Myocardial adeno-associated virus serotype 6-betaARKct gene therapy improves cardiac function and normalizes the neurohormonal axis in chronic heart failure

Canonical or non-canonical, all aspects of G protein-coupled receptor kinase 2 in heart failure

G protein-coupled receptor kinase 2 (GRK2) with its multidomain structure performs various crucial cellular functions under both normal and pathological conditions. Overexpression of GRK2 is linked to cardiovascular diseases, and its inhibition or deletion has been shown to be protective. The functions of GRK2 extend beyond G protein-coupled receptor (GPCR) signaling, influencing non-GPCR substrates as well. Increased GRK2 in heart failure (HF) initially may be protective but ultimately leads to maladaptive effects such as GPCR desensitization, insulin resistance, and apoptosis. The multifunctional nature of GRK2, including its action in hypertrophic gene expression, insulin signaling, and cardiac fibrosis, highlights its complex role in HF pathogenesis. Additionally, GRK2 is involved in mitochondrial biogenesis and lipid metabolism. GRK2 also regulates epinephrine secretion from the adrenal gland and its increase in circulating lymphocytes can be used to monitor HF status. Overall, GRK2 is a multifaceted protein with significant implications for HF and the regulation of GRK2 is crucial for understanding and treating cardiovascular diseases.

MicroRNAs in meningiomas: Potential biomarkers and therapeutic targets

Meningiomas, characterized primarily as benign intracranial or spinal tumors, present distinctive challenges due to their variable clinical behavior, with certain cases exhibiting aggressive features linked to elevated morbidity and mortality. Despite their prevalence, the underlying molecular mechanisms governing the initiation and progression of meningiomas remain insufficiently understood. MicroRNAs (miRNAs), small endogenous non-coding RNAs orchestrating post-transcriptional gene expression, have garnered substantial attention in this context. They emerge as pivotal biomarkers and potential therapeutic targets, offering innovative avenues for managing meningiomas. Recent research delves into the intricate mechanisms by which miRNAs contribute to meningioma pathogenesis, unraveling the molecular complexities of this enigmatic tumor. Meningiomas, originating from arachnoid meningothelial cells and known for their gradual growth, constitute a significant portion of intracranial tumors. The clinical challenge lies in comprehending their progression, particularly factors associated with brain invasion and heightened recurrence rates, which remain elusive. This comprehensive review underscores the pivotal role of miRNAs, accentuating their potential to advance our comprehension of meningioma biology. Furthermore, it suggests promising directions for developing diagnostic biomarkers and therapeutic interventions, holding the promise of markedly improved patient outcomes in the face of this intricate and variable disease.

Gene therapy for heart failure: A novel treatment for the age old disease

Across the globe, cardiovascular disease (CVD) is the leading cause of mortality. According to reports, around 6.2 million people in the United states have heart failure. Current standards of care for heart failure can delay but not prevent progression of disease. Gene therapy is one of the novel treatment modalities that promises to fill this limitation in the current standard of care for Heart Failure. In this paper we performed an extensive search of the literature on various advances made in gene therapy for heart failure till date. We review the delivery methods, targets, current applications, trials, limitations and feasibility of gene therapy for heart failure. Various methods have been employed till date for administering gene therapies including but not limited to arterial and venous infusion, direct myocardial injection and pericardial injection. Various strategies such as AC6 expression, S100A1 protein upregulation, VEGF-B and SDF-1 gene therapy have shown promise in recent preclinical trials. Furthermore, few studies even show that stimulation of cardiomyocyte proliferation such as through cyclin A2 overexpression is a realistic avenue. However, a considerable number of obstacles need to be overcome for gene therapy to be part of standard treatment of care such as definitive choice of gene, gene delivery systems and a suitable method for preclinical trials and clinical trials on patients. Considering the challenges and taking into account the recent advances in gene therapy research, there are encouraging signs to indicate gene therapy for heart failure to be a promising treatment modality for the future. However, the time and feasibility of this option remains in a situation of balance.

Cardiac RGS Proteins in Human Heart Failure and Atrial Fibrillation: Focus on RGS4

The regulator of G protein signaling (RGS) proteins are crucial for the termination of G protein signals elicited by G protein-coupled receptors (GPCRs). This superfamily of cell membrane receptors, by far the largest and most versatile in mammals, including humans, play pivotal roles in the regulation of cardiac function and homeostasis. Perturbations in both the activation and termination of their G protein-mediated signaling underlie numerous heart pathologies, including heart failure (HF) and atrial fibrillation (AFib). Therefore, RGS proteins play important roles in the pathophysiology of these two devasting cardiac diseases, and several of them could be targeted therapeutically. Although close to 40 human RGS proteins have been identified, each RGS protein seems to interact only with a specific set of G protein subunits and GPCR types/subtypes in any given tissue or cell type. Numerous in vitro and in vivo studies in animal models, and also in diseased human heart tissue obtained from transplantations or tissue banks, have provided substantial evidence of the roles various cardiomyocyte RGS proteins play in cardiac normal homeostasis as well as pathophysiology. One RGS protein in particular, RGS4, has been reported in what are now decades-old studies to be selectively upregulated in human HF. It has also been implicated in protection against AFib via knockout mice studies. This review summarizes the current understanding of the functional roles of cardiac RGS proteins and their implications for the treatment of HF and AFib, with a specific focus on RGS4 for the aforementioned reasons but also because it can be targeted successfully with small organic molecule inhibitors.

The therapeutic potential of targeting cardiac RGS4

G protein-coupled receptors (GPCRs) play pivotal roles in regulation of cardiac function and homeostasis. To function properly, every cell needs these receptors to be stimulated only when a specific extracellular stimulus is present, and to be silenced the moment that stimulus is removed. The regulator of G protein signaling (RGS) proteins are crucial for the latter to occur at the cell membrane, where the GPCR normally resides. Perturbations in both activation and termination of G protein signaling underlie numerous heart pathologies. Although more than 30 mammalian RGS proteins have been identified, each RGS protein seems to interact only with a specific set of G protein subunits and GPCR types/subtypes in any given tissue or cell type, and this applies to the myocardium as well. A large number of studies have provided substantial evidence for the roles various RGS proteins expressed in cardiomyocytes play in cardiac physiology and heart disease pathophysiology. This review summarizes the current understanding of the functional roles of cardiac RGS proteins and their implications for the treatment of specific heart diseases, such as heart failure and atrial fibrillation. We focus on cardiac RGS4 in particular, since this isoform appears to be selectively (among the RGS protein family) upregulated in human heart failure and is also the target of ongoing drug discovery efforts for the treatment of a variety of diseases.

GRK2 in cardiovascular disease and its potential as a therapeutic target

Cardiovascular diseases (CVDs) represent the leading cause of death globally. Despite major advances in the field of pharmacological CVD treatments, particularly in the field of heart failure (HF) research, case numbers and overall mortality remain high and have trended upwards over the last few years. Thus, identifying novel molecular targets for developing HF therapeutics remains a key research focus. G protein-coupled receptors (GPCRs) are critical myocardial signal transducers which regulate cardiac contractility, growth, adaptation and metabolism. Additionally, GPCR dysregulation underlies multiple models of cardiac pathology, and most pharmacological therapeutics currently used in HF target these receptors. Currently-approved treatments have improved patient outcomes, but therapies to stop or reverse HF are lacking. A recent focus on GPCR intracellular-regulating proteins such as GPCR kinases (GRKs) has uncovered GRK2 as a promising target for combating HF. Current literature strongly establishes increased levels and activity of GRK2 in multiple models of CVD. Additionally, the GRK2 interactome includes numerous proteins which interact with differential domains of GRK2 to modulate both beneficial and deleterious signaling pathways in the heart, indicating that these domains can be targeted with a high level of specificity unique to various cardiac pathologies. These data support the premise that GRK2 should be at the forefront of a novel investigative drug search. This perspective reviews cardiac GPCRs, describes the structure and functions of GRK2 in cardiac function and maladaptive pathology, and summarizes the ongoing and future research for targeting this critical kinase across cellular, animal and human models of cardiac dysfunction and HF.

G protein-coupled receptor signaling: transducers and effectors

G protein-coupled receptors (GPCRs) are of considerable interest due to their importance in a wide range of physiological functions and in a large number of Food and Drug Administration (FDA)-approved drugs as therapeutic entities. With continued study of their function and mechanism of action, there is a greater understanding of how effector molecules interact with a receptor to initiate downstream effector signaling. This review aims to explore the signaling pathways, dynamic structures, and physiological relevance in the cardiovascular system of the three most important GPCR signaling effectors: heterotrimeric G proteins, GPCR kinases (GRKs), and β-arrestins. We will first summarize their prominent roles in GPCR pharmacology before transitioning into less well-explored areas. As new technologies are developed and applied to studying GPCR structure and their downstream effectors, there is increasing appreciation for the elegance of the regulatory mechanisms that mediate intracellular signaling and function.

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.

AAV-mediated gene therapy: Advancing cardiovascular disease treatment

Gene therapy has revolutionized the field of medicine, offering new hope for those with common and rare diseases. For nearly three decades, adeno-associated virus (AAV) has shown significant therapeutic benefits in multiple clinical trials, mainly due to its unique replication defects and non-pathogenicity in humans. In the field of cardiovascular disease (CVD), compared with non-viral vectors, lentiviruses, poxviruses, and adenovirus vectors, AAV possesses several advantages, including high security, low immunogenicity, sustainable and stable exogenous gene expression etc., which makes AAV one of the most promising candidates for the treatment of many genetic disorders and hereditary diseases. In this review, we evaluate the current information on the immune responses, transport pathways, and mechanisms of action associated with AAV-based CVD gene therapies and further explore potential optimization strategies to improve the efficiency of AAV transduction for the improved safety and efficiency of CVD treatment. In conclusion, AAV-mediated gene therapy has great potential for development in the cardiovascular system.

Sex/Gender- and Age-Related Differences in β-Adrenergic Receptor Signaling in Cardiovascular Diseases

Sex differences in cardiovascular disease (CVD) are often recognized from experimental and clinical studies examining the prevalence, manifestations, and response to therapies. Compared to age-matched men, women tend to have reduced CV risk and a better prognosis in the premenopausal period. However, with menopause, this risk increases exponentially, surpassing that of men. Although several mechanisms have been provided, including sex hormones, an emerging role in these sex differences has been suggested for β-adrenergic receptor (β-AR) signaling. Importantly, β-ARs are the most important G protein-coupled receptors (GPCRs), expressed in almost all the cell types of the CV system, and involved in physiological and pathophysiological processes. Consistent with their role, for decades, βARs have been considered the first targets for rational drug design to fight CVDs. Of note, β-ARs are seemingly associated with different CV outcomes in females compared with males. In addition, even if there is a critical inverse correlation between β-AR responsiveness and aging, it has been reported that gender is crucially involved in this age-related effect. This review will discuss how β-ARs impact the CV risk and response to anti-CVD therapies, also concerning sex and age. Further, we will explore how estrogens impact β-AR signaling in women.

Double life: How GRK2 and β-arrestin signaling participate in diseases

G-protein coupled receptor (GPCR) kinases (GRKs) and β-arrestins play key roles in GPCR and non-GPCR cellular responses. In fact, GRKs and arrestins are involved in a plethora of pathways vital for physiological maintenance of inter- and intracellular communication. Here we review decades of research literature spanning from the discovery, identification of key structural elements, and findings supporting the diverse roles of these proteins in GPCR-mediated pathways. We then describe how GRK2 and β-arrestins partake in non-GPCR signaling and briefly summarize their involvement in various pathologies. We conclude by presenting gaps in knowledge and our prospective on the promising pharmacological potential in targeting these proteins and/or downstream signaling. Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and arrestins in metabolism and disease progression.

The RAF Kinase Inhibitor Protein (RKIP): Good as Tumour Suppressor, Bad for the Heart

The RAF kinase inhibitor protein, RKIP, is a dual inhibitor of the RAF1 kinase and the G protein-coupled receptor kinase 2, GRK2. By inhibition of the RAF1-MAPK (mitogen-activated protein kinase) pathway, RKIP acts as a beneficial tumour suppressor. By inhibition of GRK2, RKIP counteracts GRK2-mediated desensitisation of G protein-coupled receptor (GPCR) signalling. GRK2 inhibition is considered to be cardioprotective under conditions of exaggerated GRK2 activity such as heart failure. However, cardioprotective GRK2 inhibition and pro-survival RAF1-MAPK pathway inhibition counteract each other, because inhibition of the pro-survival RAF1-MAPK cascade is detrimental for the heart. Therefore, the question arises, what is the net effect of these apparently divergent functions of RKIP in vivo? The available data show that, on one hand, GRK2 inhibition promotes cardioprotective signalling in isolated cardiomyocytes. On the other hand, inhibition of the pro-survival RAF1-MAPK pathway by RKIP deteriorates cardiomyocyte viability. In agreement with cardiotoxic effects, endogenous RKIP promotes cardiac fibrosis under conditions of cardiac stress, and transgenic RKIP induces heart dysfunction. Supported by next-generation sequencing (NGS) data of the RKIP-induced cardiac transcriptome, this review provides an overview of different RKIP functions and explains how beneficial GRK2 inhibition can go awry by RAF1-MAPK pathway inhibition. Based on RKIP studies, requirements for the development of a cardioprotective GRK2 inhibitor are deduced.

Focus on the Lymphatic Route to Optimize Drug Delivery in Cardiovascular Medicine

While oral agents have been the gold standard for cardiovascular disease therapy, the new generation of treatments is switching to other administration options that offer reduced dosing frequency and more efficacy. The lymphatic network is a unidirectional and low-pressure vascular system that is responsible for the absorption of interstitial fluids, molecules, and cells from the peripheral tissue, including the skin and the intestines. Targeting the lymphatic route for drug delivery employing traditional or new technologies and drug formulations is exponentially gaining attention in the quest to avoid the hepatic first-pass effect. The present review will give an overview of the current knowledge on the involvement of the lymphatic vessels in drug delivery in the context of cardiovascular disease.

Effect of Paroxetine-Mediated G-Protein Receptor Kinase 2 Inhibition vs Placebo in Patients With Anterior Myocardial Infarction: A Randomized Clinical Trial

Importance

Left ventricular remodeling following acute myocardial infarction results in progressive myocardial dysfunction and adversely affects prognosis.

Objective

To investigate the efficacy of paroxetine-mediated G-protein-coupled receptor kinase 2 inhibition to mitigate adverse left ventricular remodeling in patients presenting with acute myocardial infarction.

Design, Setting, and Participants

This double-blind, placebo-controlled randomized clinical trial was conducted at Bern University Hospital, Bern, Switzerland. Patients with acute anterior ST-segment elevation myocardial infarction with left ventricular ejection fraction (LVEF) of 45% or less were randomly allocated to 2 study arms between October 26, 2017, and September 21, 2020.

Interventions

Patients in the experimental arm received 20 mg of paroxetine daily; patients in the control group received a placebo daily. Both treatments were provided for 12 weeks.

Main Outcomes and Measures

The primary end point was the difference in patient-level improvement of LVEF between baseline and 12 weeks as assessed by cardiac magnetic resonance tomography. Secondary end points were changes in left ventricular dimensions and late gadolinium enhancement between baseline and follow-up.

Results

Fifty patients (mean [SD] age, 62 [13] years; 41 men [82%]) with acute anterior myocardial infarction were randomly allocated to paroxetine or placebo, of whom 38 patients underwent cardiac magnetic resonance imaging both at baseline and 12 weeks. There was no difference in recovery of LVEF between the experimental group (mean [SD] change, 4.0% [7.0%]) and the control group (mean [SD] change, 6.3% [6.3%]; mean difference, -2.4% [95% CI, -6.8% to 2.1%]; P = .29) or changes in left ventricular end-diastolic volume (mean difference, 13.4 [95% CI, -12.3 to 39.0] mL; P = .30) and end-systolic volume (mean difference, 11.4 [95% CI, -3.6 to 26.4] mL; P = .13). Late gadolinium enhancement as a percentage of the total left ventricular mass decreased to a larger extent in the experimental group (mean [SD], -13.6% [12.9%]) compared with the control group (mean [SD], -4.5% [9.5%]; mean difference, -9.1% [95% CI, -16.6% to -1.6%]; P = .02).

Conclusions and Relevance

In this trial, treatment with paroxetine did not improve LVEF after myocardial infarction compared with placebo.

Trial Registration

ClinicalTrials.gov Identifier: NCT03274752.

Targeted Therapy in Cardiovascular Disease: A Precision Therapy Era

Targeted therapy refers to exploiting the specific therapeutic drugs against the pathogenic molecules (a protein or a gene) or cells. The drug specifically binds to disease-causing molecules or cells without affecting normal tissue, thus enabling personalized and precision treatment. Initially, therapeutic drugs included antibodies and small molecules, (e.g. nucleic acid drugs). With the advancement of the biology technology and immunotherapy, the gene editing and cell editing techniques are utilized for the disease treatment. Currently, targeted therapies applied to treat cardiovascular diseases (CVDs) mainly include protein drugs, gene editing technologies, nucleic acid drugs and cell therapy. Although targeted therapy has demonstrated excellent efficacy in pre-clinical and clinical trials, several limitations need to be recognized and overcome in clinical application, (e.g. off-target events, gene mutations, etc.). This review introduces the mechanisms of different targeted therapies, and mainly describes the targeted therapy applied in the CVDs. Furthermore, we made comparative analysis to clarify the advantages and disadvantages of different targeted therapies. This overview is expected to provide a new concept to the treatment of the CVDs.

Characterization of βARKct engineered cellular extracellular vesicles and model specific cardioprotection

Recent data supporting any benefit of stem cell therapy for ischemic heart disease have suggested paracrine-based mechanisms via extracellular vesicles (EVs) including exosomes. We have previously engineered cardiac-derived progenitor cells (CDCs) to express a peptide inhibitor, βARKct, of G protein-coupled receptor kinase 2, leading to improvements in cell proliferation, survival, and metabolism. In this study, we tested whether βARKct-CDC EVs would be efficacious when applied to stressed myocytes in vitro and in vivo. When isolated EVs from βARKct-CDCs and control GFP-CDCs were added to cardiomyocytes in culture, they both protected against hypoxia-induced apoptosis. We tested whether these EVs could protect the mouse heart in vivo, following exposure either to myocardial infarction (MI) or acute catecholamine toxicity. Both types of EVs significantly protected against ischemic injury and improved cardiac function after MI compared with mice treated with EVs from mouse embryonic fibroblasts; however, βARKct EVs treated mice did display some unique beneficial properties including significantly altered pro- and anti-inflammatory cytokines. Importantly, in a catecholamine toxicity model of heart failure (HF), myocardial injections of βARKct-containing EVs were superior at preventing HF compared with control EVs, and this catecholamine toxicity protection was recapitulated in vitro. Therefore, introduction of the βARKct into cellular EVs can have improved reparative properties in the heart especially against catecholamine damage, which is significant as sympathetic nervous system activity is increased in HF.NEW & NOTEWORTHY βARKct, the peptide inhibitor of GRK2, improves survival and metabolic functions of cardiac-derived progenitor cells. As any benefit of stem cells in the ischemic and injured heart suggests paracrine mechanisms via secreted EVs, we investigated whether CDC-βARKct engineered EVs would show any benefit over control CDC-EVs. Compared with control EVs, βARKct-containing EVs displayed some unique beneficial properties that may be due to altered pro- and anti-inflammatory cytokines within the vesicles.

Adenoviral βARKct Cardiac Gene Transfer Ameliorates Postresuscitation Myocardial Injury in a Porcine Model of Cardiac Arrest

OBJECTIVE

The aim of the study was to determine whether the inhibition of the G-protein-coupled receptor kinase 2 by adenoviral βARKct cardiac gene transfer can ameliorate postresuscitation myocardial injury in pigs with cardiac arrest (CA) and explore the mechanism of myocardial protection.

METHODS

Male landrace domestic pigs were randomized into the sham group (anesthetized and instrumented, but ventricular fibrillation was not induced) (n = 4), control group (ventricular fibrillation 8 min, n = 8), and βARKct group (ventricular fibrillation 8 min, n = 8). Hemodynamic parameters were monitored continuously. Blood samples were collected at baseline, 30 min, 2 h, 4 h, and 6 h after the return of spontaneous circulation (ROSC). Left ventricular ejection fraction was assessed by echocardiography at baseline and 6 h after ROSC. These animals were euthanized, and the cardiac tissue was removed for analysis at 6 h after ROSC.

RESULTS

Compared with those in the sham group, left ventricular +dp/dtmax, -dp/dtmax, cardiac output (CO), and ejection fraction (EF) in the control group and the βARKct group were significantly decreased at 6 h after the restoration of spontaneous circulation. However, the βARKct treatment produced better left ventricular +dp/dtmax, -dp/dtmax, CO, and EF after ROSC. The βARKct treatment also produced lower serum cardiac troponin I, CK-MB, and lactate after ROSC. Furthermore, the adenoviral βARKct gene transfer significantly increased β1 adrenergic receptors, SERCA2a, RyR2 levels, and decreased GRK2 levels compared to control.

CONCLUSIONS

The inhibition of GRK2 by adenoviral βARKct cardiac gene transfer can ameliorate postresuscitation myocardial injury through beneficial effects on restoring the sarcoplasmic reticulum Ca-handling proteins expression and upregulating the β1-adrenergic receptor level after cardiac arrest.

β-adrenergic activation may promote myosin light chain kinase degradation through calpain in pressure overload-induced cardiac hypertrophy: β-adrenergic activation results in MLCK degradation

BACKGROUND

β-adrenergic activation is able to exacerbate cardiac hypertrophy. Myosin light chain kinase (MLCK) and its phosphorylated substrate, phospho-myosin light chain 2 (p-MLC2), play vital roles in regulating cardiac hypertrophy. However, it is not yet clear whether there is a relationship between β-adrenergic activation and MLCK in the progression of cardiac hypertrophy. Therefore, we explored this relationship and the underlying mechanisms in this work.

METHODS

Cardiac hypertrophy and cardiomyocyte hypertrophy were induced by pressure overload and isoproterenol (ISO) stimulation, respectively. Echocardiography, histological analysis, immunofluorescence and qRT-PCR were used to confirm the successful establishment of the models. A β-blocker (metoprolol) and a calpain inhibitor (calpeptin) were administered to inhibit β-adrenergic activity in rats and calpain in cardiomyocytes, respectively. The protein expression levels of MLCK, myosin light chain 2 (MLC2), p-MLC2, myosin phosphatase 2 (MYPT2), calmodulin (CaM) and calpain were measured using western blotting. A cleavage assay was performed to assess the degradation of recombinant human MLCK by recombinant human calpain.

RESULTS

The β-blocker alleviated cardiac hypertrophy and dysfunction, increased MLCK and MLC2 phosphorylation and decreased calpain expression in pressure overload-induced cardiac hypertrophy. Additionally, the calpain inhibitor calpeptin attenuated cardiomyocyte hypertrophy, upregulated MLCK and p-MLC2 and reduced MLCK degradation in ISO-induced cardiomyocyte hypertrophy. Recombinant human calpain degraded recombinant human MLCK in vitro in concentration- and time-dependent manners, and this degradation was inhibited by the calpain inhibitor calpeptin.

CONCLUSION

Our study suggested that β-adrenergic activation may promote the degradation of MLCK through calpain in pressure overload-induced cardiac hypertrophy.

Gene therapy for inherited arrhythmias

Inherited arrhythmias are disorders caused by one or more genetic mutations that increase the risk of arrhythmia, which result in life-long risk of sudden death. These mutations either primarily perturb electrophysiological homeostasis (e.g. long QT syndrome and catecholaminergic polymorphic ventricular tachycardia), cause structural disease that is closely associated with severe arrhythmias (e.g. hypertrophic cardiomyopathy), or cause a high propensity for arrhythmia in combination with altered myocardial structure and function (e.g. arrhythmogenic cardiomyopathy). Currently available therapies offer incomplete protection from arrhythmia and fail to alter disease progression. Recent studies suggest that gene therapies may provide potent, molecularly targeted options for at least a subset of inherited arrhythmias. Here, we provide an overview of gene therapy strategies, and review recent studies on gene therapies for catecholaminergic polymorphic ventricular tachycardia and hypertrophic cardiomyopathy caused by MYBPC3 mutations.

Pharmacological inhibition of GRK2 improves cardiac metabolism and function in experimental heart failure

Aims

The effects of GRK2 inhibition on myocardial metabolism in heart failure (HF) are unchartered. In this work, we evaluated the impact of pharmacological inhibition of GRK2 by a cyclic peptide, C7, on metabolic, biochemical, and functional phenotypes in experimental HF.

Methods and results

C7 was initially tested on adult mice ventricular myocyte from wild type and GRK2 myocardial deficient mice (GRK2‐cKO), to assess the selectivity on GRK2 inhibition. Then, chronic infusion of 2 mg/kg/day of C7 was performed in HF mice with cryogenic myocardial infarction. Cardiac function in vivo was assessed by echocardiography and cardiac catheterization. Histological, biochemical, and metabolic studies were performed on heart samples at time points. C7 induces a significant increase of contractility in wild type but not in adult ventricle myocytes from GRK2‐cKO mice, thus confirming C7 selectivity for GRK2. In HF mice, 4 weeks of treatment with C7 improved metabolic features, including mitochondrial organization and function, and restored the biochemical and contractile responses.

Conclusions

GRK2 is a critical molecule in the physiological regulation of cardiac metabolism. Its alterations in the failing heart can be pharmacologically targeted, leading to the correction of metabolic and functional abnormalities observed in HF.

Loss of dynamic regulation of G protein-coupled receptor kinase 2 by nitric oxide leads to cardiovascular dysfunction with aging

Nitric oxide (NO) and S-nitrosothiol (SNO) are considered cardio- and vasoprotective substances. We now understand that one mechanism in which NO/SNOs provide cardiovascular protection is through their direct inhibition of cardiac G protein-coupled receptor (GPCR) kinase 2 (GRK2) activity via S-nitrosylation of GRK2 at cysteine 340 (C340). This maintains GPCR homeostasis, including β-adrenergic receptors, through curbing receptor GRK2-mediated desensitization. Previously, we have developed a knockin mouse (GRK2-C340S) where endogenous GRK2 is resistant to dynamic S-nitrosylation, which led to increased GRK2 desensitizing activity. This unchecked regulation of cardiac GRK2 activity resulted in significantly more myocardial damage after ischemic injury that was resistant to NO-mediated cardioprotection. Although young adult GRK2-C340S mice show no overt phenotype, we now report that as these mice age, they develop significant cardiovascular dysfunction due to the loss of SNO-mediated GRK2 regulation. This pathological phenotype is apparent as early as 12 mo of age and includes reduced cardiac function, increased cardiac perivascular fibrosis, and maladaptive cardiac hypertrophy, which are common maladies found in patients with cardiovascular disease (CVD). There are also vascular reactivity and aortic abnormalities present in these mice. Therefore, our data demonstrate that a chronic and global increase in GRK2 activity is sufficient to cause cardiovascular remodeling and dysfunction, likely due to GRK2’s desensitizing effects in several tissues. Because GRK2 levels have been reported to be elevated in elderly CVD patients, GRK2-C340 mice can give insight into the aged-molecular landscape leading to CVD.

NEW & NOTEWORTHY Research on G protein-coupled receptor kinase 2 (GRK2) in the setting of cardiovascular aging is largely unknown despite its strong established functions in cardiovascular physiology and pathophysiology. This study uses a mouse model of chronic GRK2 overactivity to further investigate the consequences of long-term GRK2 on cardiac function and structure. We report for the first time that chronic GRK2 overactivity was able to cause cardiac dysfunction and remodeling independent of surgical intervention, highlighting the importance of GRK activity in aged-related heart disease.

Adrenergic Downregulation in Critical Care: Molecular Mechanisms and Therapeutic Evidence

Catecholamines remain the mainstay of therapy for acute cardiovascular dysfunction. However, adrenergic receptors quickly undergo desensitization and downregulation after prolonged stimulation. Moreover, prolonged exposure to high circulating catecholamines levels is associated with several adverse effects on different organ systems. Unfortunately, in critically ill patients, adrenergic downregulation translates into progressive reduction of cardiovascular response to exogenous catecholamine administration, leading to refractory shock. Accordingly, there has been a growing interest in recent years toward use of noncatecholaminergic inotropes and vasopressors. Several studies investigating a wide variety of catecholamine-sparing strategies (eg, levosimendan, vasopressin, β-blockers, steroids, and use of mechanical circulatory support) have been published recently. Use of these agents was associated with improvement in hemodynamics and decreased catecholamine use but without a clear beneficial effect on major clinical outcomes. Accordingly, additional research is needed to define the optimal management of catecholamine-resistant shock.

G protein-coupled receptor kinases as therapeutic targets in the heart

G protein-coupled receptors (GPCRs) are critical cellular sensors that mediate numerous physiological processes. In the heart, multiple GPCRs are expressed on various cell types, where they coordinate to regulate cardiac function by modulating critical processes such as contractility and blood flow. Under pathological settings, these receptors undergo aberrant changes in expression levels, localization and capacity to couple to downstream signalling pathways. Conventional therapies for heart failure work by targeting GPCRs, such as β-adrenergic receptor and angiotensin II receptor antagonists. Although these treatments have improved patient survival, heart failure remains one of the leading causes of mortality worldwide. GPCR kinases (GRKs) are responsible for GPCR phosphorylation and, therefore, desensitization and downregulation of GPCRs. In this Review, we discuss the GPCR signalling pathways and the GRKs involved in the pathophysiology of heart disease. Given that increased expression and activity of GRK2 and GRK5 contribute to the loss of contractile reserve in the stressed and failing heart, inhibition of overactive GRKs has been proposed as a novel therapeutic approach to treat heart failure.

Alteration of myocardial GRK2 produces a global metabolic phenotype

A vast body of literature has established GRK2 as a key player in the development and progression of heart failure. Inhibition of GRK2 improves cardiac function post injury in numerous animal models. In recent years, discovery of several non-canonical GRK2 targets has expanded our view of this kinase. Here, we describe the novel and exciting finding that cardiac GRK2 activity can regulate whole body metabolism. Transgenic mice with cardiac-specific expression of a peptide inhibitor of GRK2 (TgβARKct) display an enhanced obesogenic phenotype when fed a high fat diet (HFD). In contrast, mice with cardiac-specific overexpression of GRK2 (TgGRK2) show resistance to HFD induced obesity. White adipose tissue (WAT) mass was significantly enhanced in HFD fed TgβARKct mice. Furthermore, regulators of adipose differentiation were differentially regulated in WAT from mice with gain or loss of GRK2 function. Using complex metabolomics we found that cardiac GRK2 signaling altered myocardial BCAA and endocannabinoid metabolism and modulated circulating BCAA and endocannabinoid metabolite profiles on a HFD, and one of the BCAA metabolites identified here enhances adipocyte differentiation in vitro. Taken together, these results suggest that metabolic changes in the heart due to GRK2 signaling on a HFD control whole body metabolism.

Predisposing factors to heart failure in diabetic nephropathy: a look at the sympathetic nervous system hyperactivity

Diabetes mellitus (DM) and heart failure (HF) are frequent comorbidities among elderly patients. HF, a leading cause of mortality and morbidity worldwide, is characterized by sympathetic nervous system hyperactivity. The prevalence of diabetes mellitus (DM) is rapidly growing and the risk of developing HF is higher among DM patients. DM is responsible for several macro- and micro-angiopathies that contribute to the development of coronary artery disease (CAD), peripheral artery disease, retinopathy, neuropathy and diabetic nephropathy (DN) as well. Independently of CAD, chronic kidney disease (CKD) and DM increase the risk of HF. Individuals with diabetic nephropathy are likely to present a distinct pathological condition, defined as diabetic cardiomyopathy, even in the absence of hypertension or CAD, whose pathogenesis is only partially known. However, several hypotheses have been proposed to explain the mechanism of diabetic cardiomyopathy: increased oxidative stress, altered substrate metabolism, mitochondrial dysfunction, activation of renin-angiotensin-aldosterone system (RAAS), insulin resistance, and autonomic dysfunction. In this review, we will focus on the involvement of sympathetic system hyperactivity in the diabetic nephropathy.

GRK5 - A Functional Bridge Between Cardiovascular and Neurodegenerative Disorders

Complex aging-triggered disorders are multifactorial programs that comprise a myriad of alterations in interconnected protein networks over a broad range of tissues. It is evident that rather than being randomly organized events, pathophysiologies that possess a strong aging component such as cardiovascular diseases (hypertensions, atherosclerosis, and vascular stiffening) and neurodegenerative conditions (dementia, Alzheimer's disease, mild cognitive impairment, Parkinson's disease), in essence represent a subtly modified version of the intricate molecular programs already in place for normal aging. To control such multidimensional activities there are layers of trophic protein control across these networks mediated by so-called "keystone" proteins. We propose that these "keystones" coordinate and interconnect multiple signaling pathways to control whole somatic activities such as aging-related disease etiology. Given its ability to control multiple receptor sensitivities and its broad protein-protein interactomic nature, we propose that G protein coupled receptor kinase 5 (GRK5) represents one of these key network controllers. Considerable data has emerged, suggesting that GRK5 acts as a bridging factor, allowing signaling regulation in pathophysiological settings to control the connectivity between both the cardiovascular and neurophysiological complications of aging.

The non-neuronal cholinergic system in the heart: A comprehensive review

The autonomic influences on the heart have a ying-yang nature, albeit oversimplified, the interplay between the sympathetic and parasympathetic system (known as the cholinergic system) is often complex and remain poorly understood. Recently, the heart has been recognized to consist of neuronal and non-neuronal cholinergic system (NNCS). The existence of cardiac NNCS has been confirmed by the presence of cholinergic markers in the cardiomyocytes, which are crucial for synthesis (choline acetyltransferase, ChAT), storage (vesicular acetylcholine transporter, VAChT), reuptake of choline for synthesis (high-affinity choline transporter, CHT1) and degradation (acetylcholinesterase, AChE) of acetylcholine (ACh). The non-neuronal ACh released from cardiomyocytes is believed to locally regulate some of the key physiological functions of the heart, such as regulation of heart rate, offsetting hypertrophic signals, maintenance of action potential propagation as well as modulation of cardiac energy metabolism via the muscarinic ACh receptor in an auto/paracrine manner. Apart from this, several studies have also provided evidence for the beneficial role of ACh released from cardiomyocytes against cardiovascular diseases such as sympathetic hyperactivity-induced cardiac remodeling and dysfunction as well as myocardial infarction, confirming the important role of NNCS in disease prevention. In this review, we aim to provide a fundamental overview of cardiac NNCS, and information about its physiological role, regulatory factors as well as its cardioprotective effects. Finally, we propose the different approaches to target cardiac NNCS as an adjunctive treatment to specifically address the withdrawal of neuronal cholinergic system in cardiovascular disease such as heart failure.

G protein-coupled receptor kinase 2 contributes to impaired fatty acid metabolism in the failing heart

Increased G protein-coupled receptor kinase (GRK)2 is central to heart failure (HF) pathogenesis, via desensitization of β-adrenergic receptors and loss of contractile reserve. Since GRK2 has been shown to compromise fatty acid (FA) oxidation, this kinase may link metabolic and contractile defects in HF. The aim of this study was to investigate the mechanistic role of GRK2 in FA metabolism and bioenergetics in the heart. For that purpose, we measured FA uptake and cluster of differentiation (CD)36 expression, phosphorylation, and ubiquitination in mice with cardiac-specific overexpression of GRK2 (TgGRK2) or expression of its c-terminus (GRK2 inhibitor- TgβARKct) or in global heterozygous GRK2 knockout (GRK2+/-) mice. Cellular bioenergetics were also measured in isolated cardiomyocytes following adenoviral delivery of exogenous GRK2, βARKct, or short hairpin GRK2 (shGRK2). Additionally, CD36 expression and phosphorylation were evaluated following transverse aortic constriction (TAC) in wild type (WT) and GRK2+/- mice. Our results show a 33% ± 0.81 reduction in FA uptake rate, accompanied by 51% ± 0.17 lower CD36 protein, and 70% ± 0.23 and 69% ± 0.18 increases in CD36 phosphorylation and ubiquitination, respectively, in the TgGRK2 mice. Moreover, an in vitro kinase assay suggests that GRK2 directly phosphorylates CD36. In isolated cardiomyocytes, GRK2 overexpression induced a 26% ± 2.21 decrease in maximal respiration, which was enhanced (20% ± 4.02-5.14) with inhibition of the kinase. Importantly, in hearts with systolic dysfunction, notable reductions in CD36 mRNA and protein, as well as a significant increase in CD36 phosphorylation were normalized in the GRK2+/- mice post-TAC. Thus, we propose that GRK2 up-regulation in HF is, at least partly, responsible for reduced FA uptake and oxidation and may be a nodal link between metabolic and contractile defects.

Designer Approaches for G Protein-Coupled Receptor Modulation for Cardiovascular Disease

The new horizon for cardiac therapy may lie beneath the surface, with the downstream mediators of G protein–coupled receptor (GPCR) activity. Targeted approaches have shown that receptor activation may be biased toward signaling through G proteins or through GPCR kinases (GRKs) and β-arrestins, with divergent functional outcomes. In addition to these canonical roles, numerous noncanonical activities of GRKs and β-arrestins have been demonstrated to modulate GPCR signaling at all levels of receptor activation and regulation. Further, research continues to identify novel GRK/effector and β-arrestin/effector complexes with distinct impacts on cardiac function in the normal heart and the diseased heart. Coupled with the identification of once orphan receptors and endogenous ligands with beneficial cardiovascular effects, this expands the repertoire of GPCR targets. Together, this research highlights the potential for focused therapeutic activation of beneficial pathways, with simultaneous exclusion or inhibition of detrimental signaling, and represents a new wave of therapeutic development.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

Proinflammatory Cytokines Mediate GPCR Dysfunction

Proinflammatory reaction by the body occurs acutely in response to injury that is considered primarily beneficial. However, sustained proinflammatory cytokines observed with chronic pathologies such as metabolic syndrome, cancer, and arthritis are detrimental and in many cases is a major cardiovascular risk factor. Proinflammatory cytokines such as interleukin-1, interleukin-6, and tumor necrosis factor α (TNFα) have long been implicated in cardiovascular risk and considered to be a major underlying cause for heart failure (HF). The failure of the anti-TNFα therapy for HF indicates our elusive understanding on the dichotomous role of proinflammatory cytokines on acutely beneficial effects versus long-term deleterious effects. Despite these well-described observations, less is known about the mechanistic underpinnings of proinflammatory cytokines especially TNFα in pathogenesis of HF. Increasing evidence suggests the existence of an active cross-talk between the TNFα receptor signaling and G-protein-coupled receptors such as β-adrenergic receptor (βAR). Given that βARs are the key regulators of cardiac function, the review will discuss the current state of understanding on the role of proinflammatory cytokine TNFα in regulating βAR function.

GRK2 as a therapeutic target for heart failure

INTRODUCTION

G protein-coupled receptor (GPCR) kinase-2 (GRK2) is a regulator of GPCRs, in particular β-adrenergic receptors (ARs), and as demonstrated by decades of investigation, it has a pivotal role in the development and progression of cardiovascular disease, like heart failure (HF). Indeed elevated levels and activity of this kinase are able to promote the dysfunction of both cardiac and adrenal α- and β-ARs and to dysregulate other protective signaling pathway, such as sphingosine 1-phospate and insulin. Moreover, recent discoveries suggest that GRK2 can signal independently from GPCRs, in a 'non-canonical' manner, via interaction with non-GPCR molecule or via its mitochondrial localization. Areas covered: Based on this premise, GRK2 inhibition or its genetic deletion has been tested in several disparate animal models of cardiovascular disease, showing to protect the heart from adverse remodeling and dysfunction. Expert opinion: HF is one of the leading cause of death worldwide with enormous health care costs. For this reason, the identification of new therapeutic targets like GRK2 and strategies such as its inhibition represents a new hope in the fight against HF development and progression. Herein, we will update the readers about the 'state-of-art' of GRK2 inhibition as a potent therapeutic strategy in HF.

Effect of β-adrenergic receptor kinase inhibitor on post-myocardial infarction heart failure in rats

OBJECTIVE

This study is to investigate the effect of β-adrenergic receptor kinase inhibitor (Adeno-βARKct) on heart failure (HF) rat model.

METHODS

Male SD rats weighted 250 g undertaken ligation of the left anterior descending branch of coronary artery to establish HF model. Survival rats were randomly divided into experimental treated group (EXP) and control treated group (CONT). Additionally, pseudo-operated rats were taken as sham-ligated group (SHAM). Adeno-βARKct particles or Adeno empty vector was injected to the rats. Multiple indicators including left ventricular ejection fraction (LVEF), index of hemodynamics, plasma and myocardial tissue catecholamine, NT-ProBNP, mRNA levels of β1AR, β2AR and βARK1, and protein level of βARK1 were measured 4 weeks later.

RESULTS

Compared with rats in SHAM group, levels of LVEF, ±dp/dt max, and catecholamine in myocardial tissue were lower while plasma NT-ProBNP and plasma catecholamine were higher in rats of EXP and CONT. Additionally, β1AR and β2AR mRNA expressions were downregulated whereas βARK1 mRNA and βARK1 protein levels were upregulated in EXP and CONT. Compared with CONT, the levels of LVEF, -dp/dt max, and catecholamine in myocardial tissue were higher, while plasma NT-ProBNP and plasma catecholamine were lower in EXP. β1AR and β2AR mRNA expressions were upregulated, whereas βARK1 mRNA expression and βARK1 protein levels were downregulated in EXP.

CONCLUSION

In vivo delivery of Adeno-βARKct by caudal vein is feasible and can improve cardiac function in rats with HF after myocardial infarction.

G Protein-Coupled Receptor Kinases in the Inflammatory Response and Signaling

G protein-coupled receptor kinases (GRKs) are serine/threonine kinases that regulate a large and diverse class of G protein-coupled receptors (GPCRs). Through GRK phosphorylation and β-arrestin recruitment, GPCRs are desensitized and their signal terminated. Recent work on these kinases has expanded their role from canonical GPCR regulation to include noncanonical regulation of non-GPCR and nonreceptor substrates through phosphorylation as well as via scaffolding functions. Owing to these and other regulatory roles, GRKs have been shown to play a critical role in the outcome of a variety of physiological and pathophysiological processes including chemotaxis, signaling, migration, inflammatory gene expression, etc. This diverse set of functions for these proteins makes them popular targets for therapeutics. Role for these kinases in inflammation and inflammatory disease is an evolving area of research currently pursued in many laboratories. In this review, we describe the current state of knowledge on various GRKs pertaining to their role in inflammation and inflammatory diseases.

Targeting GPCR-Gβγ-GRK2 signaling as a novel strategy for treating cardiorenal pathologies

The pathologic crosstalk between the heart and kidney is known as cardiorenal syndrome (CRS). While the specific mechanisms underlying this crosstalk remain poorly understood, CRS is associated with exacerbated dysfunction of either or both organs and reduced survival. Maladaptive fibrotic remodeling is a key component of both heart and kidney failure pathogenesis and progression. G-protein coupled receptor (GPCR) signaling is a crucial regulator of cardiovascular and renal function. Chronic/pathologic GPCR signaling elicits the interaction of the G-protein Gβγ subunit with GPCR kinase 2 (GRK2), targeting the receptor for internalization, scaffolding to pathologic signals, and receptor degradation. Targeting this pathologic Gβγ-GRK2 interaction has been suggested as a possible strategy for the treatment of HF. In the current review, we discuss recent updates in understanding the role of GPCR-Gβγ-GRK2 signaling as a crucial mediator of maladaptive organ remodeling detected in HF and kidney dysfunction, with specific attention to small molecule-mediated inhibition of pathologic Gβγ-GRK2 interactions. Further, we explore the potential of GPCR-Gβγ-GRK2 signaling as a possible therapeutic target for cardiorenal pathologies.

GRK2 as negative modulator of NO bioavailability: Implications for cardiovascular disease

Nitric oxide (NO), initially identified as endothelium-derived relaxing factor (EDRF), is a gaso-transmitter with important regulatory roles in the cardiovascular, nervous and immune systems. In the former, this diatomic molecule and free radical gas controls vascular tone and cardiac mechanics, among others. In the cardiovascular system, it is now understood that β-adrenergic receptor (βAR) activation is a key modulator of NO generation. Therefore, it is not surprising that the up-regulation of G protein-coupled receptor kinases (GRKs), in particular GRK2, that restrains βAR activity contributes to impaired cardiovascular functions via alteration of NO bioavailability. This review, will explore the specific interrelation between βARs, GRK2 and NO in the cardiovascular system and their inter-relationship for the pathogenesis of the onset of disease. Last, we will update the readers on the current status of GRK2 inhibitors as a potential therapeutic strategy for heart failure with an emphasis on their ability of rescuing NO bioavailability.

Neurohormonal activation in heart failure with reduced ejection fraction

Heart failure with reduced ejection fraction (HFrEF) develops when cardiac output falls as a result of cardiac injury. The most well-recognized of the compensatory homeostatic responses to a fall in cardiac output are activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS). In the short term, these 'neurohormonal' systems induce a number of changes in the heart, kidneys, and vasculature that are designed to maintain cardiovascular homeostasis. However, with chronic activation, these responses result in haemodynamic stress and exert deleterious effects on the heart and the circulation. Neurohormonal activation is now known to be one of the most important mechanisms underlying the progression of heart failure, and therapeutic antagonism of neurohormonal systems has become the cornerstone of contemporary pharmacotherapy for heart failure. In this Review, we discuss the effects of neurohormonal activation in HFrEF and highlight the mechanisms by which these systems contribute to disease progression.

Cardiac Fibroblast GRK2 Deletion Enhances Contractility and Remodeling Following Ischemia/Reperfusion Injury

RATIONALE

G protein-coupled receptor kinase 2 (GRK2) is an important molecule upregulated after myocardial injury and during heart failure. Myocyte-specific GRK2 loss before and after myocardial ischemic injury improves cardiac function and remodeling. The cardiac fibroblast plays an important role in the repair and remodeling events after cardiac ischemia; the importance of GRK2 in these events has not been investigated.

OBJECTIVE

The aim of this study is to elucidate the in vivo implications of deleting GRK2 in the cardiac fibroblast after ischemia/reperfusion injury.

METHODS AND RESULTS

We demonstrate, using Tamoxifen inducible, fibroblast-specific GRK2 knockout mice, that GRK2 loss confers a protective advantage over control mice after myocardial ischemia/reperfusion injury. Fibroblast GRK2 knockout mice presented with decreased infarct size and preserved cardiac function 24 hours post ischemia/reperfusion as demonstrated by increased ejection fraction (59.1±1.8% versus 48.7±1.2% in controls; P<0.01). GRK2 fibroblast knockout mice also had decreased fibrosis and fibrotic gene expression. Importantly, these protective effects correlated with decreased infiltration of neutrophils to the ischemia site and decreased levels of tumor necrosis factor-α expression and secretion in GRK2 fibroblast knockout mice.

CONCLUSIONS

These novel data showing the benefits of inhibiting GRK2 in the cardiac fibroblast adds to previously published data showing the advantage of GRK2 ablation and reinforces the therapeutic potential of GRK2 inhibition in the heart after myocardial ischemia.

Skeletal Muscle-specific G Protein-coupled Receptor Kinase 2 Ablation Alters Isolated Skeletal Muscle Mechanics and Enhances Clenbuterol-stimulated Hypertrophy

GRK2, a G protein-coupled receptor kinase, plays a critical role in cardiac physiology. Adrenergic receptors are the primary target for GRK2 activity in the heart; phosphorylation by GRK2 leads to desensitization of these receptors. As such, levels of GRK2 activity in the heart directly correlate with cardiac contractile function. Furthermore, increased expression of GRK2 after cardiac insult exacerbates injury and speeds progression to heart failure. Despite the importance of this kinase in both the physiology and pathophysiology of the heart, relatively little is known about the role of GRK2 in skeletal muscle function and disease. In this study we generated a novel skeletal muscle-specific GRK2 knock-out (KO) mouse (MLC-Cre:GRK2^fl/fl) to gain a better understanding of the role of GRK2 in skeletal muscle physiology. In isolated muscle mechanics testing, GRK2 ablation caused a significant decrease in the specific force of contraction of the fast-twitch extensor digitorum longus muscle yet had no effect on the slow-twitch soleus muscle. Despite these effects in isolated muscle, exercise capacity was not altered in MLC-Cre:GRK2^fl/fl mice compared with wild-type controls. Skeletal muscle hypertrophy stimulated by clenbuterol, a β₂-adrenergic receptor (β₂AR) agonist, was significantly enhanced in MLC-Cre:GRK2^fl/fl mice; mechanistically, this seems to be due to increased clenbuterol-stimulated pro-hypertrophic Akt signaling in the GRK2 KO skeletal muscle. In summary, our study provides the first insights into the role of GRK2 in skeletal muscle physiology and points to a role for GRK2 as a modulator of contractile properties in skeletal muscle as well as β₂AR-induced hypertrophy.

Radiofrequency Renal Denervation Protects the Ischemic Heart via Inhibition of GRK2 and Increased Nitric Oxide Signaling

Rationale:

Catheter-based renal denervation (RDN) is currently under development for the treatment of resistant hypertension and is thought to reduce blood pressure via interruption of sympathetic pathways that modulate cardiovascular function. The sympathetic nervous system also plays a critical role in the pathogenesis of acute myocardial infarction and heart failure.

Objective:

We examined whether treatment with radiofrequency (RF)-RDN would protect the heart against subsequent myocardial ischemia/reperfusion injury via direct effects on the myocardium.

Methods and Results:

Spontaneously hypertensive rats received either bilateral RF-RDN or sham-RDN. At 4 weeks after RF-RDN (n=14) or sham-RDN (n=14) treatment, spontaneously hypertensive rats were subjected to 30 minutes of transient coronary artery occlusion and 24 hours –7 days reperfusion. Four weeks after RF-RDN, myocardial oxidative stress was markedly attenuated, and transcription and translation of antioxidants, superoxide dismutase 1 and glutathione peroxidase-1, were significantly upregulated compared with sham-RDN spontaneously hypertensive rats. RF-RDN also inhibited myocardial G protein–coupled receptor kinase 2 pathological signaling and enhanced myocardial endothelial nitric oxide synthase function and nitric oxide signaling. RF-RDN therapy resulted in a significant reduction in myocardial infarct size per area at risk compared with sham-RDN (26.8 versus 43.9%; P<0.01) at 24 hours postreperfusion and significantly improved left ventricular function at 7 days after myocardial ischemia/reperfusion.

Conclusions:

RF-RDN reduced oxidative stress, inhibited G protein–coupled receptor kinase 2 signaling, increased nitric oxide bioavailability, and ameliorated myocardial reperfusion injury in the setting of severe hypertension. These findings provide new insights into the remote cardioprotective effects of RF-RDN acting directly on cardiac myocytes to attenuate cell death and protect against ischemic injury.

The expanding GRK interactome: Implications in cardiovascular disease and potential for therapeutic development

Heart failure (HF) is a global epidemic with the highest degree of mortality and morbidity of any disease presently studied. G protein-coupled receptors (GPCRs) are prominent regulators of cardiovascular function. Activated GPCRs are "turned off" by GPCR kinases (GRKs) in a process known as "desensitization". GRKs 2 and 5 are highly expressed in the heart, and known to be upregulated in HF. Over the last 20 years, both GRK2 and GRK5 have been demonstrated to be critical mediators of the molecular alterations that occur in the failing heart. In the present review, we will highlight recent findings that further characterize "non-canonical" GRK signaling observed in HF. Further, we will also present potential therapeutic strategies (i.e. small molecule inhibition, microRNAs, gene therapy) that may have potential in combating the deleterious effects of GRKs in HF.

β-adrenergic receptor signalling and its functional consequences in the diseased heart

BACKGROUND

To maintain the balance between the demand of the body and supply (cardiac output), cardiac performance is tightly regulated via the parasympathetic and sympathetic nervous systems. In heart failure, cardiac output (supply) is decreased due to pathologic remodelling of the heart. To meet the demands of the body, the sympathetic system is activated and catecholamines stimulate β-adrenergic receptors (β-ARs) to increase contractile performance and cardiac output. Although this is beneficial in the acute phase, chronic β-ARs stimulation initiates a cascade of alterations at the cellular level, resulting in a diminished contractile performance of the heart.

MATERIALS AND METHODS

This narrative review includes results from previously published systematic reviews and clinical and basic research publications obtained via PubMed up to May 2015.

RESULTS

We discuss the alterations that occur during sustained β-AR stimulation in diseased myocardium and emphasize the consequences of β-AR overstimulation for cardiac function. In addition, current treatment options as well as future therapeutic strategies to treat patients with heart failure to normalize consequences of β-AR overstimulation are discussed.

CONCLUSIONS

The heart is able to protect itself from chronic stimulation of the β-ARs via desensitization and reduced membrane availability of the β-ARs. However, ultimately this leads to an impaired downstream signalling and decreased protein kinase A (PKA)-mediated protein phosphorylation. β-blockers are widely used to prevent β-AR overstimulation and restore β-ARs in the failing hearts. However, novel and more specific therapeutic treatments are needed to improve treatment of HF in the future.

A peptide of the RGS domain of GRK2 binds and inhibits Gα(q) to suppress pathological cardiac hypertrophy and dysfunction

G protein-coupled receptor (GPCR) kinases (GRKs) play a critical role in cardiac function by regulating GPCR activity. GRK2 suppresses GPCR signaling by phosphorylating and desensitizing active GPCRs, and through protein-protein interactions that uncouple GPCRs from their downstream effectors. Several GRK2 interacting partners, including Gα(q), promote maladaptive cardiac hypertrophy, which leads to heart failure, a leading cause of mortality worldwide. The regulator of G protein signaling (RGS) domain of GRK2 interacts with and inhibits Gα(q) in vitro. We generated TgβARKrgs mice with cardiac-specific expression of the RGS domain of GRK2 and subjected these mice to pressure overload to trigger adaptive changes that lead to heart failure. Unlike their nontransgenic littermate controls, the TgβARKrgs mice exhibited less hypertrophy as indicated by reduced left ventricular wall thickness, decreased expression of genes linked to cardiac hypertrophy, and less adverse structural remodeling. The βARKrgs peptide, but not endogenous GRK2, interacted with Gα(q) and interfered with signaling through this G protein. These data support the development of GRK2-based therapeutic approaches to prevent hypertrophy and heart failure.

Cardiac Fibrosis: The Fibroblast Awakens

Myocardial fibrosis is a significant global health problem associated with nearly all forms of heart disease. Cardiac fibroblasts comprise an essential cell type in the heart that is responsible for the homeostasis of the extracellular matrix; however, upon injury, these cells transform to a myofibroblast phenotype and contribute to cardiac fibrosis. This remodeling involves pathological changes that include chamber dilation, cardiomyocyte hypertrophy and apoptosis, and ultimately leads to the progression to heart failure. Despite the critical importance of fibrosis in cardiovascular disease, our limited understanding of the cardiac fibroblast impedes the development of potential therapies that effectively target this cell type and its pathological contribution to disease progression. This review summarizes current knowledge regarding the origins and roles of fibroblasts, mediators and signaling pathways known to influence fibroblast function after myocardial injury, as well as novel therapeutic strategies under investigation to attenuate cardiac fibrosis.