Cardiotoxic and cardioprotective features of chronic β-adrenergic signaling

Differential Downregulation of β1-Adrenergic Receptor Signaling in the Heart

BACKGROUND

Chronic sympathetic stimulation drives desensitization and downregulation of β1 adrenergic receptor (β1AR) in heart failure. We aim to explore the differential downregulation subcellular pools of β1AR signaling in the heart.

METHODS AND RESULTS

We applied chronic infusion of isoproterenol to induced cardiomyopathy in male C57BL/6J mice. We applied confocal and proximity ligation assay to examine β1AR association with L-type calcium channel, ryanodine receptor 2, and SERCA2a ((Sarco)endoplasmic reticulum calcium ATPase 2a) and Förster resonance energy transfer-based biosensors to probe subcellular β1AR-PKA (protein kinase A) signaling in ventricular myocytes. Chronic infusion of isoproterenol led to reduced β1AR protein levels, receptor association with L-type calcium channel and ryanodine receptor 2 measured by proximity ligation (puncta/cell, 29.65 saline versus 14.17 isoproterenol, P<0.05), and receptor-induced PKA signaling at the plasma membrane (Förster resonance energy transfer, 28.9% saline versus 1.9% isoproterenol, P<0.05) and ryanodine receptor 2 complex (Förster resonance energy transfer, 30.2% saline versus 10.6% isoproterenol, P<0.05). However, the β1AR association with SERCA2a was enhanced (puncta/cell, 51.4 saline versus 87.5 isoproterenol, P<0.05), and the receptor signal was minimally affected. The isoproterenol-infused hearts displayed decreased PDE4D (phosphodiesterase 4D) and PDE3A and increased PDE2A, PDE4A, and PDE4B protein levels. We observed a reduced role of PDE4 and enhanced roles of PDE2 and PDE3 on the β1AR-PKA activity at the ryanodine receptor 2 complexes and myocyte shortening. Despite the enhanced β1AR association with SERCA2a, the endogenous norepinephrine-induced signaling was reduced at the SERCA2a complexes. Inhibiting monoamine oxidase A rescued the norepinephrine-induced PKA signaling at the SERCA2a and myocyte shortening.

CONCLUSIONS

This study reveals distinct mechanisms for the downregulation of subcellular β1AR signaling in the heart under chronic adrenergic stimulation.

Cardiogenic pulmonary edema - is it lone cardiogenic? "Missing link" between hemodynamic and other existing mechanisms

The current traditional pathophysiologic concept of pulmonary edema of cardiogenic origin explains its development by a hydrostatic effect due to increased pulmonary capillary pressure resulting in fluid flux to alveolar and interstitial areas from capillaries. However, several experimental studies and clinical data of poor response to hemodynamic and diuretic treatment in many scenarios provide further evidence of the involvement of several other contributing factors to the development of cardiogenic pulmonary edema. Several experimental and clinical studies have found that sympathetic overactivity with elevated plasma catecholamine concentrations may play an important role in the development of cardiovascular-associated pulmonary edema. Catecholamine-induced pulmonary injury may be one of the key mechanisms in acute cardiogenic pulmonary edema triggering proinflammatory cytokine overactivation, oxidative stress and myocardial injury. In the everyday treatment of acute heart failure, physicians should consider the possibility of other noncardiogenic mechanisms involved in the progression of acute pulmonary edema, particularly catecholamine overactivity, lymphatic drainage, inflammatory and oxidative stress, high surfactant protein. The classic, hemodynamic treatment approach in pulmonary edema with the coexistence of other contributing factors may not provide adequate clinical benefit during treatment.

Adenylyl cyclase isoforms 5 and 6 in the cardiovascular system: complex regulation and divergent roles

Adenylyl cyclases (ACs) are crucial effector enzymes that transduce divergent signals from upstream receptor pathways and are responsible for catalyzing the conversion of ATP to cAMP. The ten AC isoforms are categorized into four main groups; the class III or calcium-inhibited family of ACs comprises AC5 and AC6. These enzymes are very closely related in structure and have a paucity of selective activators or inhibitors, making it difficult to distinguish them experimentally. AC5 and AC6 are highly expressed in the heart and vasculature, as well as the spinal cord and brain; AC6 is also abundant in the lungs, kidney, and liver. However, while AC5 and AC6 have similar expression patterns with some redundant functions, they have distinct physiological roles due to differing regulation and cAMP signaling compartmentation. AC5 is critical in cardiac and vascular function; AC6 is a key effector of vasodilatory pathways in vascular myocytes and is enriched in fetal/neonatal tissues. Expression of both AC5 and AC6 decreases in heart failure; however, AC5 disruption is cardio-protective, while overexpression of AC6 rescues cardiac function in cardiac injury. This is a comprehensive review of the complex regulation of AC5 and AC6 in the cardiovascular system, highlighting overexpression and knockout studies as well as transgenic models illuminating each enzyme and focusing on post-translational modifications that regulate their cellular localization and biological functions. We also describe pharmacological challenges in the design of isoform-selective activators or inhibitors for AC5 and AC6, which may be relevant to developing new therapeutic approaches for several cardiovascular diseases.

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Dronedarone Attenuates Ang II-Induced Myocardial Hypertrophy Through Regulating SIRT1/FOXO3/PKIA Axis

BACKGROUND AND OBJECTIVES

Long-term pathological myocardial hypertrophy (MH) seriously affects the normal function of the heart. Dronedarone was reported to attenuate left ventricular hypertrophy of mice. However, the molecular regulatory mechanism of dronedarone in MH is unclear.

METHODS

Angiotensin II (Ang II) was used to induce cell hypertrophy of H9C2 cells. Transverse aortic constriction (TAC) surgery was performed to establish a rat model of MH. Cell size was evaluated using crystal violet staining and rhodamine phalloidin staining. Reverse transcription quantitative polymerase chain reaction and western blot were performed to detect the mRNA and protein expressions of genes. JASPAR and luciferase activity were conducted to predict and validate interaction between forkhead box O3 (FOXO3) and protein kinase inhibitor alpha (PKIA) promoter.

RESULTS

Ang II treatment induced cell hypertrophy and inhibited sirtuin 1 (SIRT1) expression, which were reversed by dronedarone. SIRT1 overexpression or PKIA overexpression enhanced dronedarone-mediated suppression of cell hypertrophy in Ang II-induced H9C2 cells. Mechanistically, SIRT1 elevated FOXO3 expression through SIRT1-mediated deacetylation of FOXO3 and FOXO3 upregulated PKIA expression through interacting with PKIA promoter. Moreover, SIRT1 silencing compromised dronedarone-mediated suppression of cell hypertrophy, while PKIA upregulation abolished the influences of SIRT1 silencing. More importantly, dronedarone improved TAC surgery-induced MH and impairment of cardiac function of rats via affecting SIRT1/FOXO3/PKIA axis.

CONCLUSIONS

Dronedarone alleviated MH through mediating SIRT1/FOXO3/PKIA axis, which provide more evidences for dronedarone against MH.

Modulation of cAMP/cGMP signaling as prevention of congenital heart defects in Pde2A deficient embryos: a matter of oxidative stress

Phosphodiesterase 2A (Pde2A) is a dual-specific PDE that breaks down both cAMP and cGMP cyclic nucleotides. We recently highlighted a direct relationship between Pde2A impairment, a consequent increase of cAMP, and the appearance of mouse congenital heart defects (CHDs). Here we aimed to characterize the pathways involved in the development of CHDs and in their prevention by pharmacological approaches targeting cAMP and cGMP signaling. Transcriptome analysis revealed a modulation of more than 500 genes affecting biological processes involved in the immune system, cardiomyocyte development and contractility, angiogenesis, transcription, and oxidative stress in hearts from Pde2A-/- embryos. Metoprolol and H89 pharmacological administration prevented heart dilatation and hypertabeculation in Pde2A-/- embryos. Metoprolol was also able to partially impede heart septum defect and oxidative stress at tissue and molecular levels. Amelioration of cardiac defects was also observed by using the antioxidant NAC, indicating oxidative stress as one of the molecular mechanisms underpinning the CHDs. In addition, Sildenafil treatment recovered cardiac defects suggesting the requirement of cAMP/cGMP nucleotides balance for the correct heart development.

Protein Kinase A Is a Master Regulator of Physiological and Pathological Cardiac Hypertrophy

BACKGROUND

The sympathoadrenergic system and its major effector PKA (protein kinase A) are activated to maintain cardiac output coping with physiological or pathological stressors. If and how PKA plays a role in physiological cardiac hypertrophy (PhCH) and pathological CH (PaCH) are not clear.

METHODS

Transgenic mouse models expressing the PKA inhibition domain (PKAi) of PKA inhibition peptide alpha (PKIalpha)-green fluorescence protein (GFP) fusion protein (PKAi-GFP) in a cardiac-specific and inducible manner (cPKAi) were used to determine the roles of PKA in physiological CH during postnatal growth or induced by swimming, and in PaCH induced by transaortic constriction (TAC) or augmented Ca2+ influx. Kinase profiling was used to determine cPKAi specificity. Echocardiography was used to determine cardiac morphology and function. Western blotting and immunostaining were used to measure protein abundance and phosphorylation. Protein synthesis was assessed by puromycin incorporation and protein degradation by measuring protein ubiquitination and proteasome activity. Neonatal rat cardiomyocytes (NRCMs) infected with AdGFP (GFP adenovirus) or AdPKAi-GFP (PKAi-GFP adenovirus) were used to determine the effects and mechanisms of cPKAi on myocyte hypertrophy. rAAV9.PKAi-GFP was used to treat TAC mice.

RESULTS

(1) cPKAi delayed postnatal cardiac growth and blunted exercise-induced PhCH; (2) PKA was activated in hearts after TAC due to activated sympathoadrenergic system, the loss of endogenous PKIα (PKA inhibition peptide α), and the stimulation by noncanonical PKA activators; (3) cPKAi ameliorated PaCH induced by TAC and increased Ca2+ influxes and blunted neonatal rat cardiomyocyte hypertrophy by isoproterenol and phenylephrine; (4) cPKAi prevented TAC-induced protein synthesis by inhibiting mTOR (mammalian target of rapamycin) signaling through reducing Akt (protein kinase B) activity, but enhancing inhibitory GSK-3α (glycogen synthase kinase-3α) and GSK-3β signals; (5) cPKAi reduced protein degradation by the ubiquitin-proteasome system via decreasing RPN6 phosphorylation; (6) cPKAi increased the expression of antihypertrophic atrial natriuretic peptide (ANP); (7) cPKAi ameliorated established PaCH and improved animal survival.

CONCLUSIONS

Cardiomyocyte PKA is a master regulator of PhCH and PaCH through regulating protein synthesis and degradation. cPKAi can be a novel approach to treat PaCH.

Role of cAMP in Cardiomyocyte Viability: Beneficial or Detrimental?

BACKGROUND

3', 5'-cyclic AMP (cAMP) regulates numerous cardiac functions. Various hormones and neurotransmitters elevate intracellular cAMP (i[cAMP]) in cardiomyocytes through activating GsPCRs (stimulatory-G-protein-coupled-receptors) and membrane-bound ACs (adenylyl cyclases). Increasing evidence has indicated that stimulating different GsPCRs and ACs exhibits distinct, even opposite effects, on cardiomyocyte viability. However, the underlying mechanisms are not fully understood.

METHODS

We used molecular and pharmacological approaches to investigate how different GsPCR/cAMP signaling differentially regulate cardiomyocyte viability with in vitro, ex vivo, and in vivo models.

RESULTS

For prodeath GsPCRs, we explored β1AR (beta1-adrenergic receptor) and H2R (histamine-H2-receptor). We found that their prodeath effects were similarly dependent on AC5 activation, ATP release to the extracellular space via PANX1 (pannexin-1) channel, and extracellular ATP (e[ATP])-mediated signaling involving in P2X7R (P2X purinoceptor 7) and CaMKII (Ca2+/calmodulin-dependent protein kinase II). PANX1 phosphorylation at Serine 206 by cAMP-dependent-PKA (protein-kinase-A) promoted PANX1 activation, which was critical in β1AR- or H2R-induced cardiomyocyte death in vitro and in vivo. β1AR or H2R was localized proximately to PANX1, which permits ATP release. For prosurvival GsPCRs, we explored adenosine-A2-receptor (A2R), CGRPR (calcitonin-gene-related-peptide-receptor), and RXFP1 (relaxin-family peptide-receptor 1). Their prosurvival effects were dependent on AC6 activation, cAMP efflux via MRP4 (multidrug resistance protein 4), extracellular cAMP metabolism to adenosine (e[cAMP]-to-e[ADO]), and e[ADO]-mediated signaling. A2R, CGRPR, or RXFP1 was localized proximately to MRP4, which enables cAMP efflux. Interestingly, exogenously increasing e[cAMP] levels by membrane-impermeable cAMP protected against cardiomyocyte death in vitro and in ex vivo and in vivo mouse hearts with ischemia-reperfusion injuries.

CONCLUSIONS

Our findings indicate that the functional diversity of different GsPCRs in cardiomyocyte viability could be achieved by their ability to form unique signaling complexes (signalosomes) that determine the fate of cAMP: either stimulate ATP release by activating PKA or directly efflux to be e[cAMP].

Ferroptosis contributes to catecholamine-induced cardiotoxicity and pathological remodeling

High levels of circulating catecholamines cause cardiac injury, pathological remodeling, and heart failure, but the underlying mechanisms remain elusive. Here we provide both in vitro and in vivo evidence that excessive β-adrenergic stimulation induces ferroptosis in cardiomyocytes, revealing a novel mechanism for catecholamine-induced cardiotoxicity and remodeling. We found that isoproterenol, a synthetic catecholamine, promoted glutathione depletion and glutathione peroxidase 4 (GPX4) degradation in cardiomyocytes, leading to GPX4 inactivation and enhanced lipid peroxidation. Isoproterenol also promoted heme oxygenase 1 (HO-1) expression by downregulating the transcription suppressor BTB and CNC homology 1 (Bach1), leading to increased labile iron accumulation through heme degradation. Moreover, isoproterenol markedly induced the accumulation of free iron and lipid reactive oxygen species (ROS) in the mitochondria, while targeted inhibition of iron overload and ROS accumulation within mitochondria effectively inhibited ferroptosis in cardiomyocytes. Importantly, isoproterenol administration markedly induced ferroptosis in the myocardium in vivo, associated with elevated non-heme iron accumulation driven by HO-1 upregulation. Strikingly, blockade of ferroptosis with ferrostatin-1 or inhibition of HO-1 activity with zinc protoporphyrin (ZnPP) effectively alleviated cardiac necrosis, pathological remodeling, and heart failure induced by isoproterenol administration. Taken together, our results reveal that catecholamine stimulation primarily induces ferroptotic cell death in cardiomyocyte through GPX4 and Bach1-HO-1 dependent signaling pathways. Targeting ferroptosis may represent a novel therapeutic strategy for catecholamine overload-induced myocardial injury and heart failure.

Takotsubo syndrome: getting closer to its causes

Takotsubo syndrome (TTS) accounts for between 1 and 4% of cases presenting clinically as an acute coronary syndrome. It typically presents as a transient cardiac phenotype of left ventricular dysfunction with spontaneous recovery. More dramatic presentations may include cardiogenic shock or cardiac arrest. Despite progress in the understanding of the condition since its first description in 1990, considerable questions remain into understanding underlying pathomechanisms. In this review article, we describe the current published data on potential underlying mechanisms associated with the onset of TTS including sympathetic nervous system over-stimulation, structural and functional alterations in the central nervous system, catecholamine secretion, alterations in the balance and distribution of adrenergic receptors, the additive impact of hormones including oestrogen, epicardial coronary or microvascular spasm, endothelial dysfunction, and genetics as potentially contributing to the cascade of events leading to the onset. These pathomechanisms provide suggestions for novel potential therapeutic strategies in patients with TTS including the role of cognitive behavioural therapy, beta-blockers, and endothelin-A antagonists. The underlying mechanism of TTS remains elusive. In reality, physical or emotional stressors likely trigger through the amygdala and hippocampus a central neurohumoral activation with the local and systemic secretion of excess catecholamine and other neurohormones, which exert its effect on the myocardium through a metabolic switch, altered cellular signalling, and endothelial dysfunction. These complex pathways exert a regional activation in the myocardium through the altered distribution of adrenoceptors and density of autonomic innervation as a protective mechanism from myocardial apoptosis. More research is needed to understand how these different complex mechanisms interact with each other to bring on the TTS phenotype.

Cyclic nucleotide phosphodiesterases as therapeutic targets in cardiac hypertrophy and heart failure

Cyclic nucleotide phosphodiesterases (PDEs) modulate the neurohormonal regulation of cardiac function by degrading cAMP and cGMP. In cardiomyocytes, multiple PDE isozymes with different enzymatic properties and subcellular localization regulate local pools of cyclic nucleotides and specific functions. This organization is heavily perturbed during cardiac hypertrophy and heart failure (HF), which can contribute to disease progression. Clinically, PDE inhibition has been considered a promising approach to compensate for the catecholamine desensitization that accompanies HF. Although PDE3 inhibitors, such as milrinone or enoximone, have been used clinically to improve systolic function and alleviate the symptoms of acute HF, their chronic use has proved to be detrimental. Other PDEs, such as PDE1, PDE2, PDE4, PDE5, PDE9 and PDE10, have emerged as new potential targets to treat HF, each having a unique role in local cyclic nucleotide signalling pathways. In this Review, we describe cAMP and cGMP signalling in cardiomyocytes and present the various PDE families expressed in the heart as well as their modifications in pathological cardiac hypertrophy and HF. We also appraise the evidence from preclinical models as well as clinical data pointing to the use of inhibitors or activators of specific PDEs that could have therapeutic potential in HF.

Myocardial infarction and oxidative damage in animal models: objective and expectations from the application of cysteine derivatives

Reactive oxygen species (ROS) and associated oxidative stress are the main contributors to pathophysiological changes following myocardial infarction (MI), which is the principal cause of death from cardiovascular disease. The glutathione (GSH)/glutathione peroxidase (GPx) system appears to be the main and most active cardiac antioxidant mechanism. Hence, enhancement of the myocardial GSH system might have protective effects in the setting of MI. It follows that by increasing antioxidant capacity, the heart will be able to reduce the damage associated with MI and even prevent/weaken the occurrence of oxidative stress, which is highly ranked among the factors responsible for the occurrence of acute MI. For these reasons, the primary goal of future investigations should be to address the effects of different antioxidative compounds and especially cysteine derivatives like N-acetyl cysteine (NAC) and L-2-oxothiazolidine-4-carboxylic acid (OTC) as precursors responsible for the enhancement of the GSH-related antioxidant system's capacity. It is assumed that this will lay down the basis for elucidation of the mechanisms throughout which applicable doses of OTC will manifest a potentially positive impact in the reduction of adverse effects of acute MI. The inclusion of OTC in the models for prediction of the distribution of oxygen in infarcted animal hearts can help to upgrade existing computational models. Such a model would be based on computational geometries of the heart, but the inclusion of biochemical redox features in addition to angiogenic therapy, despite improvement of the post-infarcted oxygenated outcome could enhance the accuracy of the predictive values of oxygenation.

Ablation of CXCR4 expression in cardiomyocytes exacerbates isoproterenol‑induced cell death and heart failure

CXCR4 is a seven‑transmembrane‑spanning Gi‑coupled receptor for the SDF‑1 chemokine and plays a critical role in cardiovascular development and post‑injury repair. However, the specific role of CXCR4 in cardiomyocytes is incompletely understood. It was hypothesized that CXCR4 activation in cardiomyocytes antagonizes β‑adrenoceptor/Gs signaling‑induced cardiac dysfunction. Cardiomyocyte‑specific CXCR4 knockout (CXCR4‑^CMKO) mice were generated by crossing CXCR4^fl/fl and MHC‑Cre^+/‑ mice. Their cardiac structure and function in the basal state are equivalent to that of the control MHC‑Cre^+/‑ littermates until at least 4 months old. However, following continuous subcutaneous administration of isoproterenol (Iso) via an osmotic mini‑pump, the ventricular myocardial contractility, dilation, cardiomyocyte apoptosis, and interstitial fibrosis are worse in CXCR4‑^CMKO mice than in MHC‑Cre^+/‑ littermates. In the cultured H9C2 cardiomyocytes, SDF‑1 treatment markedly attenuated Iso‑induced apoptosis and reduction in phospho‑Akt, and this protective effect was lost by knockdown of CXCR4 or by co‑treatment with Gi inhibitors. In conclusion, CXCR4 promotes cardiomyocyte survival and heart function during β‑adrenergic stress.

Takotsubo syndrome: A current review of presentation, diagnosis, and management

Takotsubo syndrome is a syndrome of acute heart failure due to left ventricular systolic dysfunction that is associated with increased cardiovascular morbidity and mortality. It occurs in both sexes and at all ages, but predominates in post-menopausal women for reasons that are unclear. In a patient who presents with cardiac symptoms, electrocardiographic changes, and/or biomarker elevation indicating myocardial stress (i.e. troponin elevation), this condition should be considered in the differential diagnosis. Cardiac imaging is critical for a timely diagnosis of this condition and has management implications. This syndrome can occur with or without underlying coronary artery disease, and while there are various characteristic myocardial patterns described on imaging, the most common one is left ventricular dysfunction due to apical stunning with basal hyperkinesis. In the acute phase, Takotsubo syndrome can lead to life-threatening sequelae, including cardiogenic shock, pulmonary edema, thromboembolism, and arrhythmias. Multiple pathophysiologic mechanisms are implicated, including an acute increase in left ventricular afterload in the setting of sympathetic activation with a catecholamine storm, multi-vessel coronary vasospasm, coronary endothelial microvascular dysfunction, and inflammation. In this review, we discuss the current knowledge surrounding presentation, diagnosis, and treatment of this under-diagnosed condition.

PGE2 protects against heart failure through inhibiting TGF-β1 synthesis in cardiomyocytes and crosstalk between TGF-β1 and GRK2

Inflammation plays a central role in the development of heart failure. Prostaglandin E2 (PGE2) is a key mediator of the inflammatory process in the cardiovascular system. However, the role of PGE2 in heart failure is complex and controversial. A recent report suggested that PGE2 inhibits acute β adrenergic receptor (β-AR) stimulation-enhanced cardiac contractility. The aim of this study was to characterize the influence of PGE2 on chronic β-AR stimulation-induced heart failure. Male C57BL/6 J mice received isoproterenol (ISO) or vehicle for 4 weeks. PGE2 significantly reversed ISO-induced cardiac contractile dysfunction and remodeling. Mechanically, ventricular myocytes were found to be an important source of TGF-β1 in ISO-model and PGE2 ablated TGF-β1 synthesis in cardiomyocytes through inhibition of β-AR activated PKA-CREB signaling. Furthermore, PGE2 significantly suppressed TGF-β1-GRK2 crosstalk-induced pro-hypertrophy and pro-fibrotic signaling in cardiomyocytes and cardiac fibroblasts, respectively. Pharmacological inhibition of GRK2 also attenuated contractile dysfunction and cardiac hypertrophy and fibrosis in ISO-model. These studies elucidate a novel mechanism by which PGE2 reduces TGF-β1 synthesis and its downstream signaling in heart failure and identify PGE2 or TGF-β1-GRK2 crosstalk as plausible therapeutic targets for preventing or treating heart failure induced by chronic β-AR stimulation.

Adrenal G Protein-Coupled Receptors and the Failing Heart: A Long-distance, Yet Intimate Affair

ABSTRACT

Systolic heart failure (HF) is a chronic clinical syndrome characterized by the reduction in cardiac function and still remains the disease with the highest mortality worldwide. Despite considerable advances in pharmacological treatment, HF represents a severe clinical and social burden. Chronic human HF is characterized by several important neurohormonal perturbations, emanating from both the autonomic nervous system and the adrenal glands. Circulating catecholamines (norepinephrine and epinephrine) and aldosterone elevations are among the salient alterations that confer significant hormonal burden on the already compromised function of the failing heart. This is why sympatholytic treatments (such as β-blockers) and renin-angiotensin system inhibitors or mineralocorticoid receptor antagonists, which block the effects of angiotensin II (AngII) and aldosterone on the failing heart, are part of the mainstay HF pharmacotherapy presently. The adrenal gland plays an important role in the modulation of cardiac neurohormonal stress because it is the source of almost all aldosterone, of all epinephrine, and of a significant amount of norepinephrine reaching the failing myocardium from the blood circulation. Synthesis and release of these hormones in the adrenals is tightly regulated by adrenal G protein-coupled receptors (GPCRs), such as adrenergic receptors and AngII receptors. In this review, we discuss important aspects of adrenal GPCR signaling and regulation, as they pertain to modulation of cardiac function in the context of chronic HF, by focusing on the 2 best studied adrenal GPCR types in that context, adrenergic receptors and AngII receptors (AT 1 Rs). Particular emphasis is given to findings from the past decade and a half that highlight the emerging roles of the GPCR-kinases and the β-arrestins in the adrenals, 2 protein families that regulate the signaling and functioning of GPCRs in all tissues, including the myocardium and the adrenal gland.

Tetramisole is a new IK1 channel agonist and exerts IK1 -dependent cardioprotective effects in rats

Cardiac ischemia, hypoxia, arrhythmias, and heart failure share the common electrophysiological changes featured by the elevation of intracellular Ca2+ (Ca2+ overload) and inhibition of the inward rectifier potassium (IK1 ) channel. IK1 channel agonists have been considered a new type of anti-arrhythmia and cardioprotective agents. We predicted using a drug repurposing strategy that tetramisole (Tet), a known anthelminthic agent, was a new IK1 channel agonist. The present study aimed to experimentally identify the above prediction and further demonstrate that Tet has cardioprotective effects. Results of the whole-cell patch clamp technique showed that Tet at 1-100 μmol/L enhanced IK1 current, hyperpolarized resting potential (RP), and shortened action potential duration (APD) in isolated rat cardiomyocytes, while without effects on other ion channels or transporters. In adult Sprague-Dawley (SD) rats in vivo, Tet showed anti-arrhythmia and anticardiac remodeling effects, respectively, in the coronary ligation-induced myocardial infarction model and isoproterenol (Iso, i.p., 3 mg/kg/day, 10 days) infusion-induced cardiac remodeling model. Tet also showed anticardiomyocyte remodeling effect in Iso (1 μmol/L) infused adult rat ventricular myocytes or cultured H9c2 (2-1) cardiomyocytes. Tet at 0.54 mg/kg in vivo or 30 μmol/L in vitro showed promising protections on acute ischemic arrhythmias, myocardial hypertrophy, and fibrosis. Molecular docking was performed and identified the selective binding of Tet with Kir2.1. The cardioprotection of Tet was associated with the facilitation of IK1 channel forward trafficking, deactivation of PKA signaling, and inhibition of intracellular calcium overload. Enhancing IK1 may play dual roles in anti-arrhythmia and antiventricular remodeling mediated by restoration of Ca2+ homeostasis.

Myocardial toxicity induced by silica nanoparticles in a transcriptome profile

The deleterious effects of silica nanoparticles (SiNPs) on human health and the ecological system have gradually gained attention owing to their heavy annual output and extensive global flux. The updated epidemiological or experimental investigations have demonstrated the potential myocardial toxicity triggered by SiNPs, but the underlying mechanisms and long-lasting cardiac effects are still poorly understood. Here, a rat model of sub-chronic respiratory exposure to SiNPs was conducted, and the histopathological analysis and ultrastructural investigation of heart tissues were carried out. More importantly, a comprehensive analysis of whole-genome transcription was utilized in rat heart to uncover key biological and cellular mechanisms triggered by SiNPs. The widening of myocardial space and partial fiber rupture were clearly manifested in rat heart after prolonged SiNPs exposure, particularly accompanied by mitochondrial swelling and cristae rupture. With the aid of Affymetrix GeneChips, 3153 differentially expressed genes (DEGs) were identified after SiNPs exposure, including 1916 down- and 1237 up-regulated genes. GO and KEGG analysis illustrated many important biological processes and pathways perturbed by SiNPs, mainly specializing in cellular stress, energy metabolism, actin filament dynamics and immune response. Signal-net analysis revealed that Prkaca (PKA) plays a core role in the cardiac toxification process of prolonged exposure of SiNPs to rats. Furthermore, qRT-PCR verified that PKA-mediated calcium signaling is probably responsible for SiNPs-induced cardiac injury. Conclusively, our study revealed that SiNPs caused myocardial injury, and particularly, provided transcriptomic insight into the role of PKA-calcium signaling triggered by SiNPs, which would facilitate SiNPs-based nanosafety assessment and biomedicine development.

Harnessing RKIP to Combat Heart Disease and Cancer

Cancer and heart disease are leading causes of morbidity and mortality worldwide. These diseases have common risk factors, common molecular signaling pathways that are central to their pathogenesis, and even some disease phenotypes that are interdependent. Thus, a detailed understanding of common regulators is critical for the development of new and synergistic therapeutic strategies. The Raf kinase inhibitory protein (RKIP) is a regulator of the cellular kinome that functions to maintain cellular robustness and prevent the progression of diseases including heart disease and cancer. Two of the key signaling pathways controlled by RKIP are the β-adrenergic receptor (βAR) signaling to protein kinase A (PKA), particularly in the heart, and the MAP kinase cascade Raf/MEK/ERK1/2 that regulates multiple diseases. The goal of this review is to discuss how we can leverage RKIP to suppress cancer without incurring deleterious effects on the heart. Specifically, we discuss: (1) How RKIP functions to either suppress or activate βAR (PKA) and ERK1/2 signaling; (2) How we can prevent cancer-promoting kinase signaling while at the same time avoiding cardiotoxicity.

A remarkable adaptive paradigm of heart performance and protection emerges in response to marked cardiac-specific overexpression of ADCY8

Adult (3 month) mice with cardiac-specific overexpression of adenylyl cyclase (AC) type VIII (TG^AC8) adapt to an increased cAMP-induced cardiac workload (~30% increases in heart rate, ejection fraction and cardiac output) for up to a year without signs of heart failure or excessive mortality. Here, we show classical cardiac hypertrophy markers were absent in TG^AC8, and that total left ventricular (LV) mass was not increased: a reduced LV cavity volume in TG^AC8 was encased by thicker LV walls harboring an increased number of small cardiac myocytes, and a network of small interstitial proliferative non-cardiac myocytes compared to wild type (WT) littermates; Protein synthesis, proteosome activity, and autophagy were enhanced in TG^AC8 vs WT, and Nrf-2, Hsp90α, and ACC2 protein levels were increased. Despite increased energy demands in vivo LV ATP and phosphocreatine levels in TG^AC8 did not differ from WT. Unbiased omics analyses identified more than 2,000 transcripts and proteins, comprising a broad array of biological processes across multiple cellular compartments, which differed by genotype; compared to WT, in TG^AC8 there was a shift from fatty acid oxidation to aerobic glycolysis in the context of increased utilization of the pentose phosphate shunt and nucleotide synthesis. Thus, marked overexpression of AC8 engages complex, coordinate adaptation "circuity" that has evolved in mammalian cells to defend against stress that threatens health or life (elements of which have already been shown to be central to cardiac ischemic pre-conditioning and exercise endurance cardiac conditioning) that may be of biological significance to allow for proper healing in disease states such as infarction or failure of the heart.

Chemotherapy-associated cardiomyopathy: Mechanisms of toxicity and cardioprotective strategies

OBJECTIVE

To describe the proposed mechanisms of chemotherapy-associated cardiomyopathy (CAC) and potential cardioprotective therapies for CAC including a comprehensive review of existing systematic analyses, guideline recommendations, and ongoing clinical trials.

DATA SOURCES

A literature search of MEDLINE was performed (from 1990 to June 2020) using the following search terms: anthracycline, trastuzumab, cardiomyopathy, cardiotoxicity, primary prevention, angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB), beta blocker, dexrazoxane (DEX) as well as using individual names from select therapeutic categories.

STUDY SELECTION AND DATA EXTRACTION

Existing English language systematic analyses and guidelines were considered.

DATA SYNTHESIS

The mechanisms of CAC are multifaceted, but various cardioprotective therapies target many of these pathways. To date, anthracyclines and HER-2 targeted therapies have been the focus of cardioprotective trials to date as they are the most commonly implicated therapies in CAC. While traditional neurohormonal antagonists (ACEIs, ARBs, and beta blockers) and DEX performed favorably in many small clinical trials, the quality of available evidence remains limited. Hence, major guidelines lack consensus on an approach to primary prevention of CAC. Given the uncertain role of preventive therapy, monitoring for a symptomatic or asymptomatic decline in LV function is imperative with prompt evaluation should this occur. Numerous ongoing randomized controlled trials seek to either confirm the findings of these previous studies or identify new therapeutic agents to prevent CAC. Clinical implications are derived from the available literature as well as current guideline recommendations for CAC cardioprotection.

CONCLUSION

At this time, no single therapy has a clear cardioprotective benefit in preventing CAC nor is any therapy strongly recommended by current guidelines. Additional studies are needed to determine the optimal preventative regimens.

Catecholamine-induced cardiotoxicity: A critical element in the pathophysiology of stroke-induced heart injury

Cerebrovascular diseases such as ischemic stroke, brain hemorrhage, and subarachnoid hemorrhage provoke cardiac complications such as heart failure, neurogenic stress-related cardiomyopathy and Takotsubo cardiomyopathy. With regards to the pathophysiology of stroke-induced heart injury, several mechanisms have been postulated to contribute to this complex interaction between brain and heart, including damage from gut dysbiosis, immune and systematic inflammatory responses, microvesicle- and microRNA-mediated vascular injury and damage from a surge of catecholamines. All these cerebrovascular diseases may trigger pronounced catecholamine surges through diverse ways, including stimulation of hypothalamic-pituitary adrenal axis, dysregulation of autonomic system, and secretion of adrenocorticotropic hormone. Primary catecholamines involved in this pathophysiological response include norepinephrine (NE) and epinephrine. Both are important neurotransmitters that connect the nervous system with the heart, leading to cardiac damage via myocardial ischemia, calcium (Ca²⁺) overload, oxidative stress, and mitochondrial dysfunction. In this review, we will aim to summarize the molecular mechanisms behind catecholamine-induced cardiotoxicity including Ca²⁺ overload, oxidative stress, apoptosis, cardiac hypertrophy, interstitial fibrosis, and inflammation. In addition, we will focus on how synchronization among these pathways evokes cardiotoxicity.

Immune cell β2-adrenergic receptors contribute to the development of heart failure

β-Adrenergic receptors (βARs) regulate normal and pathophysiological heart function through their impact on contractility. βARs are also regulators of immune function where they play a unique role depending on the disease condition and immune cell type. Emerging evidence suggests an important role for the β2AR subtype in regulating remodeling in the pathological heart; however, the importance of these responses has never been examined. In heart failure, catecholamines are elevated, leading to chronic βAR activation and contributing to the detrimental effects in the heart. We hypothesized that immune cell β2AR plays a critical role in the development of heart failure in response to chronic catecholamine elevations through their regulation of immune cell infiltration. To test this, chimeric mice were generated by performing bone marrow transplant (BMT) experiments using wild-type (WT) or β2AR knockout (KO) donors. WT and β2ARKO BMT mice were chronically administered the βAR agonist isoproterenol. Immune cell recruitment to the heart was examined by histology and flow cytometry. Numerous changes in immune cell recruitment were observed with isoproterenol administration in WT BMT mice including proinflammatory myeloid populations and lymphocytes with macrophages made up the majority of immune cells in the heart and which were absent in β2ARKO BMT animal. β2ARKO BMT mice had decreased cardiomyocyte death, hypertrophy, and interstitial fibrosis following isoproterenol treatment, culminating in improved function. These findings demonstrate an important role for immune cell β2AR expression in the heart's response to chronically elevated catecholamines.NEW & NOTEWORTHY Immune cell β2-adrenergic receptors (β2ARs) are important for proinflammatory macrophage infiltration to the heart in a chronic isoproterenol administration model of heart failure. Mice lacking immune cell β2AR have decreased immune cell infiltration to their heart, primarily proinflammatory macrophage populations. This decrease culminated to decreased cardiac injury with lessened cardiomyocyte death, decreased interstitial fibrosis and hypertrophy, and improved function demonstrating that β2AR regulation of immune responses plays an important role in the heart's response to persistent βAR stimulation.

Betulinic Acid Improves Cardiac-Renal Dysfunction Caused by Hypertrophy through Calcineurin-NFATc3 Signaling

Cardiac hypertrophy can lead to congestive heart failure and is a leading cause of morbidity and mortality worldwide. In recent years, it has been essential to find the treatment and prevention of cardiac hypertrophy. Betulinic acid (BA), the main active ingredient in many natural products, is known to have various physiological effects. However, as the potential effect of BA on cardiac hypertrophy and consequent renal dysfunction is unknown, we investigated the effect of BA on isoprenaline (ISO)-induced cardiac hypertrophy and related signaling. ISO was known to induce left ventricular hypertrophy by stimulating the β2-adrenergic receptor (β2AR). ISO was injected into Sprague Dawley rats (SD rats) by intraperitoneal injection once a day for 28 days to induce cardiac hypertrophy. From the 14th day onwards, the BA (10 or 30 mg/kg/day) and propranolol (10 mg/kg/day) were administered orally. The study was conducted in a total of 5 groups, as follows: C, control; Is, ISO (10 mg/kg/day); Pr, positive-control, ISO + propranolol (10 mg/kg/day); Bl, ISO + BA (10 mg/kg/day); Bh, ISO + BA (30 mg/kg/day). As a result, the total cardiac tissue and left ventricular tissue weights of the ISO group increased compared to the control group and were significantly reduced by BA treatment. In addition, as a result of echocardiography, the effect of BA on improving cardiac function, deteriorated by ISO, was confirmed. Cardiac hypertrophy biomarkers such as β-MHC, ANP, BNP, LDH, and CK-MB, which were increased by ISO, were significantly decreased by BA treatment. Also, the cardiac function improvement effect of BA was confirmed to improve cardiac function by inhibiting calcineurin/NFATc3 signaling. Renal dysfunction is a typical complication caused by cardiac hypertrophy. Therefore, the study of renal function indicators, creatinine clearance (Ccr) and osmolality (BUN) was aggravated by ISO treatment but was significantly restored by BA treatment. Therefore, it is thought that BA in cardiac hypertrophy can be used as valuable data to develop as a functional material effective in improving cardiac-renal dysfunction.

Cardiac cAMP-PKA Signaling Compartmentalization in Myocardial Infarction

Under physiological conditions, cAMP signaling plays a key role in the regulation of cardiac function. Activation of this intracellular signaling pathway mirrors cardiomyocyte adaptation to various extracellular stimuli. Extracellular ligand binding to seven-transmembrane receptors (also known as GPCRs) with G proteins and adenylyl cyclases (ACs) modulate the intracellular cAMP content. Subsequently, this second messenger triggers activation of specific intracellular downstream effectors that ensure a proper cellular response. Therefore, it is essential for the cell to keep the cAMP signaling highly regulated in space and time. The temporal regulation depends on the activity of ACs and phosphodiesterases. By scaffolding key components of the cAMP signaling machinery, A-kinase anchoring proteins (AKAPs) coordinate both the spatial and temporal regulation. Myocardial infarction is one of the major causes of death in industrialized countries and is characterized by a prolonged cardiac ischemia. This leads to irreversible cardiomyocyte death and impairs cardiac function. Regardless of its causes, a chronic activation of cardiac cAMP signaling is established to compensate this loss. While this adaptation is primarily beneficial for contractile function, it turns out, in the long run, to be deleterious. This review compiles current knowledge about cardiac cAMP compartmentalization under physiological conditions and post-myocardial infarction when it appears to be profoundly impaired.

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

Physiological And Pathological Roles Of Protein Kinase A In The Heart

Protein kinase A (PKA) is a central regulator of cardiac performance and morphology. Myocardial PKA activation is induced by a variety of hormones, neurotransmitters and stress signals, most notably catecholamines secreted by the sympathetic nervous system. Catecholamines bind β-adrenergic receptors to stimulate cAMP-dependent PKA activation in cardiomyocytes. Elevated PKA activity enhances Ca2+ cycling and increases cardiac muscle contractility. Dynamic control of PKA is essential for cardiac homeostasis, as dysregulation of PKA signaling is associated with a broad range of heart diseases. Specifically, abnormal PKA activation or inactivation contributes to the pathogenesis of myocardial ischemia, hypertrophy, heart failure, as well as diabetic, takotsubo, or anthracycline cardiomyopathies. PKA may also determine sex-dependent differences in contractile function and heart disease predisposition. Here, we describe the recent advances regarding the roles of PKA in cardiac physiology and pathology, highlighting previous study limitations and future research directions. Moreover, we discuss the therapeutic strategies and molecular mechanisms associated with cardiac PKA biology. In summary, PKA could serve as a promising drug target for cardioprotection. Depending on disease types and mechanisms, therapeutic intervention may require either inhibition or activation of PKA. Therefore, specific PKA inhibitors or activators may represent valuable drug candidates for the treatment of heart diseases.

Research progress on the role of CaMKII in heart disease

In the heart, Ca²⁺ participates in electrical activity and myocardial contraction, which is closely related to the generation of action potential and excitation contraction coupling (ECC) and plays an important role in various signal cascades and regulates different physiological processes. In the Ca²⁺ related physiological activities, CaMKII is a key downstream regulator, involving autophosphorylation and post-translational modification, and plays an important role in the excitation contraction coupling and relaxation events of cardiomyocytes. This paper reviews the relationship between CaMKII and various substances in the pathological process of myocardial apoptosis and necrosis, myocardial hypertrophy and arrhythmia, and what roles it plays in the development of disease in complex networks. This paper also introduces the drugs targeting at CaMKII to treat heart disease.

Protein Kinase Inhibitor Peptide as a Tool to Specifically Inhibit Protein Kinase A

The protein kinase enzyme family plays a pivotal role in almost every aspect of cellular function, including cellular metabolism, division, proliferation, transcription, movement, and survival. Protein kinase A (PKA), whose activation is triggered by cyclic adenosine monophosphate (cAMP), is widely distributed in various systems and tissues throughout the body and highly related to pathogenesis and progression of various kinds of diseases. The inhibition of PKA activation is essential for the study of PKA functions. Protein kinase inhibitor peptide (PKI) is a potent, heat-stable, and specific PKA inhibitor. It has been demonstrated that PKI can block PKA-mediated phosphorylase activation. Since then, researchers have a lot of knowledge about PKI. PKI is considered to be the most effective and specific method to inhibit PKA and is widely used in related research. In this review, we will first introduce the knowledge on the activation of PKA and mechanisms related on the inhibitory effects of PKI on PKA. Then, we will compare PKI-mediated PKA inhibition vs. several popular methods of PKA inhibition.

Recent Advances in β2-Agonists for Treatment of Chronic Respiratory Diseases and Heart Failure

β₂-Adrenoceptor (β₂-AR) agonists are widely used as bronchodilators. The emerge of ultralong acting β₂-agonists is an important breakthrough in pulmonary medicine. In this review, we will provide mechanistic insights into the application of β₂-agonists in asthma, chronic obstructive pulmonary disease (COPD), and heart failure (HF). Recent studies in β-AR signal transduction have revealed opposing functions of the β₁-AR and the β₂-AR on cardiomyocyte survival. Thus, β₂-agonists and β-blockers in combination may represent a novel strategy for HF management. Allosteric modulation and biased agonism at the β₂-AR also provide a theoretical basis for developing drugs with novel mechanisms of action and pharmacological profiles. Overlap of COPD and HF presents a substantial clinical challenge but also a unique opportunity for evaluation of the cardiovascular safety of β₂-agonists. Further basic and clinical research along these lines can help us develop better drugs and innovative strategies for the management of these difficult-to-treat diseases.

Multisite phosphorylation of the cardiac ryanodine receptor: a random or coordinated event?

Many proteins are phosphorylated at more than one phosphorylation site to achieve precise tuning of protein function and/or integrate a multitude of signals into the activity of one protein. Increasing the number of phosphorylation sites significantly broadens the complexity of molecular mechanisms involved in processing multiple phosphorylation sites by one or more distinct kinases. The cardiac ryanodine receptor (RYR2) is a well-established multiple phospho-target of kinases activated in response to β-adrenergic stimulation because this Ca²⁺ channel is a critical component of Ca²⁺ handling machinery which is responsible for β-adrenergic enhancement of cardiac contractility. Our review presents a selective overview of the extensive, often conflicting, literature which focuses on identifying reliable lines of evidence to establish if multiple RYR2 phosphorylation is achieved randomly or in a specific sequence, and whether phosphorylation at individual sites is functionally specific and additive or similar and can therefore be substituted.

Protein kinase A inhibitor proteins (PKIs) divert GPCR-Gαs-cAMP signaling toward EPAC and ERK activation and are involved in tumor growth

The PKA-inhibitor (PKI) family members PKIα, PKIβ, and PKIγ bind with high affinity to PKA and block its kinase activity, modulating the extent, and duration of PKA-mediated signaling events. While PKA is a well-known regulator of physiological and oncogenic events, the role of PKI proteins in these pathways has remained elusive. Here, by measuring activation of the MAPK pathway downstream of GPCR-Gαs-cAMP signaling, we show that the expression levels of PKI proteins can alter the balance of activation of two major cAMP targets: PKA and EPAC. Our results indicate that PKA maintains repressive control over MAPK signaling as well as a negative feedback on cAMP concentration. Overexpression of PKI and its subsequent repression of PKA dysregulates these signaling pathways, resulting in increased intracellular cAMP, and enhanced activation of EPAC and MAPK. We also find that amplifications of PKIA are common in prostate cancer and are associated with reduced progression free survival. Depletion of PKIA in prostate cancer cells leads to reduced migration, increased sensitivity to anoikis and reduced tumor growth. By altering PKA activity PKI can act as a molecular switch, driving GPCR-Gαs-cAMP signaling toward activation of EPAC-RAP1 and MAPK, ultimately modulating tumor growth.

GRK5 Controls SAP97-Dependent Cardiotoxic β1 Adrenergic Receptor-CaMKII Signaling in Heart Failure

RATIONALE

Cardiotoxic β₁ adrenergic receptor (β₁AR)-CaMKII (calmodulin-dependent kinase II) signaling is a major and critical feature associated with development of heart failure. SAP97 (synapse-associated protein 97) is a multifunctional scaffold protein that binds directly to the C-terminus of β₁AR and organizes a receptor signalosome.

OBJECTIVE

We aim to elucidate the dynamics of β₁AR-SAP97 signalosome and its potential role in chronic cardiotoxic β₁AR-CaMKII signaling that contributes to development of heart failure.

METHODS AND RESULTS

The integrity of cardiac β₁AR-SAP97 complex was examined in heart failure. Cardiac-specific deletion of SAP97 was developed to examine β₁AR signaling in aging mice, after chronic adrenergic stimulation, and in pressure overload hypertrophic heart failure. We show that the β₁AR-SAP97 signaling complex is reduced in heart failure. Cardiac-specific deletion of SAP97 yields an aging-dependent cardiomyopathy and exacerbates cardiac dysfunction induced by chronic adrenergic stimulation and pressure overload, which are associated with elevated CaMKII activity. Loss of SAP97 promotes PKA (protein kinase A)-dependent association of β₁AR with arrestin2 and CaMKII and turns on an Epac (exchange protein directly activated by cAMP)-dependent activation of CaMKII, which drives detrimental functional and structural remodeling in myocardium. Moreover, we have identified that GRK5 (G-protein receptor kinase-5) is necessary to promote agonist-induced dissociation of SAP97 from β₁AR. Cardiac deletion of GRK5 prevents adrenergic-induced dissociation of β₁AR-SAP97 complex and increases in CaMKII activity in hearts.

CONCLUSIONS

These data reveal a critical role of SAP97 in maintaining the integrity of cardiac β₁AR signaling and a detrimental cardiac GRK5-CaMKII axis that can be potentially targeted in heart failure therapy. Graphical Abstract: A graphical abstract is available for this article.

Effect of endostatin overexpression on angiotensin II-induced cardiac hypertrophy in rats

Background:

Endostatin, a biologically active fragment of collagen XVIII, has been observed in patients with ischemic heart disease. The aim of the present study was to investigate whether endostatin overexpression could attenuate cardiac hypertrophy by inhibiting the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) signaling pathway.

Methods:

This study was examined in vivo in rats and in vitro in primary neonatal rat cardiomyocytes treated with angiotensin (Ang) II to model cardiac hypertrophy. Twenty-four male Sprague-Dawley rats were randomized into adenovirus (Ad)-green fluorescent protein, Ang II, Ad-endostatin, and Ang II + Ad-endostatin groups (n = 6 in each group). Four weeks later, all the rats were weighed and sacrificed after transthoracic echocardiography. Cardiac function was evaluated by transthoracic echocardiography, cardiomyocyte size was evaluated by hematoxylin-eosin staining. Levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were evaluated by quantitative reverse-transcription polymerase chain reaction or Western blotting, PKA level was evaluated by Western blotting, and cAMP level was evaluated by enzyme-linked immunosorbent assay. Statistical significance among multiple groups was evaluated by one-way analysis of variance.

Results:

Endostatin overexpression reduced the increases in left ventricle (LV) mass (P = 0.0063), LV mass/body weight (BW) (P = 0.0013), interventricular septal thickness (IVS) in diastole (P = 0.0013), IVS in systole (P = 0.0056), left ventricular posterior wall thickness (LVPW) in diastole (P = 0.0291), LVPW in systole (P = 0.0080), heart weight (HW) (P = 0.0138), HW/BW (P = 0.0001), and HW/tibial length (P = 0.0372) in Ang II-treated rats. In addition, endostatin overexpression reduced cardiomyocyte cross-sectional area expansion, and reduced the levels of ANP and BNP in Ang II-treated rats (P = 0.0251 and 0.0477 for messenger RNA [mRNA]), and primary neonatal rat cardiomyocytes (P = 0.0188 and P = 0.0024 for mRNA; P = 0.0023 and 0.0013 for protein, respectively). Additionally, endostatin overexpression reduced the increase of cAMP (P = 0.0054) and PKA (P = 0.0328) levels in cardiomyocytes treated with Ang II. Treatment with cAMP reversed the effects of endostatin overexpression on ANP (P = 0.0263) and BNP (P = 0.0322) levels in cardiomyocytes induced by Ang II.

Conclusion:

Endostatin overexpression could alleviate cardiac hypertrophy by inhibiting the cAMP-PKA signaling pathway.

Investigating cardiac β-adrenergic nuclear signaling with FRET-based biosensors

By activating membrane β-adrenergic receptors (β-AR), noradrenaline and adrenaline are the most powerful stimulators of cardiac function. β-ARs are coupled to the synthesis of cAMP, which activates the cAMP-dependent protein kinase (PKA). PKA regulates the key proteins of excitation-contraction coupling but also gene expression. While an acute activation of the cAMP/PKA pathway allows adaptation of cardiac output to exercise, its chronic activation is deleterious by promoting pathological remodeling of the heart. The use of probes based on fluorescence resonance energy transfer (FRET) and located specifically at the level of the cytoplasm or the nucleus make it possible to highlight the differential mechanisms by which β-ARs control PKA activation in these two compartments. The characterization of these mechanisms is important in order to better understand the deleterious effects of chronic activation of the β-adrenergic pathway in the heart.

Exchange protein activated by cyclic-adenosine monophosphate (Epac) regulates atrial fibroblast function and controls cardiac remodelling

Aims

Heart failure (HF) produces left atrial (LA)-selective fibrosis and promotes atrial fibrillation. HF also causes adrenergic activation, which contributes to remodelling via a variety of signalling molecules, including the exchange protein activated by cAMP (Epac). Here, we evaluate the effects of Epac1-signalling on LA fibroblast (FB) function and its potential role in HF-related atrial remodelling.

Methods and results

HF was induced in adult male mongrel dogs by ventricular tachypacing (VTP). Epac1-expression decreased in LA-FBs within 12 h (-3.9-fold) of VTP onset. The selective Epac activator, 8-pCPT (50 µM) reduced, whereas the Epac blocker ESI-09 (1 µM) enhanced, collagen expression in LA-FBs. Norepinephrine (1 µM) decreased Epac1-expression, an effect blocked by prazosin, and increased FB collagen production. The β-adrenoceptor (AR) agonist isoproterenol increased Epac1 expression, an effect antagonized by ICI (β2-AR-blocker), but not by CGP (β1-AR-blocker). β-AR-activation with isoproterenol decreased collagen expression, an effect mimicked by the β2-AR-agonist salbutamol and blocked by the Epac1-antagonist ESI-09. Transforming growth factor-β1, known to be activated in HF, suppressed Epac1 expression, an effect blocked by the Smad3-inhibitor SIS3. To evaluate effects on atrial fibrosis in vivo, mice subjected to myocardial infarction (MI) received the Epac-activator Sp-8-pCPT or vehicle for 2 weeks post-MI; Sp-8-pCPT diminished LA fibrosis and attenuated cardiac dysfunction.

Conclusions

HF reduces LA-FB Epac1 expression. Adrenergic activation has complex effects on FBs, with α-AR-activation suppressing Epac1-expression and increasing collagen expression, and β2-AR-activation having opposite effects. Epac1-activation reduces cardiac dysfunction and LA fibrosis post-MI. Thus, Epac1 signalling may be a novel target for the prevention of profibrillatory cardiac remodelling.

PDE4 and mAKAPβ are nodal organizers of β2-ARs nuclear PKA signalling in cardiac myocytes

Aims

β1- and β2-adrenergic receptors (β-ARs) produce different acute contractile effects on the heart partly because they impact on different cytosolic pools of cAMP-dependent protein kinase (PKA). They also exert different effects on gene expression but the underlying mechanisms remain unknown. The aim of this study was to understand the mechanisms by which β1- and β2-ARs regulate nuclear PKA activity in cardiomyocytes.

Methods and results

We used cytoplasmic and nuclear targeted biosensors to examine cAMP signals and PKA activity in adult rat ventricular myocytes upon selective β1- or β2-ARs stimulation. Both β1- and β2-AR stimulation increased cAMP and activated PKA in the cytoplasm. Although the two receptors also increased cAMP in the nucleus, only β1-ARs increased nuclear PKA activity and up-regulated the PKA target gene and pro-apoptotic factor, inducible cAMP early repressor (ICER). Inhibition of phosphodiesterase (PDE)4, but not Gi, PDE3, GRK2 nor caveolae disruption disclosed nuclear PKA activation and ICER induction by β2-ARs. Both nuclear and cytoplasmic PKI prevented nuclear PKA activation and ICER induction by β1-ARs, indicating that PKA activation outside the nucleus is required for subsequent nuclear PKA activation and ICER mRNA expression. Cytoplasmic PKI also blocked ICER induction by β2-AR stimulation (with concomitant PDE4 inhibition). However, in this case nuclear PKI decreased ICER up-regulation by only 30%, indicating that other mechanisms are involved. Down-regulation of mAKAPβ partially inhibited nuclear PKA activation upon β1-AR stimulation, and drastically decreased nuclear PKA activation upon β2-AR stimulation in the presence of PDE4 inhibition.

Conclusions

β1- and β2-ARs differentially regulate nuclear PKA activity and ICER expression in cardiomyocytes. PDE4 insulates a mAKAPβ-targeted PKA pool at the nuclear envelope that prevents nuclear PKA activation upon β2-AR stimulation.

Hepatic PKA inhibition accelerates the lipid accumulation in liver

Background/aims

Liver lipid accumulation induced by high-fat diet (HFD) is an early onset process of non-alcoholic fatty liver diseases (NAFLD). Protein kinase A (PKA) is known to be involved in hepatic lipid metabolism. However, the role of PKA in NAFLD has not been well tested in vivo due to the lack of optimal PKA deficient mouse model.

Methods

A novel PKA-specific inhibitor gene was conditionally overexpressed in mouse (PKAi mouse) liver using LoxP/Cre system. PKA activity in the liver extract was measured with a commercial assay kit. The PKAi and control mice of 8-week age, were subjected to HFD or chow diet (CD) for 2 months. Body weight, liver index, and triglyceride in the liver were measured. RNA sequencing was performed for the liver tissues and analyzed with Gene Ontology (GO) and pathway enrichment.

Results

PKAi-GFP protein was overexpressed in the liver and the PKA activation was significantly inhibited in the liver of PKAi mouse. When fed with CD, RNA sequencing revealed 56 up-regulated and 51 down-regulated genes in PKAi mice compared with control mice, which were mainly involved in lipid metabolism though no significant differences in the body weight, liver index, triglyceride accumulation were observed between PKAi and control mice. However, when fed with HFD for 2 months, the liver was enlarged more, and the accumulation of triglyceride in the liver was more severe in PKAi mice. When comparing the transcriptomes of CD-fed and HFD-fed control mice, GO enrichment showed that the genes down-regulated by HFD were mainly enriched in immune-related GO terms, and up-regulated genes were enriched in metabolism. When comparing the transcriptomes of CD-fed and HFD-fed PKAi mice, GO analysis showed that the down-regulated genes were enriched in metabolism, while the up-regulated genes were clustered in ER stress-related pathways. When comparing HFD-fed PKAi and HFD-fed control mice, the genes with lower expression level in PKAi mice were enriched in the lipoprotein synthesis, which might explain that more TG is accumulated in PKAi liver after HFD feeding.

Conclusions

Reduced PKA activity could be a factor promoting the TG accumulation in the liver and the development of NAFLD.

The deficiency of miR-214-3p exacerbates cardiac fibrosis via miR-214-3p/NLRC5 axis

Cardiac fibrosis is a common pathological feature of many cardiovascular diseases. The regulatory mechanisms of miRNAs in cardiac fibrosis are still unknown. Previous studies on miR-214-3p in cardiac fibroblasts reached contradictory conclusions. Thus the role of miR-214-3p in cardiac fibrosis deserves further exploration. Using a combination of in vitro and in vivo studies, we identified miR-214-3p as an important regulator of cardiac fibrosis, and the proliferation and activation of cardiac fibroblasts. We demonstrated that the expression of miR-214-3p is down-regulated in TGF-β1-treated myofibroblasts and transverse aortic constriction (TAC)-induced murine model. Additionally, miR-214-3pflox/flox/FSP1-cre mice and miR-214-3pwt/wt/FSP1-cre mice were subjected to TAC operation or sham operation, and the conditional knockout of miR-214-3p in cardiac fibroblasts aggravates TAC-induced cardiac fibrosis. In vitro, our results indicate that miR-214-3p is an important repressor for fibroblasts proliferation and fibroblast-to-myofibroblast transition by functionally targeting NOD-like receptor family CARD domain containing 5 (NLRC5). In conclusion, our findings show that the deficiency of miR-214-3p exacerbates cardiac fibrosis and reveal a novel miR-214-3p/NLRC5 axis in the regulation of cardiac fibrosis.

'Acute micro-coronary syndrome': detailed coronary physiology in a patient with Takotsubo cardiomyopathy

Takotsubo cardiomyopathy (TC), otherwise known as stress cardiomyopathy, is characterised by acute, transient left ventricular systolic dysfunction with apical ballooning in the absence of obstructive epicardial coronary stenosis. The presentation of TC mimics that of acute myocardial infarction. More recently there has been a shift towards thinking of TC as a 'microvascular acute coronary syndrome'. Our case is of an 82-year-old woman who presented with TC mimicking acute anterior ST elevation myocardial infarction in the context of sepsis. Slow flow noted in the left anterior descending artery prompted us to perform coronary physiology. Her fractional flow reserve was 0.91, with an index of myocardial resistance of 117 and a coronary flow reserve of 1.6. In combination these results are indicative of microvascular coronary dysfunction in the absence of significant epicardial stenosis.

Phosphodiesterase 5 Associates With β2 Adrenergic Receptor to Modulate Cardiac Function in Type 2 Diabetic Hearts

Background

In murine heart failure models and in humans with diabetic‐related heart hypertrophy, inhibition of phosphodiesterase 5 (PDE5) by sildenafil improves cardiac outcomes. However, the mechanism by which sildenafil improves cardiac function is unclear. We have observed a relationship between PDE5 and β2 adrenergic receptor (β2AR), which is characterized here as a novel mechanistic axis by which sildenafil improves symptoms of diabetic cardiomyopathy.

Methods and Results

Wild‐type and β2AR knockout mice fed a high fat diet (HFD) were treated with sildenafil, and echocardiogram analysis was performed. Cardiomyocytes were isolated for excitation‐contraction (E‐C) coupling, fluorescence resonant energy transfer, and proximity ligation assays; while heart tissues were implemented for biochemical and histological analyses. PDE5 selectively associates with β2AR, but not β1 adrenergic receptor, and inhibition of PDE5 with sildenafil restores the impaired response to adrenergic stimulation in HFD mice and isolated ventriculomyocytes. Sildenafil enhances β adrenergic receptor (βAR)‐stimulated cGMP and cAMP signals in HFD myocytes. Consequently, inhibition of PDE5 leads to protein kinase G–, and to a lesser extent, calcium/calmodulin‐dependent kinase II–dependent improvements in adrenergically stimulated E‐C coupling. Deletion of β2AR abolishes sildenafil's effect. Although the PDE5‐β2AR association is not altered in HFD, phosphodiesterase 3 displays an increased association with the β2AR‐PDE5 complex in HFD myocytes.

Conclusions

This study elucidates mechanisms by which the β2AR‐PDE5 axis can be targeted for treating diabetic cardiomyopathy. Inhibition of PDE5 enhances β2AR stimulation of cGMP and cAMP signals, as well as protein kinase G–dependent E‐C coupling in HFD myocytes.

Studying β1 and β2 adrenergic receptor signals in cardiac cells using FRET-based sensors

Cyclic 3'-5' adenosine monophosphate (cAMP) is a key modulator of cardiac function. Thanks to the sophisticated organization of its pathway in distinct functional units called microdomains, cAMP is involved in the regulation of both inotropy and chronotropy as well as transcription and cardiac death. While visualization of cAMP microdomains can be achieved thanks to cAMP-sensitive FRET-based sensors, the molecular mechanisms through which cAMP-generating stimuli are coupled to distinct functional outcomes are not well understood. One possibility is that each stimulus activates multiple microdomains in order to generate a spatiotemporal code that translates into function. To test this hypothesis here we propose a series of experimental protocols that allow to simultaneously follow cAMP or Protein Kinase A (PKA)-dependent phosphorylation in different subcellular compartments of living cells. We investigate the responses of β Adrenergic receptors (β₁AR and β₂AR) challenged with selective drugs that enabled us to measure the actions of each receptor independently. At the whole cell level, we used a combination of co-culture with selective βAR stimulation and were able to molecularly separate cardiac fibroblasts from neonatal rat ventricular myocytes based on their cAMP responses. On the other hand, at the subcellular level, these experimental protocols allowed us to dissect the relative weight of β₁ and β₂ adrenergic receptors on cAMP signalling at the cytosol and outer mitochondrial membrane of NRVMs. We propose that experimental procedures that allow the collection of multiparametric data are necessary in order to understand the molecular mechanisms underlying the coupling between extracellular signals and cellular responses.

Exercise Attenuates Acute β-Adrenergic Overactivation-Induced Cardiac Fibrosis by Modulating Cytokines

During acute sympathetic stress, the overactivation of β-adrenergic receptors (β-ARs) causes cardiac fibrosis by triggering inflammation and cytokine expression. It is unknown whether exercise training inhibits acute β-AR overactivation-induced cytokine expression and cardiac injury. Here, we report that running exercise inhibited cardiac fibrosis and improved cardiac function in mice treated with isoproterenol (ISO), a β-AR agonist. A cytokine antibody array revealed that running exercise prevented most of the changes in cytokine expression induced by ISO. Specifically, ISO-induced upregulation of 18 cytokines was prevented by running exercise. A Kyoto encyclopedia of genes and genomes analysis of these cytokines revealed that Hedgehog and RAP1 signaling pathways were involved in the regulation of cytokine expression by exercise. The changes in the expression of some cytokines that were prevented by exercise were verified by an enzyme-linked immunosorbent assay and real-time PCR. In conclusion, running exercise prevented the cytokine expression changes after acute β-AR overactivation and therefore attenuated cardiac fibrosis. Acute sympathetic stress is an important risk factor for the patients with cardiovascular diseases, and the present study revealed that exercise training can prevent against the upregulation of cytokines and the subsequent cardiac injury induced by acute sympathetic stress, suggesting that exercise training may be beneficial for cardiovascular patients who are in risk of acute sympathetic stress. This finding provides a theoretical basis for the application of exercise training in patients who may suffer from acute sympathetic stress.

Cardiomyocyte PKA Ablation Enhances Basal Contractility While Eliminates Cardiac β-Adrenergic Response Without Adverse Effects on the Heart

RATIONALE

PKA (Protein Kinase A) is a major mediator of β-AR (β-adrenergic) regulation of cardiac function, but other mediators have also been suggested. Reduced PKA basal activity and activation are linked to cardiac diseases. However, how complete loss of PKA activity impacts on cardiac physiology and if it causes cardiac dysfunction have never been determined.

OBJECTIVES

We set to determine how the heart adapts to the loss of cardiomyocyte PKA activity and if it elicits cardiac abnormalities.

METHODS AND RESULTS

(1) Cardiac PKA activity was almost completely inhibited by expressing a PKA inhibitor peptide in cardiomyocytes (cPKAi) in mice; (2) cPKAi reduced basal phosphorylation of 2 myofilament proteins (TnI [troponin I] and cardiac myosin binding protein C), and one longitudinal SR (sarcoplasmic reticulum) protein (PLB [phospholamban]) but not of the sarcolemmal proteins (Cav1.2 α1c and PLM [phospholemman]), dyadic protein RyR2, and nuclear protein CREB (cAMP response element binding protein) at their PKA phosphorylation sites; (3) cPKAi increased the expression of CaMKII (Ca²⁺/calmodulin-dependent kinase II), the Cav1.2 β subunits and current, but decreased CaMKII phosphorylation and CaMKII-mediated phosphorylation of PLB and RyR2; (4) These changes resulted in significantly enhanced myofilament Ca²⁺ sensitivity, prolonged contraction, slowed relaxation but increased myocyte Ca²⁺ transient and contraction amplitudes; (5) Isoproterenol-induced PKA and CaMKII activation and their phosphorylation of proteins were prevented by cPKAi; (6) cPKAi abolished the increases of heart rate, and cardiac and myocyte contractility by a β-AR agonist (isoproterenol), showing an important role of PKA and a minimal role of PKA-independent β-AR signaling in acute cardiac regulation; (7) cPKAi mice have partial exercise capability probably by enhancing vascular constriction and ventricular filling during β-AR stimulation; and (8) cPKAi mice did not show any cardiac functional or structural abnormalities during the 1-year study period.

CONCLUSIONS

PKA activity suppression induces a unique Ca²⁺ handling phenotype, eliminates β-AR regulation of heart rates and cardiac contractility but does not cause cardiac abnormalities.

Protein Kinase A as a Promising Target for Heart Failure Drug Development

Heart failure (HF) is a clinical syndrome characterized by impaired ability of the heart to fill or eject blood. HF is rather prevalent and it represents the foremost reason of hospitalization in the United States. The costs linked to HF overrun those of all other causes of disabilities, and death in the United States and all over the developed as well as the developing countries which amplify the supreme significance of its prevention. Protein kinase (PK) A plays multiple roles in heart functions including, contraction, metabolism, ion fluxes, and gene transcription. Altered PKA activity is likely to cause the progression to cardiomyopathy and HF. Thus, this review is intended to focus on the roles of PKA and PKA-mediated signal transduction in the healthy heart as well as during the development of HF. Furthermore, the impact of cardiac PKA inhibition/activation will be highlighted to identify PKA as a potential target for the HF drug development.

Novel Mechanism of Foxo1 Phosphorylation in Glucagon Signaling in Control of Glucose Homeostasis

Dysregulation of hepatic glucose production (HGP) serves as a major underlying mechanism for the pathogenesis of type 2 diabetes. The pancreatic hormone glucagon increases and insulin suppresses HGP, controlling blood glucose homeostasis. The forkhead transcription factor Foxo1 promotes HGP through increasing expression of genes encoding the rate-limiting enzymes responsible for gluconeogenesis. We previously established that insulin suppresses Foxo1 by Akt-mediated phosphorylation of Foxo1 at Ser²⁵⁶ in human hepatocytes. In this study, we found a novel Foxo1 regulatory mechanism by glucagon, which promotes Foxo1 nuclear translocation and stability via cAMP- and protein kinase A-dependent phosphorylation of Foxo1 at Ser²⁷⁶ Replacing Foxo1-S276 with alanine (A) or aspartate (D) to block or mimic phosphorylation, respectively, markedly regulates Foxo1 stability and nuclear localization in human hepatocytes. To establish in vivo function of Foxo1-Ser²⁷⁶ phosphorylation in glucose metabolism, we generated Foxo1-S273A and Foxo1-S273D knock-in (KI) mice. The KI mice displayed impaired blood glucose homeostasis, as well as the basal and glucagon-mediated HGP in hepatocytes. Thus, Foxo1-Ser²⁷⁶ is a new target site identified in the control of Foxo1 bioactivity and associated metabolic diseases.

Pepducin-mediated cardioprotection via β-arrestin-biased β2-adrenergic receptor-specific signaling

Reperfusion as a therapeutic intervention for acute myocardial infarction-induced cardiac injury itself induces further cardiomyocyte death. β-arrestin (βarr)-biased β-adrenergic receptor (βAR) activation promotes survival signaling responses in vitro; thus, we hypothesize that this pathway can mitigate cardiomyocyte death at the time of reperfusion to better preserve function. However, a lack of efficacious βarr-biased orthosteric small molecules has prevented investigation into whether this pathway relays protection against ischemic injury in vivo. We recently demonstrated that the pepducin ICL1-9, a small lipidated peptide fragment designed from the first intracellular loop of β2AR, allosterically engaged pro-survival signaling cascades in a βarr-dependent manner in vitro. Thus, in this study we tested whether ICL1-9 relays cardioprotection against ischemia/reperfusion (I/R)-induced injury in vivo.

Methods: Wild-type (WT) C57BL/6, β2AR knockout (KO), βarr1KO and βarr2KO mice received intracardiac injections of either ICL1-9 or a scrambled control pepducin (Scr) at the time of ischemia (30 min) followed by reperfusion for either 24 h, to assess infarct size and cardiomyocyte death, or 4 weeks, to monitor the impact of ICL1-9 on long-term cardiac structure and function. Neonatal rat ventricular myocytes (NRVM) were used to assess the impact of ICL1-9 versus Scr pepducin on cardiomyocyte survival and mitochondrial superoxide formation in response to either serum deprivation or hypoxia/reoxygenation (H/R) in vitro and to investigate the associated mechanism(s).

Results: Intramyocardial injection of ICL1-9 at the time of I/R reduced infarct size, cardiomyocyte death and improved cardiac function in a β2AR- and βarr-dependent manner, which led to improved contractile function early and less fibrotic remodeling over time. Mechanistically, ICL1-9 attenuated mitochondrial superoxide production and promoted cardiomyocyte survival in a RhoA/ROCK-dependent manner. RhoA activation could be detected in cardiomyocytes and whole heart up to 24 h post-treatment, demonstrating the stability of ICL1-9 effects on βarr-dependent β2AR signaling.

Conclusion: Pepducin-based allosteric modulation of βarr-dependent β2AR signaling represents a novel therapeutic approach to reduce reperfusion-induced cardiac injury and relay long-term cardiac remodeling benefits.

Alamandine attenuates hypertension and cardiac hypertrophy in hypertensive rats

Oral administration of the peptide alamandine has antihypertensive and anti-fibrotic effects in rats. This work aimed to determine whether subcutaneous alamandine injection would attenuate hypertension and cardiac hypertrophy, and improve the function of a major target of hypertension-related damage, the left ventricle (LV), in spontaneously hypertensive rats (SHRs). This was examined in vivo in SHRs and normotensive rats subjected to 6-week subcutaneous infusion of alamandine or saline control, and in vitro in H9C2-derived and primary neonatal rat cardiomyocytes treated with angiotensin (Ang) II to model cardiac hypertrophy. Tail artery blood pressure measurement and transthoracic echocardiography showed that hypertension and impaired LV function in SHRs were ameliorated upon alamandine infusion. Alamandine administration also decreased the mass gains of heart and lung in SHRs, suppressed cardiomyocyte cross-sectional area expansion, and inhibited the mRNA levels of atrial natriuretic peptide and brain natriuretic peptide. The expression of alamandine receptor Mas-related G protein-coupled receptor, member D was increased in SHR hearts and in cardiomyocytes treated with Ang II. Alamandine inhibited the increases of protein kinase A (PKA) levels in the heart in SHRs and in cardiomyocytes treated with Ang II. In conclusion, the present study showed that alamandine administration attenuates hypertension, alleviates cardiac hypertrophy, and improves LV function. PKA signaling may be involved in the mechanisms underlying these effects.