Accuracy of cardiovascular magnetic resonance in myocarditis: comparison of MR and histological findings in an animal model

BACKGROUND

Because endomyocardial biopsy has low sensitivity of about 20%, it can be performed near to myocardium that presented as late gadolinium enhancement (LGE) in cardiovascular magnetic resonance (CMR). However the important issue of comparing topography of CMR and histological findings has not yet been investigated. Thus the current study was performed using an animal model of myocarditis.

RESULTS

In 10 male Lewis rats experimental autoimmune myocarditis was induced, 10 rats served as control. On day 21 animals were examined by CMR to compare topographic distribution of LGE to histological inflammation. Sensitivity, specificity, positive and negative predictive values for LGE in diagnosing myocarditis were determined for each segment of myocardium. Latter diagnostic values varied widely depending on topographic distribution of LGE and inflammation as well as on the used CMR sequence. Sensitivity of LGE was up to 76% (left lateral myocardium) and positive predictive values were up to 85% (left lateral myocardium), whereas sensitivity and positive predictive value dropped to 0-33% (left inferior myocardium).

CONCLUSIONS

Topographic distribution of LGE and histological inflammation seem to influence sensitivity, specificity, positive and negative predictive values. Nevertheless, positive predictive value for LGE of up to 85% indicates that endomyocardial biopsy should be performed "MR-guided". LGE seems to have greater sensitivity than endomyocardial biopsy for the diagnosis of myocarditis.

The collagen receptor DDR2 is expressed during early cardiac development

Discoidin Domain Receptor 2 (DDR2) is a receptor tyrosine kinase which has been shown to regulate cell migration upon binding its ligand, collagen. Expression studies determined that DDR2 mRNA and protein are present in the atrioventricular canal during epithelial-mesenchymal transformation (EMT) and the receptor is expressed in both activated endothelial and migrating mesenchymal cells in vivo.

Chondroitin sulfate expression is required for cardiac atrioventricular canal formation

Defects in cardiac valvulogenesis are a common cause of congenital heart disease, and the study of this process promises to provide mechanistic insights and lead to novel therapeutics. Normal valve development involves multiple signaling pathways, and recently roles have been identified for extracellular matrix components, including glycosaminoglycans. We, therefore, explored the role of the glycosaminoglycan chondroitin sulfate during zebrafish cardiac development. Beginning at 33 hr, there is a distinct zone of chondroitin sulfate expression in the atrioventricular (AV) boundary, in the cardiac jelly between the endocardium and myocardium. This expression is both spatially and temporally restricted, and is undetectable after 48 hr. Chemical as well as genetic inhibition of chondroitin synthesis results in AV canal (AVC) defects, including loss of the atrioventricular constriction, blood regurgitation, and failure of circulation. Lack of chondroitin disrupts a marker of cell migration, results in a loss of myocardial and endothelial markers of valvulogenesis, and misregulates bone morphogenetic protein expression, supporting an early role in AVC development. In summary, we have defined a requirement for chondroitin sulfate expression in the normal patterning of the AV boundary, suggesting that this component of the cardiac jelly provides a necessary signal in this critical transition in vertebrate cardiogenesis.

Postmortem studies on a patient with mucopolysaccharidosis type I: histopathological findings after one year of enzyme replacement therapy

Deficiency of lysosomal α-L-iduronidase results in systemic accumulation of glycosaminoglycans (GAGs). Cardiac lesions due to accumulation of GAGs include hypertrophic cardiomyopathy, valvular insufficiency/stenosis, and coronary artery stenosis due to intimal proliferation. Cardiac dysfunction is one of the most common causes of death in patients with mucopolysaccharidosis type I (MPS I). Enzyme replacement therapy (ERT) with laronidase has shown clear effects in reduction of hepatomegaly and it has been unclear whether ERT could improve or prevent the cardiac lesions. Postmortem findings in a 3 1/2-year-old boy diagnosed with MPS I at age 2 years are described. He received ERT with laronidase at 100 U/kg/week for one year. He suddenly developed cardiorespiratory failure and died the next day after C2-3 spinal surgery for instability. Postmortem examination showed hypertrophic cardiomyopathy, severe aortic valve and mitral valve thickening with shortened chordae, and endocardial fibroelastosis. Histology of the cardiac tissue revealed increased perivascular and interstitial connective tissue in the myocardium and intimal thickening causing stenosis in the cardiac vessels. Electron-microscopic (EM) studies of the thickened endocardium revealed numerous histiocytes with enlarged lysosomes. EM examination of the liver and the cardiac muscle revealed no accumulation of GAGs. ERT with laronidase showed clear effects in removing GAGs from the liver and the cardiac muscle. However, it did not show a clear effect on the thickened endocardium, myocardial perivascular and interstitial connective tissue or intimal thickening in the epicardial vessels.

Nonsecretory immunoglobulin-derived amyloidosis of the heart: diagnosis by immunohistochemistry of the endomyocardium

Primary amyloid light chain (AL) amyloidosis of the heart is a rare cause of congestive heart failure. Approximately 15% of patients with primary AL amyloidosis demonstrate no monoclonal proteins on serum or urine immunoelectrophoresis:(so-called nonsecretory immunoglobulin-derived amyloidosis). The histologic findings of endomyocardial biopsy from these patients may be indistinguishable from those with senile cardiac amyloidosis. However, the AL type may respond favourably to chemotherapy while the latter type does not. The prognosis is also better in the senile cardiac amyloid type. The precise diagnosis in the present case was made by applying immunohistochemical techniques on cardiac tissues.

Endocardial endothelial cells stimulate proliferation and collagen synthesis of cardiac fibroblasts

Given that vascular endothelial cells play an important role in the modulation of vascular structure and function, we hypothesized that endocardial endothelial cells (EECs) may have a modulator role in regulating the cardiac interstitial cells. Endocardial endothelial cells were isolated from freshly collected pig hearts and cardiac fibroblasts were isolated from 3- to 4-d-old Wistar rats. Fibroblasts were cultured in the presence or absence of conditioned medium from EECs. Proliferation of cardiac fibroblasts was measured by the incorporation of [3H]- Thymidine and collagen synthesis was assayed by the incorporation of [3H]-Proline. To determine the involvement of signaling mediators, in separate experiments, cardiac fibroblasts were incubated with BQ123 (selective ETA receptor antagonist), PD142893 (nonselective ETA/ETB receptor antagonist), Bis-indolylmaleimide (PKC inhibitor), PD 098059 (MEK inhibitor), or neutralizing anti-transforming growth factor (TGF)-beta-antibody. Endocardial endothelium-derived factors endothelin (ET)-1, TGF-beta, and Angiotensin (Ang)-II in the conditioned medium were assayed by enzyme-linked immunosorbent assay using commercially available kits. We report here evidence that suggest that endocardial endothelial cells stimulate both proliferation and collagen synthesis of cardiac fibroblasts. The response seems to be mediated by endothelin through its ETA receptor. Our results also indicate that protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways are essential for the EEC-induced proliferation of cardiac fibroblasts.

[Biochemical and morphological manifestations of endothelial dysfunction of endocardium and myocardial vessels during emotional stress in combination with hypercholesterolemia]

In experiments with white rats the influence of emotional and pain stress in combination with alimentary hypercholesterolemia on lipid content of membraneous structures of endotheliocytes of endocardium and microvessels of myocardium and their morphological manifestations has been studied. Combination of these etiological factors is followed by accumulation of free cholesterol and free fatty acids within the cells. This results in damage of single endotheliocytes, the most extreme manifestation of which is formation of endothelial bodies (cytoplasts) with development of microclasmatosis and desquamation of these cells.

Low coronary driving pressure is associated with subendocardial remodelling and left ventricular dysfunction in aortocaval fistula

1. The role of haemodynamic changes in left ventricular remodelling has been poorly investigated, especially in the context of volume overload cardiac hypertrophy. Low diastolic blood pressure and high left ventricular filling pressure are expected to affect coronary driving pressure negatively and thereby put in jeopardy subendocardial perfusion in particular. The consequences to global left ventricular remodelling remain undetermined. The aim of the present study was to investigate the role of coronary driving pressure in the development of subendocardial remodelling and the conceivable effects on cardiac function, using a rat model of aortocaval fistula. 2. Wistar rats, weighing 330-350 g, were submitted to aortocaval fistula (ACF group) or sham (control group) operations. Two haemodynamic measurements were determined following surgery, the initial measurement at week 1 and the final measurement at week 8. Cytokine expression, myeloperoxidase (MPO) activity, metalloproteinase expression and activity and fibrosis were assessed in two distinct left ventricular myocardial layers: the subendocardium (SE) and the non-subendocardium (non-SE). 3. The ACF group showed lower initial and final coronary driving pressure and lower final +dP/dt and -dP/dt compared with the control group. Multivariate analyses disclosed initial coronary driving pressure as the only haemodynamic parameter independently associated with SE fibrosis (R(2) = 0.76; P < 0.0001) and with +dP/dt (R(2) = 0.55; P = 0.0004) and -dP/dt (R(2) = 0.91; P < 0.0001). Matrix metalloproteinase (MMP)-2 expression and activity predominated in the SE of ACF animals, particularly in those with low coronary driving pressure. Increased levels of interleukin (IL)-6 and IL-1beta also predominated in the SE of the ACF group. Otherwise, MPO activity and levels of tumour necrosis factor-alpha and IL-10 were similar in both groups. Final coronary driving pressure correlated with both the expression and activity of MMP-2. 4. Low coronary driving pressure early in the course of ACF determines SE damage and, by this mechanism, interferes negatively in left ventricular function.

MEKK3 is required for endothelium function but is not essential for tumor growth and angiogenesis

Mitogen-activated protein kinase kinase kinase 3 (MEKK3) plays an essential role in embryonic angiogenesis, but its role in tumor growth and angiogenesis is unknown. In this study, we further investigated the role of MEKK3 in embryonic angiogenesis, tumor angiogenesis, and angiogenic factor production. We found that endothelial cells from Mekk3-deficient embryos showed defects in cell proliferation, apoptosis, and interactions with myocardium in the heart. We also found that MEKK3 is required for angiopoietin-1 (Ang1)-induced p38 and ERK5 activation. To study the role of MEKK3 in tumor growth and angiogenesis, we established both wild-type and Mekk3-deficient tumor-like embryonic stem cell lines and transplanted them subcutaneously into nude mice to assess their ability to grow and induce tumor angiogenesis. Mekk3-deficient tumors developed and grew similarly as control Mekk3 wild-type tumors and were also capable of inducing tumor angiogenesis. In addition, we found no differences in the production of VEGF in Mekk3-deficient tumors or embryos. Taken together, our results suggest that MEKK3 plays a critical role in Ang1/Tie2 signaling to control endothelial cell proliferation and survival and is required for endothelial cells to interact with the myocardium during early embryonic development. However, MEKK3 is not essential for tumor growth and angiogenesis.

Cellular and subcellular alternans in the canine left ventricle

Previous studies indicate that action potential duration (APD) alternans is initiated in the endocardial (END) and midmyocardial (MID) regions rather than the epicardium (EPI) in the canine left ventricle (LV). This study examines regional differences in the rate dependence of Ca(2+) transient characteristics under conditions that give rise to APD and associated T wave alternans. The role of the sarcoplasmic reticulum (SR) was further evaluated by studying Ca(2+) transient characteristics in myocytes isolated from neonates, where an organized SR is poorly developed. All studies were performed in cells and tissues isolated from the canine LV. Isolated canine ENDO, MID, and EPI LV myocytes were either field stimulated or voltage clamped, and Ca(2+) transients were measured by confocal microscopy. In LV wedge preparations, increasing the basic cycle length (BCL) from 800 to 250 ms caused alternans to appear mainly in the ENDO and MID region; alternans were not observed in EPI under these conditions. Ca(2+) transient alternans developed in response to rapid pacing, appearing in EPI cells at shorter BCL compared with MID and ENDO cells (BCL=428 +/- 17 vs. 517 +/- 29 and 514 +/- 21, respectively, P < 0.05). Further increases in pacing rate resulted in the appearance of subcellular alternans of Ca(2+) transient amplitude, which also appeared in EPI at shorter BCL than in ENDO and MID cells. Ca(2+) transient alternans was not observed in neonate myocytes. We conclude that 1) there are distinct regional differences in the vulnerability to rate-dependent Ca(2+) alternans in dog LV that may be related to regional differences in SR function and Ca(2+) cycling; 2) the development of subcellular Ca(2+) alternans suggests the presence of intracellular heterogeneities in Ca(2+) cycling; and 3) the failure of neonatal cells to develop Ca(2+) alternans provides further support that SR Ca(2+) cycling is a major component in the development of these phenomena.

Effects of sterile pericarditis on connexins 40 and 43 in the atria: correlation with abnormal conduction and atrial arrhythmias

The canine sterile pericarditis model is characterized by impaired conduction and atrial arrhythmia vulnerability. Electrical and structural remodeling processes caused by the inflammatory response likely promote these abnormalities. In the present study, we tested the hypothesis that altered distribution of atrial connexins is associated with markedly abnormal atrial conduction, thereby contributing to vulnerability to atrial flutter (AFL) and atrial fibrillation (AF) induction and maintenance. During rapid pacing and induced, sustained AFL or AF in five sterile pericarditis (SP) and five normal (NL) dogs, epicardial atrial electrograms were recorded simultaneously from both atria (380 electrodes) or from the right atrium (RA) and Bachmann's bundle (212 electrodes). Tissues from RA sites were subjected to immunostaining and immunoblotting to assess connexin (Cx) 40 and Cx43 distribution and expression. Transmural myocyte (alpha-actinin) and fibroblast (vimentin) volume were also assessed by immunostaining. RA pacing maps showed markedly abnormal conduction in SP, with uniform conduction in NL. Total RA activation time was significantly prolonged in SP vs. NL at 300-ms and 200-ms pacing-cycle lengths. Sustained arrhythmias were only inducible in SP [total: 4/5 (AFL: 3/5; AF: 1/5)]. In NL, Cx40, Cx43, alpha-actinin, and vimentin were homogeneously distributed transmurally. In SP, Cx40, Cx43, and alpha-actinin were absent epicardially, decreased midmyocardially, and normal endocardially. SP increased epicardial vimentin expression, suggesting fibroblast proliferation. Immunoblot analysis confirmed reduced expression of Cx40 and Cx43 in SP. The transmural gradient in the volume fraction of Cx40 and Cx43 in SP is associated with markedly abnormal atrial conduction and is likely an important factor in the vulnerability to induction and maintenance of AFL/AF in SP.

Patterns of expression of the Follistatin and Follistatin-like1 genes during chicken heart development: a potential role in valvulogenesis and late heart muscle cell formation

The regulation of concentration and function of growth factors is of crucial importance to proper embryonic development of the heart. The patterns of expression of three extracellular modulators of the transforming growth factor-beta superfamily of growth factors, Follistatin, Follistatin-like1, and Follistatin-like3, are described with respect to heart development. Follistatin is highly localized in the endocardium covering the developing cardiac valves. Follistatin-like1 is localized in the mesenchymal filling of the pharyngeal arches and broadly expressed in cells directly bordering myocardium. Follistatin-like3 is not expressed in the heart. Taken together, these observations are suggestive for a role for Follistatin in cardiac valvulogenesis and a role for Follistatin-like1 in controlling late heart muscle cell formation.

Early endocardial morphogenesis requires Scl/Tal1

The primitive heart tube is composed of an outer myocardial and an inner endocardial layer that will give rise to the cardiac valves and septa. Specification and differentiation of these two cell layers are among the earliest events in heart development, but the embryonic origins and genetic regulation of early endocardial development remain largely undefined. We have analyzed early endocardial development in the zebrafish using time-lapse confocal microscopy and show that the endocardium seems to originate from a region in the lateral plate mesoderm that will give rise to hematopoietic cells of the primitive myeloid lineage. Endocardial precursors appear to rapidly migrate to the site of heart tube formation, where they arrive prior to the bilateral myocardial primordia. Analysis of a newly discovered zebrafish Scl/Tal1 mutant showed an additional and previously undescribed role of this transcription factor during the development of the endocardium. In Scl/Tal1 mutant embryos, endocardial precursors are specified, but migration is severely defective and endocardial cells aggregate at the ventricular pole of the heart. We further show that the initial fusion of the bilateral myocardial precursor populations occurs independently of the endocardium and tal1 function. Our results suggest early separation of the two components of the primitive heart tube and imply Scl/Tal1 as an indispensable component of the molecular hierarchy that controls endocardium morphogenesis.

In its earliest functional form, the embryonic heart of all vertebrates is a simple linear tube consisting of two cell types. An outer muscular cell layer called the myocardium surrounds an inner vascular cell layer called the endocardium that connects the heart to the vascular system. The integration of both cell types is an important step during heart development, but the formation of the endocardial component of the heart tube is poorly understood. Here, we analyze the formation of the endocardium in the zebrafish embryo and show using time-lapse imaging that it is a highly dynamic structure. In addition, we have identified a zebrafish mutant with a specific defect during endocardial development. This defect is caused by a mutation in T cell acute leukemia 1, a gene that—when misexpressed—causes many cases of childhood leukemias. Here, we show an additional role for this gene during heart development. In mutant embryos, both endocardial and myocardial precursors are specified, but integration of both cell types does not occur properly due to a defective migration of the endocardial precursors. Given the many interactions that occur between the endocardium and the myocardium, our results will provide a more comprehensive understanding of heart development.

Signal transduction in early heart development (II): ventricular chamber specification, trabeculation, and heart valve formation

The formation of a four-chambered heart with ventricular chambers aligned in a left-right orientation begins with the rightward looping of the linear heart tube in accordance with the left-right embryonic axis. The functional specification of the ventricular chambers in the looped heart occurs with the formation of a trabeculated myocardium along the outer curvature of the realigned heart tube. Two major signal transduction pathways are involved in this process, the retinoic acid and neuregulin signaling pathways, with the retinoic acid pathway also participating in rightward heart tube looping. With the establishment of the atrial and ventricular chambers, maintenance of a unidirectional flow of blood between the two chambers must be ensured. To achieve this, heart valves develop at the atrioventricular juncture. This process begins with formation of endocardial cushions, the primordia of heart valves, and ends with formation of heart valve leaflets. Underlying this process is a complex network of signal transduction pathways that mediate communication between the endocardial and myocardial cell layers to form the endocardial cushions and nascent heart valve. Some of the signaling molecules involved are vascular endothelial growth factor, Wnts, bone morphogenetic proteins, epidermal growth factor, hyaluronic acid, neurofibromin, and calcium.

Neuropeptide Y (NPY) and NPY receptors in the cardiovascular system: implication in the regulation of intracellular calcium

The 3-dimensional confocal microscopy technique has allowed us to identify the presence of yet another cardioactive factor and its receptor, namely neuropeptide Y (NPY) and its Y1 receptor, at the level of vascular smooth muscle cells and heart cells including endocardial endothelial cells (EECs). Using this technique, we also demonstrated that NPY is able to induce an increase in both cytosolic and nuclear calcium in all these cell types. Furthermore, besides being expressed at the level of EECs, NPY is also released from these cells following a sustained increase of intracellular Ca2+. This suggests the ability of NPY to contribute to the regulation of the excitation-secretion coupling of EECs and the excitation-contraction coupling of cardiomyocytes and vascular smooth muscle cells.

Role of spatial dispersion of repolarization in inherited and acquired sudden cardiac death syndromes

This review examines the role of spatial electrical heterogeneity within the ventricular myocardium on the function of the heart in health and disease. The cellular basis for transmural dispersion of repolarization (TDR) is reviewed, and the hypothesis that amplification of spatial dispersion of repolarization underlies the development of life-threatening ventricular arrhythmias associated with inherited ion channelopathies is evaluated. The role of TDR in long QT, short QT, and Brugada syndromes, as well as catecholaminergic polymorphic ventricular tachycardia (VT), is critically examined. In long QT syndrome, amplification of TDR is often secondary to preferential prolongation of the action potential duration (APD) of M cells; in Brugada syndrome, however, it is thought to be due to selective abbreviation of the APD of the right ventricular epicardium. Preferential abbreviation of APD of the endocardium or epicardium appears to be responsible for the amplification of TDR in short QT syndrome. In catecholaminergic polymorphic VT, reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. In conclusion, long QT, short QT, Brugada, and catecholaminergic polymorphic VT syndromes are pathologies with very different phenotypes and etiologies, but they share a common final pathway in causing sudden cardiac death.

Intragraft FOXP3 mRNA Expression Reflects Antidonor Immune Reactivity in Cardiac Allograft Patients

BACKGROUND

Regulatory FOXP3+ T cells control immune responses of effector T cells. However, whether these cells regulate antidonor responses in the graft of cardiac allograft patients is unknown. Therefore, we analyzed the gene expression profiles of regulatory and effector T-cell markers during immunological quiescence and acute rejection.

METHODS

Quantitative real-time polymerase chain reaction was used to analyze mRNA expression levels in time-zero specimens (n=24) and endomyocardial biopsies (EMB; n=72) of cardiac allograft patients who remained free from rejection (nonrejectors; n=12) and patients with at least one histologically proven acute rejection episode (rejectors; International Society for Heart and Lung Transplantation [ISHLT] rejection grade>2; n=12).

RESULTS

For all analyzed regulatory and effector T-cell markers, mRNA expression levels were increased in biopsies taken after heart transplantation compared with those in time-zero specimens. Posttransplantation, the FOXP3 mRNA levels were higher in EMB assigned to a higher ISHLT rejection grade than the biopsies with grade 0: the highest mRNA levels were detected in the rejection biopsies (rejection grade>2; P=0.003). In addition, the mRNA levels of CD25, glucocorticoid-induced TNF receptor family-related gene, cytotoxic T lymphocyte-associated antigen 4, interleukin-2, and granzyme B were also significantly higher in rejecting EMB than in nonrejecting EMB (rejection grade<or=2). This increase in expression levels in relation to the histological rejection grade was only observed in patients who developed an acute rejection episode; the mRNA levels of nonrejectors remained stable irrespective of ISHLT rejection grade.

CONCLUSIONS

These observations suggest that, after clinical heart transplantation, FOXP3+ T cells do not prevent acute rejection, but rather are a response to antidonor effector T-cell activity.

Interleukin-21: An Interleukin-2 Dependent Player in Rejection Processes

BACKGROUND

Interleukin (IL)-21 is the most recently described cytokine that signals via the common cytokine receptor (gammac), is produced by activated CD4+ T-cells, and regulates expansion and effector function of CD8+ T-cells.

MATERIALS

To explore the actions of IL-21 with other gammac-dependent cytokines in alloreactivity, mRNA expression of IL-21, IL-21R alpha-chain, and IL-2 proliferation and cytotoxicity was measured after stimulation in mixed lymphocyte reactions. Additionally, IL-21 and IL-21R alpha-chain expression was studied in biopsies of heart transplant patients.

RESULTS

Analysis of mRNA expression levels of allostimulated T-cells showed a 10-fold induction of IL-21 and IL-21R alpha-chain. Interestingly, induction of IL-21 was highly dependent on IL-2 (as in the presence of anti-IL-2, anti-IL-2R alpha-chain, and the immunosuppressive drugs cyclosporine A, tacrolimus, and rapamycin) the transcription of IL-21 was almost completely inhibited, whereas in the presence of exogenous IL-2 the mRNA expression of IL-21 was even more upregulated. IL-21 functioned as a costimulator for IL-2 to augment proliferation and cytotoxic responses, while blockade of the IL-2 route abrogated these functions of IL-21. Blockade of the IL-21 route by anti-IL-21R alpha-chain monoclonal antibodies inhibited the proliferation of alloactivated T-cells. Also, in vivo alloreactivity was associated with IL-21/IL-21R alpha-chain expression. After heart transplantation, the highest intragraft IL-21, IL-21R alpha-chain, and IL-2 mRNA expression levels were measured during acute rejection (P<0.001, P=0.01, P=0.03).

CONCLUSION

IL-21 is a critical cytokine for IL-2 dependent immune processes. Blockade of the IL-21 pathway may provide a new perspective for the treatment of allogeneic responses in patients after transplantation.

Endocardiogenesis in embryoid bodies: Novel markers identified by gene expression profiling

Endocardial cells and cardiomyocytes differentiate from the cardiogenic mesoderm at about the same time during development. Although in vitro embryonic stem (ES) cell systems have been used to study the differentiation of various types of cell lineages, including cardiomyocytes, smooth muscle cells, and vascular endothelial cells, differentiation of endocardial cells, or endocardiogenesis, has not been well reported, because of a lack of specific molecular markers. In our search for cardiogenesis-associated genes expressed in embryoid bodies, we found several genes expressed in the heart region of mouse embryos, but not in cardiomyocytes. To identify the cell types expressing these genes, CD31(+) cells were taken from mouse embryos on embryonic day (E)8.5 and E9.5 and sorted, then their transcripts were analyzed using quantitative RT-PCR analyses. In those embryos, Gata4 and Nfatc1, as well as newly identified Cgnl1 and Dok4 were found to be preferentially expressed in endocardial cells, but not in yolk sac endothelial cells, while Cdh5 and Kdr were expressed in both cardiac and yolk sac endothelial cells. Immunohistochemical analyses of embryoid bodies revealed that some CD31(+) cells co-expressing Gata4 and Nfatc1 were located in close proximity to cardiomyocytes. These results suggest that embryoid bodies express endocardial specific genes and likely generate endocardial cells along with cardiomyocytes. Further, they indicate that these new marker genes are useful to study the origin and induction of endocardial cells, and identify other endocardial markers.

A novel activator of C-C chemokine, FROUNT, is expressed with C-C chemokine receptor 2 and its ligand in failing human heart

BACKGROUND

A novel activator of C-C chemokines, FROUNT, directly binds C-C chemokine receptor (CCR) 2 and plays a central role in the chemokine system. Activation of the chemokine system appears to be involved in the pathogenesis of congestive heart failure (CHF). The purpose of this study was to determine whether FROUNT is expressed with CCR2 and its ligand (CCL2) in failing human heart.

METHODS AND RESULTS

We examined endomyocardial biopsy tissues obtained from 71 patients with CHF (HF group) and 20 subjects without CHF (non-HF group). FROUNT, CCR2, and CCL2 mRNA levels were higher in the HF group than in the non-HF group (P < .001). FROUNT mRNA levels were positively correlated with CCR2 and CCL2 mRNA levels in the HF group. FROUNT and CCL2 signal was seen in the cytoplasm of cardiac myocytes in failing hearts. Levels of FROUNT mRNA were negatively correlated with left ventricular ejection fraction. FROUNT, CCR2, and CCL2 mRNA levels were higher in the severe HF subgroup than in the mild HF subgroup.

CONCLUSIONS

The expression of FOUNT-mediated CCL2/CCR2 may have important implications in the pathogenesis of CHF. The CCL2/CCR2 pathway via FROUNT may influence the clinical severity of CHF.

Mechanism of U wave and polymorphic ventricular tachycardia in a canine tissue model of Andersen-Tawil syndrome

OBJECTIVE

Andersen-Tawil syndrome (ATS) is a channelopathy affecting inward rectifier potassium I(K1) with QT prolongation, large U waves, and frequent ventricular tachycardia (VT). Although ATS is clinically defined and genetically identified, its electrophysiological mechanism is still unclear, and thus, was the subject of the current study.

METHODS AND RESULTS

We replicated the major electrophysiological features of ATS with cesium chloride (CsCl, at I(K1) blockade concentration of 5-10 mmol/l) in 23 isolated canine left ventricular tissues perfused arterially with Tyrode's solution having normal or low potassium concentrations, [K(+)](o). We mapped action potentials (APs) on the cut-exposed transmural surface of the wedges in control, after CsCl, and CsCl with 0.15 mumol/l isoproterenol (CsCl+ISP). CsCl delayed late phase 3 repolarization and prolonged the duration of the AP, more so during low [K(+)](o) perfusion. Rapid pacing induced delayed afterdepolarizations (DADs) in all low [K(+)](o) and in 71% of normal [K(+)](o) preparations after CsCl treatment. Addition of ISP induced DADs in all preparations. DADs originated in mid-to-endocardium, and initiated VT after CsCl+ISP. Migration of DAD-VT foci resulted in multifocal VT. Alternating DADs at 2 foci resulted in bidirectional VT. There were more foci and longer durations of VT at low [K(+)](o) than at normal [K(+)](o). Delayed late phase 3 repolarization of APs and DADs generated U waves. Verapamil abolished all DADs and VT.

CONCLUSIONS

CsCl blockade of I(K1) produced a ventricular wedge model of ATS. Suppressing I(K1) generated U waves by delaying late repolarization of APs and creating DADs, and promoted polymorphic VT by triggering DADs at multiple shifting sites.

Regional and tissue specific transcript signatures of ion channel genes in the non-diseased human heart

The various cardiac regions have specific action potential properties appropriate to their electrical specialization, resulting from a specific pattern of ion-channel functional expression. The present study addressed regionally defined differential ion-channel expression in the non-diseased human heart with a genomic approach. High-throughput real-time RT-PCR was used to quantify the expression patterns of 79 ion-channel subunit transcripts and related genes in atria, ventricular epicardium and endocardium, and Purkinje fibres isolated from 15 non-diseased human donor hearts. Two-way non-directed hierarchical clustering separated atria, Purkinje fibre and ventricular compartments, but did not show specific patterns for epicardium versus endocardium, nor left- versus right-sided chambers. Genes that characterized the atria (versus ventricles) included Cx40, Kv1.5 and Kir3.1 as expected, but also Cav1.3, Cav3.1, Cav alpha2 delta2, Nav beta1, TWIK1, TASK1 and HCN4. Only Kir2.1, RyR2, phospholamban and Kv1.4 showed higher expression in the ventricles. The Purkinje fibre expression-portrait (versus ventricle) included stronger expression of Cx40, Kv4.3, Kir3.1, TWIK1, HCN4, ClC6 and CALM1, along with weaker expression of mRNA encoding Cx43, Kir2.1, KChIP2, the pumps/exchangers Na(+),K(+)-ATPase, NCX1, SERCA2, and the Ca(2+)-handling proteins RYR2 and CASQ2. Transcripts that were more strongly expressed in epicardium (versus endocardium) included Cav1.2, KChIP2, SERCA2, CALM3 and calcineurin-alpha. Nav1.5 and Nav beta1 were more strongly expressed in the endocardium. For selected genes, RT-PCR data were confirmed at the protein level. This is the first report of the global portrait of regional ion-channel subunit-gene expression in the non-diseased human heart. Our data point to significant regionally determined ion-channel expression differences, with potentially important implications for understanding regional electrophysiology, arrhythmia mechanisms, and responses to ion-channel blocking drugs. Concordance with previous functional studies suggests that regional regulation of cardiac ion-current expression may be primarily transcriptional.

Identification and characterization of a novel Schwann and outflow tract endocardial cushion lineage-restricted periostin enhancer

Periostin is a fasciclin-containing adhesive glycoprotein that facilitates the migration and differentiation of cells that have undergone epithelial-mesenchymal transformation during embryogenesis and in pathological conditions. Despite the importance of post-transformational differentiation as a general developmental mechanism, little is known how periostin's embryonic expression is regulated. To help resolve this deficiency, a 3.9-kb periostin proximal promoter was isolated and shown to drive tissue-specific expression in the neural crest-derived Schwann cell lineage and in a subpopulation of periostin-expressing cells in the cardiac outflow tract endocardial cushions. In order to identify the enhancer and associated DNA binding factor(s) responsible, in vitro promoter dissection was undertaken in a Schwannoma line. Ultimately a 304-bp(peri) enhancer was identified and shown to be capable of recapitulating 3.9 kb(peri-lacZ)in vivo spatiotemporal patterns. Further mutational and EMSA analysis helped identify a minimal 37-bp region that is bound by the YY1 transcription factor. The 37-bp enhancer was subsequently shown to be essential for in vivo 3.9 kb(peri-lacZ) promoter activity. Taken together, these studies identify an evolutionary-conserved YY1-binding 37-bp region within a 304-bp periostin core enhancer that is capable of regulating simultaneous novel tissue-specific periostin expression in the cardiac outflow-tract cushion mesenchyme and Schwann cell lineages.

A simple technique of image analysis for specific nuclear immunolocalization of proteins

Colocalization of fluorescent signals in confocal microscopy is usually evaluated by inspecting merged images from different colour channels or by using commercially available software packages. We describe in this paper a simple method for assessment of nuclear localization of proteins in tissue sections through confocal immunolocalization, propidium iodide counterstaining and image analysis. Through a macro command developed for the public domain, Java-based software imagej, red, green, blue (RGB) images are automatically split in the red and green channels and a new image composed of the nonblack pixels coincident in both channels is created and inverted for better visualization. This method renders images devoid of both, extranuclear staining and background, thus emphasizing the nuclear signal. The resulting images can easily be used for comparison or quantification of the results. Given the simplicity of the technique and the worldwide diffusion of the software utilized, we think that this method could be useful in order to define standards of colocalization in confocal microscopy.

Myocyte diameter and fractional area of collagen are not associated with survival time of outpatients with idiopathic dilated cardiomyopathy: A study based on right ventricular endomyocardial biopsies

Morphometric data obtained from the analysis of endomyocardial biopsy might be useful to evaluate prognosis of patients with dilated cardiomyopathy. We measured the myocyte diameter, its coefficient of variation and the fractional area of collagen in right ventricular endomyocardial biopsies of 35 outpatients with idiopathic dilated cardiomyopathy. None of the evaluated histological parameter was associated with the survival time of the patients (range: 2 to 5588; median: 706 days). Right ventricular endomyocardial biopsy should not be indicated to predict evolution or fatal outcome in patients with idiopathic dilated cardiomyopathy.

Modeling transmural heterogeneity of K(ATP) current in rabbit ventricular myocytes

To investigate the mechanisms regulating excitation-metabolic coupling in rabbit epicardial, midmyocardial, and endocardial ventricular myocytes we extended the LabHEART model (Puglisi JL and Bers DM. Am J Physiol Cell Physiol 281: C2049-C2060, 2001). We incorporated equations for Ca(2+) and Mg(2+) buffering by ATP and ADP, equations for nucleotide regulation of ATP-sensitive K(+) channel and L-type Ca(2+) channel, Na(+)-K(+)-ATPase, and sarcolemmal and sarcoplasmic Ca(2+)-ATPases, and equations describing the basic pathways (creatine and adenylate kinase reactions) known to communicate the flux changes generated by intracellular ATPases. Under normal conditions and during 20 min of ischemia, the three regions were characterized by different I(Na), I(to), I(Kr), I(Ks), and I(Kp) channel properties. The results indicate that the ATP-sensitive K(+) channel is activated by the smallest reduction in ATP in epicardial cells and largest in endocardial cells when cytosolic ADP, AMP, PCr, Cr, P(i), total Mg(2+), Na(+), K(+), Ca(2+), and pH diastolic levels are normal. The model predicts that only K(ATP) ionophore (Kir6.2 subunit) and not the regulatory subunit (SUR2A) might differ from endocardium to epicardium. The analysis suggests that during ischemia, the inhomogeneous accumulation of the metabolites in the tissue sublayers may alter in a very irregular manner the K(ATP) channel opening through metabolic interactions with the endogenous PI cascade (PIP(2), PIP) that in turn may cause differential action potential shortening among the ventricular myocyte subtypes. The model predictions are in qualitative agreement with experimental data measured under normal and ischemic conditions in rabbit ventricular myocytes.

Post-transcriptional modifications of VEGF-A mRNA in non-ischemic dilated cardiomyopathy

Vascular endothelial growth factor (VEGF-A) is one of the most important proangiogenic factors. It has many isoforms encoded by one gene. The occurrence of these isoforms is associated with the process of alternative splicing of mRNA. Some of the splice forms are perceived as tissue specific. The aim of this study was to determine the alternative splicing of VEGF-A mRNA in dilated cardiomyopathy, especially at the level of particular myocardial layers. The assessment of post-transcriptional modifications of VEGF-A mRNA was made on specimens taken from the explanted hearts of patients undergoing cardiac transplantation. Molecular and histopathological studies were perfomed on particular layers of the myocardial muscle (endocardium, myocardium, epicardium). A molecular analysis of cardiac samples was performed by quantitative analysis of the mRNA of the studied VEGF-A isoforms (VEGF121, -145, -165, -183, -189, and -206) using QRTPCR with an ABI-PRISM 7700-TaqMan sequence detector. 72 cardiac specimens taken from the explanted hearts were analyzed. Each of the studied VEGF-A splice forms was present in the evaluated hearts, but the types of alternative splicing of mRNA were different in particular layers. Quantitative analysis revealed different amounts of the studied isoforms. Generally, significantly increased expression of the VEGF-A isoforms was observed in samples taken from hearts with post-inflammatory etiology of cardiomyopathy. Our conclusions are: 1. All the studied VEGF-A isoforms were found in the human hearts, including those thusfar considered characteristic for other tissues. 2. Significant differences were observed in the expression of the VEGF-A splice forms with respect to the myocardial layers and the location of the cardiac biopsy. 3. Repetitive and comparable results for samples with post-inflammatory etiology were obtained, and they revealed considerably higher amounts of VEGF-A isoforms compared to specimens with idiopathic etiology.

Extracellular matrix turnover and disease severity in Anderson-Fabry disease

BACKGROUND

Anderson-Fabry Disease (AFD) is an inherited metabolic disease associated with premature death secondary to cardiovascular and renal disease. Patients with AFD develop progressive left ventricular (LV) remodelling and heart failure. We hypothesized that altered extracellular matrix (ECM) turnover contributes to the pathophysiology of cardiac disease in AFD.

METHODS AND RESULTS

Twenty-nine consecutive patients (44.1 +/- 11.7 years, 15 male) with AFD and 21 normal controls (39.7 +/- 11.3 years, 10 male) had serum analysed for matrix metalloproteinase-9 (MMP-9), and tissue inhibitor of matrix metalloproteinase-1 and -2 (TIMP-1, TIMP-2). All patients underwent clinical assessment, echocardiography and Mainz Severity Score Index (MSSI) measurement, a validated severity score in AFD. MMP-9 levels were significantly higher in patients than controls (1003.8 +/- 337.8 ng/ml vs 576.7 +/- 276.3 ng/ml respectively, p < 0.001). There were no differences in TIMP levels between patients and controls. There was a positive correlation between MMP-9 levels and MSSI (r = 0.5, p = 0.01). There was a negative correlation between MMP-9 and endocardial fractional shortening (FS) (r = -0.5, p = 0.01) and mid-wall FS (r = -0.6, p = 0.001). There was no correlation between other echocardiographic parameters and MMP-9 levels. These relations were independent of age and sex using stepwise linear regression analysis.

CONCLUSIONS

Patients with AFD have abnormal ECM turnover compared to normal controls. The correlation between MMP-9 levels and systolic function suggests that altered ECM turnover is important in cardiac remodelling. The association between MMP-9 and overall disease severity suggests that circulating levels of MMP-9 may provide a useful marker for assessing the response of patients with AFD to enzyme replacement treatment.

Diminished Kv4.2/3 but not KChIP2 levels reduce the cardiac transient outward K+ current in spontaneously hypertensive rats

OBJECTIVE

A reduction of the Ca(2+)-independent transient outward potassium current (I(to)) in epicardial but not in endocardial myocytes of the left ventricle has been observed in cardiac hypertrophy and is thought to contribute to the electrical vulnerability associated with this pathology.

METHODS

In the present study we investigated the molecular mechanisms underlying regional alterations in I(to) in hypertrophied hearts of spontaneously hypertensive rats (SHR) using the whole-cell patch-clamp technique, quantitative RT-PCR and heterologous expression of underlying ion channel subunits.

RESULTS

I(to) was significantly smaller in epicardial myocytes of SHR than in Wistar-Kyoto (WKY) controls (11.1+/-0.9 pA/pF, n=20 vs. 16.8+/-1.7 pA/pF, n=20, p<0.01), but not different in endocardial myocytes from both groups. Quantitative RT-PCR analysis of the genes encoding I(to) revealed significantly lower levels of Kv4.2 and Kv4.3 mRNA in the epicardial region of SHR rats compared to WKY rats. In contrast, mRNA expression levels of all three splice variants of the beta-subunit KChIP2 were significantly higher in both endo- and epicardial myocytes from SHR than from WKY rats. In parallel, inactivation of I(to), which is negatively modulated by KChIP2, was slowed down in SHR while recovery from inactivation remained unchanged. Heterologous co-expression of increasing amounts of KChIP2b together with a fixed amount of Kv4.2 in Xenopus laevis oocytes revealed a hyperbolic relation of recovery from inactivation and inactivation time constant, demonstrating that KChIP2 preferentially affects inactivation, if its expression level is high.

CONCLUSION

These results suggest that downregulation of I(to) in the left ventricle of SHR is mediated by a reduced expression of Kv4.2 and Kv4.3 (but not of KChIP2), whereas the slower inactivation of I(to) can be explained by increased expression levels of KChIP2 in SHR.

Phospholipid and triacylglycerol fatty acid content and pattern in the cardiac endothelium of rats depleted in long-chain polyunsaturated omega 3 fatty acids

Rats depleted in long-chain polyunsaturated omega3 fatty acids (omega3-depleted rats) display several features of the metabolic syndrome including hypertension and cardiac hypertrophy. This coincides with alteration of the cardiac muscle phospholipid and triacylglycerol fatty acid content and/or pattern. In the present study, the latter variables were measured in the cardiac endothelium of normal and omega3-depleted rats. Samples derived from four rats each were obtained from 16 female normal fed rats and three groups of 36-40 female fed omega3-depleted rats each aged 8-9, 15-16 and 22-23 weeks. At comparable mean age, the ratio between the square root of the total fatty acid content of phospholipids and cubic root of the total fatty acid content of triacylglycerols was lower in omega3-depleted rats than in control animals. The total fatty acid content of triacylglycerols was inversely related to their relative content in C20:4omega6. Other differences between omega3-depleted rats and control animals consisted in a lower content of long-chain polyunsaturated omega3 fatty acids in both phospholipids and triacylglycerols, higher content of long-chain polyunsaturated omega6 fatty acids in phospholipids, higher activity of delta9-desaturase (C16:0/C16:1omega7 and C18:0/C18:1omega9 ratios) and elongase [(C16:0 + C16:1omega7)/(C18:0 + C18:1omega9) and C20:4omega6/C22:4omega6 ratios], but impaired generation of C22:6omega3 from C22:5omega3 in the former rats. These findings support the view that cardiovascular perturbations previously documented in the omega3-depleted rats may involve impaired heart endothelial function.

Hemodynamic Modulation of Endocardial Thromboresistance

Background— Patients with heart failure are at increased risk for thromboembolic events, including stroke. Historically attributed to blood stasis, little is known about the adverse effects of elevated chamber filling pressure on endocardial function, which could predispose to intracardiac thrombus formation.

Methods and Results— We investigated changes in the expression of thrombomodulin, a key component of the anticoagulant protein C pathway, in rats subjected to acute atrial pressure overload caused by aortic banding. Acute elevation of left atrial filling pressure, without an associated decline in ventricular systolic function, caused a 70% inhibition of atrial endocardial thrombomodulin expression and resulted in increased local thrombin generation. Targeted restoration of atrial thrombomodulin expression with adenovirus-mediated gene transfer successfully reduced thrombin generation to baseline levels. In vitro co-culture studies revealed that thrombomodulin downregulation is caused by the paracrine release of transforming growth factor-β from cardiac connective tissue in response to mechanical stretch. This was confirmed in vivo by administration of a neutralizing transforming growth factor-β antibody, which effectively prevented thrombomodulin downregulation during acute pressure overload.

Conclusions— These findings suggest that increased hemodynamic load adversely affects endocardial function and is a potentially important contributor to thromboembolus formation in heart failure.

Spatial distributions of Kv4 channels and KChip2 isoforms in the murine heart based on laser capture microdissection

OBJECTIVE

Regional differences in repolarizing K(+) current densities and expression levels of their molecular components are important for coordinating the pattern of electrical excitation and repolarization of the heart. The small size of hearts from mice may obscure these interventricular and/or transmural expression differences of K(+) channels. We have examined this possibility in adult mouse ventricle using a technology that provides very high spatial resolution of tissue collection.

METHODS

Conventional manual dissection and laser capture microdissection (LCM) were utilized to dissect tissue from distinct ventricular regions. RNA was isolated from epicardial, mid-myocardial and endocardial layers of both the right and left ventricles. Real-time RT-PCR was used to quantify the transcript expression in these different regions.

RESULTS

LCM revealed significant interventricular and transmural gradients for both Kv4.2 and the alpha-subunit of KChIP2. The expression profile of a second K(+) channel transcript, Kir2.1, which is responsible for the inwardly rectifying K(+) current I(k1), showed no interventricular or transmural gradients and therefore served as a negative control.

CONCLUSIONS

Our findings are in contrast to previous reports of a relatively uniform left ventricular transmural pattern of expression of Kv4.2, Kv4.3 and KChIP2 in adult mouse heart, which appear to be different than that in larger mammals. Specifically, our results demonstrate significant epi- to endocardial differences in the patterns of expression of both Kv4.2 and KChIP2.

Evidence for cystic fibrosis transmembrane conductance regulator chloride current in swine ventricular myocytes

The present study investigated whether cAMP-dependent cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel current (i.e., I(Cl.CFTR) or I(Cl.cAMP)) would be expressed in pig cardiac myocytes using whole-cell patch technique and reverse transcription polymerase chain reaction (RT-PCR). It was found that the beta-adrenoceptor agonist isoproterenol activated a time-independent current in myocytes from the ventricle, but not the atrium of pig heart. Histamine and forskolin (an adenylate cyclase activator) induced a similar current in pig ventricular cells. The current induced by isoproterenol was blocked by the PKA inhibitor H-7, reduced by the replacement of external Cl(-) ion, and inhibited by the application of 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), but not 4'-diisothiocynatostilbene-2,2'-disulfonic acid (DIDS), typical of I(Cl.CFTR). I(Cl.CFTR) showed a small difference in regional myocytes across the left ventricular wall from epicardium to endocardium. Isoproterenol-induced current was 3.1+/-0.2 (n=33), 2.8+/-0.2 (n=25) and 2.3+/-0.2 pA/pF (n=31) respectively in subepicardial, midmyocardial, and subendocardial myocytes (P<0.05, subepicardium vs. subendocardium). RT-PCR and Western blotting analysis revealed that significant differences in CFTR channel mRNA and protein levels were present in atrial and ventricular cells, but not in regional ventricular cells across the ventricular wall from subepicardium to subendocardium. These results indicate that the functional CFTR channel (i.e., I(Cl.CFTR)) is present in ventricular myocytes, but not in atrial cells of pig heart.

GENE EXPRESSION OF STRETCH-ACTIVATED CHANNELS AND MECHANOELECTRIC FEEDBACK IN THE HEART

1. Mechanoelectric feedback (MEF) in the heart is the process by which mechanical forces on the myocardium can change its electrical properties. Mechanoelectric feedback has been demonstrated in many animal models, ranging from isolated cells, through isolated hearts to whole animals. In humans, MEF has been demonstrated directly in both the atria and the ventricles. It seems likely that MEF provides either the trigger or the substrate for some types of clinically important arrhythmias. 2. Mechanoelectric feedback may arise because of the presence of stretch-sensitive (or mechano-sensitive) ion channels in the cell membrane of the cardiac myocytes. Two types have been demonstrated: (i) a non-specific cation channel (stretch-activated channel (SAC); conductance of approximately 25 pS); and (ii) a potassium channel with a conductance of approximately 100 pS. The gene coding for the SAC has not yet been identified. The gene for the potassium channel is likely to be TREK, a member of the tandem pore potassium channel gene family. We have recorded stretch-sensitive potassium channels in rat isolated myocytes that have the properties of TREK channels expressed in heterologous systems. 3. It has been shown that TREK mRNA is expressed heterogeneously in the rat ventricular wall, with 17-fold more expression in endocardial compared with epicardial cells. This difference is reflected in the TREK currents recorded from endocardial and epicardial cells using whole-cell patch-clamp techniques, although the difference in current density was less pronounced (approximately threefold). Consistent with this, we show here that when the ventricle is stretched by inflation of an intraventricular balloon in a Langendorff perfused rat isolated heart, action potential shortening was more pronounced in the endocardium (30% shortening at 40 mmHg) compared with that in the epicardium (10% shortening at the same pressure). 4. Computer models of the mechanics of the (pig) heart show pronounced spatial variations in strain in the myocardium with large transmural differences (in the left ventricle in particular) and also large differences between the base and apex of the ventricle. 5. The importance of MEF and the non-homogeneous gene expression and strain distribution for arrhythmias is discussed.

IKr contributes to the altered ventricular repolarization that determines long-term cardiac memory

OBJECTIVE

Cardiac memory (CM) is characterized by an altered T-wave morphology, which reflects altered repolarization gradients. We hypothesized that the delayed rectifier currents, I(Kr) and I(Ks), might contribute to these repolarization changes.

METHODS

We studied conscious, chronically instrumented dogs paced from the postero-lateral left ventricular (LV) wall at rates 5-10% faster than sinus rate for 3 weeks. ECGs during sinus rhythm were recorded on days 0, 7, 14 and 21 of pacing. Within 3 weeks, CM achieved steady state, hearts were excised, and epicardial and endocardial tissues and myocytes were studied.

RESULTS

In unpaced controls, action potential duration to 50% and 90% repolarization (APD) in epicardium was shorter than in endocardium (P < 0.05); in CM epicardial APD increased at CL > or = 500 ms, while endocardial APD was either unchanged or decreased such that the transmural gradient seen in controls diminished (P < 0.05). A transmural I(Kr) gradient occurred in controls (epicardium>endocardium, P < 0.05) and was reversed in CM. No I(Ks) transmural gradient was found in controls, while in CM endocardial I(Ks) was greater than epicardial at greater than +50 mV. Canine ERG (cERG) mRNA and protein in epicardium > endocardium in controls (P < 0.05), and this difference was lost in CM. Expression levels of KCNQ1 and KCNE1 protein were similar in all groups.

CONCLUSIONS

A transcriptionally induced change in epicardial I(Kr) contributes to the altered ventricular repolarization that characterizes CM.

Inotropic and lusitropic effects of ghrelin and their modulation by the endocardial endothelium, NO, prostaglandins, GHS-R1a and KCa channels

Contractile effects of ghrelin (10(-9) to 10(-6) M) were tested in rat papillary muscles of normal (n = 50) and hypertrophic (n = 16) right ventricles (RV). RV hypertrophy was induced by pulmonary hypertension using monocrotaline. In normal muscles, ghrelin was added either alone (n = 9) or after pre-treatment with indomethacin (cycloxygenase inhibitor, 10(-5) M; n = 10), L-nitro-L-arginin (NO synthase inhibitor, 10(-4) M; n = 9), D-Lys(3)-GHRP-6 (GHS-R1a antagonist; 10(-4) M; n = 8) or apamin+charybdotoxin (KCa channels blockers; 10(-6) M, n =7 ), as well as after damaging the endocardial endothelium (n = 7). In hypertrophic muscles, ghrelin was added either alone (n = 9) or after pre-treatment with apamin+charybdotoxin (10(-6 M, n=7). Ghrelin concentration-dependently decreased active tension (AT) and maximal velocity of tension rise (negative inotropic effect), as well as, maximal velocity of tension decay (negative lusitropic effect) and time to AT (onset of relaxation). These effects were maximal at 10(-6) M, similar in normal and hypertrophic muscles and were significantly altered only by apamin+charybdotoxin, indomethacin and L-nitro-L-arginin. Apamin+charybdotoxin attenuated the negative inotropic effect, while indomethacin and L-nitro-L-arginin, respectively, blunted and exacerbated the premature onset of relaxation. In conclusion, ghrelin induces negative inotropic and lusitropic effects and an earlier onset of relaxation in normal and hypertrophic myocardium, which are independent of GHS-R1a, since they were not affected by D-Lys(3)-GHRP-6. The negative inotropic effect is partly mediated by KCa channels, while the earlier onset of relaxation is modulated by prostaglandins and NO.

Evaluation of CXCL9 and CXCL10 as circulating biomarkers of human cardiac allograft rejection

Background

Cardiac allograft rejection remains a significant clinical problem in the early phase after heart transplantation and requires frequent surveillance with endomyocardial biopsy. However, this is an invasive procedure, which is unpleasant for the patient and carries a certain risk. Therefore, a sensitive non-invasive biomarker of acute rejection would be desirable.

Methods

Endomyocardial tissue samples and serum were obtained in connection with clinical biopsies from twenty consecutive heart transplant patients followed for six months. A rejection episode was observed in 14 patients (11 men and 3 women) and biopsies obtained before, during and after the episode were identified. Endomyocardial RNA, from three patients, matching these three points in time were analysed with DNA microarray. Genes showing up-regulation during rejection followed by normalization after the rejection episode were evaluated further with real-time RT-PCR. Finally, ELISA was performed to investigate whether change in gene-regulation during graft rejection was reflected in altered concentrations of the encoded protein in serum.

Results

Three potential cardiac allograft rejection biomarker genes, chemokine (C-X-C motif) ligand 9 (CXCL9), chemokine (C-X-C motif) ligand 10 (CXCL10) and Natriuretic peptide precursor A (NPPA), from the DNA microarray analysis were selected for further evaluation. CXCL9 was significantly upregulated during rejection (p < 0.05) and CXCL10 displayed a similar pattern without reaching statistical significance. Serum levels of CXCL9 and CXCL10 were measured by ELISA in samples from 10 patients before, during and after cardiac rejection. There were no changes in CXCL9 and CXCL10 serum concentrations during cardiac rejection. Both chemokines displayed large individual variations in the selected samples, but the serum levels between the two chemokines correlated (p < 0.001).

Conclusion

We conclude, that despite a distinct up-regulation of CXCL9 mRNA in human hearts during cardiac allograft rejection, this was not reflected in the serum levels of the encoded protein. Thus, in contrast to previous suggestions, serum CXCL9 does not appear to be a promising serum biomarker for cardiac allograft rejection.

Muscularizing tissues in the endocardial cushions of the avian heart are characterized by the expression of h1-calponin

Muscularization of mesenchymal tissues in the developing heart is an important event in the morphogenesis of the valvuloseptal complex in four-chambered hearts. Perturbation of muscularization has been implicated in the pathogenesis of cardiac malformations in several animal models for congenital heart disease, including the Trisomy 16 mouse and the TGFbeta2 knockout mouse. Studies to unravel the mechanism of muscularization, as well as studies to determine the extent of the process in frequently used animal-model systems for cardiac development, have, thus far, been hampered by the lack of useful differentiation markers for muscularizing tissues, albeit that it had been demonstrated that, in the mouse, muscularizing cells are characterized by an elevated level of smooth muscle actin expression. In this study, we investigated whether muscularization of endocardial cushions in the avian heart is also accompanied by the expression of smooth muscle cell markers. The results presented in this study demonstrate that, in quail and chick, a specific population of muscularizing cells is recognized by the expression of smooth muscle h1-calponin. Interestingly, other genes typically found in smooth muscle cells (e.g., smooth muscle actin and caldesmon) are not expressed in muscularizing tissues. We conclude that muscularization of cushion-derived mesenchymal tissues is associated with a discrete genetic program reflected by the expression of h1-calponin and predict that h1-calponin will prove an invaluable tool in elucidating the regulation of muscularization and other aspects related to this event.

NFATc1 expression in the developing heart valves is responsive to the RANKL pathway and is required for endocardial expression of cathepsin K

NFATc1 is necessary for remodeling endocardial cushions into mature heart valve leaflets and is also an essential effector of receptor activator of NFkappaB ligand (RANKL) signaling required for transcriptional activation of bone matrix remodeling enzymes during osteoclast differentiation. Therefore, developing heart valves were examined to determine if NFATc1 functions in the RANKL pathway during leaflet remodeling. Key components of RANKL signal transduction including RANKL, its receptor RANK, and the downstream remodeling enzyme cathepsin K (Ctsk) are expressed in the heart during valve remodeling and colocalize with NFATc1 in developing valve endocardium. However, the absence of tartrate-resistant acid phosphatase (TRAP) activity and the lack of F4/80-positive macrophage lineage contribution to the remodeling valves demonstrate that certain aspects of osteoclast RANKL function are not shared during valve formation. Analysis of NFATc1-/- mouse embryos shows that NFATc1 is specifically required for endocardial expression of RANKL and Ctsk during valve formation. In addition, RANKL treatment augments expression of NFATc1 and Ctsk in embryonic heart cultures, and the RANKL-mediated increase in Ctsk expression is dependent on NFATc1. Together, these results support a role for RANKL signaling during heart valve development and suggest that valve leaflet morphogenesis involves NFATc1-dependent expression of remodeling enzymes including Ctsk.

Differential Calcineurin/NFATc3 Activity Contributes to the I to Transmural Gradient in the Mouse Heart

Kv4 channels are differentially expressed across the mouse left ventricular free wall. Accordingly, the transient outward K + current ( I to ), which is produced by Kv4 channels, is greater in left ventricular epicardial (EPI) than in endocardial (ENDO) cells. However, the mechanisms underlying heterogeneous Kv4 expression in the heart are unclear. Here, we tested the hypothesis that differential [Ca 2+ ] i and calcineurin/NFATc3 signaling in EPI and ENDO cells contributes to the gradient of I to function in the mouse left ventricle. In support of this hypothesis, we found that [Ca 2+ ] i , calcineurin, and NFAT activity were greater in ENDO than in EPI myocytes. However, the amplitude of I to was the same in ENDO and EPI cells when [Ca 2+ ] i , calcineurin, and NFAT activity were equalized. Consistent with this, we observed complete loss of I to and Kv4 heterogeneity in NFATc3-null mice. Interestingly, Kv4.3, Kv4.2, and KChIP2 genes had different apparent thresholds for NFATc3-dependent suppression and were ordered as Kv4.3≈KChIP2>Kv4.2. Based on these data, we conclude that calcineurin and NFATc3 constitute a Ca 2+ -driven signaling module that contributes to the nonuniform distribution of Kv4 expression, and hence I to function, in the mouse left ventricle.

Increased cardiac mRNA expression of matrix metalloproteinase-1 (MMP-1) and its inhibitor (TIMP-1) in DCM patients

Left ventricular dilation and myocardial remodeling are hallmarks of dilated cardiomyopathy (DCM). It is assumed that left ventricular dilation is caused by the disintegration of the collagenous network by increased collagenolytic activity of matrix metalloproteinases (MMPs) and their adequate tissue inhibitors (TIMPs). In this study the myocardial MMP-1 and TIMP-1 mRNA expressions were investigated by using real-time quantitative PCR analysis from right septal endomyocardial biopsies of patients with dilated cardiomyopathy (n = 46) and control subjects (n = 11). The volume density (Vv%) of collagen was measured morphometrically. Classification was done according to LV diameters [left ventricular enddiastolic diameter (LVEDD, cm) calculated to body surface area (BSA, m(2))] into three DCM groups: group I (LVEDD-BSA > 2.7-3.0 cm/m(2)), group II ( > 3.0-3.6 cm/m(2)), group III ( > 3.6 cm/m(2)), controls (< 2.7 cm/m(2)). Compared with controls, the MMP-1 expression in patients with DCM was significantly increased (119.2 +/- 45.2 vs. 1.3 +/- 0.4; p < 0.001) as was TIMP-1 expression (9.6 +/- 1.2 vs. 1.3 +/- 0.4; p < 0.01). Moreover the MMP-1 and TIMP-1 expression varied according to LV diameter: group I (MMP-1: 8.7 +/- 3.5; p = 0.33; TIMP- 1: 4.5 +/- 1.2; p < 0.01); group II (MMP-1: 211.4 +/- 86.0; p < 0.001; TIMP-1: 12.5 +/- 1.9 ; p < 0.001); group III (MMP-1: 38.8 +/- 22.6; p < 0.01; TIMP-1: 8.1 +/- 1.7; p < 0.001). Compared with controls, the collagen level in DCMPt. was significantly increased: 5.0 +/- 0.6 vol% vs 1.2 +/- 0.2 vol% p < 0.001 and correlates with LV diameter. This study reveals that the overexpression of MMP-1, which is associated with an increased ratio of MMP-1/TIMP-1 in DCM, indicates an activated collagenolytic system while replacement fibrosis is accumulating. The MMP-1 overexpression is mainly found in moderately dilated DCM hearts (group II) indicating the dynamic process of LV dilation and the importance of collagenases in the early phase of LV remodeling.

Prognostic Value of Pacing-Induced Mechanical Alternans in Patients With Mild-to-Moderate Idiopathic Dilated Cardiomyopathy in Sinus Rhythm

OBJECTIVES

The relation between the occurrence of pacing-induced mechanical alternans and prognosis in patients with mild-to-moderate idiopathic dilated cardiomyopathy (IDCM) in sinus rhythm was investigated prospectively. The myocardial expression of genes for Ca2+-handling proteins in such patients was also examined.

BACKGROUND

Mechanical alternans occurs in some patients with severe heart failure, but the relation between the occurrence of mechanical alternans and prognosis in patients with IDCM has remained unknown.

METHODS

Left ventricular (LV) pressure was measured during atrial pacing, and LV endomyocardial biopsy specimens were collected in 36 IDCM patients and 8 controls. Idiopathic dilated cardiomyopathy patients were divided into two groups consisting of 22 individuals who did not develop mechanical alternans at heart rates up to 140 beats/min (group A) and of 14 individuals who did (group B). The patients were followed up for a mean of 3.7 years.

RESULTS

There was no significant difference in LV ejection fraction or the plasma concentration of brain natriuretic peptide between groups A and B. The myocardial abundance of ryanodine receptor 2 messenger ribonucleic acid (mRNA) was significantly lower in groups A and B than in controls, whereas that of sarcoplasmic reticulum Ca2+-ATPase mRNA was significantly lower in group B than in group A or controls. Stepwise multivariate analysis identified pacing-induced mechanical alternans as the strongest predictor of cardiac events. Event-free survival in group A was significantly greater than that in group B.

CONCLUSIONS

The occurrence of pacing-induced mechanical alternans is a potentially useful indicator of poor prognosis in patients with mild-to-moderate IDCM in sinus rhythm.

Fabry's disease cardiomyopathy: echocardiographic detection of endomyocardial glycosphingolipid compartmentalization

OBJECTIVES

We sought to identify echocardiographic hallmarks of Fabry's disease cardiomyopathy (FC).

BACKGROUND

The recognition of FC from other forms of left ventricular hypertrophy (LVH) by noninvasive imaging techniques is not yet available, and diagnosis, mostly in the absence of systemic manifestations, still relies on genetic and invasive studies.

METHODS

Forty consecutive patients (mean age 39 +/- 15 years, 22 men and 18 women) with an established diagnosis of Fabry's disease were submitted to echocardiographic evaluation. Control population consisted of 40 consecutive patients with hypertrophic cardiomyopathy (HCM), 40 hypertensive patients with echocardiographic evidence of LVH, and 40 age- and gender-matched healthy subjects with no LVH. All HCM patients and FC with LVH and/or cardiac symptoms underwent cardiac catheterization with left ventricular endomyocardial biopsy.

RESULTS

Echocardiography showed in 83% of FC patients (95% of FC patients with LVH) a binary appearance of endocardial border absent in all HCM, hypertensive, and healthy subjects. The sensitivity and specificity of this echocardiographic feature in detecting Fabry patients in study population were 94% and 100%, respectively. Comparison of echocardiographic with histologic and ultrastructural findings showed the binary appearance to reflect an endomyocardial glycosphingolipids compartmentalization, consisting of thickened glycolipid-rich endocardium, free glycosphingolipid subendocardial storage, and an inner severely affected myocardial layer with a clear subendocardial-midwall layer gradient of disease severity.

CONCLUSIONS

Echocardiographic binary appearance of left ventricular endocardial border, reflecting endomyocardial glycosphingolipids compartmentalization, represents a sensitive and specific diagnostic hallmark of Fabry's disease cardiomyopathy.

NPY, ET-1, and Ang II nuclear receptors in human endocardial endothelial cellsThis paper is one of a selection of papers published in this Special Issue, entitled The Nucleus: A Cell Within A Cell

Neuropeptide Y (NPY), endothelin-1 (ET-1), and angiotensin II (Ang II) are peptides that are known to play many important roles in cardiovascular homeostasis. The physiological actions of these peptides are thought to be primarily mediated by plasma membrane receptors that belong to the G-protein-coupled receptor superfamily. However, there is increasing evidence that suggests the existence of functional G-protein-coupled receptors at the level of the nucleus and that the nucleus could be a cell within a cell. Here, we review our work showing the presence in the nucleus of the NPY Y1receptor, the ETAand ETBreceptors, as well as the AT1and AT2receptors and their respective ligands. This work was carried out in 20-week-old fetal human endocardial endothelial cells. Our results demonstrate that nuclear Y1, AT1, and ETAreceptors modulate nuclear calcium in these cells.

Regional variation in mRNA transcript abundance within the ventricular wall

Previous studies have shown that regional variation in ion channel gene expression contributes to electrical heterogeneity within the walls of the cardiac ventricles. To map the extent of regional variation in gene expression in the ventricular walls and to begin to understand its genesis we have performed a microarray analysis of gene expression in the epicardial and endocardial tissues of the rat adult left ventricle. While the vast majority of the genes are expressed at uniform levels across the ventricular wall, a total of 36 transcripts (representing less than 0.1% of the genes expressed in the ventricle) are expressed more abundantly in either epicardium or endocardium. One of these differentially expressed genes is the sodium channel gene Scn5a, which is expressed at higher levels in the endocardium than in the epicardium of rat heart. The transcription factor genes Irx3, Irx5 and Etv1 were found to be expressed in transmural gradients across the ventricular wall of rat heart and also of canine heart. The Irx3 and Irx5 genes were expressed in an inverse pattern to that of the Kcnd2 (Kv4.2) gene in rat heart, suggesting that these transcription factors may act as negative regulators of Kcnd2 expression in vivo.

Chick embryos exposed to trichloroethylene in an ex ovo culture model show selective defects in early endocardial cushion tissue formation

BACKGROUND

Formation of the primitive heart is a critical step for establishing a competent circulatory system necessary for continued morphogenesis, and as such has significant potential as a target for environmental insult. The goal of this study was to identify the initial cellular events that precede more superficially observable abnormalities resulting from exposing early chick embryos to trichloroethylene (TCE).

METHODS

A whole embryo culture method was used to assess the susceptibility of endocardial epithelial-mesenchymal transformation in the early chick heart to TCE. This method has the benefits of maintaining the anatomical relationships of developing tissues and organs, instantaneously exposing precisely staged embryos to quantifiable levels of TCE in a protein-free medium, and the ability to directly monitor developmental morphology.

RESULTS

A minority of embryos (Hamburger and Hamilton [HH] stage 13-14) exposed to TCE (10-80 ppm) were not viable after 24 hr in culture and exhibited a variety of gross malformations in a dose-dependent fashion. However, the majority of treated embryos remained viable and developed into HH stage 17 embryos that were superficially indistinguishable from vehicle-treated controls. Further analysis of the hearts of these superficially normal embryos by whole-mount confocal microscopy revealed selective reduction in the number of atrioventricular canal mesenchymal cells. Additionally, those mesenchymal cells that did develop migrated abnormally as long thin cords of adherent cells.

CONCLUSIONS

The regional selectivity of these effects in the chick heart suggests a critical window of susceptibility to TCE in the epithelial-mesenchymal transformation of atrioventricular canal endocardium.

Leukemia inhibitory factor induces endothelial differentiation in cardiac stem cells

The importance of interleukin 6 (IL-6)-related cytokines in cardiac homeostasis has been studied extensively; however, little is known about their biological significance in cardiac stem cells. Here we describe that leukemia inhibitory factor (LIF), a member of IL-6-related cytokines, activated STAT3 and ERK1/2 in cardiac Sca-1+ stem cells. LIF stimulation resulted in the induction of endothelial cell-specific genes, including VE-cadherin, Flk-1, and CD31, whereas neither smooth muscle nor cardiac muscle marker genes such as GATA4, GATA6, Nkx-2.5, and calponin were up-regulated. Immunocytochemical examination showed that about 25% of total cells were positively stained with anti-CD31 antibody 14 days after LIF stimulation. Immunofluorescent microscopic analyses identified the Sca-1+ cells that were also positively stained with anti-von Willebrand factor antibody, indicating the differentiating process of Sca-1+ cells into the endothelial cells. IL-6, which did not activate STAT3 and ERK1/2, failed to induce the differentiation of cardiac stem cells into the endothelial cells. In cardiac stem cells, the transduction with dominant negative STAT3 abrogated the LIF-induced endothelial differentiation. And the inhibition of ERK1/2 with the MEK1/2 inhibitor U0126 also prevented the differentiation of Sca-1+ cells into endothelial cells. Thus, both STAT3 and ERK1/2 are required for LIF-mediated endothelial differentiation in cardiac stem cells. Collectively, it is proposed that LIF regulates the commitment of cardiac stem cells into the endothelial cell lineage, contributing to neovascularization in the process of tissue remodeling and/or regeneration.