Carvedilol Selectively Stimulates βArrestin2-Dependent SERCA2a Activity in Cardiomyocytes to Augment Contractility

Adrenoceptor Desensitization: Current Understanding of Mechanisms

G-protein coupled receptors (GPCRs) transduce a wide range of extracellular signals. They are key players in the majority of biologic functions including vision, olfaction, chemotaxis, and immunity. However, as essential as most of them are to body function and homeostasis, overactivation of GPCRs has been implicated in many pathologic diseases such as cancer, asthma, and heart failure (HF). Therefore, an important feature of G protein signaling systems is the ability to control GPCR responsiveness, and one key process to control overstimulation involves initiating receptor desensitization. A number of steps are appreciated in the desensitization process, including cell surface receptor phosphorylation, internalization, and downregulation. Rapid or short-term desensitization occurs within minutes and involves receptor phosphorylation via the action of intracellular protein kinases, the binding of β-arrestins, and the consequent uncoupling of GPCRs from their cognate heterotrimeric G proteins. On the other hand, long-term desensitization occurs over hours to days and involves receptor downregulation or a decrease in cell surface receptor protein level. Of the proteins involved in this biologic phenomenon, β-arrestins play a particularly significant role in both short- and long-term desensitization mechanisms. In addition, β-arrestins are involved in the phenomenon of biased agonism, where the biased ligand preferentially activates one of several downstream signaling pathways, leading to altered cellular responses. In this context, this review discusses the different patterns of desensitization of the α 1-, α 2- and the β adrenoceptors and highlights the role of β-arrestins in regulating physiologic responsiveness through desensitization and biased agonism. SIGNIFICANCE STATEMENT: A sophisticated network of proteins orchestrates the molecular regulation of GPCR activity. Adrenoceptors are GPCRs that play vast roles in many physiological processes. Without tightly controlled desensitization of these receptors, homeostatic imbalance may ensue, thus precipitating various diseases. Here, we critically appraise the mechanisms implicated in adrenoceptor desensitization. A better understanding of these mechanisms helps identify new druggable targets within the GPCR desensitization machinery and opens exciting therapeutic fronts in the treatment of several pathologies.

Qifu Yixin Formula Improves Heart Failure by Enhancing β-Arrestin2 Mediated the SUMOylation of SERCA2a

Purpose

This study aimed to elucidate the protective mechanism of Traditional Chinese Medicine (TCM) Qifu Yixin formula (QFYXF) to improve heart failure (HF) by promoting β-arrestin2 (β-arr2)-mediated SERCA2a SUMOylation.

Materials and Methods

The transverse aortic constriction (TAC)-induced HF mice were treated with QFYXF or carvedilol for 8 weeks. β-arr2-KO mice and their littermate wild-type (WT) mice were used as controls. Neonatal rat cardiomyocytes (NRCMs) were used in vitro. Cardiac function was evaluated by echocardiography and serum NT-proBNP. Myocardial hypertrophy and myocardial fibrosis were assessed by histological staining. β-arr2, SERCA2a, SUMO1, PLB and p-PLB expressions were detected by Western blotting, immunofluorescence and immunohistochemistry. SERCA2a SUMOylation was detected by Co-IP. The molecular docking method was used to predict the binding ability of the main active components of QFYXF to β-arr2, SERCA2a, and SUMO1, and the binding degree of SERCA2a to SUMO1 protein.

Results

The HF model was constructed 8 weeks after TAC. QFYXF ameliorated cardiac function, inhibiting myocardial hypertrophy and fibrosis. QFYXF promoted SERCA2a expression and SERCA2a SUMOylation. Further investigation showed that QFYXF promoted β-arr2 expression, whereas Barbadin (β-arr2 inhibitor) or β-arr2-KO reduced SERCA2a SUMOylation and attenuated the protective effect of QFYXF improved HF. Molecular docking showed that the main active components of QFYXF had good binding activities with β-arr2, SERCA2a, and SUMO1, and SERCA2a had a high binding degree with SUMO1 protein.

Conclusion

QFYXF improves HF by promoting β-arr2 mediated SERCA2a SUMOylation and increasing SERCA2a expression.

Nicotine Diminishes Alpha2-Adrenergic Receptor-Dependent Protection Against Oxidative Stress in H9c2 Cardiomyocytes

Introduction

Nicotine is a major component of cigarette smoke with various detrimental cardiovascular effects, including increased oxidative stress in the heart. Agonism of α2-adrenergic receptors (ARs), such as with dexmedetomidine, has been documented to exert cardioprotective effects against oxidative stress and related apoptosis and necroptosis. α2-ARs are membrane-residing G protein-coupled receptors (GPCRs) that primarily activate Gi/o proteins. They are also subjected to GPCR-kinase (GRK)-2-dependent desensitization, which entails phosphorylation of the agonist-activated receptor by GRK2 to induce its decoupling from G proteins, thus terminating α2AR-mediated G protein signaling.

Objective

In the present study, we sought to examine the effects of nicotine on α2AR signaling and effects in H9c2 cardiomyocytes exposed to H2O2 to induce oxidative cellular damage.

Methods and Results

As expected, treatment of H9c2 cardiomyocytes with H2O2 significantly decreased cell viability and increased oxidative stress, as assessed by reactive oxygen species (ROS)-associated fluorescence levels (DCF assay) and superoxide dismutase activity. Both H2O2 effects were partly rescued by α2AR activation with brimonidine in control cardiomyocytes but not in cells pretreated with nicotine for 24 hours, in which brimonidine was unable to reduce H2O2-induced cell death and oxidative stress. This was due to severe α2AR desensitization, manifested as very low Gi protein activation by brimonidine, and accompanied by GRK2 upregulation in nicotine-treated cardiomyocytes. Finally, pharmacological inhibition of adenylyl cyclase (AC) blocked H2O2-dependent oxidative damage in nicotine-pretreated H9c2 cardiomyocytes, indicating that α2AR activation protects against oxidative injury via its classic coupling to Gai-mediated AC inhibition.

Discussion/Conclusions

Nicotine can negate the cardioprotective effects of α2AR agonists against oxidative injury, which may have important implications for patients treated with this class of drugs that are chronic tobacco smokers.

Insights Into the Role of Angiotensin-II AT1 Receptor-Dependent β-Arrestin Signaling in Cardiovascular Disease

β-arrestins are a family of intracellular signaling proteins that play a key role in regulating the activity of G protein-coupled receptors. The angiotensin-II type 1 receptor is an important G protein-coupled receptor involved in the regulation of cardiovascular function and has been implicated in the progression of cardiovascular diseases. In addition to canonical G protein signaling, G protein-coupled receptors including the angiotensin-II type 1 receptor can signal via β-arrestin. Dysregulation of β-arrestin signaling has been linked to several cardiovascular diseases including hypertension, atherosclerosis, and heart failure. Understanding the role of β-arrestins in these conditions is critical to provide new therapeutic targets for the treatment of cardiovascular disease. In this review, we will discuss the beneficial and maladaptive physiological outcomes of angiotensin-II type 1 receptor-dependent β-arrestin activation in different cardiovascular diseases.

Role of G-Protein-Coupled Receptors in Cardiovascular Diseases

Cardiovascular diseases (CVDs), such as ischemic heart disease and stroke, are recognized as major causes of deaths worldwide [...].

Investigating the effects of beta-blockers on circadian heart rhythm using heart rate variability in ischemic heart disease with preserved ejection fraction

Heart failure is characterized by sympathetic activation and parasympathetic withdrawal leading to an abnormal autonomic modulation. Beta-blockers (BB) inhibit overstimulation of the sympathetic system and are indicated in heart failure patients with reduced ejection fraction. However, the effect of beta-blocker therapy on heart failure with preserved ejection fraction (HFpEF) is unclear. ECGs of 73 patients with HFpEF > 55% were recruited. There were 56 patients in the BB group and 17 patients in the without BB (NBB) group. The HRV analysis was performed for the 24-h period using a window size of 1,4 and 8-h. HRV measures between day and night for both the groups were also compared. Percentage change in the BB group relative to the NBB group was used as a measure of difference. RMSSD (13.27%), pNN50 (2.44%), HF power (44.25%) and LF power (13.53%) showed an increase in the BB group relative to the NBB group during the day and were statistically significant between the two groups for periods associated with high cardiac risk during the morning hours. LF:HF ratio showed a decrease of 3.59% during the day. The relative increase in vagal modulated RMSSD, pNN50 and HF power with a decrease in LF:HF ratio show an improvement in the parasympathetic tone and an overall decreased risk of a cardiac event especially during the morning hours that is characterized by a sympathetic surge.

Efficacy of the New Inotropic Agent Istaroxime in Acute Heart Failure

Current therapeutic strategies for acute heart failure (AHF) are based on traditional inotropic agents that are often associated with untoward effects; therefore, finding new effective approaches with a safer profile is dramatically needed. Istaroxime is a novel compound, chemically unrelated to cardiac glycosides, that is currently being studied for the treatment of AHF. Its effects are essentially related to its inotropic and lusitropic positive properties exerted through a dual mechanism of action: activation of the sarcoplasmic reticulum Ca2+ ATPase isoform 2a (SERCA2a) and inhibition of the Na+/K+-ATPase (NKA) activity. The advantages of istaroxime over the available inotropic agents include its lower arrhythmogenic action combined with its capability of increasing systolic blood pressure without augmenting heart rate. However, it has a limited half-life (1 hour) and is associated with adverse effects including pain at the injection site and gastrointestinal issues. Herein, we describe the main mechanism of action of istaroxime and we present a systematic overview of both clinical and preclinical trials testing this drug, underlining the latest insights regarding its adoption in clinical practice for AHF.