Altered expression of a limited number of genes contributes to cardiac decompensation during chronic ventricular tachypacing in dogs

Full-Length Transcriptome Sequencing: An Insight Into the Dog Model of Heart Failure

Heart failure (HF) leads to a progressive increase in morbidity and mortality rates. This study aimed to explore the transcriptional landscape during HF and identify differentially expressed transcripts (DETs) and alternative splicing events associated with HF. We generated a dog model of HF (n = 3) using right ventricular pacemaker implantation. We performed full-length transcriptome sequencing (based on nanopore platform) on the myocardial tissues and analyzed the transcripts using differential expression analysis and functional annotation methods [Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses]. Additionally, we estimated the expression of the selected genes by quantitative real-time PCR (qRT-PCR) and detected the proportion of immune cells using flow cytometry. We found that increased B-type natriuretic peptide reduced ejection fraction, and apparent clinical signs were observed in the dog model of HF. We identified 67,458 transcripts using full-length transcriptome sequencing. A total of 785 DETs were obtained from the HF and control groups. These DETs were mainly enriched in the immune responses, especially Th1, Th2, and Th17 cell differentiation processes. Furthermore, flow cytometry results revealed that the proportion of Th1 and Th17 cells increased in patients with HF compared to controls, while the proportion of Th2 cells decreased. Differentially expressed genes in the HF and control groups associated with Th1, Th2, and Th17 cell differentiation were quantified using qRT-PCR. We also identified variable splicing events of sarcomere genes (e.g., MYBPC3, TNNT2, TTN, FLNC, and TTNI3). In addition, we detected 4,892 transcription factors and 406 lncRNAs associated with HF. Our analysis based on full-length transcript sequencing provided an analysis perspective in a dog model of HF, which is valuable for molecular research in an increasingly relevant large animal model of HF.

Cardiac Remodeling: Endothelial Cells Have More to Say Than Just NO

The heart is a highly structured organ consisting of different cell types, including myocytes, endothelial cells, fibroblasts, stem cells, and inflammatory cells. This pluricellularity provides the opportunity of intercellular communication within the organ, with subsequent optimization of its function. Intercellular cross-talk is indispensable during cardiac development, but also plays a substantial modulatory role in the normal and failing heart of adults. More specifically, factors secreted by cardiac microvascular endothelial cells modulate cardiac performance and either positively or negatively affect cardiac remodeling. The role of endothelium-derived small molecules and peptides—for instance NO or endothelin-1—has been extensively studied and is relatively well defined. However, endothelial cells also secrete numerous larger proteins. Information on the role of these proteins in the heart is scattered throughout the literature. In this review, we will link specific proteins that modulate cardiac contractility or cardiac remodeling to their expression by cardiac microvascular endothelial cells. The following proteins will be discussed: IL-6, periostin, tenascin-C, thrombospondin, follistatin-like 1, frizzled-related protein 3, IGF-1, CTGF, dickkopf-3, BMP-2 and−4, apelin, IL-1β, placental growth factor, LIF, WISP-1, midkine, and adrenomedullin. In the future, it is likely that some of these proteins can serve as markers of cardiac remodeling and that the concept of endothelial function and dysfunction might have to be redefined as we learn more about other factors secreted by ECs besides NO.

Experimental Models of Cardiovascular Diseases: Overview

Cardiovascular disease is one of the most common causes of deaths in clinics. Experimental models of cardiovascular diseases are essential to understand disease mechanism, to provide accurate diagnoses, and to develop new therapies. Large numbers of experimental models have been proposed and replicated by many laboratories in the past. Models with significant advantages are chosen and became more popular. Particularly, feasibility, reproducibility, and human disease resemblance are the common key factors for frequently used cardiovascular disease models. In this chapter, we provide a brief overview of these experimental models used for in vitro, in vivo, and in silico studies of cardiovascular diseases.

Chronic ethanol increases calcium/calmodulin-dependent protein kinaseIIδ gene expression and decreases monoamine oxidase amount in rat heart muscles: Rescue effect of Zingiber officinale (ginger) extract

OBJECTIVE

Association between chronic alcohol intake and cardiac abnormality is well known; however, the precise underlying molecular mediators involved in ethanol-induced heart abnormalities remain elusive. This study investigated the effect of chronic ethanol exposure on calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) gene expression and monoamine oxidase (MAO) levels and histological changes in rat heart. It was also planned to find out whether Zingiber officinale (ginger) extract mitigated the abnormalities induced by ethanol in rat heart.

METHODS

Male wistar rats were divided into three groups of eight animals each: control, ethanol, and ginger extract treated-ethanol (GETE) groups.

RESULTS

After 6 weeks of treatment, the results revealed a significant increase in CaMKIIδtotal and isoforms δ2 and δ3 of CaMKIIδ gene expression as well as a significant decrease in the MAO levels in the ethanol group compared to that in the control group. Moreover, compared to the control group, the ethanol group showed histological changes, such as fibrosis, heart muscle cells proliferation, myocyte hypertrophy, vacuolization, and focal lymphocytic infiltration. Consumption of ginger extract along with ethanol ameliorated CaMKIIδtotal. In addition, compared to the ethanol group, isoforms gene expression changed and increased the reduced MAO levels and mitigated heart structural changes.

CONCLUSION

These findings indicate that ethanol-induced heart abnormalities may, in part, be associated with Ca2+ homeostasis changes mediated by overexpression of CaMKIIδ gene and the decrease of MAO levels and that these effects can be alleviated by using ginger extract as an antioxidant and anti-inflammatory agent.

Dynamic gene expression patterns in animal models of early and late heart failure reveal biphasic-bidirectional transcriptional activation of signaling pathways

Altered cardiac gene expression in heart failure (HF) has mostly been identified by single-point analysis of end-stage disease. This may miss earlier changes in gene expression that are transient and/or directionally opposite to those observed later. Myocardial datasets from the largest microarray data repository (Gene Expression Omnibus) yielded six HF studies with time-course data. Differentially expressed transcripts between nonfailing controls, early HF (<3 days after cardiac insult) and late HF (usually >2 wk) were determined, and analysis of KEGG pathways and predicted regulatory control elements performed. We found that gene expression followed varying patterns: Downregulation of metabolic pathways occurred early and was sustained into late-stage HF. In contrast, most signaling pathways undergo a complex biphasic pattern: Calcium signaling, p53, apoptosis, and MAPK pathways displayed a bidirectional response, declining early but rising late. These profiles were compatible with specific microRNA (miRNA) and transcription regulators: Estrogen-related receptor-α and myocyte-enhancer factor-2 binding sites were overrepresented in the promoter regions of downregulated transcripts. Concurrently, there were overrepresented binding sites for E2f and ETS family members (E-Twenty Six, including Gabp, Elf1, and Ets2), serum response and interferon regulated factor in biphasic-bidirectional and late-upregulated transcripts. Binding sites for miRNAs downregulated by HF were more common in upregulated transcripts (e.g., miRNA-22,-133a/b, and -150 in early HF and miRNA-1,-9,-499 in late HF). During the development of HF, gene expression is characterized by dynamic overlapping sets of transcripts controlled by specific interrelated regulatory mechanisms. While metabolic gene classes show early and sustained downregulation in HF, signaling pathways undergo a complex biphasic pattern with early down- and more pronounced late upregulation.

Veterinary and human biobanking practices: enhancing molecular sample integrity

Animal models have historically informed veterinary and human pathophysiology. Next-generation genomic sequencing and molecular analyses using analytes derived from tissue require integrative approaches to determine macroanalyte integrity as well as morphology for imaging algorithms that can extend translational applications. The field of biospecimen science and biobanking will play critical roles in tissue sample collection and processing to ensure the integrity of macromolecules, aid experimental design, and provide more accurate and reproducible downstream genomic data. Herein, we employ animal experiments to combine protein expression analysis by microscopy with RNA integrity number and quantitative measures of morphologic changes of autolysis. These analyses can be used to predict the effect of preanalytic variables and provide the basis for standardized methods in tissue sample collection and processing. We also discuss the application of digital imaging with quantitative RNA and tissue-based protein measurements to show that genomic methods augment traditional in vivo imaging to support biospecimen science. To make these observations, we have established a time course experiment of murine kidney tissues that predicts conventional measures of RNA integrity by RIN analysis and provides reliable and accurate measures of biospecimen integrity and fitness, in particular for time points less than 3 hours post-tissue resection.

Transcriptional profiling of left ventricle and peripheral blood mononuclear cells in a rat model of postinfarction heart failure

Background

Myocardial infarction (MI) often results in left ventricular (LV) remodeling followed by heart failure (HF). It is of great clinical importance to understand the molecular mechanisms that trigger transition from compensated LV injury to HF and to identify relevant diagnostic biomarkers. The aim of this study was to investigate gene expression in the LV and to evaluate their reflection in peripheral blood mononuclear cells (PBMCs).

Methods

MI was induced in rats by ligation of the proximal left coronary artery. Rats with small, moderate, and large MI size were included into the experiment two months after the operation. The development of heart failure was estimated by echocardiography and catheterization. Microarrays were used to compare the LV and PBMCs transcriptomes of control and experimental animals.

Results

Only rats with a large MI developed extensive LV remodeling and heart failure. 840 transcripts were altered in LV of failing hearts, and especially numerous were those associated with the extracellular matrix. In contrast, no significant gene expression changes were seen in LVs of rats with moderate or small MI that had compensated LV injury. We showed that ceruloplasmin was similarly overexpressed in the heart and blood in response to HF, whereas downregulation of tetraspanin 12 was significant only in the PBMCs.

Conclusion

A large size of infarcted area is critical for progression of LV remodeling and HF development, associated with altered gene expression in the heart. Ceruloplasmin and tetraspanin 12 are potential convenient markers in readily obtainable PBMCs.

Insights from the clustering of microarray data associated with the heart disease

Heart failure (HF) is the major of cause of mortality and morbidity in the developed world. Gene expression profiles of animal model of heart failure have been used in number of studies to understand human cardiac disease. In this study, statistical methods of analysing microarray data on cardiac tissues from dogs with pacing induced HF were used to identify differentially expressed genes between normal and two abnormal tissues. The unsupervised techniques principal component analysis (PCA) and cluster analysis were explored to distinguish between three different groups of 12 arrays and to separate the genes which are up regulated in different conditions among 23912 genes in heart failure canines' microarray data. It was found that out of 23912 genes, 1802 genes were differentially expressed in the three groups at 5% level of significance and 496 genes were differentially expressed at 1% level of significance using one way analysis of variance (ANOVA). The genes clustered using PCA and clustering analysis were explored in the paper to understand HF and a small number of differentially expressed genes related to HF were identified.

Pacing-induced regional differences in adenosine receptors mRNA expression in a swine model of dilated cardiomyopathy

The adenosinergic system is essential in the mediation of intrinsic protection and myocardial resistance to insult; it may be considered a cardioprotective molecule and adenosine receptors (ARs) represent potential therapeutic targets in the setting of heart failure (HF). The aim of the study was to test whether differences exist between mRNA expression of ARs in the anterior left ventricle (LV) wall (pacing site: PS) compared to the infero septal wall (opposite region: OS) in an experimental model of dilated cardiomyopathy. Cardiac tissue was collected from LV PS and OS of adult male minipigs with pacing-induced HF (n = 10) and from a control group (C, n = 4). ARs and TNF–α mRNA expression was measured by Real Time-PCR and the results were normalized with the three most stably expressed genes (GAPDH, HPRT1, TBP). Immunohistochemistry analysis was also performed. After 3 weeks of pacing higher levels of expression for each analyzed AR were observed in PS except for A₁R (A₁R: C = 0.6±0.2, PS = 0.1±0.04, OS = 0.04±0.01, p<0.0001 C vs. PS and OS respectively; A_2AR: C = 1.04±0.59, PS = 2.62±0.79, OS = 2.99±0.79; A_2BR: C = 1.2±0.1, PS = 5.59±2.3, OS = 1.59±0.46; A₃R: C = 0.76±0.18, PS = 8.40±3.38, OS = 4.40±0.83). Significant contractile impairment and myocardial hypoperfusion were observed at PS after three weeks of pacing as compared to OS. TNF-α mRNA expression resulted similar in PS (6.3±2.4) and in OS (5.9±2.7) although higher than in control group (3.4±1.5). ARs expression was mainly detected in cardiomyocytes. This study provided new information on ARs local changes in the setting of LV dysfunction and on the role of these receptors in relation to pacing-induced abnormalities of myocardial perfusion and contraction. These results suggest a possible therapeutic role of adenosine in patients with HF and dyssynchronous LV contraction.

Right ventricular pacing with mechanical dyssynchrony causes apoptosis interruptus and calcium mishandling

BACKGROUND

Mechanical dyssynchrony associated with rapid pacing induces cardiac cell stress and myocardial apoptotic pathway activation that has been implicated in the pathophysiology of left ventricular (LV) dysfunction. Effects of dyssynchrony per se are not fully understood. The objective of our study was to test whether ventricular dyssynchrony would elicit myocardial alterations in LV calcium handling regulation and cell survival or apoptosis signalling in right ventricular-paced swine.

METHODS

Implantation of pacemaker was performed under anaesthesia. Endocardial bipolar screw lead was inserted into the right jugular vein and positioned either in the right atrium or at the right ventricular (RV) apex. Swine were paced at 150 beats per minute for 3 weeks.

RESULTS

Compared with right atrial pacing, RV pacing led to abnormal LV sarcoplasmic reticulum calcium uptake (315 ± 65 vs 155 ± 55 nmol/min/mg, P < 0.05) and LV calcium-handling protein expression, ie, 35% reduction in ryanodine receptor 2, 25% decline in sarcoplasmic reticulum Ca(2+) ATPase, 70% increase in Na(+)/Ca(2+) exchanger, and 10% increase in phospholamban. RV pacing also elicited activation of LV apoptotic cascades without nuclear apoptosis. So-called interrupted apoptosis was the result of increased expression of X-linked inhibitor of apoptosis protein. Apoptosis and calcium mishandling were documented in absence of depressed heart function (ejection fraction 62 ± 8% vs 57 ± 12%, in right atrial- and RV-paced hearts, respectively, P > 0.05).

CONCLUSIONS

Slow rate RV pacing causes mechanical dyssynchrony and profound LV alterations in both apoptotic pathways and calcium handling in the early stages of pacing-induced cardiomyopathy.

Cardiac-specific deletion of the microtubule-binding protein CENP-F causes dilated cardiomyopathy

CENP-F is a large multifunctional protein with demonstrated regulatory roles in cell proliferation, vesicular transport and cell shape through its association with the microtubule (MT) network. Until now, analysis of CENP-F has been limited to in vitro analysis. Here, using a Cre-loxP system, we report the in vivo disruption of CENP-F gene function in murine cardiomyocytes, a cell type displaying high levels of CENP-F expression. Loss of CENP-F function in developing myocytes leads to decreased cell division, blunting of trabeculation and an initially smaller, thin-walled heart. Still, embryos are born at predicted mendelian ratios on an outbred background. After birth, hearts lacking CENP-F display disruption of their intercalated discs and loss of MT integrity particularly at the costamere; these two structures are essential for cell coupling/electrical conduction and force transduction in the heart. Inhibition of myocyte proliferation and cell coupling as well as loss of MT maintenance is consistent with previous reports of generalized CENP-F function in isolated cells. One hundred percent of these animals develop progressive dilated cardiomyopathy with heart block and scarring, and there is a 20% mortality rate. Importantly, although it has long been postulated that the MT cytoskeleton plays a role in the development of heart disease, this study is the first to reveal a direct genetic link between disruption of this network and cardiomyopathy. Finally, this study has broad implications for development and disease because CENP-F loss of function affects a diverse array of cell-type-specific activities in other organs.

Experimental Mapping of the Canine KCNJ2 and KCNJ12 Gene Structures and Functional Analysis of the Canine K(IR)2.2 ion Channel

For many model organisms traditionally in use for cardiac electrophysiological studies, characterization of ion channel genes is lacking. We focused here on two genes encoding the inward rectifier current, KCNJ2 and KCNJ12, in the dog heart. A combination of RT-PCR, 5′-RACE, and 3′-RACE demonstrated the status of KCNJ2 as a two exon gene. The complete open reading frame (ORF) was located on the second exon. One transcription initiation site was mapped. Four differential transcription termination sites were found downstream of two consensus polyadenylation signals. The canine KCNJ12 gene was found to consist of three exons, with its ORF located on the third exon. One transcription initiation and one termination site were found. No alternative splicing was observed in right ventricle or brain cortex. The gene structure of canine KCNJ2 and KCNJ12 was conserved amongst other vertebrates, while current GenBank gene annotation was determined as incomplete. In silico translation of KCN12 revealed a non-conserved glycine rich stretch located near the carboxy-terminus of the K_IR2.2 protein. However, no differences were observed when comparing dog with human K_IR2.2 protein upon ectopic expression in COS-7 or HEK293 cells with respect to subcellular localization or electrophysiological properties.

Monoamine oxidases (MAO) in the pathogenesis of heart failure and ischemia/reperfusion injury

Recent evidence highlights monoamine oxidases (MAO) as another prominent source of oxidative stress. MAO are a class of enzymes located in the outer mitochondrial membrane, deputed to the oxidative breakdown of key neurotransmitters such as norepinephrine, epinephrine and dopamine, and in the process generate H(2)O(2). All these monoamines are endowed with potent modulatory effects on myocardial function. Thus, when the heart is subjected to chronic neuro-hormonal and/or peripheral hemodynamic stress, the abundance of circulating/tissue monoamines can make MAO-derived H(2)O(2) production particularly prominent. This is the case of acute cardiac damage due to ischemia/reperfusion injury or, on a more chronic stand, of the transition from compensated hypertrophy to overt ventricular dilation/pump failure. Here, we will first briefly discuss mitochondrial status and contribution to acute and chronic cardiac disorders. We will illustrate possible mechanisms by which MAO activity affects cardiac biology and function, along with a discussion as to their role as a prominent source of reactive oxygen species. Finally, we will speculate on why MAO inhibition might have a therapeutic value for treating cardiac affections of ischemic and non-ischemic origin. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Oxidant-NO dependent gene regulation in dogs with type I diabetes: impact on cardiac function and metabolism

Background

The mechanisms responsible for the cardiovascular mortality in type I diabetes (DM) have not been defined completely. We have shown in conscious dogs with DM that: 1) baseline coronary blood flow (CBF) was significantly decreased, 2) endothelium-dependent (ACh) coronary vasodilation was impaired, and 3) reflex cholinergic NO-dependent coronary vasodilation was selectively depressed. The most likely mechanism responsible for the depressed reflex cholinergic NO-dependent coronary vasodilation was the decreased bioactivity of NO from the vascular endothelium. The goal of this study was to investigate changes in cardiac gene expression in a canine model of alloxan-induced type 1 diabetes.

Methods

Mongrel dogs were chronically instrumented and the dogs were divided into two groups: one normal and the other diabetic. In the diabetic group, the dogs were injected with alloxan monohydrate (40-60 mg/kg iv) over 1 min. The global changes in cardiac gene expression in dogs with alloxan-induced diabetes were studied using Affymetrix Canine Array. Cardiac RNA was extracted from the control and DM (n = 4).

Results

The array data revealed that 797 genes were differentially expressed (P < 0.01; fold change of at least ±2). 150 genes were expressed at significantly greater levels in diabetic dogs and 647 were significantly reduced. There was no change in eNOS mRNA. There was up regulation of some components of the NADPH oxidase subunits (gp91 by 2.2 fold, P < 0.03), and down-regulation of SOD1 (3 fold, P < 0.001) and decrease (4 - 40 fold) in a large number of genes encoding mitochondrial enzymes. In addition, there was down-regulation of Ca²⁺ cycling genes (ryanodine receptor; SERCA2 Calcium ATPase), structural proteins (actin alpha). Of particular interests are genes involved in glutathione metabolism (glutathione peroxidase 1, glutathione reductase and glutathione S-transferase), which were markedly down regulated.

Conclusion

our findings suggest that type I diabetes might have a direct effect on the heart by impairing NO bioavailability through oxidative stress and perhaps lipid peroxidases.

Potential mechanisms of low-sodium diet-induced cardiac disease: superoxide-NO in the heart

RATIONALE

Patients on a low salt (LS) diet have increased mortality.

OBJECTIVE

To determine whether reduction in NO bioactivity may contribute to the LS-induced cardiac dysfunction and mortality.

METHODS AND RESULTS

Adult male mongrel dogs were placed on LS (0.05% sodium chloride) for 2 weeks. Body weight (25.4 + or - 0.4 to 23.6 + or - 0.4 kg), left ventricular systolic pressure (137.0 + or - 3.4 to 124.0 + or - 6.7 mm Hg), and mean aortic pressure (111 + or - 3.1 to 98 + or - 4.3 mm Hg) decreased. Plasma angiotensin II concentration increased (4.4 + or - 0.7 to 14.8 + or - 3.7 pg/mL). Veratrine-induced (5 microg/kg) NO-mediated vasodilation was inhibited by 44% in LS; however, the simultaneous intravenous infusion of ascorbic acid or apocynin acutely and completely reversed this inhibition. In LS heart tissues, lucigenin chemiluminescence was increased 2.3-fold to angiotensin II (10(-8) mol/L), and bradykinin (10(-4) mol/L) induced reduction of myocardial oxygen consumption in vitro was decreased (40 + or - 1.3% to 16 + or - 6.3%) and completely restored by coincubation with tiron, tempol or apocynin. Switching of substrate uptake from free fatty acid to glucose by the heart was observed (free fatty acid: 8.97 + or - 1.39 to 4.53 + or - 1.12 micromol/min; glucose: 1.31 + or - 0.52 to 6.86 + or - 1.78 micromol/min). Western blotting indicated an increase in both p47(phox) (121%) and gp91(phox) (44%) as did RNA microarray analysis (433 genes changed) showed an increase in p47(phox) (1.6-fold) and gp91(phox) (2.0 fold) in the LS heart tissue.

CONCLUSIONS

LS diet induces the activation of the renin-angiotensin system, which increases oxidative stress via the NADPH oxidase and attenuates NO bioavailability in the heart.

Transition from compensated hypertrophy to systolic heart failure in the spontaneously hypertensive rat: Structure, function, and transcript analysis

Gene expression, determined by micro-array analysis, and left ventricular (LV) remodeling associated with the transition to systolic heart failure (HF) were examined in the spontaneously hypertensive rat (SHR). By combining transcript and gene set enrichment analysis (GSEA) of the LV with assessment of function and structure in age-matched SHR with and without HF, we aimed to better understand the molecular events underlying the onset of hypertensive HF. Failing hearts demonstrated depressed LV ejection fraction, systolic blood pressure, and LV papillary muscle force while LV end-diastolic and systolic volume and ventricular mass increased. 1431 transcripts were differentially expressed between failing and non-failing animals. GSEA identified multiple enriched gene sets, including those involving inflammation, oxidative stress, cell degradation and cell death, as well as TGF-beta and insulin signaling pathways. Our findings support the concept that these pathways and mechanisms may contribute to deterioration of cardiac function and remodeling associated with hypertensive HF.

Decreased triadin and increased calstabin2 expression in Great Danes with dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a common cardiac disease of Great Dane dogs, yet very little is known about the underlying molecular abnormalities that contribute to disease.

OBJECTIVE

Discover a set of genes that are differentially expressed in Great Dane dogs with DCM as a way to identify candidate genes for further study as well as to better understand the molecular abnormalities that underlie the disease.

ANIMALS

Three Great Dane dogs with end-stage DCM and 3 large breed control dogs.

METHODS

Prospective study. Transcriptional activity of 42,869 canine DNA sequences was determined with a canine-specific oligonucleotide microarray. Genome expression patterns of left ventricular tissue samples from affected Great Dane dogs were evaluated by measuring the relative amount of complementary RNA hybridization to the microarray probes and comparing it with expression from large breed dogs with noncardiac disease.

RESULTS

Three hundred and twenty-three transcripts were differentially expressed (> or = 2-fold change). The transcript with the greatest degree of upregulation (+61.3-fold) was calstabin2 (FKBP12.6), whereas the transcript with the greatest degree of downregulation (-9.07-fold) was triadin. Calstabin2 and triadin are both regulatory components of the cardiac ryanodine receptor (RyR2) and are critical to normal intracellular Ca2+ release and excitation-contraction coupling.

CONCLUSION AND CLINICAL IMPORTANCE

Great Dane dogs with DCM demonstrate abnormal calstabin2 and triadin expression. These changes likely affect Ca2+ flux within cardiac cells and may contribute to the pathophysiology of disease. Microarray-based analysis identifies calstabin2, triadin, and RyR2 function as targets of future study.

Global gene expression profiling in the failing myocardium

Heart failure (HF) is a syndrome that involves multiple cellular mechanisms leading to a common phenotype of reduced ventricular contraction and cardiac chamber dilation. To clarify the mechanisms, a number of microarray analyses of the failing myocardium have been conducted. Gene expression profiles are usually compared between opposing pairs of samples, such as non-failing vs failing hearts, ischemic vs non-ischemic hearts, male vs female failing hearts or atria vs ventricles of failing hearts. Apart from these conventional methods, a different novel approach identified cardiac myosin light chain kinase (MLCK) as a HF-related gene by the comprehensive search for the genes that had an expression level that strongly correlated with the severity of HF; further investigations proved the important role of cardiac MLCK in HF. Moreover, a robust gene expression signature composed of 27 genes was revealed on analysis of 4 independent microarray data sets from the failing myocardium of dilated cardiomyopathy. The authors newly demonstrate 107 HF-related genes that were listed in 2 or more of 7 microarray data sets previously reported. Among these genes, many were observed to be involved in mitochondrial dysfunction and oxidative phosphorylation and 3 extracellular molecules, including periostin, pleiotrophin, and SERPINA3, which might become novel diagnostic and therapeutic targets for HF. These novel strategies warrant the new identification of specific genes that are linked to the pathophysiology of HF.

Cardiac resynchronization therapy corrects dyssynchrony-induced regional gene expression changes on a genomic level

BACKGROUND

Cardiac electromechanical dyssynchrony causes regional disparities in workload, oxygen consumption, and myocardial perfusion within the left ventricle. We hypothesized that such dyssynchrony also induces region-specific alterations in the myocardial transcriptome that are corrected by cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Adult dogs underwent left bundle branch ablation and right atrial pacing at 200 bpm for either 6 weeks (dyssynchronous heart failure, n=12) or 3 weeks, followed by 3 weeks of resynchronization by biventricular pacing at the same pacing rate (CRT, n=10). Control animals without left bundle branch block were not paced (n=13). At 6 weeks, RNA was isolated from the anterior and lateral left ventricular (LV) walls and hybridized onto canine-specific 44K microarrays. Echocardiographically, CRT led to a significant decrease in the dyssynchrony index, while dyssynchronous heart failure and CRT animals had a comparable degree of LV dysfunction. In dyssynchronous heart failure, changes in gene expression were primarily observed in the anterior LV, resulting in increased regional heterogeneity of gene expression within the LV. Dyssynchrony-induced expression changes in 1050 transcripts were reversed by CRT to levels of nonpaced hearts (false discovery rate <5%). CRT remodeled transcripts with metabolic and cell signaling function and greatly reduced regional heterogeneity of gene expression as compared with dyssynchronous heart failure.

CONCLUSIONS

Our results demonstrate a profound effect of electromechanical dyssynchrony on the regional cardiac transcriptome, causing gene expression changes primarily in the anterior LV wall. CRT corrected the alterations in gene expression in the anterior wall, supporting a global effect of biventricular pacing on the ventricular transcriptome that extends beyond the pacing site in the lateral wall.

A new class of 5-HT2B antagonists possesses favorable potency, selectivity, and rat pharmacokinetic properties

We have been exploring the potential of 5-HT(2B) antagonists as a therapy for chronic heart failure. To assess the potential of this therapeutic approach, we sought compounds possessing the following attributes: (a) potent and selective antagonism of the 5-HT(2B) receptor, (b) low impact of serum proteins on potency, and (c) desirable pharmacokinetic properties. This Letter describes our investigation of a biphenyl benzimidazole class of compounds that resulted in 5-HT(2B) antagonists possessing the above attributes. Improving potency in a human serum albumin shift assay proved to be the most significant SAR discovery.

Review Paper: Gene Expression Profiling in Veterinary and Human Medicine: Overview of Applications and Proposed Quality Control Practices

High throughput molecular analysis of veterinary tissue samples is being applied to a wide range of research questions aimed at improving survival, development of diagnostic assays, and improving the economics of commercial production of animal products. Many of these efforts also, implicitly or explicitly, have ramifications for the clinical care of humans and, potentially, animals. Here we provide an overview of applications of gene expression profiling in veterinary research and practice. We then focus on the current state of quality control and quality assurance efforts in gene expression profiling studies, underscoring lessons learned from such analysis of human samples. Finally, we propose practices aimed at ensuring the reliability and reproducibility of such assays. The implementation of quality assurance practices by a trained pathologist is an essential link in the chain of events leading ultimately to reliable and reproducible research findings and appropriate clinical care.

Cardiac hypertrophy and thyroid hormone signaling

Thyroid hormone exerts a large number of influences on the cardiovascular system. Increased thyroid hormone action increases the force and speed of systolic contraction and the speed of diastolic relaxation and these are largely beneficial effects. Furthermore, thyroid hormone has marked electrophysiological effects increasing heart rate and the propensity for atrial fibrillation and these effects are largely mal-adaptive. In addition, thyroid hormone markedly increases cardiac angiogenesis and decreases vascular tone. These multiple thyroid hormone effects are largely mediated by the action of nuclear based thyroid hormone receptors (TR) the thyroid hormone receptor alpha and beta. TRα is the predominant isoform in the heart. Rapid nongenomic thyroid hormone effects also occur, which can be clearly demonstrated in ex-vivo experiments. Some of the most marked thyroid hormone effects in cardiac myocytes involve influences on calcium flux, with thyroid hormone promoting expression of the gene encoding the calcium pump of the sarcoplasmic reticulum (SERCa2). In contrast, in hypothyroid animals phospholamban levels, which inhibit the SERCa2 pump, are increased. In addition, marked effects are exerted on the calcium channel of the sarcoplasmic reticulum the ryanodine channel. Related to myofibrillar proteins, myosin heavy chain alpha is increased by T3 and MHC beta is decreased. Complex and interesting interactions occur between cardiac hypertrophy induced by excess thyroid hormone action and cardiac hypertrophy occurring with heart failure. The thyroid hormone mediated cardiac hypertrophy in its initial phases presents a physiological hypertrophy with increases in SERCa2 levels and decreased expression of MHC beta. In contrast, pressure overload induced heart failure leads to a “pathological” cardiac hypertrophy which is largely mediated by activation of the calcineurin system and the MAPkinases signaling system. Recent evidence indicates that heart failure can lead to a downregulation of the thyroid hormone signaling system in the heart. In the failing heart, decreases of thyroid hormone receptor levels occur. In addition, serum levels of T4 and T3 are decreased with heart failure in the frame of the non-thyroidal illness syndrome. The decrease in T3 serves as an indicator for a bad prognosis in the heart failure patient being linked to increased mortality. In animal models, it can be shown that in pressure overload-induced cardiac hypertrophy a decrease of thyroid hormone receptor levels occurs. Cardiac function can be improved by increasing expression of thyroid hormone receptors mediated by adeno-associated virus based gene transfer. The failing heart may develop a “hypothyroid” status contributing to diminished cardiac contractile function.

Key pathways associated with heart failure development revealed by gene networks correlated with cardiac remodeling

Heart failure (HF) is the leading cause of morbidity and mortality in the industrialized world. While the transcriptomic changes in end-stage failing myocardium have received much attention, no information is available on the gene expression patterns associated with the development of HF in large mammals. Therefore, we used a well-controlled canine model of tachycardia-induced HF to examine global gene expression in left ventricular myocardium with Affymetrix canine oligonucleotide arrays at various stages after initiation of rapid ventricular pacing (days 3, 7, 14, and 21). The gene expression data were complemented with measurements of action potential duration, conduction velocity, and left ventricular end diastolic pressure, and dP/dt(max) over the time course of rapid ventricular pacing. As a result, we present a phenotype-centered gene association network, defining molecular systems that correspond temporally to hemodynamic and electrical remodeling processes. Gene Ontology analysis revealed an orchestrated regulation of oxidative phosphorylation, ATP synthesis, cell signaling pathways, and extracellular matrix components, which occurred as early as 3 days after the initiation of ventricular pacing, coinciding with the early decline in left ventricular pump function and prolongation of action potential duration. The development of clinically overt left ventricular dysfunction was associated with few additional changes in the myocardial transcriptome. We conclude that the majority of tachypacing-induced transcriptional changes occur early after initiation of rapid ventricular pacing. As the transition to overt HF is characterized by few additional transcriptional changes, posttranscriptional modifications may be more critical in regulating myocardial structure and function during later stages of HF.