Early and transient gene expression changes in pressure overload-induced cardiac hypertrophy in mice

Proteomic Insights into Cardiac Fibrosis: From Pathophysiological Mechanisms to Therapeutic Opportunities

Cardiac fibrosis is a common pathophysiologic process in nearly all forms of heart disease which refers to excessive deposition of extracellular matrix proteins by cardiac fibroblasts. Activated fibroblasts are the central cellular effectors in cardiac fibrosis, and fibrotic remodelling can cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance. Recently, there is a rising focus on the proteomic studies of cardiac fibrosis for pathogenesis elucidation and potential biomarker mining. This paper summarizes the current knowledge of molecular mechanisms underlying cardiac fibrosis, discusses the potential of imaging and circulating biomarkers available to recognize different phenotypes of this lesion, reviews the currently available and potential future therapies that allow individualized management in reversing progressive fibrosis, as well as the recent progress on proteomic studies of cardiac fibrosis. Proteomic approaches using clinical specimens and animal models can provide the ability to track pathological changes and new insights into the mechanisms underlining cardiac fibrosis. Furthermore, spatial and cell-type resolved quantitative proteomic analysis may also serve as a minimally invasive method for diagnosing cardiac fibrosis and allowing for the initiation of prophylactic treatment.

Differential mRNA Expression and Circular RNA-Based Competitive Endogenous RNA Networks in the Three Stages of Heart Failure in Transverse Aortic Constriction Mice

Background

The murine transverse aortic constriction (TAC) model is frequently used to investigate molecular mechanisms underlying heart failure. However, limited data is available regarding the expression of mRNAs and circRNAs in murine heart failure progression induced by pressure overload.

Methods

Transverse aortic constriction was used to induce pressure overload for 2, 4, and 8 weeks in mice. Echocardiographic measurements in B-mode and M-mode, as well as blood flow Doppler data were collected in mice without (sham) and with (2W-, 4W-, and 8W-post-TAC) pressure load. Hearts were excised and morphology, cardiomyocyte size, and fibrosis were determined. RNA sequencing, circRNA microarray, functional mRNA enrichment analysis, hub gene identification, target miRNA interaction, and competitive endogenous RNA (ceRNA) network construction were conducted.

Results

Heart weight, cardiomyocyte hypertrophy, and fibrosis gradually increased over time in the hearts with pressure overload. The 2W-post-TAC hearts displayed concentric hypertrophy, thickened left ventricular walls, and increased EF and FS. The 4W-post-TAC hearts were characterized by preserved EF and FS, dilated atria, and increased left ventricle (LV) systolic volume. The 8W-post-TAC hearts presented with ventricular and atrial dilation, increased LV systolic and diastolic volume, reduced EF and FS, and increased ejection time (MV ET). mRNA expression analysis suggested that cardiac remodeling, immune response dysregulation, and metabolic disorder were the key cellular events in heart failure progression. Depression in chemotaxis and mitochondrial function were predicted in 4W- and 8W-post-TAC myocardia, respectively. A ceRNA network analysis demonstrated that the circRNAs targeted the expression of genes enriched in metabolism dysregulation in the 2W-post-TAC hypertrophic hearts, while they targeted genes enriched in cardiac remodeling in the 4W-post-TAC EF-preserved hearts and in the suppression of oxidative phosphorylation and cardiac contraction in the 8W-post-TAC EF-reduced hearts.

Conclusion

Our work empirically demonstrates that distinctive features of heart failure, including ventricular hypertrophy, heart failure with preserved EF (HFpEF), and heart failure with reduced EF (HFrEF) are present in the murine pressure overload models. The three stages of heart failure vary in terms of mRNA and circRNA expression, as well as ceRNA regulation in a manner consistent with their structural, functional, and pathological differences.

Study on diverse pathological characteristics of heart failure in different stages based on proteomics

Heart failure is a process characterized by significant disturbance of protein turnover. To elucidate the alterations in cardiac protein expression during the various phases of heart failure and to understand the nature of the processes involved, we analysed the proteome in an established heart failure model at different time points to monitor thousands of different proteins simultaneously. Here, heart failure was induced by transverse aortic constriction (TAC) in KM mice. At 2, 4 and 12 weeks after operation, protein expression profiles were determined in sham‐operated (controls) and TAC mice, using label‐free quantitative proteomics, leading to identification and quantification of almost 4000 proteins. The results of the KEGG pathway enrichment analysis and GO function annotation revealed critical pathways associated with the transition from cardiac hypertrophy to heart failure, such as energy pathways and matrix reorganization. Our study suggests that in the pathophysiology of heart failure, alterations of protein groups related to cardiac energy substrate metabolism and cytoskeleton remodelling could play the more dominant roles for the signalling that eventually results in contractile dysfunction and heart failure.

Functional genomics meta-analysis to identify gene set enrichment networks in cardiac hypertrophy

In order to take advantage of the continuously increasing number of transcriptome studies, it is important to develop strategies that integrate multiple expression datasets addressing the same biological question to allow a robust analysis. Here, we propose a meta-analysis framework that integrates enriched pathways identified through the Gene Set Enrichment Analysis (GSEA) approach and calculates for each meta-pathway an empirical p-value. Validation of our approach on benchmark datasets showed comparable or even better performance than existing methods and an increase in robustness with increasing number of integrated datasets. We then applied the meta-analysis framework to 15 functional genomics datasets of physiological and pathological cardiac hypertrophy. Within these datasets we grouped expression sets measured at time points that represent the same hallmarks of heart tissue remodeling ('aggregated time points') and performed meta-analysis on the expression sets assigned to each aggregated time point. To facilitate biological interpretation, results were visualized as gene set enrichment networks. Here, our meta-analysis framework identified well-known biological mechanisms associated with pathological cardiac hypertrophy (e.g., cardiomyocyte apoptosis, cardiac contractile dysfunction, and alteration in energy metabolism). In addition, results highlighted novel, potentially cardioprotective mechanisms in physiological cardiac hypertrophy involving the down-regulation of immune cell response, which are worth further investigation.

SLIT3 deficiency attenuates pressure overload-induced cardiac fibrosis and remodeling

In pulmonary hypertension and certain forms of congenital heart disease, ventricular pressure overload manifests at birth and is an obligate hemodynamic abnormality that stimulates myocardial fibrosis, which leads to ventricular dysfunction and poor clinical outcomes. Thus, an attractive strategy is to attenuate the myocardial fibrosis to help preserve ventricular function. Here, by analyzing RNA-sequencing databases and comparing the transcript and protein levels of fibrillar collagen in WT and global-knockout mice, we found that slit guidance ligand 3 (SLIT3) was present predominantly in fibrillar collagen-producing cells and that SLIT3 deficiency attenuated collagen production in the heart and other nonneuronal tissues. We then performed transverse aortic constriction or pulmonary artery banding to induce left and right ventricular pressure overload, respectively, in WT and knockout mice. We discovered that SLIT3 deficiency abrogated fibrotic and hypertrophic changes and promoted long-term ventricular function and overall survival in both left and right ventricular pressure overload. Furthermore, we found that SLIT3 stimulated fibroblast activity and fibrillar collagen production, which coincided with the transcription and nuclear localization of the mechanotransducer yes-associated protein 1. These results indicate that SLIT3 is important for regulating fibroblast activity and fibrillar collagen synthesis in an autocrine manner, making it a potential therapeutic target for fibrotic diseases, especially myocardial fibrosis and adverse remodeling induced by persistent afterload elevation.

Serelaxin Improves Regional Myocardial Function in Experimental Heart Failure: An In Vivo Cardiac Magnetic Resonance Study

Background Animal studies demonstrated that serelaxin lessens fibrosis in heart failure. This study assessed its effect on myocardial deformation using cardiac magnetic resonance and elucidated its relationship to gene regulation and histology in a mouse heart failure model. Methods and Results C57BL/6J mice were subjected to SHAM (n=4) or transverse aortic constriction (TAC). At week 10, TAC mice were randomized to receive either serelaxin (0.5 mg/kg per day; n=11) or vehicle (n=13) for 4 weeks. Cardiac magnetic resonance imaging was performed at baseline and repeated at the end of the study (week 14). Cine images were used to calculate left ventricular (LV) global longitudinal, circumferential, and radial strain. Hearts were examined for histology and gene expression. Compared with SHAM, mice 10 weeks after TAC showed increased LV mass with significant decreases in LV deformation parameters, indicating subclinical deterioration of myocardial function. At week 14, TAC mice given serelaxin demonstrated significant improvements in all LV strain parameters and no decrease in LV stroke volume and ejection fraction compared with TAC mice given vehicle. A significant positive correlation between global circumferential strain and the extent of myocardial fibrosis was found, and global circumferential strain correlated significantly with the expression of heart failure genes in serelaxin-treated mice. Conclusions Serelaxin improved cardiac magnetic resonance-derived myocardial deformation parameters as well as histomorphometric and gene expression findings in mice with heart failure. Cardiac magnetic resonance-derived myocardial mechanics correlate with histology and gene expression, stressing its utilization in myocardial remodeling.

Time- and Ventricular-Specific Expression Profiles of Genes Encoding Z-Disk Proteins in Pressure Overload Model of Left Ventricular Hypertrophy

Mechanotransduction is an essential mechanism of transforming external mechanical stimulus to biochemical response. In cardiomyocytes mechanotransduction plays an important role in contraction, stretch sensing and homeostasis regulation. One of the major mechanosensitive area in cardiomyocytes, the Z-disk, consists of numbers of structural and signaling proteins, that may undergo conformational or gene expression changes under pathological stress conditions. In present study we examined a rat model of pressure overload cardiac hypertrophy validated by echocardiographic and histopathological examinations. We revealed, that during hypertrophy progression expression of several genes encoding Z-disk proteins (Actn2, Ldb3, Cmya5, Nebl) is different at early and late points of cardiac remodeling. Moreover, expression patterns of several genes are opposite in myocardium of overloaded left ventricle and hemodynamically unaffected right ventricle, and expression profiles in interventricular septum are more similar to right ventricle. Additionally, we revealed inconsistencies between mRNA and protein level changes of Actn2, one of the major structural Z-disk element. All these findings point out, that investigated Z-disk proteins participate in pathological stress adaptation through undergoing the gene expression changes, and suggest the novel important role of hypertrophic response modulation during different stages of cardiac remodeling.

Modeling the effect of ascites-induced compression on ovarian cancer multicellular aggregates

Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy. EOC dissemination is predominantly via direct extension of cells and multicellular aggregates (MCAs) into the peritoneal cavity, which adhere to and induce retraction of peritoneal mesothelium and proliferate in the submesothelial matrix to generate metastatic lesions. Metastasis is facilitated by the accumulation of malignant ascites (500 ml to >2 l), resulting in physical discomfort and abdominal distension, and leading to poor prognosis. Although intraperitoneal fluid pressure is normally subatmospheric, an average intraperitoneal pressure of 30 cmH2O (22.1 mmHg) has been reported in women with EOC. In this study, to enable experimental evaluation of the impact of high intraperitoneal pressure on EOC progression, two new in vitro model systems were developed. Initial experiments evaluated EOC MCAs in pressure vessels connected to an Instron to apply short-term compressive force. A Flexcell Compression Plus system was then used to enable longer-term compression of MCAs in custom-designed hydrogel carriers. Results show changes in the expression of genes related to epithelial-mesenchymal transition as well as altered dispersal of compressed MCAs on collagen gels. These new model systems have utility for future analyses of compression-induced mechanotransduction and the resulting impact on cellular responses related to intraperitoneal metastatic dissemination.This article has an associated First Person interview with the first authors of the paper.

Comparative proteomic analysis of mouse models of pathological and physiological cardiac hypertrophy, with selection of biomarkers of pathological hypertrophy by integrative Proteogenomics

To determine fundamental characteristics of pathological cardiac hypertrophy, protein expression profiles in two widely accepted models of cardiac hypertrophy (swimming-trained mouse for physiological hypertrophy and pressure-overload-induced mouse for pathological hypertrophy) were compared using a label-free quantitative proteomics approach. Among 3955 proteins (19,235 peptides, false-discovery rate < 0.01) identified in these models, 486 were differentially expressed with a log2 fold difference ≥ 0.58, or were detected in only one hypertrophy model (each protein from 4 technical replicates, p < .05). Analysis of gene ontology biological processes and KEGG pathways identified cellular processes enriched in one or both hypertrophy models. Processes unique to pathological hypertrophy were compared with processes previously identified in cardiac-hypertrophy models. Individual proteins with differential expression in processes unique to pathological hypertrophy were further confirmed using the results of previous targeted functional analysis studies. Using a proteogenomic approach combining transcriptomic and proteomic analyses, similar patterns of differential expression were observed for 23 proteins and corresponding genes associated with pathological hypertrophy. A total of 11 proteins were selected as early-stage pathological-hypertrophy biomarker candidates, and the results of western blotting for five of these proteins in independent samples confirmed the patterns of differential expression in mouse models of pathological and physiological cardiac hypertrophy.

Successful knock-in of Hypertrophic Cardiomyopathy-mutation R723G into the MYH7 gene mimics HCM pathology in pigs

Familial Hypertrophic Cardiomyopathy (HCM) is the most common inherited cardiac disease. About 30% of the patients are heterozygous for mutations in the MYH7 gene encoding the ß-myosin heavy chain (MyHC). Hallmarks of HCM are cardiomyocyte disarray and hypertrophy of the left ventricle, the symptoms range from slight arrhythmias to sudden cardiac death or heart failure. To gain insight into the underlying mechanisms of the diseases' etiology we aimed to generate genome edited pigs with an HCM-mutation. We used TALEN-mediated genome editing and successfully introduced the HCM-point mutation R723G into the MYH7 gene of porcine fibroblasts and subsequently cloned pigs that were heterozygous for the HCM-mutation R723G. No off-target effects were determined in the R723G-pigs. Surprisingly, the animals died within 24 h post partem, probably due to heart failure as indicated by a shift in the a/ß-MyHC ratio in the left ventricle. Most interestingly, the neonatal pigs displayed features of HCM, including mild myocyte disarray, malformed nuclei, and MYH7-overexpression. The finding of HCM-specific pathology in neonatal R723G-piglets suggests a very early onset of the disease and highlights the importance of novel large animal models for studying causative mechanisms and long-term progression of human cardiac diseases.

Three TF Co-expression Modules Regulate Pressure-Overload Cardiac Hypertrophy in Male Mice

Pathological cardiac hypertrophy, a dynamic remodeling process, is a major risk factor for heart failure. Although a number of key regulators and related genes have been identified, how the transcription factors (TFs) dynamically regulate the associated genes and control the morphological and electrophysiological changes during the hypertrophic process are still largely unknown. In this study, we obtained the time-course transcriptomes at five time points in four weeks from male murine hearts subjected to transverse aorta banding surgery. From a series of computational analyses, we identified three major co-expression modules of TF genes that may regulate the gene expression changes during the development of cardiac hypertrophy in mice. After pressure overload, the TF genes in Module 1 were up-regulated before the occurrence of significant morphological changes and one week later were down-regulated gradually, while those in Modules 2 and 3 took over the regulation as the heart size increased. Our analyses revealed that the TF genes up-regulated at the early stages likely initiated the cascading regulation and most of the well-known cardiac miRNAs were up-regulated at later stages for suppression. In addition, the constructed time-dependent regulatory network reveals some TFs including Egr2 as new candidate key regulators of cardiovascular-associated (CV) genes.

Trimetazidine attenuates pressure overload-induced early cardiac energy dysfunction via regulation of neuropeptide Y system in a rat model of abdominal aortic constriction

Background

Metabolism remodeling has been recognized as an early event following cardiac pressure overload. However, its temporal association with ventricular hypertrophy has not been confirmed. Moreover, whether trimetazidine could favorably affect this process also needs to be determined. The aim of the study was to explore the temporal changes of myocardial metabolism remodeling following pressure-overload induced ventricular hypertrophy and the potential favorable effect of trimetazidine on myocardial metabolism remodeling.

Methods

A rat model of abdominal aortic constriction (AAC)-induced cardiac pressure overload was induced. These rats were grouped as the AAC (no treatment) or TMZ group according to whether oral trimetazidine (TMZ, 40 mg/kg/d, for 5 days) was administered. Changes in cardiac structures were sequentially evaluated via echocardiography. The myocardial ADP/ATP ratio was determined to reflect the metabolic status, and changes in serum neuropeptide Y systems were evaluated.

Results

Myocardial metabolic disorder was acutely induced as evidenced by an increased ADP/ATP ratio within 7 days of AAC before the morphological changes in the myocardium, accompanied by up-regulation of serum oxidative stress markers and expression of fetal genes related to hypertrophy. Moreover, the serum NPY and myocardial NPY-1R, 2R, and 5R levels were increased within the acute phase of AAC-induced cardiac pressure overload. Pretreatment with TMZ could partly attenuate myocardial energy metabolic homeostasis, decrease serum levels of oxidative stress markers, attenuate the induction of hypertrophy-related myocardial fetal genes, inhibit the up-regulation of serum NPY levels, and further increase the myocardial expression of NPY receptors.

Conclusions

Cardiac metabolic remodeling is an early change in the myocardium before the presence of typical morphological ventricular remodeling following cardiac pressure overload, and pretreatment with TMZ may at least partly reverse the acute metabolic disturbance, perhaps via regulation of the NPY system.

Integrated glycoprotein immobilization method for glycopeptide and glycan analysis of cardiac hypertrophy

Post-translational modifications of proteins can have a major role in disease initiation and progression. Incredible efforts have recently been made to study the regulation of glycoproteins for disease prognosis and diagnosis. It is essential to elucidate glycans and intact glycoproteins to understand the role of glycosylation in diseases. Sialylated N-glycans play crucial roles in physiological and pathological processes; however, it is laborious to study sialylated glycoproteins due to the labile nature of sialic acid residues. In this study, an integrated platform is developed for the analysis of intact glycoproteins and glycans using a chemoenzymatic approach for immobilization and derivatization of sialic acids. N-Glycans, deglycosylated proteins, and intact glycoproteins from heart tissues of wild type (WT) and transverse aortic constriction (TAC) mouse models were analyzed. We identified 291 unique glycopeptides from 195 glycoproteins; the comparative studies between WT and TAC mice indicate the overexpression of extracellular proteins for heart matrix remodeling and the down-regulation of proteins associated with energy metabolism in cardiac hypertrophy. The integrated platform is a powerful tool for the analysis of glycans and glycoproteins in the discovery of potential cardiac hypertrophy biomarkers.

Role of miRNAs and alternative mRNA 3'-end cleavage and polyadenylation of their mRNA targets in cardiomyocyte hypertrophy

miRNAs play critical roles in heart disease. In addition to differential miRNA expression, miRNA-mediated control is also affected by variable miRNA processing or alternative 3'-end cleavage and polyadenylation (APA) of their mRNA targets. To what extent these phenomena play a role in the heart remains unclear. We sought to explore miRNA processing and mRNA APA in cardiomyocytes, and whether these change during cardiac hypertrophy. Thoracic aortic constriction (TAC) was performed to induce hypertrophy in C57BL/6J mice. RNA extracted from cardiomyocytes of sham-treated, pre-hypertrophic (2 days post-TAC), and hypertrophic (7 days post-TAC) mice was subjected to small RNA- and poly(A)-test sequencing (PAT-Seq). Differential expression analysis matched expectations; nevertheless we identified ~400 mRNAs and hundreds of noncoding RNA loci as altered with hypertrophy for the first time. Although multiple processing variants were observed for many miRNAs, there was little change in their relative proportions during hypertrophy. PAT-Seq mapped ~48,000 mRNA 3'-ends, identifying novel 3' untranslated regions (3'UTRs) for over 7000 genes. Importantly, hypertrophy was associated with marked changes in APA with a net shift from distal to more proximal mRNA 3'-ends, which is predicted to decrease overall miRNA repression strength. We independently validated several examples of 3'UTR proportion change and showed that alternative 3'UTRs associate with differences in mRNA translation. Our work suggests that APA contributes to altered gene expression with the development of cardiomyocyte hypertrophy and provides a rich resource for a systems-level understanding of miRNA-mediated regulation in physiological and pathological states of the heart.

Calcium-mediated histone modifications regulate alternative splicing in cardiomyocytes

In cardiomyocytes, calcium is known to control gene expression at the level of transcription, whereas its role in regulating alternative splicing has not been explored. Here we report that, in mouse primary or embryonic stem cell-derived cardiomyocytes, increased calcium levels induce robust and reversible skipping of several alternative exons from endogenously expressed genes. Interestingly, we demonstrate a calcium-mediated splicing regulatory mechanism that depends on changes of histone modifications. Specifically, the regulation occurs through changes in calcium-responsive kinase activities that lead to alterations in histone modifications and subsequent changes in the transcriptional elongation rate and exon skipping. We demonstrate that increased intracellular calcium levels lead to histone hyperacetylation along the body of the genes containing calcium-responsive alternative exons by disrupting the histone deacetylase-to-histone acetyltransferase balance in the nucleus. Consequently, the RNA polymerase II elongation rate increases significantly on those genes, resulting in skipping of the alternative exons. These studies reveal a mechanism by which calcium-level changes in cardiomyocytes impact on the output of gene expression through altering alternative pre-mRNA splicing patterns.

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.

The ginsenoside Rg1 prevents transverse aortic constriction-induced left ventricular hypertrophy and cardiac dysfunction by inhibiting fibrosis and enhancing angiogenesis

BACKGROUND

Ginsenoside Rg1, an important and active ingredient of Panax ginseng, has been shown to exert cardioprotective effects in vivo. The present study aimed to test the hypothesis that ginsenoside Rg1 attenuates cardiac dysfunction in a transverse aortic constriction (TAC)-induced left ventricular hypertrophy in vivo via proangiogenic and antifibrotic effects.

METHODS

This study investigated the effects of ginsenoside Rg1 in a rat model of TAC-induced left ventricular hypertrophy. Cardiac function was assessed by echocardiography. The antifibrotic and proangiogenic effects were assessed by histopathology and mRNA expression of procollagen I, III, and vascular endothelial growth factor (VEGF) through quantitative real-time PCR. The expression of phosphorylation of Akt, p38 mitogen-activated protein kinase (MAPK), hypoxia inducible factor-1 (HIF-1), and VEGF proteins were examined by Western blotting.

RESULTS

Ginsenoside Rg1 treatment significantly decreased TAC-induced myocardial fibrosis and left ventricular hypertrophy, and preserved cardiac function. Ginsenoside Rg1 administration enhanced angiogenesis by increasing the expression of HIF-1 and VEGF. These cardioprotective effects of ginsenoside Rg1 are partially related to the activation of phospho-Akt and inhibition of p38 MAPK.

CONCLUSIONS

Ginsenoside Rg1 exhibited protective effect against TAC-induced left ventricular hypertrophy and cardiac dysfunction, which is potentially associated with phospho-Akt activation and p38 MAPK inhibition.

Fibroblast growth factor receptor 1 signaling in adult cardiomyocytes increases contractility and results in a hypertrophic cardiomyopathy

Fibroblast growth factors (FGFs) and their receptors are highly conserved signaling molecules that have been implicated in postnatal cardiac remodeling. However, it is not known whether cardiomyocyte-expressed FGF receptors are necessary or sufficient for ventricular remodeling in the adult heart. To determine whether cardiomyocytes were competent to respond to an activated FGF receptor, and to determine if this signal would result in the development of hypertrophy, we engineered a doxycycline (DOX)-inducible, cardiomyocyte-specific, constitutively active FGF receptor mouse model (αMHC-rtTA, TRE-caFgfr1-myc). Echocardiographic and hemodynamic analysis indicated that acute expression of caFGFR1 rapidly and directly increased cardiac contractility, while chronic expression resulted in significant hypertrophy with preservation of systolic function. Subsequent histologic analysis showed increased cardiomyocyte cross-sectional area and regions of myocyte disarray and fibrosis, classic features of hypertrophic cardiomyopathy (HCM). Analysis of downstream pathways revealed a lack of clear activation of classical FGF-mediated signaling pathways, but did demonstrate a reduction in Serca2 expression and troponin I phosphorylation. Isolated ventricular myocytes showed enhanced contractility and reduced relaxation, an effect that was partially reversed by inhibition of actin-myosin interactions. We conclude that adult cardiomyocytes are competent to transduce FGF signaling and that FGF signaling is sufficient to promote increased cardiomyocyte contractility in vitro and in vivo through enhanced intrinsic actin-myosin interactions. Long-term, FGFR overexpression results in HCM with a dynamic outflow tract obstruction, and may serve as a unique model of HCM.

Nebivolol prevents desensitization of β-adrenoceptor signaling and induction of cardiac hypertrophy in response to isoprenaline beyond β1-adrenoceptor blockage

The importance of chronic stimulation of β-adrenoceptors in the development of cardiac dysfunction is the rationale for the use of β-blockers in the treatment of heart failure. Nebivolol is a third-generation β-blocker, which has further properties including stimulation of endothelial nitric oxide synthase and/or β3-adrenoceptors. The aim of this study was to investigate whether nebivolol has additional effects on β-adrenoceptor-mediated functional responses along with morphologic and molecular determinants of cardiac hypertrophy compared with those of metoprolol, a selective β1-adrenoceptor blocker. Rats infused by isoprenaline (100 μg·kg−1·day−1, 14 days) were randomized into three groups according to the treatment with metoprolol (30 mg·kg−1·day−1), nebivolol (10 mg·kg−1·day−1), or placebo for 13 days starting on day 1 after implantation of minipump. Both metoprolol and nebivolol caused a similar reduction on heart rate. Nebivolol mediated a significant improvement on cardiac mass, coronary flow, mRNA expression levels of sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and atrial natriuretic peptide and phospholamban (PLN)/SERCA2a and phospho-PLN/PLN ratio compared with metoprolol and placebo. Nebivolol prevented the detrimental effects of isoprenaline infusion on isoprenaline (68% of control at 30 μM), BRL37344 (63% of control at 0.1 μM), and forskolin (64% of control at 1 μM) responses compared with metoprolol (isoprenaline, 34% of control; BRL37344, no response; forskolin, 26% of control) and placebo (isoprenaline, 33% of control; BRL37344, 28% of control; forskolin, 12% of control). Both β-blockers improved the changes in mRNA expressions of β1- and β3-adrenoceptors. Our results suggest that nebivolol partially protects the responsiveness of β-adrenoceptor signaling and the development of cardiac hypertrophy independent of its β1-adrenoceptor blocking effect.

Variable phenotype in murine transverse aortic constriction

BACKGROUND

In mice, transverse aortic constriction (TAC) is variably characterized as a model of pressure overload-induced hypertrophy (left ventricular [LV] hypertrophy, or LVH) or heart failure (HF). While commonly used, variability in the TAC model is poorly defined. The objectives of this study were to characterize the variability in the TAC model and to define a simple, noninvasive method of prospectively identifying mice with HF versus compensated LVH after TAC.

METHODS

Eight-week-old male C57BL/6J mice underwent TAC or sham and then echocardiography at 3 weeks post-TAC. A group of sham and TAC mice were euthanized after the 3-week echocardiogram, while the remainder underwent repeat echocardiography and were euthanized at 9 weeks post-TAC. The presence of TAC was assessed with two-dimensional echocardiography, anatomic aortic m-mode and color flow, and pulsed-wave Doppler examination of the transverse aorta (TA) and by LV systolic pressure (LVP). Trans-TAC pressure gradient was assessed invasively in a subset of mice. HF was defined as lung/body weight>upper limit in sham-operated mice.

RESULTS

As compared with sham, TAC mice had higher TA velocity, LVP and LV weight, and lower ejection fraction (EF) at 3 or 9 weeks post-TAC. Only a subset of TAC mice (28%) developed HF. As compared with compensated LVH, HF mice were characterized by similar TA velocity and higher percent TA stenosis, but lower LVP, higher LV weight, larger LV cavity, lower EF and stress-corrected midwall fiber shortening, and more fibrosis. Both EF and LV mass measured by echocardiography at 3 weeks post-TAC were predictive of the presence of HF at 3 or 9 weeks post-TAC.

CONCLUSIONS

In wild-type mice, TAC produces a variable cardiac phenotype. Marked abnormalities in LV mass and EF at echocardiography 3 weeks post-TAC identify mice with HF at autopsy. These data are relevant to appropriate design and interpretation of murine studies.

Deep RNA sequencing reveals novel cardiac transcriptomic signatures for physiological and pathological hypertrophy

Although both physiological hypertrophy (PHH) and pathological hypertrophy (PAH) of the heart have similar morphological appearances, only PAH leads to fatal heart failure. In the present study, we used RNA sequencing (RNA-Seq) to determine the transcriptomic signatures for both PHH and PAH. Approximately 13-20 million reads were obtained for both models, among which PAH showed more differentially expressed genes (DEGs) (2,041) than PHH (245). The expression of 417 genes was barely detectable in the normal heart but was suddenly activated in PAH. Among them, Foxm1 and Plk1 are of particular interest, since Ingenuity Pathway Analysis (IPA) using DEGs and upstream motif analysis showed that they are essential hub proteins that regulate the expression of downstream proteins associated with PAH. Meanwhile, 52 genes related to collagen, chemokines, and actin showed opposite expression patterns between PHH and PAH. MAZ-binding motifs were enriched in the upstream region of the participating genes. Alternative splicing (AS) of exon variants was also examined using RNA-Seq data for PAH and PHH. We found 317 and 196 exon inclusions and exon exclusions, respectively, for PAH, and 242 and 172 exon inclusions and exclusions, respectively for PHH. The AS pattern was mostly related to gains or losses of domains, changes in activity, and localization of the encoded proteins. The splicing variants of 8 genes (i.e., Fhl1, Rcan1, Ndrg2, Synpo, Ttll1, Cxxc5, Egfl7, and Tmpo) were experimentally confirmed. Multilateral pathway analysis showed that the patterns of quantitative (DEG) and qualitative (AS) changes differ depending on the type of pathway in PAH and PHH. One of the most significant changes in PHH is the severe downregulation of autoimmune pathways accompanied by significant AS. These findings revealed the unique transcriptomic signatures of PAH and PHH and also provided a more comprehensive understanding at both the quantitative and qualitative levels.

Mitochondrial adaptations to physiological vs. pathological cardiac hypertrophy

Cardiac hypertrophy is a stereotypic response of the heart to increased workload. The nature of the workload increase may vary depending on the stimulus (repetitive, chronic, pressure, or volume overload). If the heart fully adapts to the new loading condition, the hypertrophic response is considered physiological. If the hypertrophic response is associated with the ultimate development of contractile dysfunction and heart failure, the response is considered pathological. Although divergent signalling mechanisms may lead to these distinct patterns of hypertrophy, there is some overlap. Given the close relationship between workload and energy demand, any form of cardiac hypertrophy will impact the energy generation by mitochondria, which are the key organelles for cellular ATP production. Significant changes in the expression of nuclear and mitochondrially encoded transcripts that impact mitochondrial function as well as altered mitochondrial proteome composition and mitochondrial energetics have been described in various forms of cardiac hypertrophy. Here, we review mitochondrial alterations in pathological and physiological hypertrophy. We suggest that mitochondrial adaptations to pathological and physiological hypertrophy are distinct, and we shall review potential mechanisms that might account for these differences.

Temporal correlation between transcriptional changes and increased synthesis of hyaluronan in experimental cardiac hypertrophy

The role of hyaluronan in cardiac growth has become evident, previously shown by increased myocardial levels of hyaluronan in a rat model of cardiac hypertrophy. To further investigate the role of hyaluronan and regulation of its synthesis in cardiac hypertrophy, quantitative measurements of myocardial hyaluronan concentration was correlated to gene transcription in hypertrophic cardiac tissue. Factor analysis was used to study this correlation over time. A subset of differentially expressed genes was identified with a transcriptional regulation correlating to the increased synthesis of hyaluronan, suggesting a common regulatory pathway. Four transcription factors, Myc, Fos, Junb and Egr1, were also up-regulated. Furthermore, the Ace gene was up-regulated, representing increase of angiotensin II, an inducer of these transcription factors and fetal genes in cardiac hypertrophy. This demonstrates a coordinated synthesis of hyaluronan and pro-hypertrophic gene expression, regulated by immediate early genes, with angiotensin II as a possible mediator.

Immediate response of myocardium to pressure overload includes transient regulation of genes associated with mitochondrial bioenergetics and calcium availability

Ventricular hypertrophy is one of the major myocardial responses to pressure overload (PO). Most studies on early myocardial response focus on the days or even weeks after induction of hypertrophic stimuli. Since mechanotransduction pathways are immediately activated in hearts undergoing increased work load, it is reasonable to infer that the myocardial gene program may be regulated in the first few hours. In the present study, we monitored the expression of some genes previously described in the context of myocardial hypertrophic growth by using the Northern blot technique, to estimate the mRNA content of selected genes in rat myocardium for the periods 1, 3, 6, 12 and 48 h after PO stimuli. Results revealed an immediate switch in the expression of genes encoding alpha and beta isoforms of myosin heavy chain, and up-regulation of the cardiac isoform of alpha actin. We also detected transitory gene regulation as the increase in mitochondrial cytochrome c oxidase 1 gene expression, parallel to down-regulation of genes encoding sarco(endo)plasmic reticulum Ca⁺² ATPase and sodium-calcium exchanger. Taken together, these results indicate that initial myocardial responses to increased work load include alterations in the contractile properties of sarcomeres and transitory adjustment of mitochondrial bioenergetics and calcium availability.

Salutary effects of Corydalis yanhusuo extract on cardiac hypertrophy due to pressure overload in rats

We have evaluated the effects of an alcohol extract from the rhizome of Corydalis yanhusuo W.T. (CY), a well-known traditional Chinese medicinal herb, on pressure-overloaded cardiac hypertrophy induced by transverse abdominal aorta constriction (TAAC) in rats. Rats were given vehicle or CY extract (200 or 50 mg kg−1 per day) from the second week after induction of pressure overload, for a period of 7 weeks. Haemodynamic parameters, relative heart weight and myocyte cross-sectional area were measured in each group. We also estimated left ventricular (LV) collagen volume fraction (CVF) using Masson trichrome staining, and type I collagen expression by Western blot assay. Chronic TAAC caused notable cardiac hypertrophy and heart dysfunction. Significant collagen deposition and greater type I collagen expression were found in model control rats. These changes were not significantly reversed after treatment with 50 mgkg−1 CY, whereas 200 mgkg−1 significantly improved heart function and prevented cardiac hypertrophy, with parallel reductions in myocardial fibrosis, as evidenced by reduced LV CVF and reduced levels of type I collagen. In conclusion, chronic treatment of rats with CY extract attenuated development of cardiac hypertrophy.

Mitochondrial biogenesis in cardiac pathophysiology

Cardiac performance depends on a fine balance between the work the heart has to perform to satisfy the needs of the body and the energy that it is able to produce. Thus, energy production by oxidative metabolism, the main energy source of the cardiac muscle, has to be strictly regulated to adapt to cardiac work. Mitochondrial biogenesis is the mechanism responsible for mitochondrial component synthesis and assembly. This process controls mitochondrial content and thus correlates with energy production that, in turn, sustains cardiac contractility. Mitochondrial biogenesis should be finely controlled to match cardiac growth and cardiac work. When the heart is subjected to an increase in work in response to physiological and pathological challenges, it adapts by increasing its mass and expressing a new genetic program. In response to physiological stimuli such as endurance training, mitochondrial biogenesis seems to follow a program involving increased cardiac mass. But in the context of pathological hypertrophy, the modifications of this mechanism remain unclear. What appears clear is that mitochondrial biogenesis is altered in heart failure, and the imbalance between cardiac work demand and energy production represents a major factor in the development of heart failure.

Speckle tracking echocardiography in the assessment of mouse models of cardiac dysfunction

Two-dimensional (2-D) speckle tracking echocardiography (STE) accurately quantifies circumferential strain (S(circ)) and radial strain (S(rad)) in humans and in large and small animals. This study was performed to assess sensitivity of S(circ) and S(rad) to left ventricular (LV) dysfunction in mouse models. We performed 2-D and M-mode echocardiography 1) in 6 mice during superficial and profound isoflurane anesthesia, 2) serially in 12 mice to monitor the development of heart failure induced by transverse aortic constriction (TAC) and in 8 corresponding control mice, and 3) in 26 mice with varying degrees of TAC-induced heart failure and 12 corresponding control mice immediately before euthanasia. Fractional shortening (FS) and LV mass were measured from standard M-mode tracings, whereas S(circ) and S(rad) were derived by STE. Percent fibrosis and myocyte diameters were assessed from whole heart cross-sectional specimens stained by Masson trichrome. Profound isoflurane anesthesia decreased S(circ) (P = 0.027) but not S(rad) (P > 0.05). Mice subjected to TAC showed an immediate and sustained decrease in FS (P = 0.035), S(circ) (P = 0.016), and S(rad) (P = 0.012). S(circ) showed better correlation with FS (r = 0.56 and P < 0.0001) and LV mass (r = 0.42 and P = 0.0003) than S(rad) (r = 0.54 and P < 0.0001 for FS and r = 0.37 and P = 0.014 for LV mass, respectively). Percent fibrosis correlated better with S(circ) (r = 0.46 and P = 0.004) than with S(rad) (r = -0.32 and P = 0.05), whereas myocyte diameter showed similar correlation with both strains (r = 0.45 and r = -0.44, respectively, and P = 0.006 for both). STE correctly identifies LV dysfunction and histological changes in mice and can be used for the serial assessment of cardiac remodeling in murine models.

Time-warped comparison of gene expression in adaptive and maladaptive cardiac hypertrophy

BACKGROUND

Cardiac hypertrophy is classically regarded as a compensatory response, yet the active tissue remodeling processes triggered by various types of mechanical stress can enhance or diminish the function of the heart. Despite the disparity in outcomes, there are similarities in the hypertrophic responses. We hypothesized that a generic genetic response that is not dependent on the particular nature of the hypertrophic stimulus exists. To test our hypothesis, we compared the temporal evolution of transcriptomes measured in hearts subjected to either adaptive (exercise-induced) or maladaptive (aortic banding-induced) hypertrophy.

METHODS AND RESULTS

Generic hypertrophy-associated genes were identified and distinguished from stimulus-dependent transcripts by coupling a metric of cardiac growth with a dynamic time-warping algorithm to align transcriptome changes with respect to the hypertrophy response. The major differences in expression between the adaptive and maladaptive hypertrophy models were centered around the genes involved in metabolism, fibrosis, and immune response. Conversely, transcripts with common expression patterns in both hypertrophy models were associated with signal transduction, cytoskeletal development, and muscle contraction. Thus, despite the apparent differences in the expression response of the heart to either athletic conditioning or pressure overload, there is a set of genes that displays similar expression profiles.

CONCLUSIONS

This finding lends support to the notion of a generalized cardiac growth mechanism that is activated in response to mechanical perturbation. The common and unique genetic signatures of adaptive and maladaptive hypertrophy may be useful in the diagnosis and treatment of pathological myocardial remodeling.

Transcriptomic analysis of PPARalpha-dependent alterations during cardiac hypertrophy

Peroxisome proliferator-activated receptor (PPAR)alpha regulates lipid metabolism at the transcriptional level and modulates the expression of genes involved in inflammation, cell proliferation, and differentiation. Although PPARalpha has been shown to mitigate cardiac hypertrophy, knowledge about underlying mechanisms and the nature of signaling pathways involved is fragmentary and incomplete. The aim of this study was to identify the processes and signaling pathways regulated by PPARalpha in hearts challenged by a chronic pressure overload by means of whole genome transcriptomic analysis. PPARalpha-/- and wild-type mice were subjected to transverse aortic constriction (TAC) for 28 days, and left ventricular gene expression profile was determined with Affymetrix GeneChip Mouse Genome 430 2.0 arrays containing >45,000 probe sets. In unchallenged hearts, the mere lack of PPARalpha resulted in 821 differentially expressed genes, many of which are related to lipid metabolism and immune response. TAC resulted in a more pronounced cardiac hypertrophy and more extensive changes in gene expression (1,910 and 312 differentially expressed genes, respectively) in PPARalpha-/- mice than in wild-type mice. Many of the hypertrophy-related genes were related to development, signal transduction, actin filament organization, and collagen synthesis. Compared with wild-type hypertrophied hearts, PPARalpha-/- hypertrophied hearts revealed enrichment of gene clusters related to extracellular matrix remodeling, immune response, oxidative stress, and inflammatory signaling pathways. The present study therefore demonstrates that, in addition to lipid metabolism, PPARalpha is an important modulator of immune and inflammatory response in cardiac muscle.

Altered myocardial gene expression reveals possible maladaptive processes in heterozygous and homozygous cardiac myosin-binding protein C knockout mice

Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease characterized by left ventricular hypertrophy (LVH) predominantly affecting the interventricular septum. Cardiac myosin-binding protein C (cMyBP-C) mutations are common causes of FHC. Gene expression profiling was performed in left ventricles of 9-week-old wild-type mice, heterozygous cMyBP-C KO mice displaying asymmetric septal hypertrophy, and homozygous mice developing eccentric LVH. Knocking out one or two cMyBP-C genes leads primarily to gene expression changes indicating an increased energy demand, activation of the JNK and p38 parts of the MAPK pathway and deactivation of the ERK part, and induction of apoptosis. Altered gene expression for processes related to cardiac structure, contractile proteins, and protein turnover was also identified. Many of the changes were more pronounced in the homozygous KO mice. These alterations point to physiological and pathological adaptations in the prehypertrophic heterozygous KO mice and the hypertrophic homozygous mice.

Propranolol causes a paradoxical enhancement of cardiomyocyte foetal gene response to hypertrophic stimuli

BACKGROUND AND PURPOSE

Pathological cardiac hypertrophy is associated with the expression of a gene profile reminiscent of foetal development. The non selective beta-adrenoceptor antagonist propranolol is able to blunt cardiomyocyte hypertrophic response in pressure-overloaded hearts. It remains to be determined whether propranolol also attenuates the expression of hypertrophy-associated foetal genes.

EXPERIMENTAL APPROACH

To address this question, the foetal gene programme, of which atrial natriuretic peptide (ANP), the beta-isoform of myosin heavy chain (beta-MHC), and the alpha-skeletal muscle isoform of actin (skACT) are classical members, was induced by thoracic aortic coarctation (TAC) in C57BL/6 mice, or by phenylephrine, a selective alpha(1)-adrenoceptor agonist, in cultured rat neonatal cardiomyocytes.

KEY RESULTS

In TAC mice, the left ventricular weight-to-body weight (LVW/BW) ratio increased by 35% after 2 weeks. Levels of ANP, beta-MHC and skACT mRNA in the left ventricles increased 2.2-fold, 2.0-fold and 12.1-fold, respectively, whereas alpha-MHC and SERCA mRNA levels decreased by approximately 50%. Although propranolol blunted cardiomyocyte growth, with approximately an 11% increase in the LVW/BW ratio, it enhanced the expression of ANP, beta-MHC and skACT genes (10.5-fold, 27.7-fold and 22.7-fold, respectively). Propranolol also enhanced phenylephrine-stimulated ANP and beta-MHC gene expression in cultured cardiomyocytes. Similar results were obtained with metoprolol, a selective beta(1)-adrenoceptor antagonist, but not with ICI 118551, a beta(2)-adrenoceptor antagonist.

CONCLUSIONS AND IMPLICATIONS

Propranolol enhances expression of the hypertrophy-associated foetal genes mainly via the beta(1)-adrenoceptor blockade. Our results also suggest that, in pressure-overloaded hearts, cardiomyocyte growth and foetal gene expression occur as independent processes.

Ameliorative Effect of Combination of Fenofibrate and Rosiglitazone in Pressure Overload-Induced Cardiac Hypertrophy in Rats

The present study has been designed to investigate the effects of fenofibrate, a peroxisome proliferator-activated receptor (PPAR)alpha agonist, rosiglitazone, a PPARgamma agonist and the combination of both fenofibrate and rosiglitazone in partial abdominal aortic constriction (PAAC)-induced pathological cardiac hypertrophy in rats. Rats were subjected to PAAC for 4 weeks to produce pathological cardiac hypertrophy. The fenofibrate (3 mg/kg day(-1), p.o.), rosiglitazone (3 mg/kg day(-1), p.o.) and the combination of both fenofibrate (3 mg/kg day(-1), p.o.) and rosiglitazone (3 mg/kg day(-1), p.o.) were administered 3 days before PAAC and continued for 4 weeks after PAAC. The development of cardiac hypertrophy was assessed in terms of measuring ratio of left ventricular (LV) weight to body weight (LVW/BW), LV wall thickness (LVWT), LV protein content and LV collagen content. Further, the collagen accumulation in left ventricle was analyzed using picrosirius red staining. Moreover, the cross-sectional area (CSA) of cardiomyocytes was assessed using hematoxylin and eosin staining and measured using a NIH Scion image analyzer. The PAAC produced cardiac hypertrophy by increasing LVW/BW, LVWT, LV protein content, LV collagen content and mean CSA of cardiomyocytes. However, treatment with fenofibrate and rosiglitazone either alone or in combination significantly attenuated PAAC-induced increase in LVW/BW, LVWT, LV protein content, LV collagen content and mean CSA of cardiomyocytes. The combination of fenofibrate and rosiglitazone was more effective in attenuating the PAAC-induced cardiac hypertrophy than either drug alone. Thus, it may be concluded that dual activation of PPARalpha and PPARgamma may provide synergistic benefits in preventing the development of pathological cardiac hypertrophy.