Carvedilol induces biased β1 adrenergic receptor-nitric oxide synthase 3-cyclic guanylyl monophosphate signalling to promote cardiac contractility

Qifu yixin prescription ameliorates cardiac fibrosis by activating soluble guanylate cyclase (sGC) in heart failure

ETHNOPHARMACOLOGICAL RELEVANCE

Qifu yixin prescription (QYP), an effective traditional Chinese medicine formula, has been utilized in the clinical treatment of cardiovascular diseases for over two decades and has been granted a national invention patent in China. It has demonstrated the ability to improve clinical symptoms in patients with heart failure. However, its precise effects and underlying molecular mechanisms remain unclear.

AIM OF THE STUDY

To evaluate the efficacy of QYP in treating HF and the underlying mechanisms.

MATERIALS AND METHODS

The heart failure (HF) model in mice was established using transverse aortic constriction (TAC), while neonatal rat cardiac fibroblasts (CFs) were utilized for in vitro experiments. The bioactive compounds in QYP were identified through high-performance liquid chromatography (HPLC). Cardiac hypertrophy, function, and fibrosis were assessed using morphological observations, echocardiography, and histomorphometric analyses. To investigate the underlying mechanisms by which QYP alleviates HF, transcriptomic analysis was conducted, and network pharmacology was employed to explore its potential mechanisms of action. Mechanistically, the expression levels of sGC, PKG, ERK, and p-ERK were analyzed using western blotting, immunohistochemistry, and immunofluorescence. Molecular docking was conducted to assess the binding affinity of the compounds of QYP to sGC. Additionally, the effects of QYP on CFs were investigated through cell-based assays.

RESULTS

We identified 33 bioactive compounds in QYP. Histomorphometric and transcriptomic analyses indicated that QYP alleviates cardiac fibrosis in HF. Network pharmacological analysis suggested that the sGC/cGMP/PKG and MAPK pathways are key mechanisms underlying the effects of QYP on cardiac fibrosis. The findings confirmed that QYP activates sGC, leading to the inhibition of ERK phosphorylation. Molecular docking revealed that the compounds of QYP exhibit strong binding affinity to sGC. Additionally, cell-based experiments demonstrated that QYP effectively suppresses CFs activation by stimulating sGC.

CONCLUSIONS

These results indicate QYP improves cardiac fibrosis in HF by activating sGC to inhibit ERK phosphorylation. We propose that QYP is a potential treatment for HF with anti-fibrotic properties.

Mechanical loading reveals an intrinsic cardiomyocyte stiffness contribution to diastolic dysfunction in murine cardiometabolic disease

Cardiometabolic syndromes including diabetes and obesity are associated with occurrence of heart failure with diastolic dysfunction. There are no specific treatments for diastolic dysfunction, and therapies to manage symptoms have limited efficacy. Understanding of the cardiomyocyte origins of diastolic dysfunction is an important priority to identify new therapeutics. The investigative goal was to experimentally define in vitro stiffness properties of isolated cardiomyocytes derived from rodent hearts exhibiting diastolic dysfunction in vivo in response to dietary induction of cardiometabolic disease. Male mice fed a high fat/sugar diet (HFSD vs. control) exhibited diastolic dysfunction (echo E/e' Doppler ratio). Intact paced cardiomyocytes were functionally investigated in three conditions: non-loaded, loaded and stretched. Mean stiffness of HFSD cardiomyocytes was 70% higher than control. E/e' for the HFSD hearts was elevated by 35%. A significant relationship was identified between in vitro cardiomyocyte stiffness and in vivo dysfunction severity. With conversion from the non-loaded to loaded condition, the decrement in maximal sarcomere lengthening rate was more accentuated in HFSD cardiomyocytes (vs. control). With stretch, the Ca2+ transient decay time course was prolonged. With increased pacing, cardiomyocyte stiffness was elevated, yet diastolic Ca2+ elevation was attenuated. Our findings show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non-loaded shortening. Collectively, these findings demonstrate that a component of cardiac diastolic dysfunction in cardiometabolic disease is derived from cardiomyocyte stiffness. Differential responses to load, stretch and pacing suggest that a previously undescribed alteration in myofilament-Ca2+ interaction contributes to intrinsic cardiomyocyte stiffness in cardiometabolic disease. KEY POINTS: Understanding cardiomyocyte stiffness components is an important priority for identifying new therapeutics for diastolic dysfunction, a key feature of cardiometabolic disease. In this study cardiac function was measured in vivo (echocardiography) for mice fed a high-fat/sugar diet (HFSD, ≥25 weeks). Performance of intact isolated cardiomyocytes derived from the same hearts was measured during pacing under non-loaded, loaded and stretched conditions in vitro. Calibrated cardiomyocyte stretches demonstrated that stiffness (stress/strain) was elevated in HFSD cardiomyocytes in vitro and correlated with diastolic dysfunction (E/e') in vivo. HFSD cardiomyocyte Ca2+ transient decay was prolonged in response to stretch. Stiffness was accentuated with pacing increase while the elevation in diastolic Ca2+ was attenuated. Data show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non-loaded shortening. These findings suggest that stretch-dependent augmentation of the myofilament-Ca2+ response during diastole partially underlies elevated cardiomyocyte stiffness and diastolic dysfunction of hearts of animals with cardiometabolic disease.

Mechanical loading reveals an intrinsic cardiomyocyte stiffness contribution to diastolic dysfunction in murine cardiometabolic disease

Cardiometabolic syndromes including diabetes and obesity are associated with occurrence of heart failure with diastolic dysfunction. There are no specific treatments for diastolic dysfunction, and therapies to manage symptoms have limited efficacy. Understanding of the cardiomyocyte origins of diastolic dysfunction is an important priority to identify new therapeutics. The investigative goal was to experimentally define in vitro stiffness properties of isolated cardiomyocytes derived from rodent hearts exhibiting diastolic dysfunction in vivo in response to dietary induction of cardiometabolic disease. Male mice fed a high fat/sugar diet (HFSD vs control) exhibited diastolic dysfunction (echo E/e' doppler ratio). Intact paced cardiomyocytes were functionally investigated in three conditions: non-loaded, loaded and stretched. Mean stiffness of HFSD cardiomyocytes was 70% higher than control. E/e' for the origin hearts was elevated by 35%. A significant relationship was identified between in vitro cardiomyocyte stiffness and in vivo dysfunction severity. With conversion from non-loaded to loaded condition, the decrement in maximal sarcomere lengthening rate was more accentuated in HFSD cardiomyocytes (vs control). With stretch, the Ca2+ transient decay time course was prolonged. With increased pacing, cardiomyocyte stiffness was elevated, yet diastolic Ca2+ elevation was attenuated. Our findings show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non-loaded shortening. Collectively, these findings demonstrate that a component of cardiac diastolic dysfunction in cardiometabolic disease is derived from cardiomyocyte stiffness. Differential responses to load, stretch and pacing suggest that a previously undescribed alteration in myofilament-Ca2+ interaction contributes to intrinsic cardiomyocyte stiffness in cardiometabolic disease.

Mechanistic insights into carvedilol's potential protection against doxorubicin-induced cardiotoxicity

Doxorubicin (DOX) is an anthracycline chemotherapy drug widely employed in the treatment of various cancers, known for its potent antineoplastic properties but often associated with dose-dependent cardiotoxicity, limiting its clinical use. This review explores the complex molecular details that determine the heart-protective effectiveness of carvedilol in relation to cardiotoxicity caused by DOX. The harmful effects of DOX on heart cells could include oxidative stress, DNA damage, iron imbalance, disruption of autophagy, calcium imbalance, apoptosis, dysregulation of topoisomerase 2-beta, arrhythmogenicity, and inflammatory responses. This review carefully reveals how carvedilol serves as a strong protective mechanism, strategically reducing each aspect of cardiac damage caused by DOX. Carvedilol's antioxidant capabilities involve neutralizing free radicals and adjusting crucial antioxidant enzymes. It skillfully manages iron balance, controls autophagy, and restores the calcium balance essential for cellular stability. Moreover, the anti-apoptotic effects of carvedilol are outlined through the adjustment of Bcl-2 family proteins and activation of the Akt signaling pathway. The medication also controls topoisomerase 2-beta and reduces the renin-angiotensin-aldosterone system, together offering a thorough defense against cardiotoxicity induced by DOX. These findings not only provide detailed understanding into the molecular mechanisms that coordinate heart protection by carvedilol but also offer considerable potential for the creation of targeted treatment strategies intended to relieve cardiotoxicity caused by chemotherapy.

Carvedilol Activates a Myofilament Signaling Circuitry to Restore Cardiac Contractility in Heart Failure

Phosphorylation of myofilament proteins critically regulates beat-to-beat cardiac contraction and is typically altered in heart failure (HF). β-Adrenergic activation induces phosphorylation in numerous substrates at the myofilament. Nevertheless, how cardiac β-adrenoceptors (βARs) signal to the myofilament in healthy and diseased hearts remains poorly understood. The aim of this study was to uncover the spatiotemporal regulation of local βAR signaling at the myofilament and thus identify a potential therapeutic target for HF. Phosphoproteomic analysis of substrate phosphorylation induced by different βAR ligands in mouse hearts was performed. Genetically encoded biosensors were used to characterize cyclic adenosine and guanosine monophosphate signaling and the impacts on excitation-contraction coupling induced by β1AR ligands at both the cardiomyocyte and whole-heart levels. Myofilament signaling circuitry was identified, including protein kinase G1 (PKG1)-dependent phosphorylation of myosin light chain kinase, myosin phosphatase target subunit 1, and myosin light chain at the myofilaments. The increased phosphorylation of myosin light chain enhances cardiac contractility, with a minimal increase in calcium (Ca2+) cycling. This myofilament signaling paradigm is promoted by carvedilol-induced β1AR-nitric oxide synthetase 3 (NOS3)-dependent cyclic guanosine monophosphate signaling, drawing a parallel to the β1AR-cyclic adenosine monophosphate-protein kinase A pathway. In patients with HF and a mouse HF model of myocardial infarction, increasing expression and association of NOS3 with β1AR were observed. Stimulating β1AR-NOS3-PKG1 signaling increased cardiac contraction in the mouse HF model. This research has characterized myofilament β1AR-PKG1-dependent signaling circuitry to increase phosphorylation of myosin light chain and enhance cardiac contractility, with a minimal increase in Ca2+ cycling. The present findings raise the possibility of targeting this myofilament signaling circuitry for treatment of patients with HF.

The role of serine/threonine protein kinases in cardiovascular disease and potential therapeutic methods

Protein phosphorylation is an important link in a variety of signaling pathways, and most of the important life processes in cells involve protein phosphorylation. Based on the amino acid residues of phosphorylated proteins, protein kinases can be categorized into the following families: serine/threonine protein kinases, tyrosine-specific protein kinases, histidine-specific protein kinases, tryptophan kinases, and aspartate/glutamyl protein kinases. Of all the protein kinases, most are serine/threonine kinases, where serine/threonine protein kinases are protein kinases that catalyze the phosphorylation of serine or threonine residues on target proteins using ATP as a phosphate donor. The current socially accepted classification of serine/threonine kinases is to divide them into seven major groups: protein kinase A, G, C (AGC), CMGC, Calmodulin-dependent protein kinase (CAMK), Casein kinase (CK1), STE, Tyrosine kinase (TKL) and others. After decades of research, a preliminary understanding of the specific classification and respective functions of serine/threonine kinases has entered a new period of exploration. In this paper, we review the literature of the previous years and introduce the specific signaling pathways and related therapeutic modalities played by each of the small protein kinases in the serine/threonine protein kinase family, respectively, in some common cardiovascular system diseases such as heart failure, myocardial infarction, ischemia-reperfusion injury, and diabetic cardiomyopathy. To a certain extent, the current research results, including molecular mechanisms and therapeutic methods, are fully summarized and a systematic report is made for the prevention and treatment of cardiovascular diseases in the future.

From "contraindicated" to "first line" - Current mechanistic insights beyond canonical β-receptor signaling

β-blockers are a solid pillar in the treatment of cardiovascular diseases. However, they are highly discussed regarding effectiveness for certain indications and side-effects. Even though there are up to 20 licensed compounds, only four are used for heart failure (HF) therapy. On the receptor level several key characteristics seem to influence the clinical outcome: subtype selectivity, antagonistic vs (inverse/biased) agonistic properties and -in particular- ancillary capacities. On a molecular level, divergent and novel signaling patterns are being identified and extra-cardiac effects on e.g. inflammation, metabolism and oxidative stress are highlighted. This review discusses different well-known and newly discovered characteristics that need to be considered for HF therapy and in the context of co-morbidities.

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.

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.

The mechanism of 25-hydroxycholesterol-mediated suppression of atrial β1-adrenergic responses

25-Hydroxycholesterol (25HC) is a biologically active oxysterol, whose production greatly increases during inflammation by macrophages and dendritic cells. The inflammatory reactions are frequently accompanied by changes in heart regulation, such as blunting of the cardiac β-adrenergic receptor (AR) signaling. Here, the mechanism of 25HC-dependent modulation of responses to β-AR activation was studied in the atria of mice. 25HC at the submicromolar levels decreased the β-AR-mediated positive inotropic effect and enhancement of the Ca2+ transient amplitude, without changing NO production. Positive inotropic responses to β1-AR (but not β2-AR) activation were markedly attenuated by 25HC. The depressant action of 25HC on the β1-AR-mediated responses was prevented by selective β3-AR antagonists as well as inhibitors of Gi protein, Gβγ, G protein-coupled receptor kinase 2/3, or β-arrestin. Simultaneously, blockers of protein kinase D and C as well as a phosphodiesterase inhibitor did not preclude the negative action of 25HC on the inotropic response to β-AR activation. Thus, 25HC can suppress the β1-AR-dependent effects via engaging β3-AR, Gi protein, Gβγ, G protein-coupled receptor kinase, and β-arrestin. This 25HC-dependent mechanism can contribute to the inflammatory-related alterations in the atrial β-adrenergic signaling.

CP-25 inhibits the hyperactivation of rheumatic synoviocytes by suppressing the switch in Gαs-Gαi coupling to the β2-adrenergic receptor

In essence, the β2 adrenergic receptor (β2AR) plays an antiproliferative role by increasing the intracellular cyclic 3',5'-adenosine monophosphate (cAMP) concentration through Gαs coupling, but interestingly, β2AR antagonists are able to effectively inhibit fibroblast-like synoviocytes (FLSs) proliferation, thus ameliorating experimental RA, indicating that the β2AR signalling pathway is impaired in RA FLSs via unknown mechanisms. The local epinephrine (Epi) level was found to be much higher in inflammatory joints than in normal joints, and high-level stimulation with Epi or isoproterenol (ISO) directly promoted FLSs proliferation and migration due to impaired β2AR signalling and cAMP production. By applying inhibitor of receptor internalization, and small interfering RNA (siRNA) of Gαs and Gαi, and by using fluorescence resonance energy transfer and coimmunoprecipitation assays, a switch in Gαs-Gαi coupling to β2AR was observed in inflammatory FLSs as well as in FLSs with chronic ISO stimulation. This Gαi coupling was then revealed to be initiated by G protein coupled receptor kinase 2 (GRK2) but not β-arrestin2 or protein kinase A-mediated phosphorylation of β2AR. Inhibiting the activity of GRK2 with the novel GRK2 inhibitor paeoniflorin-6'-O-benzene sulfonate (CP-25), a derivative of paeoniflorin, or the accepted GRK2 inhibitor paroxetine effectively reversed the switch in Gαs-Gαi coupling to β2AR during inflammation and restored the intracellular cAMP level in ISO-stimulated FLSs. As expected, CP-25 significantly inhibited the hyperplasia of FLSs in a collagen-induced arthritis (CIA) model (CIA FLSs) and normal FLSs stimulated with ISO and finally ameliorated CIA in rats. Together, our findings revealed the pathological changes in β2AR signalling in CIA FLSs, determined the underlying mechanisms and identified the pharmacological target of the GRK2 inhibitor CP-25 in treating CIA. Video Abstract.

Past and present of beta arrestins: A new perspective on insulin secretion and effect

BACKGROUND

Beta arrestins had been known as intracellular adaptors that uncouple and inactivate the G protein-coupled receptors that they interact with. Their roles as signal initiators for some receptors have recently been recognized.

SCOPE OF REVIEW

In this review, we focused on their role in mediating metabolic modulation primarily in relation to insulin signaling. Commenced by the upstream receptor, they seem to act like intracellular hubs that divert the metabolic profile of the cell. The amount of metabolic substrates in circulation and their usage/deposition by tissues are controlled by the contribution of all systems in the organism. This control is enabled by the release of hormones such as insulin, glucagon and glucagon-like peptide-1. Intriguingly, some ligands -either agonists or antagonists-of different classes of receptors have preferential properties mediated by β arrestins. This is not surprizing considering that substrate supply and usage should parallel physiological function such as hormone release or muscle contraction.

MAJOR CONCLUSIONS

Available data indicate that β arrestins conduct the regulatory role in insulin secretion and action. They may be good candidates to target when the upstream signal demands the function that may compromise the cell. An example is carvedilol that is protective by preventing the stimulatory effects of excessive catecholamines, stimulates mitochondrial function and has preferential clinical outcomes in metabolic disorders.

Chronic β-adrenergic stress contributes to cardiomyopathy in rodents with collagen-induced arthritis

Patients with rheumatoid arthritis (RA) have a much higher incidence of cardiac dysfunction, which contributes to the high mortality rate of RA despite anti-arthritic drug therapy. In this study, we investigated dynamic changes in cardiac function in classic animal models of RA and examined the potential effectors of RA-induced heart failure (HF). Collagen-induced arthritis (CIA) models were established in rats and mice. The cardiac function of CIA animals was dynamically monitored using echocardiography and haemodynamics. We showed that cardiac diastolic and systolic dysfunction occurred in CIA animals and persisted after joint inflammation and that serum proinflammatory cytokine (IL-1β, TNF-α) levels were decreased. We did not find evidence of atherosclerosis (AS) in arthritic animals even though cardiomyopathy was significant. We observed that an impaired cardiac β1AR-excitation contraction coupling signal was accompanied by sustained increases in blood epinephrine levels in CIA rats. Furthermore, serum epinephrine concentrations were positively correlated with the heart failure biomarker NT-proBNP in RA patients (r2 = +0.53, P < 0.0001). In CIA mice, treatment with the nonselective βAR blocker carvedilol (2.5 mg·kg-1·d-1, for 4 weeks) or the specific GRK2 inhibitor paroxetine (2.5 mg·kg-1·d-1, for 4 weeks) effectively rescued heart function. We conclude that chronic and persistent β-adrenergic stress in CIA animals is a significant contributor to cardiomyopathy, which may be a potential target for protecting RA patients against HF.

New Therapeutics for Heart Failure: Focusing on cGMP Signaling

Current drugs for treating heart failure (HF), for example, angiotensin II receptor blockers and β-blockers, possess specific target molecules involved in the regulation of the cardiac circulatory system. However, most clinically approved drugs are effective in the treatment of HF with reduced ejection fraction (HFrEF). Novel drug classes, including angiotensin receptor blocker/neprilysin inhibitor (ARNI), sodium-glucose co-transporter-2 (SGLT2) inhibitor, hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker, soluble guanylyl cyclase (sGC) stimulator/activator, and cardiac myosin activator, have recently been introduced for HF intervention based on their proposed novel mechanisms. SGLT2 inhibitors have been shown to be effective not only for HFrEF but also for HF with preserved ejection fraction (HFpEF). In the myocardium, excess cyclic adenosine monophosphate (cAMP) stimulation has detrimental effects on HFrEF, whereas cyclic guanosine monophosphate (cGMP) signaling inhibits cAMP-mediated responses. Thus, molecules participating in cGMP signaling are promising targets of novel drugs for HF. In this review, we summarize molecular pathways of cGMP signaling and clinical trials of emerging drug classes targeting cGMP signaling in the treatment of HF.

Probing spatiotemporal PKA activity at the ryanodine receptor and SERCA2a nanodomains in cardomyocytes

Spatiotemporal regulation of subcellular protein kinase A (PKA) activity for precise substrate phosphorylation is essential for cellular responses to hormonal stimulation. Ryanodine receptor 2 (RyR2) and (sarco)endoplasmic reticulum calcium ATPase 2a (SERCA2a) represent two critical targets of β adrenoceptor (βAR) signaling on the sarcoplasmic reticulum membrane for cardiac excitation and contraction coupling. Using novel biosensors, we show that cardiac β1AR signals to both RyR2 and SERCA2a nanodomains in cardiomyocytes from mice, rats, and rabbits, whereas the β2AR signaling is restricted from these nanodomains. Phosphodiesterase 4 (PDE4) and PDE3 control the baseline PKA activity and prevent β2AR signaling from reaching the RyR2 and SERCA2a nanodomains. Moreover, blocking inhibitory G protein allows β2AR signaling to the RyR2 but not the SERCA2a nanodomains. This study provides evidence for the differential roles of inhibitory G protein and PDEs in controlling the adrenergic subtype signaling at the RyR2 and SERCA2a nanodomains in cardiomyocytes.

Gi-protein-coupled β 1-adrenergic receptor: re-understanding the selectivity of β 1-adrenergic receptor to G protein

β ₁-adrenergic receptor (β ₁-AR), a member in the family of G-protein-coupled receptors, is a transmembrane receptor of great significance in the heart. Physiologically, catecholamines activate β ₁-AR to initiate a positive chronotropic, inotropic, and dromotropic change. It is believed that β ₁-AR couples to Gs protein and transmits the signal through second messenger cAMP. However, increasing research shows that β ₁-AR can also bind with Gi protein in addition to Gs. When β ₁-AR-Gi is biasedly activated, cardioprotective effects are introduced by the activated cGMP-protein kinase G (PKG) pathway and the transactivation of epidermal growth factor receptor (EGFR) pathway. The discovery of β ₁-AR-Gi signaling makes us reconsider the selectivity of G protein with regard to β ₁-AR, which also provides new ideas for the treatment of heart diseases. This review summarizes the discovery of β ₁-AR-Gi pathway, including the evidence that supports β ₁-AR's capability to couple Gi, details of the transduction process and functions of the β ₁-AR-Gi signaling pathway.

Activation of PKG-CREB-KLF15 by melatonin attenuates Angiotensin II-induced vulnerability to atrial fibrillation via enhancing branched-chain amino acids catabolism

Mitochondrial reactive oxygen species (ROS) damage and atrial remodeling serve as the crucial substrates for the genesis of atrial fibrillation (AF). Branched-chain amino acids (BCAAs) catabolic defect plays critical roles in multiple cardiovascular diseases. However, the alteration of atrial BCAA catabolism and its role in AF remain largely unknown. This study aimed to explore the role of BCAA catabolism in the pathogenesis of AF and to further evaluate the therapeutic effect of melatonin with a focus on protein kinase G (PKG)-cAMP response element binding protein (CREB)-Krüppel-like factor 15 (KLF15) signaling. We found that angiotensin II-treated atria exhibited significantly elevated BCAA level, reduced BCAA catabolic enzyme activity, increased AF vulnerability, aggravated atrial electrical and structural remodeling, and enhanced mitochondrial ROS damage. These deleterious effects were attenuated by melatonin co-administration while exacerbated by BCAA oral supplementation. Melatonin treatment ameliorated BCAA-induced atrial damage and reversed BCAA-induced down-regulation of atrial PKGIα expression, CREB phosphorylation as well as KLF15 expression. However, inhibition of PKG partly abolished melatonin-induced beneficial actions. In summary, these data demonstrated that atrial BCAA catabolic defect contributed to the pathogenesis of AF by aggravating tissue fibrosis and mitochondrial ROS damage. Melatonin treatment ameliorated Ang II-induced atrial structural as well as electrical remodeling by activating PKG-CREB-KLF15. The present study reveals additional mechanisms contributing to AF genesis and highlights the opportunity of a novel therapy for AF by targeting BCAA catabolism. Melatonin may serve as a potential therapeutic agent for AF intervention.

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

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

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

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

Biased agonism at β-adrenergic receptors

The β-adrenergic receptors (βARs) include three subtypes, β₁, β₂ and β₃. These receptors are widely expressed and regulate numerous physiological processes including cardiovascular and metabolic functions and airway tone. The βARs are also important targets in the treatment of many diseases including hypertension, heart failure and asthma. In some cases, the use of current βAR ligands to treat a disease is suboptimal and can lead to severe side effects. One strategy to potentially improve such treatments is the development of biased agonists that selectively regulate a subset of βAR signaling pathways and responses. Here we discuss the compounds identified to date that preferentially activate a G_s- or β-arrestin-mediated signaling pathway through βARs. Mechanistic insight on how these compounds bias signaling sheds light on the potential development of even more selective compounds that should have increased utility in treating disease.

Cardiac α1A-adrenergic receptors: emerging protective roles in cardiovascular diseases

α1-Adrenergic receptors (ARs) are catecholamine-activated G protein-coupled receptors (GPCRs) that are expressed in mouse and human myocardium and vasculature, and play essential roles in the regulation of cardiovascular physiology. Though α1-ARs are less abundant in the heart than β1-ARs, activation of cardiac α1-ARs results in important biologic processes such as hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Data from the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) indicate that nonselectively blocking α1-ARs is associated with a twofold increase in adverse cardiac events, including heart failure and angina, suggesting that α1-AR activation might also be cardioprotective in humans. Mounting evidence implicates the α1A-AR subtype in these adaptive effects, including prevention and reversal of heart failure in animal models by α1A agonists. In this review, we summarize recent advances in our understanding of cardiac α1A-ARs.