Segregation of atrial-specific and inducible expression of an atrial natriuretic factor transgene in an in vivo murine model of cardiac hypertrophy

SIRT5 deficiency suppresses mitochondrial ATP production and promotes AMPK activation in response to energy stress

Sirtuin 5 (SIRT5) is a member of the NAD+-dependent sirtuin family of protein deacylase that catalyzes removal of post-translational modifications, such as succinylation, malonylation, and glutarylation on lysine residues. In light of the SIRT5's roles in regulating mitochondrion function, we show here that SIRT5 deficiency leads to suppression of mitochondrial NADH oxidation and inhibition of ATP synthase activity. As a result, SIRT5 deficiency decreases mitochondrial ATP production, increases AMP/ATP ratio, and subsequently activates AMP-activated protein kinase (AMPK) in cultured cells and mouse hearts under energy stress conditions. Moreover, Sirt5 knockout attenuates transverse aortic constriction (TAC)-induced cardiac hypertrophy and cardiac dysfunction in mice, which is associated with decreased ATP level, increased AMP/ATP ratio and enhanced AMPK activation. Our study thus uncovers an important role of SIRT5 in regulating cellular energy metabolism and AMPK activation in response to energy stress.

GRK2 and GRK5 as therapeutic targets and their role in maladaptive and pathological cardiac hypertrophy

INTRODUCTION

One in every four deaths in the United States is attributed to cardiovascular disease, hence the development and employment of novel and effective therapeutics are necessary to improve the quality of life and survival of affected patient. Pathological hypertrophy is a maladaptive response by the heart to relieve wall stress that could result from cardiovascular disease. Maladaptive hypertrophy can lead to further disease progression and complications such as heart failure; hence, efforts to target hypertrophy to prevent and treat further morbidity and mortality are necessary. Areas covered: This review summarizes the compelling literature that describes the mechanistic role of GRK2 and GRK5 in maladaptive cardiac hypertrophy; it examines the approaches to inhibit these kinases in hypertrophic animal models and furthermore, it assesses the potential of GRK2 and GRK5 as therapeutic targets for hypertrophy. Expert opinion: GRK2 and GRK5 are novel therapeutic targets for pathological hypertrophy and may have added benefits of ameliorating morbidity and mortality. Despite the lesser researched role of GRK2 in cardiac hypertrophy, it may be the advantageous strategy for treating cardiac hypertrophy because of its role in other maladaptive pathways. Anti-GRK2 therapy optimization and the discovery and development of specific GRK2 and GRK5 small-molecule inhibitors is necessary for the eventual application of successful, effective therapeutics.

Combinatorial interactions of genetic variants in human cardiomyopathy

Dilated cardiomyopathy (DCM) is a leading cause of morbidity and mortality worldwide; yet how genetic variation and environmental factors impact DCM heritability remains unclear. Here, we report that compound genetic interactions between DNA sequence variants contribute to the complex heritability of DCM. By using genetic data from a large family with a history of DCM, we discovered that heterozygous sequence variants in the TROPOMYOSIN 1 (TPM1) and VINCULIN (VCL) genes cose-gregate in individuals affected by DCM. In vitro studies of patient-derived and isogenic human-pluripotent-stem-cell-derived cardio-myocytes that were genome-edited via CRISPR to create an allelic series of TPM1 and VCL variants revealed that cardiomyocytes with both TPM1 and VCL variants display reduced contractility and sarcomeres that are less organized. Analyses of mice genetically engineered to harbour these human TPM1 and VCL variants show that stress on the heart may also influence the variable penetrance and expressivity of DCM-associated genetic variants in vivo. We conclude that compound genetic variants can interact combinatorially to induce DCM, particularly when influenced by other disease-provoking stressors.

Chronic CaMKII inhibition reverses cardiac function and cardiac reserve in HF mice

AIMS

The present study was to explore the impact of KN93 - a specific inhibitor of CaMKII - on cardiac function and cardiac reserve in HF mice.

MAIN METHODS

We have generated pressure-overload HF mice using modified transverse aortic constriction (TAC) method. For acute inhibition (AI) experiment, HF mice were randomly divided into HF group, HF + KN93 AI group and HF + KN92 AI group, using sham mice as control. Mice in HF + KN93 AI group and HF + KN92 AI group were injected with CaMKII inhibitor KN93 or its inactive analogue KN92 on post-TAC day 15, while mice in HF group and Sham group were treated with saline. For chronic inhibition (CI) experiment, mice were injected daily with KN93, KN92 or saline for one week. At baseline and after isoproterenol (Iso) injection, in vivo cardiac function was assessed by echocardiography and left ventricular pressure-volume catheter.

KEY FINDINGS

Acute inhibition of CaMKII leads to decreased -dP/dtmin, increased EF, FS, longitudinal strain, longitudinal strain rate, ESPVR, dP/dtmax-EDV, PRSW, Tau and EDPVR, and unaltered reactivity to Iso in HF mice. Chronic inhibition results in increased EF, FS, longitudinal strain, longitudinal strain rate, ESPVR, dP/dtmax-EDV and PRSW, without alteration in -dP/dtmin, Tau and EDPVR. In addition, chronic inhibition reverses the effect of Iso on HF mice.

SIGNIFICANCE

Although acute CaMKII inhibition can repair systolic function in HF mice, it also exacerbates the diastolic function, whereas chronic inhibition improves both systolic function and cardiac reserve to β-adrenergic stimulation without impairing diastolic function.

A Mitochondrial Progesterone Receptor Increases Cardiac Beta-Oxidation and Remodeling

Progesterone is primarily a pregnancy-related hormone, produced in substantial quantities after ovulation and during gestation. Traditionally known to function via nuclear receptors for transcriptional regulation, there is also evidence of nonnuclear action. A previously identified mitochondrial progesterone receptor (PR-M) increases cellular respiration in cell models. In these studies, we demonstrated that expression of PR-M in rat H9c2 cardiomyocytes resulted in a ligand-dependent increase in oxidative cellular respiration and beta-oxidation. Cardiac expression in a TET-On transgenic mouse resulted in gene expression of myofibril proteins for remodeling and proteins involved in oxidative phosphorylation and fatty acid metabolism. In a model of increased afterload from constant transverse aortic constriction, mice expressing PR-M showed a ligand-dependent preservation of cardiac function. From these observations, we propose that PR-M is responsible for progesterone-induced increases in cellular energy production and cardiac remodeling to meet the physiological demands of pregnancy.

Mixed lineage kinase-3 prevents cardiac dysfunction and structural remodeling with pressure overload

Myocardial hypertrophy is an independent risk factor for heart failure (HF), yet the mechanisms underlying pathological cardiomyocyte growth are incompletely understood. The c-Jun NH2-terminal kinase (JNK) signaling cascade modulates cardiac hypertrophic remodeling, but the upstream factors regulating myocardial JNK activity remain unclear. In this study, we sought to identify JNK-activating molecules as novel regulators of cardiac remodeling in HF. We investigated mixed lineage kinase-3 (MLK3), a master regulator of upstream JNK-activating kinases, whose role in the remodeling process had not previously been studied. We observed increased MLK3 protein expression in myocardium from patients with nonischemic and hypertrophic cardiomyopathy and in hearts of mice subjected to transverse aortic constriction (TAC). Mice with genetic deletion of MLK3 (MLK3-/-) exhibited baseline cardiac hypertrophy with preserved cardiac function. MLK3-/- mice subjected to chronic left ventricular (LV) pressure overload (TAC, 4 wk) developed worsened cardiac dysfunction and increased LV chamber size compared with MLK3+/+ littermates ( n = 8). LV mass, pathological markers of hypertrophy ( Nppa, Nppb), and cardiomyocyte size were elevated in MLK3-/- TAC hearts. Phosphorylation of JNK, but not other MAPK pathways, was selectively impaired in MLK3-/- TAC hearts. In adult rat cardiomyocytes, pharmacological MLK3 kinase inhibition using URMC-099 blocked JNK phosphorylation induced by neurohormonal agents and oxidants. Sustained URMC-099 exposure induced cardiomyocyte hypertrophy. These data demonstrate that MLK3 prevents adverse cardiac remodeling in the setting of pressure overload. Mechanistically, MLK3 activates JNK, which in turn opposes cardiomyocyte hypertrophy. These results support modulation of MLK3 as a potential therapeutic approach in HF. NEW & NOTEWORTHY Here, we identified a role for mixed lineage kinase-3 (MLK3) as a novel antihypertrophic and antiremodeling molecule in response to cardiac pressure overload. MLK3 regulates phosphorylation of the stress-responsive JNK kinase in response to pressure overload and in cultured cardiomyocytes stimulated with hypertrophic agonists and oxidants. This study reveals MLK3-JNK signaling as a novel cardioprotective signaling axis in the setting of pressure overload.

Insights into the pulmonary vascular complications of heart failure with preserved ejection fraction

Pulmonary hypertension in the setting of heart failure with preserved ejection fraction (PH-HFpEF) is a growing public health problem that is increasing in prevalence. While PH-HFpEF is defined by a high mean pulmonary artery pressure, high left ventricular end-diastolic pressure and a normal ejection fraction, some HFpEF patients develop PH in the presence of pulmonary vascular remodelling with a high transpulmonary pressure gradient or pulmonary vascular resistance. Ageing, increased left atrial pressure and stiffness, mitral regurgitation, as well as features of metabolic syndrome, which include obesity, diabetes and hypertension, are recognized as risk factors for PH-HFpEF. Qualitative studies have documented that patients with PH-HFpEF develop more severe symptoms than those with HFpEF and are associated with more significant exercise intolerance, frequent hospitalizations, right heart failure and reduced survival. Currently, there are no effective therapies for PH-HFpEF, although a number of candidate drugs are being evaluated, including soluble guanylate cyclase stimulators, phosphodiesterase type 5 inhibitors, sodium nitrite and endothelin receptor antagonists. In this review we attempt to provide an updated overview of recent findings pertaining to the pulmonary vascular complications in HFpEF in terms of clinical definitions, epidemiology and pathophysiology. Mechanisms leading to pulmonary vascular remodelling in HFpEF, a summary of pre-clinical models of HFpEF and PH-HFpEF, and new candidate therapeutic strategies for the treatment of PH-HFpEF are summarized.

The deubiquitinase ubiquitin-specific protease 20 is a positive modulator of myocardial β1-adrenergic receptor expression and signaling

Reversible ubiquitination of G protein-coupled receptors regulates their trafficking and signaling; whether deubiquitinases regulate myocardial β₁-adrenergic receptors (β₁ARs) is unknown. We report that ubiquitin-specific protease 20 (USP20) deubiquitinates and attenuates lysosomal trafficking of the β₁AR. β₁AR-induced phosphorylation of USP20 Ser-333 by protein kinase A-α (PKAα) was required for optimal USP20-mediated regulation of β₁AR lysosomal trafficking. Both phosphomimetic (S333D) and phosphorylation-impaired (S333A) USP20 possess intrinsic deubiquitinase activity equivalent to WT activity. However, unlike USP20 WT and S333D, the S333A mutant associated poorly with the β₁AR and failed to deubiquitinate the β₁AR. USP20-KO mice showed normal baseline systolic function but impaired β₁AR-induced contractility and relaxation. Dobutamine stimulation did not increase cAMP in USP20-KO left ventricles (LVs), whereas NKH477-induced adenylyl cyclase activity was equivalent to WT. The USP20 homolog USP33, which shares redundant roles with USP20, had no effect on β₁AR ubiquitination, but USP33 was up-regulated in USP20-KO hearts suggesting compensatory regulation. Myocardial β₁AR expression in USP20-KO was drastically reduced, whereas β₂AR expression was maintained as determined by radioligand binding in LV sarcolemmal membranes. Phospho-USP20 was significantly increased in LVs of wildtype (WT) mice after a 1-week catecholamine infusion and a 2-week chronic pressure overload induced by transverse aortic constriction (TAC). Phospho-USP20 was undetectable in β₁AR KO mice subjected to TAC, suggesting a role for USP20 phosphorylation in cardiac response to pressure overload. We conclude that USP20 regulates β₁AR signaling in vitro and in vivo Additionally, β₁AR-induced USP20 phosphorylation may serve as a feed-forward mechanism to stabilize β₁AR expression and signaling during pathological insults to the myocardium.

A secretory pathway kinase regulates sarcoplasmic reticulum Ca2+ homeostasis and protects against heart failure

Ca²⁺ signaling is important for many cellular and physiological processes, including cardiac function. Although sarcoplasmic reticulum (SR) proteins involved in Ca²⁺ signaling have been shown to be phosphorylated, the biochemical and physiological roles of protein phosphorylation within the lumen of the SR remain essentially uncharacterized. Our laboratory recently identified an atypical protein kinase, Fam20C, which is uniquely localized to the secretory pathway lumen. Here, we show that Fam20C phosphorylates several SR proteins involved in Ca²⁺ signaling, including calsequestrin2 and Stim1, whose biochemical activities are dramatically regulated by Fam20C mediated phosphorylation. Notably, phosphorylation of Stim1 by Fam20C enhances Stim1 activation and store-operated Ca²⁺ entry. Physiologically, mice with Fam20c ablated in cardiomyocytes develop heart failure following either aging or induced pressure overload. We extended these observations to show that non-muscle cells lacking Fam20C display altered ER Ca²⁺ signaling. Overall, we show that Fam20C plays an overarching role in ER/SR Ca²⁺ homeostasis and cardiac pathophysiology.

Therapeutic Delivery of miR-148a Suppresses Ventricular Dilation in Heart Failure

Heart failure is preceded by ventricular remodeling, changes in left ventricular mass, and myocardial volume after alterations in loading conditions. Concentric hypertrophy arises after pressure overload, involves wall thickening, and forms a substrate for diastolic dysfunction. Eccentric hypertrophy develops in volume overload conditions and leads wall thinning, chamber dilation, and reduced ejection fraction. The molecular events underlying these distinct forms of cardiac remodeling are poorly understood. Here, we demonstrate that miR-148a expression changes dynamically in distinct subtypes of heart failure: while it is elevated in concentric hypertrophy, it decreased in dilated cardiomyopathy. In line, antagomir-mediated silencing of miR-148a caused wall thinning, chamber dilation, increased left ventricle volume, and reduced ejection fraction. Additionally, adeno-associated viral delivery of miR-148a protected the mouse heart from pressure-overload-induced systolic dysfunction by preventing the transition of concentric hypertrophic remodeling toward dilation. Mechanistically, miR-148a targets the cytokine co-receptor glycoprotein 130 (gp130) and connects cardiomyocyte responsiveness to extracellular cytokines by modulating the Stat3 signaling. These findings show the ability of miR-148a to prevent the transition of pressure-overload induced concentric hypertrophic remodeling toward eccentric hypertrophy and dilated cardiomyopathy and provide evidence for the existence of separate molecular programs inducing distinct forms of myocardial remodeling.

The two-pore domain potassium channel TREK-1 mediates cardiac fibrosis and diastolic dysfunction

Cardiac two-pore domain potassium channels (K2P) exist in organisms from Drosophila to humans; however, their role in cardiac function is not known. We identified a K2P gene, CG8713 (sandman), in a Drosophila genetic screen and show that sandman is critical to cardiac function. Mice lacking an ortholog of sandman, TWIK-related potassium channel (TREK-1, also known Kcnk2), exhibit exaggerated pressure overload-induced concentric hypertrophy and alterations in fetal gene expression, yet retain preserved systolic and diastolic cardiac function. While cardiomyocyte-specific deletion of TREK-1 in response to in vivo pressure overload resulted in cardiac dysfunction, TREK-1 deletion in fibroblasts prevented deterioration in cardiac function. The absence of pressure overload-induced dysfunction in TREK-1-KO mice was associated with diminished cardiac fibrosis and reduced activation of JNK in cardiomyocytes and fibroblasts. These findings indicate a central role for cardiac fibroblast TREK-1 in the pathogenesis of pressure overload-induced cardiac dysfunction and serve as a conceptual basis for its inhibition as a potential therapy.

Estrogen rescues heart failure through estrogen receptor Beta activation

Background

Recently, we showed that exogenous treatment with estrogen (E2) rescues pre-existing advanced heart failure (HF) in mice. Since most of the biological actions of E2 are mediated through the classical estrogen receptors alpha (ERα) and/or beta (ERβ), and both these receptors are present in the heart, we examined the role of ERα and ERβ in the rescue action of E2 against HF.

Methods

Severe HF was induced in male mice by transverse aortic constriction-induced pressure overload. Once the ejection fraction (EF) reached ~ 35%, mice were treated with selective agonists for ERα (PPT, 850 μg/kg/day), ERβ (DPN, 850 μg/kg/day), or E2 (30 μg/kg/day) together with an ERβ-antagonist (PHTPP, 850 μg/kg/day) for 10 days.

Results

EF of HF mice was significantly improved to 45.3 ± 2.1% with diarylpropionitrile (DPN) treatment, but not with PPT (31.1 ± 2.3%). E2 failed to rescue HF in the presence of PHTPP, as there was no significant improvement in the EF at the end of the 10-day treatment (32.5 ± 5.2%). The improvement of heart function in HF mice treated with ERβ agonist DPN was also associated with reduced cardiac fibrosis and increased cardiac angiogenesis, while the ERα agonist PPT had no significant effect on either cardiac fibrosis or angiogenesis. Furthermore, DPN improved hemodynamic parameters in HF mice, whereas PPT had no significant effect.

Conclusions

E2 treatment rescues pre-existing severe HF mainly through ERβ. Rescue of HF by ERβ activation is also associated with stimulation of cardiac angiogenesis, suppression of fibrosis, and restoration of hemodynamic parameters.

TFAM overexpression reduces pathological cardiac remodeling

Heart failure (HF) is a functional lack of myocardial performance due to a loss of molecular control over increases in calcium and ROS, resulting in proteolytic degradative advances and cardiac remodeling. Mitochondria are the molecular powerhouse of cells, shifting the sphere of cardiomyocyte stability and performance. Functional mitochondria rely on the molecular abilities of safety factors such as TFAM to maintain physiological parameters. Mitochondrial transcription factor A (TFAM) creates a mitochondrial nucleoid structure around mtDNA, protecting it from mutation, inhibiting NFAT (ROS activator/hypertrophic stimulator), and transcriptionally activates Serca2a to decrease calcium mishandling. Calpain1 and MMP9 are proteolytic degratory factors that play a major role in cardiomyocyte decline in HF. Current literature depicts major decreases in TFAM as HF progresses. We aim to assess TFAM function against Calpain1 and MMP9 proteolytic activity and its role in cardiac remodeling. To this date, no publication has surfaced describing the effects of aortic banding (AB) as a surgical HF model in TFAM-TG mice. HF models were created via AB in TFAM transgenic (TFAM-TG) and C57BLJ-6 (WT) mice. Eight weeks post AB, functional analysis revealed a successful banding procedure, resulting in cardiac hypertrophy as observed via echocardiography. Pulse wave and color doppler show increased aortic flow rates as well as turbulent flow at the banding site. Preliminary results of cardiac tissue immuno-histochemistry of HF-control mice show decreased TFAM and compensatory increases in Serca2a fluorescent expression, along with increased Calpain1 and MMP9 expression. Protein, RNA, and IHC analysis will further assess TFAM-TG results post-banding. Echocardiography shows more cardiac stability and functionality in HF-induced TFAM-TG mice than the control counterpart. These findings complement our published in vitro results. Overall, this suggests that TFAM has molecular therapeutic potential to reduce protease expression.

Cardiac Hypertrophy is Positively Regulated by MicroRNA‑24 in Rats

Background:

MicroRNA-24 (miR-24) plays an important role in heart failure by reducing the efficiency of myocardial excitation-contraction coupling. Prolonged cardiac hypertrophy may lead to heart failure, but little is known about the role of miR-24 in cardiac hypertrophy. This study aimed to preliminarily investigate the function of miR-24 and its mechanisms in cardiac hypertrophy.

Methods:

Twelve Sprague-Dawley rats with a body weight of 50 ± 5 g were recruited and randomly divided into two groups: a transverse aortic constriction (TAC) group and a sham surgery group. Hypertrophy index was measured and calculated by echocardiography and hematoxylin and eosin staining. TargetScans algorithm-based prediction was used to search for the targets of miR-24, which was subsequently confirmed by a real-time polymerase chain reaction and luciferase assay. Immunofluorescence labeling was used to measure the cell surface area, and ³H-leucine incorporation was used to detect the synthesis of total protein in neonatal rat cardiac myocytes (NRCMs) with the overexpression of miR-24. In addition, flow cytometry was performed to observe the alteration in the cell cycle. Statistical analysis was carried out with GraphPad Prism v5.0 and SPSS 19.0. A two-sided P < 0.05 was considered as the threshold for significance.

Results:

The expression of miR-24 was abnormally increased in TAC rat cardiac tissue (t = −2.938, P < 0.05). TargetScans algorithm-based prediction demonstrated that CDKN1B (p27, Kip1), a cell cycle regulator, was a putative target of miR-24, and was confirmed by luciferase assay. The expression of p27 was decreased in TAC rat cardiac tissue (t = 2.896, P < 0.05). The overexpression of miR-24 in NRCMs led to the decreased expression of p27 (t = 4.400, P < 0.01), and decreased G0/G1 arrest in cell cycle and cardiomyocyte hypertrophy.

Conclusion:

MiR-24 promotes cardiac hypertrophy partly by affecting the cell cycle through down-regulation of p27 expression.

Pressure Overload in Mice With Haploinsufficiency of Striated Preferentially Expressed Gene Leads to Decompensated Heart Failure

Striated preferentially expressed gene (Speg) is a member of the myosin light chain kinase family of proteins. Constitutive Speg deficient (Speg^−/−) mice develop a dilated cardiomyopathy, and the majority of these mice die in utero or shortly after birth. In the present study we assessed the importance of Speg in adult mice. Speg^−/− mice that survived to adulthood, or adult striated muscle-specific Speg knockout mice (Speg-KO), demonstrated cardiac dysfunction and evidence of increased left ventricular (LV) internal diameter and heart to body weight ratio. To determine whether heterozygosity of Speg interferes with the response of the heart to pathophysiologic stress, Speg^+/− mice were exposed to pressure overload induced by transverse aortic constriction (TAC). At baseline, Speg^+/+ and Speg^+/− hearts showed no difference in cardiac function. However, 4 weeks after TAC, Speg^+/− mice had a marked reduction in LV function. This defect was associated with an increase in LV internal diameter and enhanced heart weight to body weight ratio, compared with Speg^+/+ mice after TAC. The response of Speg^+/− mice to pressure overload also included increased fibrotic deposition in the myocardium, disruption of transverse tubules, and attenuation in cell contractility, compared with Speg^+/+ mice. Taken together, these data demonstrate that Speg is necessary for normal cardiac function and is involved in the complex adaptation of the heart in response to TAC. Haploinsufficiency of Speg results in decompensated heart failure when exposed to pressure overload.

Ablation of Sirtuin5 in the postnatal mouse heart results in protein succinylation and normal survival in response to chronic pressure overload

Mitochondrial Sirtuin 5 (SIRT5) is an NAD+-dependent demalonylase, desuccinylase, and deglutarylase that controls several metabolic pathways. A number of recent studies point to SIRT5 desuccinylase activity being important in maintaining cardiac function and metabolism under stress. Previously, we described a phenotype of increased mortality in whole-body SIRT5KO mice exposed to chronic pressure overload compared with their littermate WT controls. To determine whether the survival phenotype we reported was due to a cardiac-intrinsic or cardiac-extrinsic effect of SIRT5, we developed a tamoxifen-inducible, heart-specific SIRT5 knockout (SIRT5KO) mouse model. Using our new animal model, we discovered that postnatal cardiac ablation of Sirt5 resulted in persistent accumulation of protein succinylation up to 30 weeks after SIRT5 depletion. Succinyl proteomics revealed that succinylation increased on proteins of oxidative metabolism between 15 and 31 weeks after ablation. Heart-specific SIRT5KO mice were exposed to chronic pressure overload to induce cardiac hypertrophy. We found that, in contrast to whole-body SIRT5KO mice, there was no difference in survival between heart-specific SIRT5KO mice and their littermate controls. Overall, the data presented here suggest that survival of SIRT5KO mice may be dictated by a multitissue or prenatal effect of SIRT5.

The Role of Psychological Stress on Heart Autophagy in Mice With Heart Failure

OBJECTIVE

Psychological stress in chronic heart failure (CHF) is associated with systemic neurohormonal and immune system responses and increased mortality. Autophagy refers to the biological process of degradation and recycling of dysfunctional cellular components. We investigated the role of psychological stress on autophagy function in CHF mice.

METHODS

C57BL/6 mice underwent transverse aortic constriction, with or without combined acoustic and restraint stress, and cardiac function was assessed by echocardiography analysis. Serum corticosterone and angiotensin II (Ang II) were determined using enzyme-linked immunosorbent assay (ELISA). Autophagy and oxidative stress were measured with immunohistochemistry and quantitative polymerase chain reaction, and chloroquine and rapamycin were used to detect autophagy flux. In vivo, cardiomyocytes were cultured with or without Ang II or N-acetylcysteine, and autophagy and oxidative stress were also detected.

RESULTS

A 1-week stress exposure significantly increased serum levels of corticosterone and Ang II (p = .000), increased levels of oxidative stress, induced overt heart failure, and increased mortality (p = .002). Furthermore, stress exposure unregulated messenger RNA expression of Bcl-2-interacting coiled-coil protein 1 (10.891 [3.029] versus 4.754 [1.713], p = .001), cysteine-rich domain containing beclin-1 interacting (6.403 [1.813] versus 3.653 [0.441], p = .006), and autophagy 7 (111.696 [4.049] versus 6.189 [1.931], p = .017), increased expression of autophagosomal, and decreased clearance of autophagosomes. In vitro, Ang II significantly increased autophagy flux in cultured cardiomyocytes, which could be partly inhibited by N-acetylcysteine.

CONCLUSIONS

Psychological stress may contribute to the development of CHF by enhancing heart oxidative stress and impairing autophagy flux.

Linker of nucleoskeleton and cytoskeleton complex proteins in cardiomyopathy

The linker of nucleoskeleton and cytoskeleton (LINC) complex couples the nuclear lamina to the cytoskeleton. The LINC complex and its associated proteins play diverse roles in cells, ranging from genome organization, nuclear morphology, gene expression, to mechanical stability. The importance of a functional LINC complex is highlighted by the large number of mutations in genes encoding LINC complex proteins that lead to skeletal and cardiac myopathies. In this review, the structure, function, and interactions between components of the LINC complex will be described. Mutations that are known to cause cardiomyopathy in patients will be discussed alongside their respective mouse models. Furthermore, future challenges for the field and emerging technologies to investigate LINC complex function will be discussed.

The serine/threonine-protein kinase/endoribonuclease IRE1α protects the heart against pressure overload-induced heart failure

Heart failure is associated with induction of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The serine/threonine protein kinase/endoribonuclease IRE1α is a key protein in ER stress signal transduction. IRE1α activity can induce both protective UPR and apoptotic downstream signaling events, but the specific role for IRE1α activity in the heart is unknown. A major aim of this study was to characterize the specific contribution of IRE1α in cardiac physiology and pathogenesis. We used both cultured myocytes and a transgenic mouse line with inducible and cardiomyocyte-specific IRE1α overexpression as experimental models to achieve targeted IRE1α activation. IRE1α expression induced a potent but transient ER stress response in cardiomyocytes and did not cause significant effects in the intact heart under normal physiological conditions. Furthermore, the IRE1α-activated transgenic heart responding to pressure overload exhibited preserved function and reduced fibrotic area, associated with increased adaptive UPR signaling and with blunted inflammatory and pathological gene expression. Therefore, we conclude that IRE1α induces transient ER stress signaling and confers a protective effect against pressure overload-induced pathological remodeling in the heart. To our knowledge, this report provides first direct evidence of a specific and protective role for IRE1α in the heart and reveals an interaction between ER stress signaling and inflammatory regulation in the pathologically stressed heart.

Pathophysiological Mapping of Experimental Heart Failure: Left and Right Ventricular Remodeling in Transverse Aortic Constriction Is Temporally, Kinetically and Structurally Distinct

A growing proportion of heart failure (HF) patients present with impairments in both ventricles. Experimental pressure-overload (i.e., transverse aortic constriction, TAC) induces left ventricle (LV) hypertrophy and failure, as well as right ventricle (RV) dysfunction. However, little is known about the coordinated progression of biventricular dysfunction that occurs in TAC. Here we investigated the time course of systolic and diastolic function in both the LV and RV concurrently to improve our understanding of the chronology of events in TAC. Hemodynamic, histological, and morphometric assessments were obtained from the LV and RV at 2, 4, 9, and 18 weeks post-surgery. Results: Systolic pressures peaked in both ventricles at 4 weeks, thereafter steadily declining in the LV, while remaining elevated in the RV. The LV and RV followed different structural and functional timelines, suggesting the patterns in one ventricle are independent from the opposing ventricle. RV hypertrophy/fibrosis and pulmonary arterial remodeling confirmed a progressive right-sided pathology. We further identified both compensation and decompensation in the LV with persistent concentric hypertrophy in both phases. Finally, diastolic impairments in both ventricles manifested as an intricate progression of multiple parameters that were not in agreement until overt systolic failure was evident. Conclusion: We establish pulmonary hypertension was secondary to LV dysfunction, confirming TAC is a model of type II pulmonary hypertension. This study also challenges some common assumptions in experimental HF (e.g., the relationship between fibrosis and filling pressure) while addressing a knowledge gap with respect to temporality of RV remodeling in pressure-overload.

S-Nitrosylation of β-Arrestins Biases Receptor Signaling and Confers Ligand Independence

Most G protein-coupled receptors (GPCRs) signal through both heterotrimeric G proteins and β-arrestins (βarr1 and βarr2). Although synthetic ligands can elicit biased signaling by G protein- vis-à-vis βarr-mediated transduction, endogenous mechanisms for biasing signaling remain elusive. Here we report that S-nitrosylation of a novel site within βarr1/2 provides a general mechanism to bias ligand-induced signaling through GPCRs by selectively inhibiting βarr-mediated transduction. Concomitantly, S-nitrosylation endows cytosolic βarrs with receptor-independent function. Enhanced βarr S-nitrosylation characterizes inflammation and aging as well as human and murine heart failure. In genetically engineered mice lacking βarr2-Cys253 S-nitrosylation, heart failure is exacerbated in association with greatly compromised β-adrenergic chronotropy and inotropy, reflecting βarr-biased transduction and β-adrenergic receptor downregulation. Thus, S-nitrosylation regulates βarr function and, thereby, biases transduction through GPCRs, demonstrating a novel role for nitric oxide in cellular signaling with potentially broad implications for patho/physiological GPCR function, including a previously unrecognized role in heart failure.

Caveolin 3-dependent loss of t-tubular ICa during hypertrophy and heart failure in mice

NEW FINDINGS

What is the central question of this study? Heart failure is associated with redistribution of L-type Ca²⁺ current (I_Ca ) away from the t-tubule membrane to the surface membrane of cardiac ventricular myocytes. However, the underlying mechanism and its dependence on severity of pathology (hypertrophy versus failure) are unclear. What is the main finding and its importance? Increasing severity of response to transverse aortic constriction, from hypertrophy to failure, was accompanied by graded loss of t-tubular I_Ca and loss of regulation of I_Ca by caveolin 3. Thus, the pathological loss of t-tubular I_Ca , which contributes to impaired excitation-contraction coupling and thereby cardiac function in vivo, appears to be attributable to loss of caveolin 3-dependent stimulation of t-tubular I_Ca .

ABSTRACT

Previous work has shown redistribution of L-type Ca²⁺ current (I_Ca ) from the t-tubules to the surface membrane of rat ventricular myocytes after myocardial infarction. However, whether this occurs in all species and in response to other insults, the relationship of this redistribution to the severity of the pathology, and the underlying mechanism, are unknown. We have therefore investigated the response of mouse hearts and myocytes to pressure overload induced by transverse aortic constriction (TAC). Male C57BL/6 mice underwent TAC or equivalent sham operation 8 weeks before use. I_Ca and Ca²⁺ transients were measured in isolated myocytes, and expression of caveolin 3 (Cav3), junctophilin 2 (Jph2) and bridging integrator 1 (Bin1) was determined. C3SD peptide was used to disrupt Cav3 binding to its protein partners. Some animals showed cardiac hypertrophy in response to TAC with little evidence of heart failure, whereas others showed greater hypertrophy and pulmonary congestion. These graded changes were accompanied by graded cellular hypertrophy, t-tubule disruption, decreased expression of Jph2 and Cav3, and decreased t-tubular I_Ca density, with no change at the cell surface, and graded impairment of Ca²⁺ release at t-tubules. C3SD decreased I_Ca density in control but not in TAC myocytes. These data suggest that the graded changes in cardiac function and size that occur in response to TAC are paralleled by graded changes in cell structure and function, which will contribute to the impaired function observed in vivo. They also suggest that loss of t-tubular I_Ca is attributable to loss of Cav3-dependent stimulation of I_Ca .

A Closed-chest Model to Induce Transverse Aortic Constriction in Mice

Research on cardiac hypertrophy and heart failure is frequently based on pressure overload mouse models induced by TAC. The standard procedure is to perform a partial thoracotomy to visualize the transverse aortic arch. However, the surgical trauma caused by the thoracotomy in open-chest models changes the respiratory physiology as the ribs are dissected and left unattached after chest closure. To prevent this, we established a minimally invasive, closed chest approach via lateral thoracotomy. Herein we approach the aortic arch via the 2^nd intercostal space without entering the chest cavities, leaving the mouse with a less traumatic injury to recover from. We perform this operation using standard laboratory settings for open chest TAC procedures with equal survival rates. Apart from maintaining physiological breathing patterns due to the closed chest approach, the mice seem to benefit by showing rapid recovery, as the less invasive technique appears to facilitate a fast healing process and to reduce immune response after trauma.

Structure and function of the Nppa-Nppb cluster locus during heart development and disease

Atrial natriuretic factor and brain natriuretic peptide are two important biomarkers in clinical cardiology. These two natriuretic peptide hormones are encoded by the paralogous genes Nppa and Nppb, which are evolutionary conserved. Both genes are predominantly expressed by the heart muscle during the embryonic and fetal stages, and in particular Nppa expression is strongly reduced in the ventricles after birth. Upon cardiac stress, Nppa and Nppb are strongly upregulated in the ventricular myocardium. Much is known about the molecular and physiological ques inducing Nppa and Nppb expression; however, the transcriptional regulatory mechanisms of the Nppa-Nppb cluster in vivo has proven to be quite complex and is not well understood. In this review, we will provide recent insights into the dynamic and complex regulation of Nppa and Nppb during heart development and hypertrophy, and the association of this gene cluster with the cardiomyocyte-intrinsic program of heart regeneration.

Afterload promotes maturation of human induced pluripotent stem cell derived cardiomyocytes in engineered heart tissues

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) grown in engineered heart tissue (EHT) can be used for drug screening, disease modeling, and heart repair. However, the immaturity of hiPSC-CMs currently limits their use. Because mechanical loading increases during development and facilitates cardiac maturation, we hypothesized that afterload would promote maturation of EHTs. To test this we developed a system in which EHTs are suspended between a rigid post and a flexible one, whose resistance to contraction can be modulated by applying braces of varying length. These braces allow us to adjust afterload conditions over two orders of magnitude by increasing the flexible post resistance from 0.09 up to 9.2 μN/μm. After three weeks in culture, optical tracking of post deflections revealed that auxotonic twitch forces increased in correlation with the degree of afterload, whereas twitch velocities decreased with afterload. Consequently, the power and work of the EHTs were maximal under intermediate afterloads. When studied isometrically, the inotropy of EHTs increased with afterload up to an intermediate resistance (0.45 μN/μm) and then plateaued. Applied afterload increased sarcomere length, cardiomyocyte area and elongation, which are hallmarks of maturation. Furthermore, progressively increasing the level of afterload led to improved calcium handling, increased expression of several key markers of cardiac maturation, including a shift from fetal to adult ventricular myosin heavy chain isoforms. However, at the highest afterload condition, markers of pathological hypertrophy and fibrosis were also upregulated, although the bulk tissue stiffness remained the same for all levels of applied afterload tested. Together, our results indicate that application of moderate afterloads can substantially improve the maturation of hiPSC-CMs in EHTs, while high afterload conditions may mimic certain aspects of human cardiac pathology resulting from elevated mechanical overload.

miR-139-5p inhibits isoproterenol-induced cardiac hypertrophy by targetting c-Jun

Hypertrophic cardiomyopathy (HCM) is a serious monogenic disease characterized by cardiac hypertrophy, fibrosis, sudden cardiac death, and heart failure. Previously, we identified that miR-139-5p was down-regulated in HCM patients. However, the regulatory effects of miR-139-5p remain unclear. Thus, we investigated the role of miR-139-5p in the regulation of cardiac hypertrophy. The expression of miR-139-5p in left ventricular tissues in HCM patients and mice subjected to transverse aortic constriction (TAC) was significantly down-regulated. Knockdown of miR-139-5p expression in neonatal rat cardiomyocytes (NRCMs) induced cardiomyocyte enlargement and increased atrial natriuretic polypeptide (ANP) expression. Overexpression of miR-139-5p antagonized isoproterenol (ISO)-induced cardiomyocyte enlargement and ANP/brain natriuretic peptide (BNP) up-regulation. More importantly, we found that c-Jun expression was inhibited by miR-139-5p in NRCMs. Knockdown of c-Jun expression significantly attenuated cardiac hypertrophy induced by miR-139-5p deprivation. Our data indicated that miR-139-5p was down-regulated in the hearts of HCM patients and that it inhibited cardiac hypertrophy by targetting c-Jun expression.

Luma is not essential for murine cardiac development and function

AIMS

Luma is a recently discovered, evolutionarily conserved protein expressed in mammalian heart, which is associated with the LInker of Nucleoskeleton and Cytoskeleton (LINC) complex. The LINC complex structurally integrates the nucleus and the cytoplasm and plays a critical role in mechanotransduction across the nuclear envelope. Mutations in several LINC components in both humans and mice result in various cardiomyopathies, implying they play essential, non-redundant roles. A single amino acid substitution of serine 358 to leucine (S358L) in Luma is the unequivocal cause of a distinct form of arrhythmogenic cardiomyopathy. However, the role of Luma in heart has remained obscure. In addition, it also remains to be determined how the S358L mutation in Luma leads to cardiomyopathy.

METHODS AND RESULTS

To determine the role of Luma in the heart, we first determined the expression pattern of Luma in mouse heart. Luma was sporadically expressed in cardiomyocytes throughout the heart, but was highly and uniformly expressed in cardiac fibroblasts and vascular smooth muscle cells. We also generated germline null Luma mice and discovered that germline null mutants were viable and exhibited normal cardiac function. Luma null mice also responded normally to pressure overload induced by transverse aortic constriction. In addition, localization and expression of other LINC complex components in both cardiac myocytes and fibroblasts was unaffected by global loss of Luma. Furthermore, we also generated and characterized Luma S358L knock-in mice, which displayed normal cardiac function and morphology.

CONCLUSION

Our data suggest that Luma is dispensable for murine cardiac development and function and that the Luma S358L mutation alone may not cause cardiomyopathy in mice.

Central-acting therapeutics alleviate respiratory weakness caused by heart failure-induced ventilatory overdrive

Diaphragmatic weakness is a feature of heart failure (HF) associated with dyspnea and exertional fatigue. Most studies have focused on advanced stages of HF, leaving the cause unresolved. The long-standing theory is that pulmonary edema imposes a mechanical stress, resulting in diaphragmatic remodeling, but stable HF patients rarely exhibit pulmonary edema. We investigated how diaphragmatic weakness develops in two mouse models of pressure overload-induced HF. As in HF patients, both models had increased eupneic respiratory pressures and ventilatory drive. Despite the absence of pulmonary edema, diaphragmatic strength progressively declined during pressure overload; this decline correlated with a reduction in diaphragm cross-sectional area and preceded evidence of muscle weakness. We uncovered a functional codependence between angiotensin II and β-adrenergic (β-ADR) signaling, which increased ventilatory drive. Chronic overdrive was associated with increased PERK (double-stranded RNA-activated protein kinase R-like ER kinase) expression and phosphorylation of EIF2α (eukaryotic translation initiation factor 2α), which inhibits protein synthesis. Inhibition of β-ADR signaling after application of pressure overload normalized diaphragm strength, Perk expression, EIF2α phosphorylation, and diaphragmatic cross-sectional area. Only drugs that were able to penetrate the blood-brain barrier were effective in treating ventilatory overdrive and preventing diaphragmatic atrophy. These data provide insight into why similar drugs have different benefits on mortality and symptomatology, despite comparable cardiovascular effects.

Experimental modelling of cardiac pressure overload hypertrophy: Modified technique for precise, reproducible, safe and easy aortic arch banding-debanding in mice

Pressure overload left ventricular hypertrophy is a known precursor of heart failure with ominous prognosis. The development of experimental models that reproduce this phenomenon is instrumental for the advancement in our understanding of its pathophysiology. The gold standard of these models is the controlled constriction of the mid aortic arch in mice according to Rockman's technique (RT). We developed a modified technique that allows individualized and fully controlled constriction of the aorta, improves efficiency and generates a reproducible stenosis that is technically easy to perform and release. An algorithm calculates, based on the echocardiographic arch diameter, the intended perimeter at the constriction, and a suture is prepared with two knots separated accordingly. The aorta is encircled twice with the suture and the loop is closed with a microclip under both knots. We performed controlled aortic constriction with Rockman's and the double loop-clip (DLC) techniques in mice. DLC proved superiority in efficiency (mortality and invalid experiments) and more homogeneity of the results (transcoarctational gradients, LV mass, cardiomyocyte hypertrophy, gene expression) than RT. DLC technique optimizes animal use and generates a consistent and customized aortic constriction with homogeneous LV pressure overload morphofunctional, structural, and molecular features.

AMPK activation counteracts cardiac hypertrophy by reducing O-GlcNAcylation

AMP-activated protein kinase (AMPK) has been shown to inhibit cardiac hypertrophy. Here, we show that submaximal AMPK activation blocks cardiomyocyte hypertrophy without affecting downstream targets previously suggested to be involved, such as p70 ribosomal S6 protein kinase, calcineurin/nuclear factor of activated T cells (NFAT) and extracellular signal-regulated kinases. Instead, cardiomyocyte hypertrophy is accompanied by increased protein O-GlcNAcylation, which is reversed by AMPK activation. Decreasing O-GlcNAcylation by inhibitors of the glutamine:fructose-6-phosphate aminotransferase (GFAT), blocks cardiomyocyte hypertrophy, mimicking AMPK activation. Conversely, O-GlcNAcylation-inducing agents counteract the anti-hypertrophic effect of AMPK. In vivo, AMPK activation prevents myocardial hypertrophy and the concomitant rise of O-GlcNAcylation in wild-type but not in AMPKα2-deficient mice. Treatment of wild-type mice with O-GlcNAcylation-inducing agents reverses AMPK action. Finally, we demonstrate that AMPK inhibits O-GlcNAcylation by mainly controlling GFAT phosphorylation, thereby reducing O-GlcNAcylation of proteins such as troponin T. We conclude that AMPK activation prevents cardiac hypertrophy predominantly by inhibiting O-GlcNAcylation.

Alterations of Ocular Hemodynamics Impair Ophthalmic Vascular and Neuroretinal Function

Hypertension is associated with numerous diseases, but its direct impact on the ocular circulation and neuroretinal function remains unclear. Herein, mouse eyes were challenged with different levels of hemodynamic insult via transverse aortic coarctation, which increased blood pressure and flow velocity by 50% and 40%, respectively, in the right common carotid artery, and reduced those parameters by 30% and 40%, respectively, in the left common carotid artery. Blood velocity in the right central retinal artery gradually increased up to 40% at 4 weeks of transverse aortic coarctation, and the velocity in the left central retinal artery gradually decreased by 20%. The fundus and retinal architecture were unaltered by hemodynamic changes. Endothelium-dependent vasodilations to acetylcholine and adenosine were reduced only in right (hypertensive) ophthalmic arteries. Increased cellularity in the nerve fiber/ganglion cell layers, enhanced glial fibrillary acidic protein expression, and elevated superoxide level were found only in hypertensive retinas. The electroretinogram showed decreased scotopic b-waves in the hypertensive eyes and decreased scotopic oscillatory potentials in both hypertensive and hypotensive eyes. In conclusion, hypertension sustained for 4 weeks causes ophthalmic vascular dysfunction, retinal glial cell activation, oxidative stress, and neuroretinal impairment. Although ophthalmic vasoregulation is insensitive to hypotensive insult, the ocular hypoperfusion causes neuroretinal dysfunction.

Effects of chronically increased VEGF-A on the aging heart

Whether approaches to chronically increase VEGF-A in the heart may have beneficial effects and prevent the development of heart failure, in part by improving cardiac perfusion, or whether this increase could have detrimental effects on cardiac performance in the aging heart, has not been tested yet. In this study, a genetic mouse model with a chronic increase in VEGF-A in the heart is shown to have increased cardiac angiogenesis and develop cardiac hypertrophy with enhanced basal cardiac performance with age progression. However, in aged hearts, this increase in VEGF-A was associated with higher expression of fetal cardiac genes and reduced cardiac performance after β-agonistic stress, features consistent with pathologic cardiac hypertrophy. Expression of Nod-like receptor protein (NLRP)-3 was increased in the hearts of the mice, and its genetic inactivation prevented increased fetal cardiac gene expression and partially rescued the impaired cardiac performance after β-agonistic stimulation in aged hearts without reducing cardiac angiogenesis or hypertrophy. Thus, although a chronic increase in cardiac VEGF-A may improve cardiac perfusion, long-term upregulation of VEGF-A leads to reduced cardiac performance under stress, an effect that can be partially inhibited by NLRP3 inactivation. Targeting NLRP3 shifts the VEGF-A-induced cardiac hypertrophy from a pathologic toward a more physiologic hypertrophy.-Marneros, A. G. Effects of chronically increased VEGF-A on the aging heart.

Conventional Method of Transverse Aortic Constriction in Mice

Transverse aortic constriction is a widely used surgical model to reflect the progression from cardiac hypertrophy to heart failure states due to left ventricular pressure overload in mice. It produces afterload increase on the left ventricle in which compensated hypertrophy initially occurs in the first 2 weeks. This develops into maladaptive remodeling of the left ventricle and atrium, leading to heart failure. This model is useful for cardiac studies since transverse aortic constriction can be consistently replicated and has low surgical mortality. Additionally, the gradual progression to cardiac failure makes it a valuable method to evaluate the efficacy of potential therapeutic intervention. We introduce this chapter to offer practical approaches to facilitate a simple methodology for transverse aortic constriction.

Gene expression analysis to identify mechanisms underlying heart failure susceptibility in mice and humans

Genetic factors are known to modulate cardiac susceptibility to ventricular hypertrophy and failure. To determine how strain influences the transcriptional response to pressure overload-induced heart failure (HF) and which of these changes accurately reflect the human disease, we analyzed the myocardial transcriptional profile of mouse strains with high (C57BL/6J) and low (129S1/SvImJ) susceptibility for HF development, which we compared to that of human failing hearts. Following transverse aortic constriction (TAC), C57BL/6J mice developed overt HF while 129S1/SvImJ did not. Despite a milder aortic constriction, impairment of ejection fraction and ventricular remodeling (dilation, fibrosis) was more pronounced in C57BL/6J mice. Similarly, changes in myocardial gene expression were more robust in C57BL/6J (461 genes) compared to 129S1/SvImJ mice (71 genes). When comparing these patterns to human dilated cardiomyopathy (1344 genes), C57BL/6J mice tightly grouped to human hearts. Overlay and bioinformatic analysis of the transcriptional profiles of C57BL/6J mice and human failing hearts identified six co-regulated genes (POSTN, CTGF, FN1, LOX, NOX4, TGFB2) with established link to HF development. Pathway enrichment analysis identified angiotensin and IGF-1 signaling as most enriched putative upstream regulator and pathway, respectively, shared between TAC-induced HF in C57BL/6J mice and in human failing hearts. TAC-induced heart failure in C57BL/6J mice more closely reflects the gene expression pattern of human dilated cardiomyopathy compared to 129S1/SvImJ mice. Unbiased as well as targeted gene expression and pathway analyses identified periostin, angiotensin signaling, and IGF-1 signaling as potential causes of increased HF susceptibility in C57BL/6J mice and as potentially useful drug targets for HF treatment.

Immunotherapy for cardiovascular disease

Heart failure (HF), the final stage of pathological cardiac hypertrophy, is a major cause of hospitalization and mortality. The role of inflammation in the pathogenesis of HF has been extensively studied, with great emphasis on proinflammatory cytokines. Yet, clinical trials targeting these cytokines failed to become a credible therapeutic strategy for HF. More recent studies are increasingly highlighting an active role for T cells in the progression of HF pathology. As a result, a number of novel immunotherapy strategies are emerging for the treatment of HF and other cardiovascular diseases, via the targeting of adaptive immunity. Here we provide an overview of the background, details, and expected outcomes of these attempts.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

Sirtuin 5 is required for mouse survival in response to cardiac pressure overload

In mitochondria, the sirtuin SIRT5 is an NAD+-dependent protein deacylase that controls several metabolic pathways. Although a wide range of SIRT5 targets have been identified, the overall function of SIRT5 in organismal metabolic homeostasis remains unclear. Given that SIRT5 expression is highest in the heart and that sirtuins are commonly stress-response proteins, we used an established model of pressure overload-induced heart muscle hypertrophy caused by transverse aortic constriction (TAC) to determine SIRT5's role in cardiac stress responses. Remarkably, SIRT5KO mice had reduced survival upon TAC compared with wild-type mice but exhibited no mortality when undergoing a sham control operation. The increased mortality with TAC was associated with increased pathological hypertrophy and with key abnormalities in both cardiac performance and ventricular compliance. By combining high-resolution MS-based metabolomic and proteomic analyses of cardiac tissues from wild-type and SIRT5KO mice, we found several biochemical abnormalities exacerbated in the SIRT5KO mice, including apparent decreases in fatty acid oxidation and glucose oxidation as well as an overall decrease in mitochondrial NAD+/NADH. Together, these abnormalities suggest that SIRT5 deacylates protein substrates involved in cellular oxidative metabolism to maintain mitochondrial energy production. Overall, the functional and metabolic results presented here suggest an accelerated development of cardiac dysfunction in SIRT5KO mice in response to TAC, explaining increased mortality upon cardiac stress. Our findings reveal a key role for SIRT5 in maintaining cardiac oxidative metabolism under pressure overload to ensure survival.

Cardiac myocyte miR-29 promotes pathological remodeling of the heart by activating Wnt signaling

Chronic cardiac stress induces pathologic hypertrophy and fibrosis of the myocardium. The microRNA-29 (miR-29) family has been found to prevent excess collagen expression in various organs, particularly through its function in fibroblasts. Here, we show that miR-29 promotes pathologic hypertrophy of cardiac myocytes and overall cardiac dysfunction. In a mouse model of cardiac pressure overload, global genetic deletion of miR-29 or antimiR-29 infusion prevents cardiac hypertrophy and fibrosis and improves cardiac function. Targeted deletion of miR-29 in cardiac myocytes in vivo also prevents cardiac hypertrophy and fibrosis, indicating that the function of miR-29 in cardiac myocytes dominates over that in non-myocyte cell types. Mechanistically, we found cardiac myocyte miR-29 to de-repress Wnt signaling by directly targeting four pathway factors. Our data suggests that, cell- or tissue-specific antimiR-29 delivery may have therapeutic value for pathological cardiac remodeling and fibrosis.

MicroRNA-29 is known to reduce collagen production in fibroblasts thereby inhibiting fibrosis in various organs. Here, Sassi et al. show that miR-29 can also enhance fibrotic signalling and pathological hypertrophy of the heart through its action in cardiomyocytes.

Stromal interaction molecule 1 haploinsufficiency causes maladaptive response to pressure overload

Stromal interaction molecule 1 (STIM1), an endo/sarcoplasmic reticulum Ca²⁺ sensor, has been shown to control a Ca²⁺-dependent signal that promotes cardiac hypertrophy. However, whether STIM1 has adaptive role that helps to protect against cardiac overload stress remains unknown. We hypothesized that STIM1 deficiency causes a maladaptive response to pressure overload stress. We investigated STIM1 heterozygous KO (STIM1^+/–) mice hearts, in which STIM1 protein levels decreased to 27% of wild-type (WT) with no compensatory increase in STIM2. Under stress-free conditions, no significant differences were observed in electrocardiographic and echocardiographic parameters or blood pressure between STIM1^+/–and WT mice. However, when STIM1^+/–mice were subjected to transverse aortic constriction (TAC), STIM1^+/–mice had a higher mortality rate than WT mice. The TAC-induced increase in the heart weight to body weight ratio (mean mg/g ± standard error of the mean) was significantly inhibited in STIM1^+/–mice (WT sham, 4.12 ± 0.14; WT TAC, 6.23 ± 0.40; STIM1^+/–sham, 4.53 ± 0.16; STIM1^+/–TAC, 4.63 ± 0.08). Reverse transcription-polymerase chain reaction analysis of the left ventricles of TAC-treated STIM1^+/–mice showed inhibited induction of cardiac fetal genes, including those encoding brain and atrial natriuretic proteins. Western blot analysis showed upregulated expression of transient receptor potential channel 1 (TRPC1) in TAC-treated WT mice, but suppressed expression in TAC-treated STIM1^+/–mice. Taken together, the hearts of STIM1 haploinsufficient mice had a superficial resemblance to the WT phenotype under stress-free conditions; however, STIM1 haploinsufficient mice showed a maladaptive response to cardiac pressure overload.

Myocardial fibrosis: biomedical research from bench to bedside

Myocardial fibrosis refers to a variety of quantitative and qualitative changes in the interstitial myocardial collagen network that occur in response to cardiac ischaemic insults, systemic diseases, drugs, or any other harmful stimulus affecting the circulatory system or the heart itself. Myocardial fibrosis alters the architecture of the myocardium, facilitating the development of cardiac dysfunction, also inducing arrhythmias, influencing the clinical course and outcome of heart failure patients. Focusing on myocardial fibrosis may potentially improve patient care through the targeted diagnosis and treatment of emerging fibrotic pathways. The European Commission funded the FIBROTARGETS consortium as a multinational academic and industrial consortium with the primary aim of performing a systematic and collaborative search of targets of myocardial fibrosis, and then translating these mechanisms into individualized diagnostic tools and specific therapeutic pharmacological options for heart failure. This review focuses on those methodological and technological aspects considered and developed by the consortium to facilitate the transfer of the new mechanistic knowledge on myocardial fibrosis into potential biomedical applications.

Cardiomyocyte proliferation prevents failure in pressure overload but not volume overload

Induction of the cell cycle is emerging as an intervention to treat heart failure. Here, we tested the hypothesis that enhanced cardiomyocyte renewal in transgenic mice expressing cyclin D2 would be beneficial during hemodynamic overload. We induced pressure overload by transthoracic aortic constriction (TAC) or volume overload by aortocaval shunt in cyclin D2-expressing and WT mice. Although cyclin D2 expression dramatically improved survival following TAC, it did not confer a survival advantage to mice following aortocaval shunt. Cardiac function decreased following TAC in WT mice, but was preserved in cyclin D2-expressing mice. On the other hand, cardiac structure and function were compromised in response to aortocaval shunt in both WT and cyclin D2-expressing mice. The preserved function and improved survival in cyclin D2-expressing mice after TAC was associated with an approximately 50% increase in cardiomyocyte number and exaggerated cardiac hypertrophy, as indicated by increased septum thickness. Aortocaval shunt did not further impact cardiomyocyte number in mice expressing cyclin D2. Following TAC, cyclin D2 expression attenuated cardiomyocyte hypertrophy, reduced cardiomyocyte apoptosis, fibrosis, calcium/calmodulin-dependent protein kinase IIδ phosphorylation, brain natriuretic peptide expression, and sustained capillarization. Thus, we show that cyclin D2-induced cardiomyocyte renewal reduced myocardial remodeling and dysfunction after pressure overload but not after volume overload.

Th1 effector T cells selectively orchestrate cardiac fibrosis in nonischemic heart failure

Despite emerging data indicating a role for T cells in profibrotic cardiac repair and healing after ischemia, little is known about whether T cells directly impact cardiac fibroblasts (CFBs) to promote cardiac fibrosis (CF) in nonischemic heart failure (HF). Recently, we reported increased T cell infiltration in the fibrotic myocardium of nonischemic HF patients, as well as the protection from CF and HF in TCR-α^-/- mice. Here, we report that T cells activated in such a context are mainly IFN-γ⁺, adhere to CFB, and induce their transition into myofibroblasts. Th1 effector cells selectively drive CF both in vitro and in vivo, whereas adoptive transfer of Th1 cells, opposite to activated IFN-γ^-/- Th cells, partially reconstituted CF and HF in TCR-α^-/- recipient mice. Mechanistically, Th1 cells use integrin α4 to adhere to and induce TGF-β in CFB in an IFN-γ-dependent manner. Our findings identify a previously unrecognized role for Th1 cells as integrators of perivascular CF and cardiac dysfunction in nonischemic HF.

A microfluidic platform for the high-throughput study of pathological cardiac hypertrophy

Current in vitro models fall short in deciphering the mechanisms of cardiac hypertrophy induced by volume overload. We developed a pneumatic microfluidic platform for high-throughput studies of cardiac hypertrophy that enables repetitive (hundreds of thousands of times) and robust (over several weeks) manipulation of cardiac μtissues. The platform is reusable for stable and reproducible mechanical stimulation of cardiac μtissues (each containing only 5000 cells). Heterotypic and homotypic μtissues produced in the device were pneumatically loaded in a range of regimes, with real-time on-chip analysis of tissue phenotypes. Concentrated loading of the three-dimensional cardiac tissue faithfully recapitulated the pathology of volume overload seen in native heart tissue. Sustained volume overload of μtissues was sufficient to induce pathological cardiac remodeling associated with upregulation of the fetal gene program, in a dose-dependent manner.