ED10.5-11.5, demonstrating that atrial function is essential for embryogenesis. Our data also address two longstanding questions in cardiovascular development: the connection between function and form during cardiac morphogenesis, and the requirement for cardiac function during vascular development. Diminished atrial function in MLC2a-null embryos resulted in a number of consistent secondary abnormalities in both cardiac morphogenesis and angiogenesis. Our results unequivocally demonstrate that normal cardiac function is directly linked to normal morphogenic development of heart and vasculature. These data have important implications for the etiology of congenital heart disease.     

Quantification of left ventricular mechanical dyssynchrony by conductance catheter in heart failure patients

Mechanical dyssynchrony is an important codeterminant of cardiac dysfunction in heart failure. Treatment, either medical, surgical, or by pacing, may improve cardiac function partly by improving mechanical synchrony. Consequently, the quantification of ventricular mechanical (dys)synchrony may have important diagnostic and prognostic value and may help to determine optimal therapy. Therefore, we introduced new indexes to quantify temporal and spatial aspects of mechanical dyssynchrony derived from online segmental conductance catheter signals obtained during diagnostic cardiac catheterization. To test the feasibility and usefulness of our approach, we determined cardiac function and left ventricular mechanical dyssynchrony by the conductance catheter in heart failure patients with intraventricular conduction delay (n = 12) and in patients with coronary artery disease (n = 6) and relatively preserved left ventricular function. The heart failure patients showed depressed systolic and diastolic function. However, the most marked hemodynamic differences between the groups were found for mechanical dyssynchrony, indicating a high sensitivity and specificity of the new indexes. Comparison of conductance catheter-derived indexes with septal-to-lateral dyssynchrony derived by tissue-Doppler velocity imaging showed highly significant correlations. The proposed indexes provide additional, new, and quantitative information on temporal and spatial aspects of mechanical dyssynchrony. They may refine diagnosis of cardiac dysfunction and evaluation of interventions, and ultimately help to select optimal therapy.     

Role of proteases in the pathophysiology of cardiac disease

Cardiovascular disease is a major cause of death and thus a great deal of effort has been made in salvaging the diseased myocardium. Although various factors have been identified as possible causes of different cardiac diseases such as heart failure and ischemic heart disease, there is a real need to elucidate their role for the better understanding of the cardiac disease pathology and formulation of strategies for developing newer therapeutic interventions. In view of the intimate involvement of different types of proteases in maintaining cellular structure, the role of proteases in various cardiac diseases has become the focus of recent research. Proteases are present in the cytosol as well as are localized in a number of subcellular organelles in the cell. These are known to use extracellular matrix, cytoskeletal, sarcolemmal, sarcoplasmic reticular, mitochondrial and myofibrillar proteins as substrates. Work from different laboratories using a wide variety of techniques has shown that the activation of proteases causes alterations of a number of specific proteins leading to subcellular remodeling and cardiac dysfunction. Inhibition of protease action by different drugs and agents, therefore, has a clinical relevance and is expected to form a part of new treatment paradigm for improving heart function. This review examines the biochemistry and localization of some of the proteases in the cardiac tissue in addition to identification of the sites of action of some protease inhibitors.     

Proteasome functional insufficiency in cardiac pathogenesis

The ubiquitin-proteasome system (UPS) is responsible for the degradation of most cellular proteins. Alterations in cardiac UPS, including changes in the degradation of regulatory proteins and proteasome functional insufficiency, are observed in many forms of heart disease and have been shown to play an important role in cardiac pathogenesis. In the past several years, remarkable progress in understanding the mechanisms that regulate UPS-mediated protein degradation has been achieved. A transgenic mouse model of benign enhancement of cardiac proteasome proteolytic function has been created. This has led to the first demonstration of the necessity of proteasome functional insufficiency in the genesis of important pathological processes. Cardiomyocyte-restricted enhancement of proteasome proteolytic function by overexpression of proteasome activator 28α protects against cardiac proteinopathy and myocardial ischemia-reperfusion injury. Additionally, exciting advances have recently been achieved in the search for a pharmacological agent to activate the proteasome. These breakthroughs are expected to serve as an impetus to further investigation into the involvement of UPS dysfunction in molecular pathogenesis and to the development of new therapeutic strategies for combating heart disease. An interplay between the UPS and macroautophagy is increasingly suggested in noncardiac systems but is not well understood in the cardiac system. Further investigations into the interplay are expected to provide a more comprehensive picture of cardiac protein quality control and degradation.     

Targeting neuronal dysfunction and receptor imaging

The sympathetic nervous system has great influence on cardiovascular physiology, and the importance of cardiac innervation abnormalities in the physiopathology of various cardiac diseases has been emphasized. Cardiac neurotransmission imaging with single-photon emission computed tomography (SPECT) allows in vivo assessment of the myocardial nervous system. At present, the most commonly used SPECT tracer to assess cardiac neurotransmission is metaiodobenzylguanidine labelled with iodine-123 ((123)I-MIBG). In patients with heart transplantation, ischemic heart disease, dysautonomias and drug-induced cardiotoxicity, assessment of neuronal function can help characterise the disease and improve the prognostic stratification. Cardiac (123)I-MIBG scintigraphy allows autonomic neuropathy to be detected in the early stages of diabetes mellitus. In patients with heart failure, the assessment of cardiac sympathetic activity has important prognostic implications. Future directions in cardiac sympathetic neurotransmission include the development of new tracers, targeting of second-messenger molecules and early assessment of cardiac neurotransmission in genetically predisposed subjects for prevention of heart failure.     

Chronic cardiac insufficiency, a disease of adaptation]

Cardiac hypertrophy due to a mechanical overload is not a disease per se but the physiological reaction of the heart to a disease which is usually arterial hypertension and/or coronary insufficiency. It results from the put into play of several changes in gene expression, frequently species-specific, which explain the thermodynamic improvement of the cardiac function and the physiological adaptation of the heart to the new environmental requirements. Some of these modifications can have detrimental consequences and explain the modifications of ventricular compliance and the high incidence of arrhythmias in ventricular hypertrophy. The most important changes in the genetic expression which have been reported so far after pressure overload are located on contractile proteins and on membrane proteins.     

Mitochondria in the human heart

The heart relies mainly on mitochondrial metabolism to provide the energy needed for pumping blood to oxygenate the organs of the body. The study of mitochondrial function in the human heart faces many obstacles and elucidation of the role of mitochondria in cardiac diseases has relied mainly on studies with animal models. Cardiac diseases are the leading cause of mortality worldwide. With the emergence of new therapies to treat and prevent heart disease, some aiming at metabolic modulation, a need for acquiring a better understanding of mitochondrial function in the human heart becomes apparent. Our review is aimed at specific evaluation of the human heart in terms of (1) methods to understand mitochondrial function, with particular emphasis on integrated function, (2) data on the role of mitochondrial dysfunction in cardiovascular disease, and (3) possible applications of this knowledge in the treatment of patients with cardiac disease.     

Role of proteases in the pathophysiology of cardiac disease

Cardiovascular disease is a major cause of death and thus a great deal of effort has been made in salvaging the diseased myocardium. Although various factors have been identified as possible causes of different cardiac diseases such as heart failure and ischemic heart disease, there is a real need to elucidate their role for the better understanding of the cardiac disease pathology and formulation of strategies for developing newer therapeutic interventions. In view of the intimate involvement of different types of proteases in maintaining cellular structure, the role of proteases in various cardiac diseases has become the focus of recent research. Proteases are present in the cytosol as well as are localized in a number of subcellular organelles in the cell. These are known to use extracellular matrix, cytoskeletal, sarcolemmal, sarcoplasmic reticular, mitochondrial and myofibrillar proteins as substrates. Work from different laboratories using a wide variety of techniques has shown that the activation of proteases causes alterations of a number of specific proteins leading to subcellular remodeling and cardiac dysfunction. Inhibition of protease action by different drugs and agents, therefore, has a clinical relevance and is expected to form a part of new treatment paradigm for improving heart function. This review examines the biochemistry and localization of some of the proteases in the cardiac tissue in addition to identification of the sites of action of some protease inhibitors. (Mol Cell Biochem 263: 241–256, 2004)     

Pathophysiological roles of G-protein-coupled receptor kinases

G-protein-coupled receptor kinases (GRKs) interact with the agonist-activated form of G-protein-coupled receptors (GPCRs) to effect receptor phosphorylation and to initiate profound impairment of receptor signalling, or desensitization. GPCRs form the largest family of cell surface receptors known and defects in GRK function have the potential consequence to affect GPCR-stimulated biological responses in many pathological situations. This review focuses on the physiological role of GRKs revealed by genetically modified animals but also develops the involvement of GRKs in human diseases as, Oguchi disease, heart failure, hypertension or rhumatoid arthritis. Furthermore, the regulation of GRK levels in opiate addiction, cancers, psychiatric diseases, cystic fibrosis and cardiac diseases is discussed. Both transgenic mice and human pathologies have demonstrated the importance of GRKs in the signalling pathways of rhodopsin, beta-adrenergic and dopamine-1 receptors. The modulation of GRK activity in animal models of cardiac diseases can be effective to restore cardiac function in heart failure and opens a novel therapeutic strategy in diseases with GPCR dysregulation.     

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

A number of studies have been conducted recently on the model organism Drosophila to determine the function of genes involved in human disease, including those implicated in neurological disorders, cancer and metabolic and cardiovascular diseases. The simple structure and physiology of the Drosophila heart tube together with the available genetics provide a suitable in vivo assay system for studying cardiac gene functions. In our study, we focus on analysis of the role of dystrophin (Dys) in heart physiology. As in humans, the Drosophila dys gene encodes multiple isoforms, of which the large isoforms ( DLPs ) and a truncated form ( Dp117 ) are expressed in the adult heart. Here, we show that the loss of dys function in the heart leads to an age-dependent disruption of the myofibrillar organization within the myocardium as well as to alterations in cardiac performance. dys RNAi-mediated knockdown in the mesoderm also shortens lifespan. Knockdown of all or deletion of the large isoforms increases the heart rate by shortening the diastolic intervals (relaxation phase) of the cardiac cycle. Morphologically, loss of the large DLPs isoforms causes a widening of the cardiac tube and a lower fractional shortening, a phenotype reminiscent of dilated cardiomyopathy. The dilated dys mutant phenotype was reversed by expressing a truncated mammalian form of dys ( Dp116 ). Our results illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and other muscular-dystrophy-associated phenotypes.     

Epigenetics in cardiac development,function, and disease

Substantial new knowledge has accrued, over the past few years, concerning the epigenetic regulation of heart development and disease. Epigenetic mechanisms comprise DNA methylation, ATP-dependent chromatin remodeling, histone modifications, and non-coding RNAs. Many of these processes have been ascertained to influence the tight spatiotemporal control of gene expression during cardiac development. Nevertheless, the relative contribution of each mechanism and their potentially complex interplay remain largely unexplored. Cardiac development and disease are linked through the reactivation of fetal genes upon cardiac hypertrophy and failure. In cardiac disease, changes in gene expression are accompanied and influenced by distinct changes in histone modifications. Detailed knowledge about the epigenetic pathways of cardiac development and function is expected ultimately to lead to novel therapeutic strategies for heart disease and regenerative medicine.     

MicroRNAs in a hypertrophic heart: from foetal life to adulthood

The heart is the first organ to form and undergoes adaptive remodelling with age. Ventricular hypertrophy is one such adaptation, which allows the heart to cope with an increase in cardiac demand. This adaptation is necessary as part of natural growth from foetal life to adulthood. It may also occur in response to resistance in blood flow due to various insults on the heart and vessels that accumulate with age. The heart can only compensate to this increase in workload to a certain extent without losing its functional architecture, ultimately resulting in heart failure. Many genes have been implicated in cardiac hypertrophy, however none have been shown conclusively to be responsible for pathological cardiac hypertrophy. MicroRNAs offer an alternative mechanism for cellular regulation by altering gene expression. Since 1993 when the function of a non‐coding DNA sequence was first discovered in the model organism Caenorhabditis elegans, many microRNAs have been implicated in having a central role in numerous physiological and pathological cellular processes. The level of control these antisense oligonucleotides offer can often be exploited to manipulate the expression of target genes. Moreover, altered levels of microRNAs can serve as diagnostic biomarkers, with the prospect of diagnosing a disease process as early as during foetal life. Therefore, it is vital to ascertain and investigate the function of microRNAs that are involved in heart development and subsequent ventricular remodelling. Here we present an overview of the complicated network of microRNAs and their target genes that have previously been implicated in cardiogenesis and hypertrophy. It is interesting to note that microRNAs in both of these growth processes can be of possible remedial value to counter a similar disease pathophysiology.     

Beta-adrenergic axis and heart disease

Beta-adrenergic receptors (beta-ARs) belong to a large family of G-protein-coupled receptors (GPCRs) that form the interface between the sympathetic nervous system and the cardiovascular system. The beta-AR signal system is one of the most powerful regulators of cardiac function, mediated by the effects of the sympathetic transmitters epinephrine and norepinephrine. In a number of cardiac diseases, however, the biology of beta-AR signaling pathways is altered dramatically. Here we discuss the role of beta-AR signaling in the normal and abnormal heart and how the use of genetically engineered mouse models has helped in our understanding of the pathophysiology of cardiac disease.     

Trypanosoma cruzi: parasite persistence in tissues in chronic chagasic Brazilian patients

Chagas disease in the chronic phase may develop into cardiac and/or digestive forms. The pathogenesis of the disease is not yet clear and studies have been carried out to elucidate the role of parasite persistence in affected organs. The aim of this study was to detect and quantify Trypanosoma cruzi in paraffin-embedded tissue samples from chronic patients using NPCR (nested polymerase chain reaction) and QPCR (quantitative polymerase chain reaction) methods. These results were correlated to anatomopathological alterations in the heart and gastrointestinal tract (GIT). Of the 23 patients studied, 18 presented the cardiac form and five presented the cardiodigestive form of Chagas disease. DNA samples were randomly isolated from formalin-fixed paraffin-embedded sections of heart and GIT tissue of 23 necropsies and were analyzed through NPCR amplification. T. cruzi DNA was detected by NPCR in 48/56 (85.7%) heart and 35/42 (83.3%) GIT samples from patients with the cardiac form. For patients with the cardiodigestive form, NPCR was positive in 12/14 (85.7%) heart and in 14/14 (100%) GIT samples. QPCR, with an efficiency of 97.6%, was performed in 13 samples (11 from cardiac and 2 from cardiodigestive form) identified previously as positive by NPCR. The number of T. cruzi copies was compared to heart weight and no statistical significance was observed. Additionally, we compared the number of copies in different tissues (both heart and GIT) in six samples from the cardiac form and two samples from the cardiodigestive form. The parasite load observed was proportionally higher in heart tissues from patients with the cardiac form. These results show that the presence of the parasite in tissues is essential to Chagas disease pathogenesis.     

Osteopontin-stimulated expression of matrix metalloproteinase-9 causes cardiomyopathy in the mdx model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is a common and lethal form of muscular dystrophy. With progressive disease, most patients succumb to death from respiratory or heart failure, or both. However, the mechanisms, especially those governing cardiac inflammation and fibrosis in DMD, remain less understood. Matrix metalloproteinase (MMPs) are a group of extracellular matrix proteases involved in tissue remodeling in both physiologic and pathophysiologic conditions. Previous studies have shown that MMP-9 exacerbates myopathy in dystrophin-deficient mdx mice. However, the role and the mechanisms of action of MMP-9 in cardiac tissue and the biochemical mechanisms leading to increased levels of MMP-9 in mdx mice remain unknown. Our results demonstrate that the levels of MMP-9 are increased in the heart of mdx mice. Genetic ablation of MMP-9 attenuated cardiac injury, left ventricle dilation, and fibrosis in 1-y-old mdx mice. Echocardiography measurements showed improved heart function in Mmp9-deficient mdx mice. Deletion of the Mmp9 gene diminished the activation of ERK1/2 and Akt kinase in the heart of mdx mice. Ablation of MMP-9 also suppressed the expression of MMP-3 and MMP-12 in the heart of mdx mice. Finally, our experiments have revealed that osteopontin, an important immunomodulator, contributes to the increased amounts of MMP-9 in cardiac and skeletal muscle of mdx mice. This study provides a novel mechanism for development of cardiac dysfunction and suggests that MMP-9 and OPN are important therapeutic targets to mitigating cardiac abnormalities in patients with DMD.     

Screening assays for heart function mutants in Drosophila

The rapid life cycle and genetic tractability of Drosophila make it an ideal organism for large-scale genetic screens. Here we describe a novel assay for pupal heart rate and rhythmicity as well as techniques to measure adult cardiac stress response. These assays can be powerfully combined to concurrently screen for both mutations affecting cardiac function and mutations affecting the age-dependent decline in adult cardiac stress response. Mutations identified in such screens have the potential to contribute greatly to the understanding of both congenital heart disease and the regulation of age-dependent decline in cardiac function in the human population.