Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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Calcium regulation in the human heart is impaired during idiopathic dilated cardiomyopathy (IDC). Here, we analyze the structural basis for impairment in the regulatory mechanism. Regulation of contractility was monitored by MgATPase and Ca2+-binding assays as a function of calcium. Myofibrillar proteolysis and expression of troponin T isoforms were established by gel electrophoresis and by Western blots. Myofibrillar ATPase assays in low salt however, revealed a drastic lowering of calcium sensitivity in IDC myofibrils as indicated by reductions in both activation by high calcium and in EGTA-mediated inhibition of MgATPase. Structural changes in myofilament proteins were found in most IDC hearts, specifically proteolysis of myosin light chain 2 (LC2), troponin T and I (TnT and TnI), and sometimes a large isoform shift in TnT. IDC did not induce mutations in LC2 and troponin C (TnC), as established by cDNA sequence data from IDC cases, thus, calcium binding to IDC myofibrils was unaffected. Reassociation of IDC myofibrils with native LC2 raised MgATPase activation at high Ca2+ to control levels, while repletion with intact, canine TnI/TnT restored inhibition at low Ca2+. A model, identifying possible steps in the steric blocking mechanism of regulation, is proposed to explain IDC-induced changes in Ca2+-regulation. Moreover, shifts in TnT isoforms may imply either a genetic or a compensatory factor in the development and pathogenesis of some forms of IDC.
Mol Cell Biochem 1999 Apr
PMID:Calcium regulation in the human myocardium affected by dilated cardiomyopathy: a structural basis for impaired Ca2+-sensitivity. 1039 Nov 53

A neutral protease, mekratin, active in human hearts at end stage idiopathic dilated cardiomyopathy (IDC), mediates the breakdown of cardiac myosin LC2. Myosin purified from IDC heart tissue forms unusually short synthetic thick filaments. Therefore, determination of filament length and mekratin distribution in IDC heart muscle were initiated. Native thick filaments were prepared directly from control and IDC tissues and analyzed. Also, paraffin-embedded tissue sections were stained with a fluorescently-labeled anti-protease antibody to establish its distribution in myocardial tissues. Control sections had only very weak, background levels of fluorescence whereas IDC sections stained intensely throughout, indicating a wide ranging distribution of the protease within the myocyte cytoplasm. SDS-PAGE revealed LC2 to be present in stoichiometric amounts in control but greatly reduced in IDC heart muscle. Native thick filaments from control myocardium were structurally stable. They had a median length of 1.65 microm with well-defined bare zones and displayed the 43 nm helical periodicity typical of the relaxed arrangement of myosin heads close to the filaments' shafts. In contrast, native IDC filaments were less stable, and had a median length of 0.9 microm. These filaments were highly disordered: they had no surface periodicity and myosin heads were positioned away from the filaments' shafts. The shorter, less stable, aperiodic thick filaments from IDC hearts appear to result from depletion of LC2 caused by increased activity of mekratin in the IDC myocardium.
Mol Cell Biochem 1999 May
PMID:Myofibrillar protein structure and assembly during idiopathic dilated cardiomyopathy. 1039 63

The present study investigates intracellular enzymatic pathways involved in the elimination of reactive oxygen species in the left ventricular myocardium of 10 individuals without heart failure and 12 patients with end-stage heart failure due to idiopathic dilated cardiomyopathy. Left ventricular enzyme activities, mRNA and protein levels of the hydrogen peroxide scavenging enzymes catalase (CAT) and glutathione peroxidase (GPX), and the superoxide anion scavenging enzymes mitochondrial (Mn-SOD) and cytosolic (Cu/Zn-SOD) superoxide dismutases were measured. In failing myocardium, there was a significant decrease in CAT activity (4.83+/-0.32 U/mg v 6.59+/-0.52, P<0.01) despite unchanged mRNA expression and protein levels. GPX, Mn-SOD and Cu/Zn-SOD were similar concerning activity, mRNA and protein levels. As indirect free radical markers, similar levels of the products of lipid peroxidation, malondialdehyde and 4-hydroxy-alkenals, and similar tissue nitrotyrosin content were measured. The decrease in CAT activity appears to be a post-transcriptional mechanism. A decreased myocardial capacity to scavenge hydrogen peroxide might lead to a shift in the intracellular redox balance which potentially results in activation of redox sensitive signalling pathways. Direct reactive oxygen species mediated damage was not detected by the methods applied.
J Mol Cell Cardiol 2000 Jan
PMID:Antioxidative enzymes in human hearts with idiopathic dilated cardiomyopathy. 1065 96

In an earlier paper, we described a new method for phylogenetic tree reconstruction called the Disk Covering Method, or DCM. This is a general method which can be used with any existing phylogenetic method in order to improve its performance. We showed analytically and experimentally that when DCM is used in conjunction with polynomial time distance-based methods, it improves the accuracy of the trees reconstructed. In this paper, we discuss a variant on DCM, that we call DCM2. DCM2 is designed to be used with phylogenetic methods whose objective is the solution of NP-hard optimization problems. We show that DCM2 can be used to accelerate searches for Maximum Parsimony trees. We also motivate the need for solutions to NP-hard optimization problems by showing that on some very large and important datasets, the most popular (and presumably best performing) polynomial time distance methods have poor accuracy.
Proc Int Conf Intell Syst Mol Biol 1999
PMID:Solving large scale phylogenetic problems using DCM2. 1078 94

A substantial body of evidence suggests involvement of the human beta1-adrenoceptor (beta1-AR) gene in the pathophysiology of dilated cardiomyopathy (DCM), a severe heart disease of significant public health impact. Beta1-AR-mediated signal transduction is dramatically altered due to downregulation, resulting in an impairment of myocardial response. The important role of genetic factors in idiopathic dilated cardiomyopathy (IDCM) recently recognized, we analyzed this prime candidate gene for genetic variation in carefully selected patients and controls. In this preliminary study, 18 single nucleotide polymorphisms were observed, 17 of which were located in the N-terminal and C-terminal region of the coding exon, resulting in 7 amino acid exchanges: Ser-49-Gly, Ala-59-Ser, Gly-389-Arg, Arg-399-Cys, His-402-Arg, Thr-404-Ala, and Pro-418-Ala. These mutations resulted in 11 different beta1-AR genotypes. Importantly, the genotypes carrying the Ser-49-Gly mutation in the N-terminus of the molecule in a heterozygous or homozygous form were observed significantly more frequently in the group of IDCM patients. The present results may provide a clue on the molecular mechanisms involved in IDCM, and add moreover interesting information on nature, distribution, and evolutionary aspects of sequence variation in human adrenergic receptor genes.
J Mol Med (Berl) 2000
PMID:Beta1-adrenoceptor gene variations: a role in idiopathic dilated cardiomyopathy? 1079 44

Chronic heart failure (HF) is associated with morphologic abnormalities of cardiac mitochondria including hyperplasia, reduced organelle size and compromised structural integrity. In this study, we examined whether functional abnormalities of mitochondrial respiration are also present in myocardium of patients with advanced HF. Mitochondrial respiration was examined using a Clark electrode in an oxygraph cell containing saponin-skinned muscle bundles obtained from myocardium of failed explanted human hearts due to ischemic (ICM, n=9) or idiopathic dilated (IDC, n=9) cardiomyopathy. Myocardial specimens from five normal donor hearts served as controls (CON). Basal respiratory rate, respiratory rate after addition of the substrates glutamate and malate (V(SUB)), state 3 respiration (after addition of ADP, V(ADP)) and respiration after the addition of atractyloside (V(AT)) were measured in scar-free muscle bundles obtained from the subendocardial (ENDO) and subepicardial (EPI) thirds of the left ventricular (LV) free wall, interventricular septum and right ventricular (RV) free wall. There were no differences in basal and substrate-supported respiration between CON and HF regardless of etiology. V(ADP)was significantly depressed both in ICM and IDC compared to CON in all the regions studied. The respiratory control ratio, V(ADP)/V(AT), was also significantly decreased in HF compared to CON. In both ICM and IDC, V(ADP)was significantly lower in ENDO compared to EPI. The results indicate that mitochondrial respiration is abnormal in the failing human heart. The findings support the concept of low myocardial energy production in HF via oxidative phosphorylation, an abnormality with a potentially impact on global cardiac performance.
J Mol Cell Cardiol 2000 Dec
PMID:Abnormal mitochondrial respiration in failed human myocardium. 1111 11

Congestive heart failure is associated with a high risk of life-threatening ventricular re-entrant arrhythmias. Down-regulation of the principal gap-junctional protein of the ventricular myocytes, connexin43, has previously been implicated in arrhythmia in ischaemic heart disease, but it is not known whether connexin43 is similarly reduced in heart failure due to idiopathic dilated cardiomyopathy, whether disease-related connexin43 down-regulation occurs at the level of transcription or translation, or whether the expression of other connexin isotypes is altered in congestive heart failure. We therefore investigated the expression of the four connexins expressed in the heart-connexins 43, 40, 45 and 37-at the mRNA and protein levels in explanted hearts from transplant patients with end-stage heart failure (NYHA class 4) by immunoconfocal analysis, and northern and western blotting. Connexin43 mRNA and protein were markedly downregulated in the left ventricle in end-stage heart failure due both to ischaemic cardiomyopathy and idiopathic dilated cardiomyopathy. Connexin43 content was spatially heterogeneous in the diseased ventricle. Connexin40 mRNA was increased in the ischaemic group, more so in the left ventricle than the right. This correlated with an increased depth of connexin40 protein expression in myocytes at the endocardial surface. Connexin45 mRNA and protein, present only in very low quantities, followed a similar trend to connexin43, while connexin37 (exclusively expressed in endothelium) showed no change. Our findings show that congestive heart failure is associated with significantly reduced levels of the principal gap junction protein, connexin43, in the left ventricle, potentially contributing to enhanced arrhythmogenicity and contractile dysfunction. This down-regulation is due predominantly to a reduced transcript steady-state level. Elevated connexin40 may represent a compensatory response that improves the spread of depolarization in the otherwise compromised ischaemic ventricle.
J Mol Cell Cardiol 2001 Feb
PMID:Altered connexin expression in human congestive heart failure. 1116 39

The Na,K-ATPase function appears impaired in human heart failure with dilation; however little is known in animal model with idiopathic dilated cardiomyopathy. We studied Na,K-ATPase isoform composition and activity from cardiomyopathic hamsters of the MS 200 strain with pure dilated cardiomyopathy and compared them with those of healthy Syrian hamsters. 150-day-old male MS 200 Syrian hamsters (n = 16) and sex- and age-matched healthy Syrian hamsters (n = 15) were used. Antibodies specific for the three alpha-isoforms and against the beta1-isoform were used to study Na,K-ATPase isoform expression in ventricular myocardium. Na,K-ATPase activity was quantified in homogenate and membrane fractions. There was no significant change in left ventricular mass. Morphological examination revealed a decreased septum thickness in the dilated cardiomyopathy compared with control hamster. Idiopathic dilated cardiomyopathy in hamsters presented significantly reduced membrane alpha1 and beta1 abundances and reduced Na,K-ATPase activity (-35% vs. healthy control, p<0.05). Chronic heart failure had no effect on the Na,K-ATPase alpha2-subunit protein. We have demonstrated for the first time that dilated cardiomyopathy induces a specific reduction of both membrane alpha1- and beta1-isoform abundance and Na,K-ATPase activity in hamsters similar to those previously reported in human dilated heart failure.
Cell Mol Biol (Noisy-le-grand) 2001 Mar
PMID:Defective activity and isoform of the Na,K-ATPase in the dilated cardiomyopathic hamster. 1135 98

The left ventricle (LV) plays a central role in the maintenance of health of children and adults due to its role as the major pump of the heart. In cases of LV dysfunction, a significant percentage of affected individuals develop signs and symptoms of congestive heart failure (CHF), leading to the need for therapeutic intervention. Therapy for these patients include anticongestive medications and, in some, placement of devices such as aortic balloon pump or left ventricular assist device (LVAD), or cardiac transplantation. In the majority of patients the etiology is unknown, leading to the term idiopathic dilated cardiomyopathy (IDC). During the past decade, the basis of LV dysfunction has begun to unravel. In approximately 30-40% of cases, the disorder is inherited; autosomal dominant inheritance is most common (although X-linked, autosomal recessive and mitochondrial inheritance occurs). In the remaining patients, the disorder is presumed to be acquired, with inflammatory heart disease playing an important role. In the case of familial dilated cardiomyopathy (FDCM), the genetic basis is beginning to unfold. To date, two genes for X-linked FDCM (dystrophin, G4.5) have been identified and four genes for the autosomal dominant form (actin, desmin, lamin A/C, delta-sarcoglycan) have been described. In one form of inflammatory heart disease, coxsackievirus myocarditis, inflammatory mediators and dystrophin cleavage play a role in the development of LV dysfunction. In this review, we will describe the molecular genetics of LV dysfunction and provide evidence for a "final common pathway" responsible for the phenotype.
Curr Mol Med 2001 Mar
PMID:Molecular genetics of left ventricular dysfunction. 1189 44

Little is known about the effects of altered sympathetic innervation on the efficiency of the cardiomyopathic heart. Thus, it was the aim of this study to determine non-invasively the relationship between the metabolic cost of cardiac work and alterations of the sympathetic nervous system. In ten patients with chronic idiopathic dilated cardiomyopathy, left ventricular function and geometry were assessed by tomographic radionuclide angiography. Myocardial oxidative metabolism was quantified by the clearance constant k(mono) for carbon-11 acetate, determined by positron emission tomography (PET). Cardiac efficiency was then estimated by the work-metabolic index [WMI = stroke volume index x heart rate x systolic pressure/k(mono)]. Additionally, myocardial presynaptic sympathetic innervation was investigated in the same PET session using 11C-hydroxyephedrine, and plasma norepinephrine levels were determined by high-performance liquid chromatography. The WMI was 3.0+/-1.3 mmHg x ml x 10(6)/m2 and correlated significantly with left ventricular ejection fraction (19%+/-10%; r=0.66, P<0.04) and peripheral vascular resistance (3,638+/-1,085 dynes x s/cm5; r=-0.75, P<0.01). Cardiac hydroxyephedrine retention, reflecting integrity of presynaptic innervation, was abnormally low in 58%+/-38% of the left ventricle. Cardiac hydroxyephedrine retention (r=0.65, P<0.05) and plasma norepinephrine concentration (r=-0.80, P<0.01) both correlated significantly with the WMI. At multivariate stepwise linear regression, only plasma norepinephrine and peripheral vascular resistance were independent determinants of the WMI. In conclusion, metabolic performance of the cardiomyopathic heart decreases with increasing alterations of the sympathetic nervous system. Increasing afterload and effects of systemic sympathetic activation, however, seem to play a dominant role while direct alterations of cardiac presynaptic sympathetic innervation are not independently associated.
Eur J Nucl Med Mol Imaging 2002 Feb
PMID:Alterations of the sympathetic nervous system and metabolic performance of the cardiomyopathic heart. 1192 82


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