beta(2)-adrenergic receptor overexpression exacerbates development of heart failure after aortic stenosis

Coupling of β-adrenergic and Hippo pathway signaling: Implications for heart failure pathophysiology and metabolic therapy

Activation of the sympatho-β-adrenergic receptor (βAR) system is the hallmark of heart disease with adverse consequences that facilitate the onset and progression of heart failure (HF). Use of β-blocking drugs has become the front-line therapy for HF. Last decade has witnessed progress in research demonstrating a pivotal role of Hippo pathway in cardiomyopathy and HF. Clinical studies have revealed myocardial Hippo pathway activation/YAP-TEAD1 inactivation in several types of human cardiomyopathy. Experimental activation of cardiac Hippo signaling or inhibition of YAP-TEAD1 have been shown to leads dilated cardiomyopathy with severe mitochondrial dysfunction and metabolic reprogramming. Studies have also convincingly shown that stimulation of βAR activates cardiac Hippo pathway with inactivation of the down-stream effector molecules YAP/TAZ. There is strong evidence for the adverse consequences of the βAR-Hippo signaling leading to HF. In addition to promoting cardiomyocyte death and fibrosis, recent progress is the demonstration of mitochondrial dysfunction and metabolic reprogramming mediated by βAR-Hippo pathway signaling. Activation of cardiac βAR-Hippo signaling is potent in downregulating a range of mitochondrial and metabolic genes, whereas expression of pro-inflammatory and pro-fibrotic factors are upregulated. Coupling of βAR-Hippo pathway signaling is mediated by several kinases, mechanotransduction and/or Ca2+ signaling, and can be blocked by β-antagonists. Demonstration of the converge of βAR signaling and Hippo pathway bears implications for a better understanding on the role of enhanced sympathetic nervous activity, efficacy of β-antagonists, and metabolic therapy targeting this pathway in HF. In this review we summarize the progress and discuss future research directions in this field.

Molecular Imaging of Diffuse Cardiac Fibrosis with a Radiotracer That Targets Proteolyzed Collagen IV

Purpose To develop an approach for in vivo detection of interstitial cardiac fibrosis using PET with a peptide tracer targeting proteolyzed collagen IV (T-peptide). Materials and Methods T-peptide was conjugated to the copper chelator MeCOSar (chemical name, 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid) and radiolabeled with copper 64 (64Cu). PET/CT scans were acquired following intravenous delivery of 64Cu-T-peptide-MeCOSar (0.25 mg/kg; 18 MBq ± 2.7 [SD]) to male transgenic mice overexpressing β2-adrenergic receptors with intermediate (7 months of age; n = 4 per group) to severe (10 months of age; n = 11 per group) cardiac fibrosis and their wild-type controls. PET scans were also performed following coadministration of the radiolabeled probe with nonlabeled T-peptide in excess to confirm binding specificity. PET data were analyzed by t tests for static scans and analysis of variance tests (one- or two-way) for dynamic scans. Results PET/CT scans revealed significantly elevated (2.24-4.26-fold; P < .05) 64Cu-T-peptide-MeCOSar binding in the fibrotic hearts of aged transgenic β2-adrenergic receptor mice across the entire 45-minute acquisition period compared with healthy controls. The cardiac tracer accumulation and presence of diffuse cardiac fibrosis in older animals were confirmed by gamma counting (P < .05) and histologic evaluation, respectively. Coadministration of a nonradiolabeled probe in excess abolished the elevated radiotracer binding in the aged transgenic hearts. Importantly, PET tracer accumulation was also detected in younger (7 months of age) transgenic mice with intermediate cardiac fibrosis, although this was only apparent from 20 minutes following injection (1.6-2.2-fold binding increase; P < .05). Conclusion The T-peptide PET tracer targeting proteolyzed collagen IV provided a sensitive and specific approach of detecting diffuse cardiac fibrosis at varying degrees of severity in a transgenic mouse model. Keywords: Diffuse Cardiac Fibrosis, Molecular Peptide Probe, Molecular Imaging, PET/CT © RSNA, 2024.

Vidarabine, an anti-herpes agent, improves Porphyromonas gingivalis lipopolysaccharide-induced cardiac dysfunction in mice

In this work, we examined the involvement of type 5 adenylyl cyclase (AC5) in cardiac dysfunction induced in mice given Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose equivalent to the circulating levels in periodontitis (PD) patients. Cardiac function was significantly decreased in mice given PG-LPS compared to the control, but treatment for 1 week with the AC5 inhibitor vidarabine ameliorated the dysfunction. Cardiac fibrosis and myocyte apoptosis were significantly increased in the PG-LPS group, but vidarabine blocked these changes. The PG-LPS-induced cardiac dysfunction was associated with activation of cyclic AMP/Ca2+-calmodulin-dependent protein kinase II signaling and increased phospholamban phosphorylation at threonine 17. These results suggest that pharmacological AC5 inhibition may be a promising approach to treat PD-associated cardiovascular disease.

Pathophysiology and pharmacology of G protein-coupled receptors in the heart

G protein-coupled receptors (GPCRs), comprising the largest superfamily of cell surface receptors, serve as fundamental modulators of cardiac health and disease owing to their key roles in the regulation of heart rate, contractile dynamics, and cardiac function. Accordingly, GPCRs are heavily pursued as drug targets for a wide variety of cardiovascular diseases ranging from heart failure, cardiomyopathy, and arrhythmia to hypertension and coronary artery disease. Recent advancements in understanding the signalling mechanisms, regulation, and pharmacological properties of GPCRs have provided valuable insights that will guide the development of novel therapeutics. Herein, we review the cellular signalling mechanisms, pathophysiological roles, and pharmacological developments of the major GPCRs in the heart, highlighting the β-adrenergic, muscarinic, and angiotensin receptors as exemplar subfamilies.

Adrenergic Receptor Regulation of Mitochondrial Function in Cardiomyocytes

ABSTRACT

Adrenergic receptors (ARs) are G protein-coupled receptors that are stimulated by catecholamines to induce a wide array of physiological effects across tissue types. Both α1- and β-ARs are found on cardiomyocytes and regulate cardiac contractility and hypertrophy through diverse molecular pathways. Acute activation of cardiomyocyte β-ARs increases heart rate and contractility as an adaptive stress response. However, chronic β-AR stimulation contributes to the pathobiology of heart failure. By contrast, mounting evidence suggests that α1-ARs serve protective functions that may mitigate the deleterious effects of chronic β-AR activation. Here, we will review recent studies demonstrating that α1- and β-ARs differentially regulate mitochondrial biogenesis and dynamics, mitochondrial calcium handling, and oxidative phosphorylation in cardiomyocytes. We will identify potential mechanisms of these actions and focus on the implications of these findings for the modulation of contractile function in the uninjured and failing heart. Collectively, we hope to elucidate important physiological processes through which these well-studied and clinically relevant receptors stimulate and fuel cardiac contraction to contribute to myocardial health and disease.

Sympatho-adrenergic mechanisms in heart failure: new insights into pathophysiology

The sympathetic nervous system is activated in the setting of heart failure (HF) to compensate for hemodynamic instability. However, acute sympathetic surge or sustained high neuronal firing rates activates β-adrenergic receptor (βAR) signaling contributing to myocardial remodeling, dysfunction and electrical instability. Thus, sympatho-βAR activation is regarded as a hallmark of HF and forms pathophysiological basis for β-blocking therapy. Building upon earlier research findings, studies conducted in the recent decades have significantly advanced our understanding on the sympatho-adrenergic mechanism in HF, which forms the focus of this article. This review notes recent research progress regarding the roles of cardiac β2AR or α1AR in the failing heart, significance of β1AR-autoantibodies, and βAR signaling through G-protein independent signaling pathways. Sympatho-βAR regulation of immune cells or fibroblasts is specifically discussed. On the neuronal aspects, knowledge is assembled on the remodeling of sympathetic nerves of the failing heart, regulation by presynaptic α2AR of NE release, and findings on device-based neuromodulation of the sympathetic nervous system. The review ends with highlighting areas where significant knowledge gaps exist but hold promise for new breakthroughs.

Collagen-Targeted Peptides for Molecular Imaging of Diffuse Cardiac Fibrosis

Background Cardiac fibrosis is the excessive deposition of extracellular matrix in the heart, triggered by a cardiac insult, aging, genetics, or environmental factors. Molecular imaging of the cardiac extracellular matrix with targeted probes could improve diagnosis and treatment of heart disease. However, although this technology has been used to demonstrate focal scarring arising from myocardial infarction, its capacity to demonstrate extracellular matrix expansion and diffuse cardiac fibrosis has not been assessed. Methods and Results Here, we report the use of collagen-targeted peptides labeled with near-infrared fluorophores for the detection of diffuse cardiac fibrosis in the β2-AR (β-2-adrenergic receptor) overexpressing mouse model and in ischemic human hearts. Two approaches were evaluated, the first based on a T peptide that binds matrix metalloproteinase-2-proteolyzed collagen IV, and the second on the cyclic peptide EP-3533, which targets collagen I. The systemic and cardiac uptakes of both peptides (intravenously administered) were quantified ex vivo by near-infrared imaging of whole organs, tissue sections, and heart lysates. The peptide accumulation profiles corresponded to an immunohistochemically-validated increase in collagen types I and IV in hearts of transgenic mice versus littermate controls. The T peptide could encouragingly demonstrate both the intermediate (7 months old) and severe (11 months old) cardiomyopathic phenotypes. Co-immunostainings of fluorescent peptides and collagens, as well as reduced collagen binding of a control peptide, confirmed the collagen specificity of the tracers. Qualitative analysis of heart samples from patients with ischemic cardiomyopathy compared with nondiseased donors supported the collagen-enhancement capabilities of these peptides also in the clinical settings. Conclusions Together, these observations demonstrate the feasibility and translation potential of molecular imaging with collagen-binding peptides for noninvasive imaging of diffuse cardiac fibrosis.

Impact of Aldosterone on the Failing Myocardium: Insights from Mitochondria and Adrenergic Receptors Signaling and Function

The mineralocorticoid aldosterone regulates electrolyte and blood volume homeostasis, but it also adversely modulates the structure and function of the chronically failing heart, through its elevated production in chronic human post-myocardial infarction (MI) heart failure (HF). By activating the mineralocorticoid receptor (MR), a ligand-regulated transcription factor, aldosterone promotes inflammation and fibrosis of the heart, while increasing oxidative stress, ultimately induding mitochondrial dysfunction in the failing myocardium. To reduce morbidity and mortality in advanced stage HF, MR antagonist drugs, such as spironolactone and eplerenone, are used. In addition to the MR, aldosterone can bind and stimulate other receptors, such as the plasma membrane-residing G protein-coupled estrogen receptor (GPER), further complicating it signaling properties in the myocardium. Given the salient role that adrenergic receptor (ARs)—particularly βARs—play in cardiac physiology and pathology, unsurprisingly, that part of the impact of aldosterone on the failing heart is mediated by its effects on the signaling and function of these receptors. Aldosterone can significantly precipitate the well-documented derangement of cardiac AR signaling and impairment of AR function, critically underlying chronic human HF. One of the main consequences of HF in mammalian models at the cellular level is the presence of mitochondrial dysfunction. As such, preventing mitochondrial dysfunction could be a valid pharmacological target in this condition. This review summarizes the current experimental evidence for this aldosterone/AR crosstalk in both the healthy and failing heart, and the impact of mitochondrial dysfunction in HF. Recent findings from signaling studies focusing on MR and AR crosstalk via non-conventional signaling of molecules that normally terminate the signaling of ARs in the heart, i.e., the G protein-coupled receptor-kinases (GRKs), are also highlighted.

Loss of the long non-coding RNA OIP5-AS1 exacerbates heart failure in a sex-specific manner

Long non-coding RNAs (lncRNAs) have been demonstrated to influence numerous biological processes, being strongly implicated in the maintenance and physiological function of various tissues including the heart. The lncRNA OIP5-AS1 (1700020I14Rik/Cyrano) has been studied in several settings; however its role in cardiac pathologies remains mostly uncharacterized. Using a series of in vitro and ex vivo methods, we demonstrate that OIP5-AS1 is regulated during cardiac development in rodent and human models and in disease settings in mice. Using CRISPR, we engineered a global OIP5-AS1 knockout (KO) mouse and demonstrated that female KO mice develop exacerbated heart failure following cardiac pressure overload (transverse aortic constriction [TAC]) but male mice do not. RNA-sequencing of wild-type and KO hearts suggest that OIP5-AS1 regulates pathways that impact mitochondrial function. Thus, these findings highlight OIP5-AS1 as a gene of interest in sex-specific differences in mitochondrial function and development of heart failure.

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The lncRNA OIP5-AS1 is enriched in striated muscles in mice and humans.

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OIP5-AS1 is regulated during heart development and in models of heart disease.

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Global deletion of OIP5-AS1 exacerbates heart failure specifically in female mice.

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Transcriptomics analysis suggests that loss OIP5-AS1 alters mitochondrial function.

Endothelial-specific overexpression of cationic amino acid transporter-1 prevents loss of kidney function in heart failure

Heart failure (HF) is associated with impaired L-arginine transport. In the present study, we tested the hypothesis that augmented L-arginine transport prevents the loss of kidney function in HF. Renal function was assessed in wildtype mice (WT), transgenic mice with HF (dilated cardiomyopathy, DCM) and double transgenic mice (double transgenic mice with DCM and CAT-1 overexpression, HFCAT-1) with HF and endothelial-specific overexpression of the predominant L-arginine transporter, cationic amino acid transporter-1 (CAT-1) (n=4-8/group). Cardiac function was assessed via echocardiography and left ventricular catheterisation. Renal function was assessed via quantification of albuminuria and creatinine clearance. Plasma nitrate and nitrite levels together with renal fibrosis and inflammatory markers were also quantified at study end. Albumin/creatinine ratio was two-fold greater in DCM mice than in WT mice (P=0.002), and tubulointerstitial and glomerular fibrosis were approximately eight- and three-fold greater, respectively, in DCM mice than in WT mice (P≤0.02). Critically, urinary albumin/creatinine ratio and tubulointerstitial and glomerular fibrosis were less in HFCAT-1 mice than in DCM mice (P<0.05). Renal CAT-1 expression and plasma nitrate and nitrite levels were less in DCM mice compared with WT (P≤0.03) but was greater in HFCAT-1 mice than in DCM mice (P≤0.009). Renal expression of IL-10 was less in DCM mice compared with WT (P<0.001) but was greater in HFCAT-1 mice compared with DCM mice (P=0.02). Our data provide direct evidence that augmented L-arginine transport prevents renal fibrosis, inflammation and loss of kidney function in HF.

Cardiac voltage gated calcium channels and their regulation by β-adrenergic signaling

Voltage-gated calcium channels (VGCCs) are the predominant source of calcium influx in the heart leading to calcium-induced calcium release and ultimately excitation-contraction coupling. In the heart, VGCCs are modulated by the β-adrenergic signaling. Signaling through β-adrenergic receptors (βARs) and modulation of VGCCs by β-adrenergic signaling in the heart are critical signaling and changes to these have been significantly implicated in heart failure. However, data related to calcium channel dysfunction in heart failure is divergent and contradictory ranging from reduced function to no change in the calcium current. Many recent studies have highlighted the importance of functional and spatial microdomains in the heart and that may be the key to answer several puzzling questions. In this review, we have briefly discussed the types of VGCCs found in heart tissues, their structure, and significance in the normal and pathological condition of the heart. More importantly, we have reviewed the modulation of VGCCs by βARs in normal and pathological conditions incorporating functional and structural aspects. There are different types of βARs, each having their own significance in the functioning of the heart. Finally, we emphasize the importance of location of proteins as it relates to their function and modulation by co-signaling molecules. Its implication on the studies of heart failure is speculated.

N-Acetylcysteine Attenuates the Development of Renal Fibrosis in Transgenic Mice with Dilated Cardiomyopathy

Mechanisms underlying the renal pathology in cardiorenal syndrome (CRS) type 2 remain elusive. We hypothesised that renal glutathione deficiency is central to the development of CRS type 2. Glutathione precursor, N-acetylcysteine (NAC;40 mg/kg/day; 8 weeks) or saline were administered to transgenic mice with dilated cardiomyopathy (DCM) and wild-type (WT) controls. Cardiac structure, function and glutathione levels were assessed at the end of this protocol. Renal fibrosis, glutathione content, expression of inflammatory and fibrotic markers, and function were also evaluated. In both genotypes, NAC had minimal effect on cardiac glutathione, structure and function (P ≥ 0.20). In NAC treated DCM mice, loss of glomerular filtration rate (GFR), tubulointerstitial and glomerular fibrosis and renal oxidised glutathione levels were attenuated by 38%, 99%, 70% and 52% respectively, compared to saline treated DCM mice (P ≤ 0.01). Renal expression of PAI-1 was greater in saline treated DCM mice than in WT mice (P < 0.05). Renal PAI-1 expression was less in NAC treated DCM mice than in vehicle treated DCM mice (P = 0.03). Renal IL-10 expression was greater in the former cohort compared to the latter (P < 0.01). These data indicate that normalisation of renal oxidized glutathione levels attenuates PAI-1 expression and renal inflammation preventing loss of GFR in experimental DCM.

G protein, phosphorylated-GATA4 and VEGF expression in the hearts of transgenic mice overexpressing β1- and β2-adrenergic receptors

β₁- and β₂-adrenergic receptors (ARs) regulate cardiac contractility, calcium handling and protein phosphorylation. The present study aimed to examine the expression levels of vascular endothelial growth factor A (VEGF-A) and several G proteins, and the phosphorylation of transcription factor GATA binding protein 4 (GATA4), by western blot analysis, using isolated hearts from 6 month-old transgenic (TG) mice that overexpress β₁AR or β₂AR. Cardiac contractility/relaxation and heart rate was increased in both β₁AR TG and β₂AR TG mouse hearts compared with wild type; however, no significant differences were observed between the β₁- and β₂AR TG mouse hearts. Protein expression levels of inhibitory guanine nucleotide-binding protein (Gi) 2, Gi3 and G-protein-coupled receptor kinase 2 were upregulated in both TG mice, although the upregulation of Gi2 was more prominent in the β₂AR TG mice. VEGF-A expression levels were also increased in both TG mice, and were highest in the β₁AR TG mice. In addition, the levels of phosphorylated-GATA4 expression were increased in β₁- and β₂AR TG mice. In conclusion, the present study demonstrated that cardiac contractility/relaxation and heart rate is increased in β₁AR TG and β₂AR TG mice, and indicated that this increase may be related to the overexpression of G proteins and G-protein-associated proteins.

High-fat diet induces protein kinase A and G-protein receptor kinase phosphorylation of β2 -adrenergic receptor and impairs cardiac adrenergic reserve in animal hearts

Key points

Patients with diabetes show a blunted cardiac inotropic response to β‐adrenergic stimulation despite normal cardiac contractile reserve.

Acute insulin stimulation impairs β‐adrenergically induced contractile function in isolated cardiomyocytes and Langendorff‐perfused hearts.

In this study, we aimed to examine the potential effects of hyperinsulinaemia associated with high‐fat diet (HFD) feeding on the cardiac β₂‐adrenergic receptor signalling and the impacts on cardiac contractile function.

We showed that 8 weeks of HFD feeding leads to reductions in cardiac functional reserve in response to β‐adrenergic stimulation without significant alteration of cardiac structure and function, which is associated with significant changes in β₂‐adrenergic receptor phosphorylation at protein kinase A and G‐protein receptor kinase sites in the myocardium.

The results suggest that clinical intervention might be applied to subjects in early diabetes without cardiac symptoms to prevent further cardiac complications.

Abstract

Patients with diabetes display reduced exercise capability and impaired cardiac contractile reserve in response to adrenergic stimulation. We have recently uncovered an insulin receptor and adrenergic receptor signal network in the heart. The aim of this study was to understand the impacts of high‐fat diet (HFD) on the insulin–adrenergic receptor signal network in hearts. After 8 weeks of HFD feeding, mice exhibited diabetes, with elevated insulin and glucose concentrations associated with body weight gain. Mice fed an HFD had normal cardiac structure and function. However, the HFD‐fed mice displayed a significant elevation of phosphorylation of the β₂‐adrenergic receptor (β₂AR) at both the protein kinase A site serine 261/262 and the G‐protein‐coupled receptor kinase site serine 355/356 and impaired adrenergic reserve when compared with mice fed on normal chow. Isolated myocytes from HFD‐fed mice also displayed a reduced contractile response to adrenergic stimulation when compared with those of control mice fed normal chow. Genetic deletion of the β₂AR led to a normalized adrenergic response and preserved cardiac contractile reserve in HFD‐fed mice. Together, these data indicate that HFD promotes phosphorylation of the β₂AR, contributing to impairment of cardiac contractile reserve before cardiac structural and functional remodelling, suggesting that early intervention in the insulin–adrenergic signalling network might be effective in prevention of cardiac complications in diabetes.

Patients with diabetes show a blunted cardiac inotropic response to β‐adrenergic stimulation despite normal cardiac contractile reserve.

Acute insulin stimulation impairs β‐adrenergically induced contractile function in isolated cardiomyocytes and Langendorff‐perfused hearts.

In this study, we aimed to examine the potential effects of hyperinsulinaemia associated with high‐fat diet (HFD) feeding on the cardiac β₂‐adrenergic receptor signalling and the impacts on cardiac contractile function.

We showed that 8 weeks of HFD feeding leads to reductions in cardiac functional reserve in response to β‐adrenergic stimulation without significant alteration of cardiac structure and function, which is associated with significant changes in β₂‐adrenergic receptor phosphorylation at protein kinase A and G‐protein receptor kinase sites in the myocardium.

The results suggest that clinical intervention might be applied to subjects in early diabetes without cardiac symptoms to prevent further cardiac complications.

Osborne-Mendel rats simultaneously develop cardiac and renal dysfunction, left atrial thrombosis, peripheral artery occlusion, and ascending aortic dissection

Although chronic kidney disease (CKD) is strongly associated with onsets of cardiovascular disease (CVD), the pathogenic mechanism between these diseases has not been fully understood. To develop and validate new therapeutic strategies for this complication, appropriate experimental models that reflect the complexity of the underlying pathophysiology are needed. The Osborne-Mendel (OM) rat was identified as an atherosclerosis-prone and a premature-death rat strain among 16 inbred rat strains when fed high-cholesterol containing diet. When fed high-cholesterol diet, OM rats showed simultaneous occurrence of aortic aneurysm, aortic dissection, peripheral artery occlusion, and left atrial thrombosis. OM rats had significantly lower max dP/dt and higher min dP/dt than F344 rats did, indicating impaired left ventricle contractility and relaxation. OM rats developed renal dysfunction, showing increased urinary albumin excretion. OM rats also showed mild hypertension, decreased endothelial function, and enhanced coagulation and platelet aggregation, compared with F344 rats. We now report that OM rat would be a novel spontaneous animal model which simultaneously demonstrates cardiac and renal dysfunction, and CVD events. This model could be a useful model for the pre-clinical testing of pharmacological therapies and could provide new insight into potential targets and pathways for the treatment of CKD and CVD.

Cardiac physiologic regulation of sub-type specific adrenergic receptors in transgenic mice overexpressing β1- and β2-adrenergic receptors

Objective

Combination of β₁-adrenergic receptor (AR) blockade and β₂-AR activation might be a potential novel therapy for treating heart failure. However, use of β-AR agonists and/or antagonists in the clinical setting is controversial because of the lack of information on cardiac inotropic or chronotropic regulation by AR signaling.

Methods

In this study, we performed hemodynamic evaluation by examining force frequency response (FFR), Frank-Starling relationship, and response to a non-selective β-AR agonist (isoproterenol) in hearts isolated from 6-month-old transgenic (TG) mice overexpressing β₁- and β₂-ARs (β₁- and β₂-AR TG mice, respectively).

Results

Cardiac physiologic consequences of β₁- and β₂-AR overexpression resulted in similar maximal response to isoproterenol and faster temporary decline of positive inotropic response in β₂-AR TG mice. β₁-AR TG mice showed a pronounced negative limb of FFR, whereas β₂-AR TG mice showed high stimulation frequencies with low contractile depression during FFR. In contrast, Frank-Starling relationship was equally enhanced in both β₁- and β₂-AR TG mice.

Conclusion

Hemodynamic evaluation performed in the present showed a difference in β₁- and β₂-AR signaling, which may be due to the difference in the desensitization of β₁- and β₂-ARs.

Disruption of Epac1 protects the heart from adenylyl cyclase type 5-mediated cardiac dysfunction

Type 5 adenylyl cyclase (AC5) plays an important role in the development of chronic catecholamine stress-induced heart failure and arrhythmia in mice. Epac (exchange protein activated by cAMP), which is directly activated by cAMP independent of protein kinase A, has been recently identified as a novel mediator of cAMP signaling in the heart. However, the role of Epac in AC5-mediated cardiac dysfunction and arrhythmias remains poorly understood. We therefore generated AC5 transgenic mice (AC5TG) with selective disruption of the Epac1 gene (AC5TG-Epac1KO), and compared their phenotypes with those of AC5TG after chronic isoproterenol (ISO) infusion. Decreased cardiac function as well as increased susceptibility to pacing-induced atrial fibrillation (AF) in response to ISO were significantly attenuated in AC5TG-Epac1KO mice, compared to AC5TG mice. Increased cardiac apoptosis and cardiac fibrosis were also concomitantly attenuated in AC5TG-Epac1KO mice compared to AC5TG mice. These findings indicate that Epac1 plays an important role in AC5-mediated cardiac dysfunction and AF susceptibility.

N-acetylcysteine attenuates the development of cardiac fibrosis and remodeling in a mouse model of heart failure

Oxidative stress plays a central role in the pathogenesis of heart failure. We aimed to determine whether the antioxidant N‐acetylcysteine can attenuate cardiac fibrosis and remodeling in a mouse model of heart failure. Minipumps were implanted subcutaneously in wild‐type mice (n = 20) and mice with cardiomyopathy secondary to cardiac specific overexpression of mammalian sterile 20‐like kinase 1 (MST‐1; n = 18) to administer N‐acetylcysteine (40 mg/kg per day) or saline for a period of 8 weeks. At the end of this period, cardiac remodeling and function was assessed via echocardiography. Fibrosis, oxidative stress, and expression of collagen types I and III were quantified in heart tissues. Cardiac perivascular and interstitial fibrosis were greater by 114% and 209%, respectively, in MST‐1 compared to wild type (P ≤ 0.001). In MST‐1 mice administered N‐acetylcysteine, perivascular and interstitial fibrosis were 40% and 57% less, respectively, compared to those treated with saline (P ≤ 0. 03). Cardiac oxidative stress was 119% greater in MST‐1 than in wild type (P < 0.001) and N‐acetylcysteine attenuated oxidative stress in MST‐1 by 42% (P = 0.005). These data indicate that N‐acetylcysteine can blunt cardiac fibrosis and related remodeling in the setting of heart failure potentially by reducing oxidative stress. This study provides the basis to investigate the role of N‐acetylcysteine in chronic heart failure.

Expressing an inhibitor of PLCβ1b sustains contractile function following pressure overload

The activity of phospholipase Cβ1b (PLCβ1b) is selectively elevated in failing myocardium and cardiac expression of PLCβ1b causes contractile dysfunction. PLCβ1b can be selectively inhibited by expressing a peptide inhibitor that prevents sarcolemmal localization. The inhibitory peptide, PLCβ1b-CT was expressed in heart from a mini-gene using adeno-associated virus (rAAV6-PLCβ1b-CT). rAAV6-PLCβ1b-CT, or blank virus, was delivered IV (4×10(9)vg/g body weight) and trans-aortic-constriction (TAC) or sham-operation was performed 8weeks later. Expression of PLCβ1b-CT prevented the loss of contractile function, eliminated lung congestion and improved survival following TAC with either a 'moderate' or 'severe' pressure gradient. Hypertrophy was attenuated but not eliminated. Expression of the PLCβ1b-CT peptide 2-3weeks after TAC reduced contractile dysfunction and lung congestion, without limiting hypertrophy. PLCβ1b inhibition ameliorates pathological responses following acute pressure overload. The targeting of PLCβ1b to the sarcolemma provides the basis for the development of a new class of inotropic agent.

Correlation between endogenous polyamines in human cardiac tissues and clinical parameters in patients with heart failure

Polyamines contribute to several physiological and pathological processes, including cardiac hypertrophy in experimental animals. This involves an increase in ornithine decarboxylase (ODC) activity and intracellular polyamines associated with cyclic adenosine monophosphate (cAMP) increases. The aim of the study was to establish the role of these in the human heart in living patients. For this, polyamines (by high performance liquid chromatography) and the activity of ODC and N¹‐acetylpolyamine oxidases (APAO) were determined in the right atrial appendage of 17 patients undergoing extracorporeal circulation to correlate with clinical parameters. There existed enzymatic activity associated with the homeostasis of polyamines. Left atria size was positively associated with ODC (r = 0.661, P = 0.027) and negatively with APAO‐N¹‐acetylspermine (r = −0.769, P = 0.026), suggesting that increased levels of polyamines are associated with left atrial hemodynamic overload. Left ventricular ejection fraction (LVEF) and heart rate were positively associated with spermidine (r = 0.690, P = 0.003; r = 0.590, P = 0.021) and negatively with N¹‐acetylspermidine (r = −0.554, P = 0.032; r = −0.644, P = 0.018). LVEF was negatively correlated with cAMP levels (r = −0.835, P = 0.001) and with cAMP/ODC (r = −0.794, P = 0.011), cAMP/spermidine (r = −0.813, P = 0.001) and cAMP/spermine (r = −0.747, P = 0.003) ratios. Abnormal LVEF patients showed decreased ODC activity and spermidine, and increased N¹‐acetylspermidine, and cAMP. Spermine decreased in congestive heart failure patients. The trace amine isoamylamine negatively correlated with septal wall thickness (r = −0.634, P = 0.008) and was increased in cardiac heart failure. The results indicated that modifications in polyamine homeostasis might be associated with cardiac function and remodelling. Increased cAMP might have a deleterious effect on function. Further studies should confirm these findings and the involvement of polyamines in different stages of heart failure.

The atypical 'b' splice variant of phospholipase Cβ1 promotes cardiac contractile dysfunction

The activity of the early signaling enzyme, phospholipase Cβ1b (PLCβ1b), is selectively elevated in diseased myocardium and activity increases with disease progression. We aimed to establish the contribution of heightened PLCβ1b activity to cardiac pathology. PLCβ1b, the alternative splice variant, PLCβ1a, and a blank virus were expressed in mouse hearts using adeno-associated viral vectors (rAAV6-FLAG-PLCβ1b, rAAV6-FLAG-PLCβ1a, or rAAV6-blank) delivered intravenously (IV). Following viral delivery, FLAG-PLCβ1b was expressed in all of the chambers of the mouse heart and was localized to the sarcolemma. Heightened PLCβ1b expression caused a rapid loss of contractility, 4-6 weeks, that was fully reversed, within 5 days, by inhibition of protein kinase Cα (PKCα). PLCβ1a did not localize to the sarcolemma and did not affect contractile function. Expression of PLCβ1b, but not PLCβ1a, caused downstream dephosphorylation of phospholamban and depletion of the Ca(2+) stores of the sarcoplasmic reticulum. We conclude that heightened PLCβ1b activity observed in diseased myocardium contributes to pathology by PKCα-mediated contractile dysfunction. PLCβ1b is a cardiac-specific signaling system, and thus provides a potential therapeutic target for the development of well-tolerated inotropic agents for use in failing myocardium.

Pathological hypertrophy reverses β2-adrenergic receptor-induced angiogenesis in mouse heart

β-adrenergic activation and angiogenesis are pivotal for myocardial function but the link between both events remains unclear. The aim of this study was to explore the cardiac angiogenesis profile in a mouse model with cardiomyocyte-restricted overexpression of β₂-adrenoceptors (β₂-TG), and the effect of cardiac pressure overload. β₂-TG mice had heightened cardiac angiogenesis, which was essential for maintenance of the hypercontractile phenotype seen in this model. Relative to controls, cardiomyocytes of β₂-TGs showed upregulated expression of vascular endothelial growth factor (VEGF), heightened phosphorylation of cAMP-responsive-element-binding protein (CREB), and increased recruitment of phospho-CREB, CREB-binding protein (CBP), and p300 to the VEGF promoter. However, when hearts were subjected to pressure overload by transverse aortic constriction (TAC), angiogenic signaling in β₂-TGs was inhibited within 1 week after TAC. β₂-TG hearts, but not controls, exposed to pressure overload for 1–2 weeks showed significant increases from baseline in phosphorylation of Ca²⁺/calmodulin-dependent kinase II (CaMKIIδ) and protein expression of p53, reduction in CREB phosphorylation, and reduced abundance of phospho-CREB, p300 and CBP recruited to the CREB-responsive element (CRE) site of VEGF promoter. These changes were associated with reduction in both VEGF expression and capillary density. While non-TG mice with TAC developed compensatory hypertrophy, (₂-TGs exhibited exaggerated hypertrophic growth at week-1 post-TAC, followed by LV dilatation and reduced fractional shortening measured by serial echocardiography. In conclusion, angiogenesis was enhanced by the cardiomyocyte (₂AR/CREB/VEGF signaling pathway. Pressure overload rapidly inhibited this signaling, likely as a consequence of activated CaMKII and p53, leading to impaired angiogenesis and functional decompensation.

Chronic activation of the low affinity site of β1-adrenoceptors stimulates haemodynamics but exacerbates pressure-overload cardiac remodelling

BACKGROUND AND PURPOSE

The β1-adrenoceptor has at least two binding sites, high and low affinity sites (β1H and β1L, respectively), which mediate cardiostimulation. While β1H-adrenoceptor can be blocked by all clinically used β-blockers, β1L-adrenoceptor is relatively resistant to blockade. Thus, chronic β1L-adrenoceptor activation may mediate persistent cardiostimulation, despite the concurrent blockade of β1H-adrenoceptors. Hence, it is important to determine the potential significance of β1L-adrenoceptors in vivo, particularly in pathological situations.

EXPERIMENTAL APPROACH

C57Bl/6 male mice were used. Chronic (4 or 8 weeks) β1L-adrenoceptor activation was achieved by treatment, via osmotic mini pumps, with (-)-CGP12177 (10 mg·kg(-1)·day(-1)). Cardiac function was assessed by echocardiography and micromanometry.

KEY RESULTS

(-)-CGP12177 treatment of healthy mice increased heart rate and left ventricular (LV) contractility. (-)-CGP12177 treatment of mice subjected to transverse aorta constriction (TAC), during weeks 4-8 or 4-12 after TAC, led to a positive inotropic effect and exacerbated fibrogenic signalling while cardiac hypertrophy tended to be more severe. (-)-CGP12177 treatment of mice with TAC also exacerbated the myocardial expression of hypertrophic, fibrogenic and inflammatory genes compared to untreated TAC mice. Washout of (-)-CGP12177 revealed a more pronounced cardiac dysfunction after 12 weeks of TAC.

CONCLUSIONS AND IMPLICATIONS

β1L-adrenoceptor activation provides functional support to the heart, in both normal and pathological (pressure overload) situations. Sustained β1L-adrenoceptor activation in the diseased heart exacerbates LV remodelling and therefore may promote disease progression from compensatory hypertrophy to heart failure.

Inhibiting mitochondrial Na+/Ca2+ exchange prevents sudden death in a Guinea pig model of heart failure

RATIONALE

In cardiomyocytes from failing hearts, insufficient mitochondrial Ca(2+) accumulation secondary to cytoplasmic Na(+) overload decreases NAD(P)H/NAD(P)(+) redox potential and increases oxidative stress when workload increases. These effects are abolished by enhancing mitochondrial Ca(2+) with acute treatment with CGP-37157 (CGP), an inhibitor of the mitochondrial Na(+)/Ca(2+) exchanger.

OBJECTIVE

Our aim was to determine whether chronic CGP treatment mitigates contractile dysfunction and arrhythmias in an animal model of heart failure (HF) and sudden cardiac death (SCD).

METHODS AND RESULTS

Here, we describe a novel guinea pig HF/SCD model using aortic constriction combined with daily β-adrenergic receptor stimulation (ACi) and show that chronic CGP treatment (ACi plus CGP) attenuates cardiac hypertrophic remodeling, pulmonary edema, and interstitial fibrosis and prevents cardiac dysfunction and SCD. In the ACi group 4 weeks after pressure overload, fractional shortening and the rate of left ventricular pressure development decreased by 36% and 32%, respectively, compared with sham-operated controls; in contrast, cardiac function was completely preserved in the ACi plus CGP group. CGP treatment also significantly reduced the incidence of premature ventricular beats and prevented fatal episodes of ventricular fibrillation, but did not prevent QT prolongation. Without CGP treatment, mortality was 61% in the ACi group <4 weeks of aortic constriction, whereas the death rate in the ACi plus CGP group was not different from sham-operated animals.

CONCLUSIONS

The findings demonstrate the critical role played by altered mitochondrial Ca(2+) dynamics in the development of HF and HF-associated SCD; moreover, they reveal a novel strategy for treating SCD and cardiac decompensation in HF.

Genetic maneuvers to ameliorate ventricular function in heart failure: therapeutic potential and future implications

Gene therapy to treat heart failure has evolved into a growing field of investigation yielding remarkable results in preclinical models. Whether these results will persist in clinical trials remains to be seen. However, researchers still face a number of obstacles that need to be overcome before this treatment can be employed effectively. Efforts are required to identify better vectors with minimal side effects and maximal efficiency and durability. There is also a need to develop less invasive and more effective techniques to deliver these vectors. This review will discuss different methods to achieve these goals, the various pathologic mechanisms that have been targeted so far and those with strong potential for use in the future.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Carvedilol: a third-generation β-blocker should be a first-choice β-blocker

β-Blockers are a standard of care in many clinical settings such as acute myocardial infarction, heart failure and patients at risk for a coronary event. However, not all β-blockers are the same and they vary in properties such as lipophilicity, metabolic profile, receptor inhibition, hemodynamics, tolerability and antioxidant/anti-inflammatory effects. It has been unclear whether these differences affect outcomes or if one β-blocker should be preferred over another. This review will summarize the properties of metoprolol, atenolol and carvedilol, as well as comparative experimental and clinical trials between these agents. We will provide compelling evidence of why carvedilol should be a first-line β-blocker and why it offers many advantages over the β1-selective β-blockers.

Ventricular function during exercise in mice and rats

The mouse has many advantages over other experimental models for the molecular investigation of left ventricular (LV) function. Accordingly, there is a keen interest in, as well as an intense need for, a conscious, chronically instrumented, freely moving mouse model for the determination of cardiac function. To address this need, we used a telemetry device for repeated measurements of LV function in conscious mice at rest and during exercise. For reference, we compared the responses in mice to the responses in identically instrumented conscious rats. The transmitter body of the telemetry device (rat PA-C40; mouse PA-C10; Data Sciences International, St. Paul, MN) was placed in the intraperitoneal space through a ventral abdominal approach (rat) or subcutaneously on the left flank (mouse). The pressure sensor, located within the tip of a catheter, was inserted into the left ventricle through an apical stab wound (18 gauge for rat; 21 gauge for mouse) for continuous, nontethered, recordings of pulsatile LV pressure. A minimum of 1 wk was allowed for recovery and for the animals to regain their presurgical weight. During the recovery period, the animals were handled, weighed, and acclimatized to the laboratory, treadmill, and investigators. Subsequently, LV parameters were recorded at rest and during a graded exercise test. The results document, for the first time, serial assessment of ventricular function during exercise in conscious mice and rats. This methodology may be adopted for advancing the concepts and ideas that drive cardiovascular research.

Cardiac pressure overload hypertrophy is differentially regulated by β-adrenergic receptor subtypes

In isolated myocytes, hypertrophy induced by norepinephrine is mediated via α(1)-adrenergic receptors (ARs) and not β-ARs. However, mice with deletions of both major cardiac α(1)-ARs still develop hypertrophy in response to pressure overload. Our purpose was to better define the role of β-AR subtypes in regulating cardiac hypertrophy in vivo, important given the widespread clinical use of β-AR antagonists and the likelihood that patients treated with these agents could develop conditions of further afterload stress. Mice with deletions of β(1), β(2), or both β(1)- and β(2)-ARs were subjected to transverse aortic constriction (TAC). After 3 wk, β(1)(-/-) showed a 21% increase in heart to body weight vs. sham controls, similar to wild type, whereas β(2)(-/-) developed exaggerated (49% increase) hypertrophy. Only when both β-ARs were ablated (β(1)β(2)(-/-)) was hypertrophy totally abolished. Cardiac function was preserved in all genotypes. Several known inhibitors of cardiac hypertrophy (FK506 binding protein 5, thioredoxin interacting protein, and S100A9) were upregulated in β(1)β(2)(-/-) compared with the other genotypes, whereas transforming growth factor-β(2), a positive mediator of hypertrophy was upregulated in all genotypes except the β(1)β(2)(-/-). In contrast to recent reports suggesting that angiogenesis plays a critical role in regulating cardiac hypertrophy-induced heart failure, we found no evidence that angiogenesis or its regulators (VEGF, Hif1α, and p53) play a role in compensated cardiac hypertrophy. Pressure overload hypertrophy in vivo is dependent on a coordination of signaling through both β(1)- and β(2)-ARs, mediated through several key cardiac remodeling pathways. Angiogenesis is not a prerequisite for compensated cardiac hypertrophy.

β₂-Adrenoceptors, NADPH oxidase, ROS and p38 MAPK: another 'radical' road to heart failure?

Persistent activation of the cardiac β-adrenergic system may contribute to the pathogenesis of congestive heart failure. Both β₁- and β₂-adrenoceptors are known to mediate these noxious effects, yet the β₁-adrenoceptor-PKA axis has received greater attention with less information available on β₂-adrenoceptor driven pathways. In the present issue, Xu and colleagues provide new evidence, showing that β₂-adrenoceptor over-expression leads to increased reactive oxygen species (ROS) emission, mainly caused by up-regulation of reduced nicotinamide adenine dinucleotide phosphate oxidase (Nox) 2 and 4. Increase in ROS levels is accompanied by p38 mitogen-activated protein kinase activation, fibrosis, apoptosis and cardiac dysfunction. Both Nox inhibition and administration of the antioxidant N-acetyl cysteine prevent these adverse effects. Interestingly, antioxidant treatment also prevents the increase in Nox expression, suggesting that β₂-adrenoceptor stimulation triggers a vicious cycle eventually amplified by both Nox isoforms. The possible existence of a circuitry to enhance ROS signalling and detrimental consequences on myocardial remodelling are also discussed, in light of the recent description of intracellular localization of Nox4.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Does aortic valve replacement mitigate the risk of preoperative heart failure?

Congestive heart failure complicating aortic valve disease has been reported to increase the operative mortality associated with aortic valve replacement. To determine whether this adverse effect remains late after aortic valve replacement, we analyzed prospectively collected and survival data of 849 patients who underwent aortic valve replacement between 1999 and 2008. There were 243 (29%) cases of heart failure preoperatively (138 current and 105 prior). Both operative and late mortality rates (up to 10 years) were significantly higher in heart failure patients. Current congestive heart failure caused a 3-fold increase in operative mortality and an 86% increase in late mortality, whereas previous history of heart failure caused a doubling of late mortality. Preoperative heart failure still compromises early and late survival after aortic valve replacement. Surgery should be considered early in patients with aortic valve disease and deferred, when possible, in those with frank heart failure.

PI3K(p110 alpha) protects against myocardial infarction-induced heart failure: identification of PI3K-regulated miRNA and mRNA

OBJECTIVE

Myocardial infarction (MI) is a serious complication of atherosclerosis associated with increasing mortality attributable to heart failure. Activation of phosphoinositide 3-kinase [PI3K(p110 alpha)] is considered a new strategy for the treatment of heart failure. However, whether PI3K(p110 alpha) provides protection in a setting of MI is unknown, and PI3K(p110 alpha) is difficult to target because it has multiple actions in numerous cell types. The goal of this study was to assess whether PI3K(p110 alpha) is beneficial in a setting of MI and, if so, to identify cardiac-selective microRNA and mRNA that mediate the protective properties of PI3K(p110 alpha).

METHODS AND RESULTS

Cardiomyocyte-specific transgenic mice with increased or decreased PI3K(p110 alpha) activity (caPI3K-Tg and dnPI3K-Tg, respectively) were subjected to MI for 8 weeks. The caPI3K-Tg subjected to MI had better cardiac function than nontransgenic mice, whereas dnPI3K-Tg had worse function. Using microarray analysis, we identified PI3K-regulated miRNA and mRNA that were correlated with cardiac function, including growth factor receptor-bound 14. Growth factor receptor-bound 14 is highly expressed in the heart and positively correlated with PI3K(p110 alpha) activity and cardiac function. Mice deficient in growth factor receptor-bound 14 have cardiac dysfunction.

CONCLUSIONS

Activation of PI3K(p110 alpha) protects the heart against MI-induced heart failure. Cardiac-selective targets that mediate the protective effects of PI3K(p110 alpha) represent new drug targets for heart failure.

Beta-receptor selectivity of carvedilol and metoprolol succinate in patients with heart failure (SELECT trial): a randomized dose-ranging trial

STUDY OBJECTIVE

To determine whether metoprolol succinate (a beta(1)-selective beta-blocker) remains beta(1)-selective compared with carvedilol (a nonselective beta-blocker) during upward titration of doses in patients with American College of Cardiology (ACC) stage C heart failure.

DESIGN

Prospective, randomized, parallel-arm study. Setting. General clinical research center.

PATIENTS

Twenty-five beta-blocker-naïve adults with New York Heart Association functional classes II or III heart failure (i.e., ACC stage C). Intervention. Patients received either immediate-release carvedilol 3.125 mg twice/day or controlled-release metoprolol succinate 25 mg once/day; doses were titrated upward by doubling the dose every 2 weeks until reaching a maximum tolerated dose or a goal dose of carvedilol 25 mg twice/day and metoprolol 200 mg/day. Before each dose titration, terbutaline (a beta-receptor agonist) was infused at 6 mg/kg over 1 hour for determination of beta(2)-blockade.

MEASUREMENTS AND MAIN RESULTS

Patients were studied at baseline and after each dose titration of metoprolol succinate (at 25, 50, 100, and 200 mg once/day) and immediate-release carvedilol (at 3.125, 6.25, 12.5, and 25 mg twice/day). Glucose and potassium concentrations were measured twice serially at baseline, every 10 minutes during infusion, every 15 minutes for the first hour after infusion, and every 30 minutes for the second hour after infusion. The median area under the concentration-time curve (AUC) was calculated for changes in glucose and potassium concentrations. As assessed by glucose AUC, there was no significant difference in the degree of beta(2)-blockade between metoprolol 200 mg and carvedilol 25 mg. In contrast to these data, the degree of beta(2)-blockade as assessed by potassium AUC was greater for carvedilol compared with metoprolol across all doses.

CONCLUSION

In this ACC stage C heart failure population, carvedilol was nonselective at all clinically relevant doses, whereas metoprolol succinate was beta(1)-selective at low doses and became progressively nonselective at higher doses.

Reduced phosphoinositide 3-kinase (p110alpha) activation increases the susceptibility to atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia presenting at cardiology departments. A limited understanding of the molecular mechanisms responsible for the development of AF has hindered treatment strategies. The purpose of this study was to assess whether reduced activation of phosphoinositide 3-kinase (PI3K, p110alpha) makes the compromised heart susceptible to AF. Risk factors for AF, including aging, obesity, and diabetes, have been associated with insulin resistance that leads to depressed/defective PI3K signaling. However, to date, there has been no link between PI3K(p110alpha) and AF. To address this question, we crossed a cardiac-specific transgenic mouse model of dilated cardiomyopathy (DCM) with a cardiac-specific transgenic mouse expressing a dominant negative mutant of PI3K (dnPI3K; reduces PI3K activity). Adult ( approximately 4.5 months) double-transgenic (dnPI3K-DCM), single-transgenic (DCM-Tg, dnPI3K-Tg), and nontransgenic mice were subjected to morphological, functional/ECG, microarray, and biochemical analyses. dnPI3K-DCM mice developed AF and had depressed cardiac function as well as greater atrial enlargement and fibrosis than DCM-Tg mice. AF was not detected in other groups. Aged DCM-Tg mice ( approximately 15 months) with a similar phenotype to dnPI3K-DCM mice (4.5 months) did not develop AF, suggesting loss of PI3K activity directly contributed to the AF phenotype. Furthermore, increasing PI3K activity reduced atrial fibrosis and improved cardiac conduction in DCM-Tg mice. Finally, in atrial appendages from patients with AF, PI3K activation was lower compared with tissue from patients in sinus rhythm. These results suggest a link between PI3K(p110alpha) and AF.

Gene therapy in heart failure

With increasing knowledge of basic molecular mechanisms governing the development of heart failure (HF), the possibility of specifically targeting key pathological players is evolving. Technology allowing for efficient in vivo transduction of myocardial tissue with long-term expression of a transgene enables translation of basic mechanistic knowledge into potential gene therapy approaches. Gene therapy in HF is in its infancy clinically with the predominant amount of experience being from animal models. Nevertheless, this challenging and promising field is gaining momentum as recent preclinical studies in larger animals have been carried out and, importantly, there are 2 newly initiated phase I clinical trials for HF gene therapy. To put it simply, 2 parameters are needed for achieving success with HF gene therapy: (1) clearly identified detrimental/beneficial molecular targets; and (2) the means to manipulate these targets at a molecular level in a sufficient number of cardiac cells. However, several obstacles do exist on our way to efficient and safe gene transfer to human myocardium. Some of these obstacles are discussed in this review; however, it primarily focuses on the molecular target systems that have been subjected to intense investigation over the last decade in an attempt to make gene therapy for human HF a reality.

Endogenous relaxin does not affect chronic pressure overload-induced cardiac hypertrophy and fibrosis

The effect of endogenous relaxin on the development of cardiac hypertrophy, dysfunction, and fibrosis remains completely unknown. We addressed this question by subjecting relaxin-1 deficient (Rln1-/-) and littermate control (Rln1+/+) mice of both genders to chronic transverse aortic constriction (TAC). The extent of left ventricular (LV) remodeling and dysfunction were studied by serial echocardiography over an 8-wk period and by micromanometry. The degree of hypertrophy was estimated by LV weight, cardiomyocyte size, and expression of relevant genes. Cardiac fibrosis was determined by hydroxyproline assay and quantitative histology. Expression of endogenous relaxin during the course of TAC was also examined. In response to an 8-wk period of pressure overload, TAC mice of both genotypes developed significant LV hypertrophy, fibrosis, hypertrophy related gene profile, and signs indicating congestive heart failure when compared with respective sham controls. The severity of these alterations was not statistically different between the two genotypes of either gender. Relaxin mRNA expression was up-regulated, whereas that of its receptor was unchanged in the hypertrophic myocardium of wild-type mice. Collectively, the extent of pressure overload-induced LV hypertrophy, fibrosis, and dysfunction were comparable between Rln1+/+ and Rln1-/- mice. Thus, although up-regulated in its expression, endogenous relaxin had no significant effect on the progression of cardiac maladaptation and dysfunction in the setting of chronic pressure overload.

Knockout of beta(1)- and beta(2)-adrenoceptors attenuates pressure overload-induced cardiac hypertrophy and fibrosis

BACKGROUND AND PURPOSE

The role of beta-adrenoceptors in heart disease remains controversial. Although beta-blockers ameliorate the progression of heart disease, the mechanism remains undefined. We investigated the effect of beta-adrenoceptors on cardiac hypertrophic growth using beta(1)- and beta(2)-adrenoreceptor knockout and wild-type (WT) mice.

EXPERIMENTAL APPROACH

Mice were subjected to aortic banding or sham surgery, and their cardiac function was determined by echocardiography and micromanometry.

KEY RESULTS

At 4 and 12 weeks after aortic banding, the left ventricle:body mass ratio was increased by 80-87% in wild-type mice, but only by 15% in knockouts, relative to sham-operated groups. Despite the blunted hypertrophic growth, ventricular function in knockouts was maintained. WT mice responded to pressure overload with up-regulation of gene expression of inflammatory cytokines and fibrogenic growth factors, and with severe cardiac fibrosis. All these effects were absent in the knockout animals.

CONCLUSION AND IMPLICATIONS

Our findings of a markedly attenuated cardiac hypertrophy and fibrosis following pressure overload in this knockout model emphasize that beta-adrenoceptor signalling plays a central role in cardiac hypertrophy and maladaptation following pressure overload.

Adenovirus-mediated delivery of relaxin reverses cardiac fibrosis

We have evaluated the effectiveness of systemic adenovirally delivered mouse relaxin on reversing fibrosis in a transgenic murine model of fibrotic cardiomyopathy due to beta(2)-adrenergic receptor (beta(2)AR) overexpression. Recombinant adenoviruses expressing green fluorescent protein (Ad-GFP), rat relaxin (Ad-rRLN) and mouse relaxin (Ad-mRLN) were generated and Ad-rRLN and Ad-mRLN were demonstrated to direct the expression of bioactive relaxin peptides in vitro. A single systemic injection of Ad-mRLN resulted in transgene expression in the liver and bioactive relaxin peptide in the plasma. Ad-mRLN, but not Ad-GFP, treatment reversed the increased left ventricular collagen content in beta(2)AR mice to control levels without affecting collagen levels in other heart chambers or in the lung and kidney. Hence a single systemic injection of adenovirus producing mouse relaxin reverses cardiac fibrosis without adversely affecting normal collagen levels in other organs and establishes the potential for the use of relaxin gene therapy for the treatment of cardiac fibrosis.

Genetically changed mice with chronic deficiency or overexpression of the β-adrenoceptors—what can we learn for the therapy of heart failure?

Heart failure is one of the most common medical diseases-almost every third 55-year-old person in the Western world is going to develop heart failure in his or her life. The development of heart failure is associated with pivotal restructuring of the beta-adrenergic system. The beta-adrenoceptor antagonists have emerged to be an essential part of the therapy of chronic heart failure. Three different beta-adrenoceptors could be identified and characterized so far. The beta1-adrenoceptors are being down-regulated, while the beta3-adrenoceptors are being up-regulated. The mechanisms that are responsible for the positive impact of beta-adrenoceptor antagonists are not completely understood up to now. Therefore, it is necessary to point out the crucial role of the beta-adrenergic system for the regulation of the cardiovascular system and the pathogenesis of heart failure. In the recent couple of years, numerous transgenic mouse models have proven to be helpful to gain a better understanding of the function and the relevance of these receptors. This review gives an overview of the pathophysiological relevance of the beta-adrenergic system for heart failure and outlines the most important insights concerning heart function, which could be derived from genetically changed mice with chronic deficiency and overexpression of the beta-adrenoceptor.

OPTIMIZING DOSAGE OF KETAMINE AND XYLAZINE IN MURINE ECHOCARDIOGRAPHY

1. Ketamine and xylazine (KX) mixture is the most commonly used anaesthetic drug during echocardiography in mice to induce sedation and immobility. Nevertheless, the doses of KX reported in the literature vary substantially with associated significant difference in cardiac function. To explore the optimal KX dosage and observation time for murine echocardiography, we compared the effects of various KX combinations on echocardiographic measurement. 2. Mice were anaesthetized with ketamine (50 or 100 mg/kg) and xylazine (0-10 mg/kg). Echocardiography was performed 5, 10, 20 and 40 min after induction of anaesthesia. Also, cardiac function was assessed in mice with and without pressure-overload induced left ventricle (LV) hypertrophy and dysfunction, either under anaesthesia with KX or whilst conscious. 3. Ketamine at 100 mg/kg alone or together with xylazine at 0.1 mg/kg was associated with a high and stable heart rate (HR), a high fractional shortening (FS) and produced the least effect on LV inner dimension at end of diastole (LVIDd). Ketamine and xylazine at 100 and 10 mg/kg, respectively, produced a lower and stable FS, but with a low and unstable HR. All other combinations resulted in depressed and unstable cardiac function during this period. 4. The dose-dependent suppression of FS by xylazine was counteracted partly by ketamine. 5. Although in the chronic pressure-overload model LV hypertrophy can be detected accurately in both the anaesthetized or conscious state, systolic dysfunction was masked partially by higher doses of xylazine (2.5 or 10 mg/kg) combined with ketamine at 100 mg/kg. 6. With KX anaesthesia, both the dose of xylazine and the anaesthetic duration are critical in achieving an ideal condition for murine echocardiography. Ketamine at 100 mg/kg alone produces acceptable anaesthesia, stable cardiac function with a minimal depressant effect and is therefore recommended if single-dose anaesthetic is to be used.

Down-regulation of mitofusin-2 expression in cardiac hypertrophy in vitro and in vivo

Mitofusin-2 (Mfn2) suppresses smooth muscle cell proliferation through inhibition of the Ras-extracellular signal-regulated kinases (ERK1/2) pathway. Since the ERK1/2 pathway is implicated in mediating hypertrophic signaling, we studied the changes in Mfn2 in cardiac hypertrophy using in vitro and in vivo models. Phenylephrine was used to induce hypertrophy in neonatal rat ventricular myocytes (NRVMs). In vivo hypertrophy models included spontaneously hypertensive rats (SHR), pressure-overload hypertrophy by transverse aortic constriction (TAC), hypertrophy of non-infarcted myocardium following myocardial infarction (MI), and cardiomyopathy due to cardiac-restricted overexpression of beta(2)-adrenergic receptors (beta(2)-TG). We determined hypertrophic parameters and analysed expression of atrial natriuretic peptide (ANP) and Mfn2 by real-time PCR. Phosphorylated-ERK1/2 (phospho-ERK) was measured by Western blot. Mfn2 was downregulated in phenylephrine treated NRCMs (by approximately 40%), hypertrophied hearts from SHR (by approximately 80%), mice with TAC (at 1 and 3 weeks, by approximately 50%), and beta(2)-TG mice (by approximately 20%). However, Mfn2 was not downregulated in hypertrophied hearts with 15 weeks of TAC, nor in hypertrophied non-infarcted myocardium following MI. phospho-ERK1/2 was increased in hypertrophied myocardium at 1 week post-TAC, but not in non-infarcted myocardium after MI, indicating that downregulated Mfn2 may be accompanied by an increase of phospho-ERK1/2. This study shows, for the first time, downregulated Mfn2 expression in hypertrophied hearts, which depends on the etiology and time course of hypertrophy. Further study is required to examine the causal relationship between Mfn2 and cardiac hypertrophy.