Induction of cardiac fibrosis by β-blocker in G protein-independent and G protein-coupled receptor kinase 5/β-arrestin2-dependent Signaling pathways

Targeting G protein-coupled receptors for heart failure treatment

Heart failure remains a leading cause of morbidity and mortality worldwide. Current treatment for patients with heart failure include drugs targeting G protein-coupled receptors such as β-adrenoceptor antagonists (β-blockers) and angiotensin II type 1 receptor antagonists (or angiotensin II receptor blockers). However, many patients progress to advanced heart failure with persistent symptoms, despite treatment with available therapeutics that have been shown to reduce mortality and mortality. GPCR targets currently being explored for the development of novel heart failure therapeutics include adenosine receptor, formyl peptide receptor, relaxin/insulin-like family peptide receptor, vasopressin receptor, endothelin receptor and the glucagon-like peptide 1 receptor. Many GPCR drug candidates are limited by insufficient efficacy and/or dose-limiting unwanted effects. Understanding the current challenges hindering successful clinical translation and the potential to overcome existing limitations will facilitate the future development of novel heart failure therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

β-blockers are not all the same: pharmacologic similarities and differences, potential combinations and clinical implications

β-blockers are a heterogeneous class, with individual agents distinguished by selectivity for β1- vs. β2- and α-adrenoceptors, presence or absence of partial agonist activity at one of more β-receptor subtype, presence or absence of additional vasodilatory properties, and lipophilicity, which determines the ease of entry the drug into the central nervous system. Cardioselectivity (β1-adrenoceptor selectivity) helps to reduce the potential for adverse effects mediated by blockade of β2-adrenoceptors outside the myocardium, such as cold extremities, erectile dysfunction, or exacerbation of asthma or chronic obstructive pulmonary disease. According to recently updated guidelines from the European Society of Hypertension, β-blockers are included within the five major drug classes recommended as the basis of antihypertensive treatment strategies. Adding a β-blocker to another agent with a complementary mechanism may provide a rational antihypertensive combination that minimizes the adverse impact of induced sympathetic overactivity for optimal blood pressure-lowering efficacy and clinical outcomes benefit.

Promising Therapeutic Treatments for Cardiac Fibrosis: Herbal Plants and Their Extracts

Cardiac fibrosis is closely associated with multiple heart diseases, which are a prominent health issue in the global world. Neurohormones and cytokines play indispensable roles in cardiac fibrosis. Many signaling pathways participate in cardiac fibrosis as well. Cardiac fibrosis is due to impaired degradation of collagen and impaired fibroblast activation, and collagen accumulation results in increasing heart stiffness and inharmonious activity, leading to structure alterations and finally cardiac function decline. Herbal plants have been applied in traditional medicines for thousands of years. Because of their naturality, they have attracted much attention for use in resisting cardiac fibrosis in recent years. This review sheds light on several extracts from herbal plants, which are promising therapeutics for reversing cardiac fibrosis.

Gαq protein-biased ligand of angiotensin II type 1 receptor mediates myofibroblast differentiation through TGF-β1/ERK axis in human cardiac fibroblasts

Angiotensin II receptors are members of G protein-coupled receptor superfamily that manifest biased signals toward G protein- and β-arrestin-dependent pathways. However, the role of angiotensin II receptor-biased ligands and the mechanisms underlying myofibroblast differentiation in human cardiac fibroblasts have not been fully elucidated. Our results demonstrated that antagonism of angiotensin II type 1 receptor (AT₁ receptor) and blockade of G_αq protein suppressed angiotensin II (Ang II)-induced fibroblast proliferation, overexpression of collagen I and α-smooth muscle actin (α-SMA), and stress fibre formation, indicating the AT₁ receptor/G_αq axis is necessary for fibrogenic effects of Ang II. Stimulation of AT₁ receptors by their G_αq-biased ligand (TRV120055), but not β-arrestin-biased ligand (TRV120027), substantially exerted fibrogenic effects at a level similar to that of Ang II, suggesting that AT₁ receptor induced cardiac fibrosis in a G_αq-dependent and β-arrestin-independent manner. Valsartan prevents TRV120055-mediated fibroblast activation. TRV120055 mediated the upregulation of transforming growth factor-beta1 (TGF-β1) through the AT₁ receptor/G_αq cascade. In addition, G_αq protein and TGF-β1 were necessary for ERK1/2 activation induced by Ang II and TRV120055. Collectively, TGF-β1 and ERK1/2 are downstream effectors of the G_αq-biased ligand of AT₁ receptor for the induction of cardiac fibrosis.

GRK5-mediated inflammation and fibrosis exert cardioprotective effects during the acute phase of myocardial infarction

During myocardial infarction (MI), cardiac cells at the infarcted area undergo cell death. In response, cardiac myofibroblasts, which are mainly differentiated from resident fibroblasts upon inflammation, produce extracellular matrix proteins such as collagen to fill the damaged areas of the heart to prevent cardiac rupture. In this study, we identified a cardioprotective role of G-protein-coupled receptor kinase 5 (GRK5) in MI. GRK5 expression was found to increase in the mouse heart after MI and was highly expressed in cardiac fibroblasts/myofibroblasts. In fibroblasts/myofibroblasts, GRK5 promoted the expression of inflammation-related genes through nuclear factor-κB activation, leading to an increase in the expression levels of fibrosis-related genes. Bone marrow transfer experiments confirmed that GRK5 in fibroblasts/myofibroblasts, but not in infiltrated macrophages in the infarcted area, is mainly responsible for GRK5-mediated inflammation in infarcted hearts. In addition, inflammation and fibrosis at the infarcted area were significantly suppressed in GRK5 knockout mice, resulting in increased mortality compared with that in wild-type mice. These data indicate that GRK5 in cardiac fibroblasts/myofibroblasts promotes inflammation and fibrosis to ameliorate the damage after MI.

Carvedilol ameliorates dexamethasone-induced myocardial injury in rats independent of its action on the α1-adrenergic receptor

The current study aimed to investigate the cardiotoxic effect of dexamethasone-high-dose in rats, the therapeutic effect of carvedilol and the role of α1-adrenergic receptor (α1AR). The experiment involved 6 groups: control, dexamethasone (10 mg/kg), carvedilol (10 mg/kg), phenylephrine (1 mg/kg), phenylephrine plus carvedilol and propranolol (30 mg/kg). Drugs and vehicles were given for 7 days. Dexamethasone was given with the drugs in the last 4 groups. On the 8th-day and after overnight fasting, serum and cardiac samples were collected. Serum levels of cardiac troponin I and creatine kinase-myoglobin as well as cardiac levels of diacylglycerol, malondialdehyde, kinase activity of Akt, transforming growth factor-β, Smad3 and alpha smooth muscle actin were measured. Cardiac samples were also used for histopathological examination using hematoxylin-eosin and Sirius red stains, in addition to immunohistochemical examination using β-arrestin2 antibody. Dexamethasone induced cardiac injury via increasing oxidative stress, apoptosis and profibrotic signals. Carvedilol significantly reduced the dexamethasone-induced cardiotoxicity. Using phenylephrine, a competitive α1-agonist, with carvedilol potentiated the cardioprotective actions of carvedilol. Propranolol, a β-blocker without activity on α1ARs, showed higher cardiac protection than carvedilol. Dexamethasone-high-dose upregulates cardiac oxidative stress, apoptotic and profibrotic signals and induces cardiac injury. Blocking the α1-adrenergic receptor by carvedilol attenuates its cardioprotective effects against dexamethasone-induced cardiotoxicity.

Targeting Myocardial Fibrosis—A Magic Pill in Cardiovascular Medicine?

Fibrosis, characterized by an excessive accumulation of extracellular matrix, has long been seen as an adaptive process that contributes to tissue healing and regeneration. More recently, however, cardiac fibrosis has been shown to be a central element in many cardiovascular diseases (CVDs), contributing to the alteration of cardiac electrical and mechanical functions in a wide range of clinical settings. This paper aims to provide a comprehensive review of cardiac fibrosis, with a focus on the main pathophysiological pathways involved in its onset and progression, its role in various cardiovascular conditions, and on the potential of currently available and emerging therapeutic strategies to counteract the development and/or progression of fibrosis in CVDs. We also emphasize a number of questions that remain to be answered, and we identify hotspots for future research.

Sympathetic Denervation Ameliorates Renal Fibrosis via Inhibition of Cellular Senescence

Objective

Continuous overactivation of the renal sympathetic nerve is considered to be an important cause of renal fibrosis. Accumulated senescent cells in the damaged kidney have metabolic activities and secrete amounts of proinflammatory factors as part of the SASP (the senescence-associated secretory phenotype), which induce chronic inflammation and fibrosis. It is still unclear whether renal sympathetic nerves affect renal inflammation and fibrosis by regulating cellular senescence. Therefore, we hypothesize that sympathetic activation in the injured kidney induces cellular senescence, which contributes to progressive renal inflammation and fibrosis.

Methods

Renal denervation was performed 2 days before the UUO (unilateral ureteral obstruction) and UIRI (unilateral ischemia-reperfusion injury) models. The effects of renal denervation on renal fibrosis and cellular senescence were observed. In vitro, cellular senescence was induced in renal proximal tubular epithelial cell lines (TKPTS cells) by treatment with norepinephrine (NE). The selective α_2A-adrenergic receptor (α_2A-AR) antagonists BRL44408 and β-arrestin2 siRNA, were administered to inhibit NE-induced cellular senescence. A significantly altered pathway was identified through immunoblotting, immunofluorescence, immunocytochemistry, and functional assays involved in mitochondrial function.

Results

Renal fibrosis and cellular senescence were significantly increased in UUO and UIRI models, which were partially reversed by renal denervation. In vitro, NE induced epithelial cells secreting proinflammatory cytokines and promoted cell senescence by activating α_2A-AR. Importantly, the effects of NE during cellular senescence were blocked by α_2A-AR selective antagonist and β-arrestin2 (downstream of α_2A-AR) siRNA.

Conclusion

Renal sympathetic activation and cellular senescence are important neurometabolic and neuroimmune mechanisms in the development of renal fibrosis. Renal sympathetic neurotransmitter NE acting on the α_2A-AR of epithelial cells promotes cellular senescence through the downstream β-arrestin2 signaling, which is a potential preventive target for renal fibrosis.

Polymorphic Variants in the GRK5 Gene Promoter Are Associated With Diastolic Dysfunction in Coronary Artery Bypass Graft Surgery Patients

BACKGROUND

The G-protein-coupled receptor kinase 5 (GRK5) is a mediator of cardiovascular homeostasis and participates in inflammation and cardiac fibrosis, both being involved in the development of diastolic dysfunction (DD). While mechanisms of transcriptional regulation of the GRK5 promoter are unclear, we tested the hypotheses, that (1) GRK5 expression varies depending on functional single nucleotide polymorphisms (SNPs) in the GRK5 promoter and (2) this is associated with DD in patients undergoing coronary artery bypass graft (CABG) surgery.

METHODS

We amplified and sequenced the GRK5 promoter followed by cloning, reporter assays, and electrophoretic mobility shift assays (EMSA). GRK5 messenger ribonucleic acid (mRNA) expression was determined in right atrial tissue sampled from 50 patients undergoing CABG surgery. In another prospective study, GRK5 genotypes were associated with determinants of diastolic function using transesophageal echocardiography in 255 patients with CABG with normal systolic left ventricular (LV) function. Specifically, we measured ejection fraction (EF), transmitral Doppler early filling velocity (E), tissue Doppler early diastolic lateral mitral annular velocity (E' lateral), and calculated E/E', E' norm and the difference of E' lateral and E' norm to account for age-related changes in diastolic function.

RESULTS

We identified 6 SNPs creating 3 novel haplotypes with the greatest promoter activation in haplotype tagging (ht) SNP T(-678)C T-allele constructs (P < .001). EMSAs showed allele-specific transcription factor binding proving functional activity. GRK5 mRNA expression was greatest in TT genotypes (TT: 131 fg/µg [95% CI, 108-154]; CT: 109 [95% confidence interval {CI}, 93-124]; CC: 83 [95% CI, 54-112]; P = .012). Moreover, GRK5 genotypes were significantly associated with determinants of diastolic function. Grading of DD revealed more grade 3 patients in TT compared to CT and CC genotypes (58% vs 38% vs 4%; P = .023). E´ lateral was lowest in TT genotypes (P = .007) and corresponding E/E' measurements showed 1.27-fold increased values in TT versus CC genotypes (P = .01), respectively. While E' norm values were not different between genotypes (P = .182), the difference between E' lateral and E' norm was significantly higher in TT genotypes compared to CC and CT genotypes (-1.2 [interquartile range {IQR}, 2.7], -0.5 [IQR, 3.4], and -0.4 [IQR, 4.2; P = .035], respectively).

CONCLUSIONS

A functional GRK5 SNP results in allele-dependent differences in GRK5 promoter activity and mRNA expression. This is associated with altered echocardiographic determinants of diastolic function. Thus, SNPs in the GRK5 promoter are associated with altered perioperative diastolic cardiac function. In the future, preoperative testing for these and other SNPs might allow to initiate more specific diagnostic and perioperative pathways to benefit patients at risk.

In cardiac muscle cells, both adrenergic agonists and antagonists induce reactive oxygen species from NOX2 but mutually attenuate each other's effects

In cardiac muscle cells adrenergic agonists stimulate the generation of reactive oxygen species, followed by redox signaling. We postulated that the antagonists would attenuate such reactive oxygen species generation by the agonists. H9c2 cardiac myoblasts, neonatal rat cardiac myocytes, and HEK293 cells expressing β1/β2 adrenoceptors were stimulated with several agonists and antagonists. All the agonists and antagonists independently generated reactive oxygen species; but its generation was minimum whenever an agonists was added together with an antagonist. We monitored the Ca++ signaling in the treated cells and obtained similar results. In all treatment sets, superoxide and H2O2 were generated in the mitochondria and the cytosol respectively. NOX2 inhibitor gp91ds-tat blocked reactive oxygen species generation by both the agonists and the antagonists. The level of p47phox subunit of NOX2 rapidly increased upon treatment, and it translocated to the plasma membrane, confirming NOX2 activation. Inhibitor studies showed that the activation of NOX2 involves ERK, PI3K, and tyrosine kinases. Recombinant promoter-reporter assays showed that reactive oxygen species generated by both the agonists and antagonists modulated downstream gene expression. Mice injected with the β-adrenergic agonist isoproterenol and fed with the antagonist metoprolol showed a robust induction of p47phox in the heart. We conclude that both the agonism and antagonism of adrenoceptors initiate redox signaling but when added together, they mutually counteract each other's effects. Our study thus highlights the importance of reactive oxygen species in adrenoceptor agonism and antagonism with relevance to the therapeutic use of the β blockers.

Origanum majorana L. Extract Protects Against Isoproterenol-Induced Cardiotoxicity in Rats

Coronary artery diseases are the major causes of disabilities and death worldwide. Evidence from the literature has demonstrated that Origanum majorana L. (marjoram) acts as an antioxidant, anti-inflammatory, antiplatelet, and assists in hormonal regulation. However, there is limited scientific evidence describing the signaling pathways associated with the marjoram's positive effect on cardiac injury. Therefore, we aimed to understand the mechanistic protective effects of marjoram on isoproterenol (ISO)-induced myocardial injury in rats. Sprague Dawley rats were randomly assigned into six groups. Marjoram was administrated by oral gavage and isoproterenol was administrated subcutaneously (ISO; 85 mg/kg). Heart weight, cardiac enzymes, inflammatory, and oxidative stress biomarkers were measured. The ISO-induced cardiac injury was confirmed by the significant increase in the levels of cardiac enzymes (P value < 0.05), whereas pre-treatment with marjoram normalized these cardiac injury parameters. We also determined that marjoram had a protective effect against ISO-induced increase in C-reactive protein (CRP), IL-6, IL-13, and TNF-α. Additionally, marjoram significantly decreased cardiac thiobarbituric acid reactive substances (TBARS) levels (P value < 0.05) and protected against ISO-induced oxidative stress. We have demonstrated that marjoram decreased both cardiac oxidative stress and inflammation, thus establishing the beneficial effects of marjoram on ISO-induced cardiac injury in rats.

Drug screening with zebrafish visual behavior identifies carvedilol as a potential treatment for an autosomal dominant form of retinitis pigmentosa

Retinitis Pigmentosa (RP) is a mostly incurable inherited retinal degeneration affecting approximately 1 in 4000 individuals globally. The goal of this work was to identify drugs that can help patients suffering from the disease. To accomplish this, we screened drugs on a zebrafish autosomal dominant RP model. This model expresses a truncated human rhodopsin transgene (Q344X) causing significant rod degeneration by 7 days post-fertilization (dpf). Consequently, the larvae displayed a deficit in visual motor response (VMR) under scotopic condition. The diminished VMR was leveraged to screen an ENZO SCREEN-WELL REDOX library since oxidative stress is postulated to play a role in RP progression. Our screening identified a beta-blocker, carvedilol, that ameliorated the deficient VMR of the RP larvae and increased their rod number. Carvedilol may directly on rods as it affected the adrenergic pathway in the photoreceptor-like human Y79 cell line. Since carvedilol is an FDA-approved drug, our findings suggest that carvedilol can potentially be repurposed to treat autosomal dominant RP patients.

Adrenal angiotensin II type 1 receptor biased signaling: The case for "biased" inverse agonism for effective aldosterone suppression

Angiotensin II (AngII) uses two distinct G protein-coupled receptor (GPCR) types, AT₁R and AT₂R, to exert a plethora of physiologic effects in the body and to significantly affect cardiovascular homeostasis. Although not much is known about the signaling of the AT₂R, AT₁R signaling is known to be quite pleiotropic, mobilizing a variety of signal transducers inside cells to produce a biological outcome. When the outcome in question is aldosterone production from the adrenal cortex, the main transducers activated specifically by the adrenocortical AT₁R to signal toward that cellular effect are the G_q/11 protein alpha subunits and the β-arrestins (also known as Arrestin-2 and -3). The existence of various downstream pathways the AT₁R signal can travel down on has led to the ever-expanding filed of GPCR pharmacology termed "biased" signaling, which refers to a ligand preferentially activating one signaling pathway over others downstream of the same receptor in the same cell. However, "biased" signaling or "biased" agonism is therapeutically desirable only when the downstream pathways lead to different or opposite cellular outcomes, so the pathway promoting the beneficial effect can be selectively activated over the pathway that leads to detrimental consequences. In the case of the adrenal AT₁R, both G_q/11 proteins and β-arrestins mediate signaling to the same end-result: aldosterone synthesis and secretion. Therefore, both pathways need to remain inactive in the adrenal cortex to fully suppress the production of aldosterone, which is one of the culprit hormones elevated in chronic heart failure, hypertension, and various other cardiovascular diseases. Variations in the effectiveness of the AT₁R antagonists, which constitute the angiotensin receptor blocker (ARB) class of drugs (also known as sartans), at the relative blockade of these two pathways downstream of the adrenal AT₁R opens the door to the flip term "biased" inverse agonism at the AT₁R. ARBs that are unbiased and equipotent inverse agonists for both G proteins and β-arrestins at this receptor, like candesartan and valsartan, are the most preferred agents with the best efficacy at reducing circulating aldosterone, thereby ameliorating heart failure. In the present review, the biased signaling of the adrenal AT₁R, particularly in relation to aldosterone production, is examined and the term "biased" inverse agonism at the AT₁R is introduced and explained, as a means of pharmacological categorization of the various agents within the ARB drug class.

β-arrestin2 deficiency protects against hepatic fibrosis in mice and prevents synthesis of extracellular matrix

Hepatic fibrosis is a disease of the wound-healing response following chronic liver injury, and activated hepatic stellate cells (HSCs) play a crucial role in the progression of hepatic fibrosis. β-arrestin2 functions as a multiprotein scaffold to coordinate complex signal transduction networks. Although β-arrestin2 transduces diverse signals in cells, little is known about its involvement in the regulation of liver fibrosis. Our current study utilized a porcine serum-induced liver fibrosis model and found increased expression of β-arrestin2 in hepatic tissues with the progression of hepatic fibrosis, which was positively correlated with collagen levels. Furthermore, changes in human fibrotic samples were also observed. We next used β-arrestin2^−/− mice to demonstrate that β-arrestin2 deficiency ameliorates CCl₄-induced liver fibrosis and decreases collagen deposition. The in vitro depletion and overexpression experiments showed that decreased β-arrestin2 inhibited HSCs collagen production and elevated TβRIII expression, thus downregulating the TGF-β1 pathway components Smad2, Smad3 and Akt. These findings suggest that β-arrestin2 deficiency ameliorates liver fibrosis in mice, and β-arrestin2 may be a potential treatment target in hepatic fibrosis.

Angiotensin-converting-enzyme inhibitor prevents skeletal muscle fibrosis in myocardial infarction mice

BACKGROUND

Transforming growth factor beta (TGF-β)-Smad2/3 is the major signaling pathway of fibrosis, which is characterized by the excessive production and accumulation of extracellular matrix (ECM) components, including collagen. Although the ECM is an essential component of skeletal muscle, fibrosis may be harmful to muscle function. On the other hand, our previous studies have shown that levels of angiotensin II, which acts upstream of TGF-β-Smad2/3 signaling, is increased in mice with myocardial infarction (MI). In this study, we found higher skeletal muscle fibrosis in MI mice compared with control mice, and we investigated the mechanisms involved therein. Moreover, we administered an inhibitor based on the above mechanism and investigated its preventive effects on skeletal muscle fibrosis.

METHODS

Male C57BL/6 J mice with MI were created, and sham-operated mice were used as controls. The time course of skeletal muscle fibrosis post-MI was analyzed by picrosirius-red staining (days 1, 3, 7, and 14). Mice were then divided into 3 groups: sham + vehicle (Sham + Veh), MI + Veh, and MI + lisinopril (an angiotensin-converting enzyme [ACE] inhibitor, 20 mg/kg body weight/day in drinking water; MI + Lis). Lis or Veh was administered from immediately after the surgery to 14 days postsurgery.

RESULTS

Skeletal muscle fibrosis was significantly increased in MI mice compared with sham mice from 3 to 14 days postsurgery. Although mortality was lower in the MI + Lis mice than the MI + Veh mice, there was no difference in cardiac function between the 2 groups at 14 days. Skeletal muscle fibrosis and hydroxyproline (a key marker of collagen content) were significantly increased in MI + Veh mice compared with the Sham + Veh mice. Consistent with these results, protein expression of TGF-β and phosphorylated Smad2/3 in the skeletal muscle during the early time points after surgery (days 1-7 postsurgery) and blood angiotensin II at 14 days postsurgery was increased in MI mice compared with sham mice. These impairments were improved in MI + Lis mice, without any effects on spontaneous physical activity, muscle strength, muscle weight, and blood pressure.

CONCLUSIONS

ACE inhibitor administration prevents increased skeletal muscle fibrosis during the early phase after MI. Our findings indicate a new therapeutic target for ameliorating skeletal muscle abnormalities in heart diseases.

The peripheral CB1 receptor antagonist JD5037 attenuates liver fibrosis via a CB1 receptor/β-arrestin1/Akt pathway

BACKGROUND AND PURPOSE

Liver fibrosis is a serious cause of morbidity and mortality worldwide and has no adequate treatment. Accumulating evidence suggests that cannabinoid CB₁ receptors regulate a variety of physiological and pathological processes in the liver, and blockage of CB₁ receptor signalling shows promise as a new therapy for several liver diseases. The aim of this study was to investigate the potential therapeutic effects of CB₁ receptors and a peripheral CB₁ receptor antagonist JD5037 in liver fibrogenesis.

EXPERIMENTAL APPROACH

Liver samples from both humans and mouse models were investigated. The peripheral CB₁ receptor antagonist JD5037, β-arr1 wild type (β-arr1-WT) and β-arr1 knockout (β-arr1-KO) littermate models, and primary hepatic stellate cells (HSCs) were also used. The mechanisms underlying CB₁ receptor-regulated HSCs activation in fibrosis and the therapeutic potential of JD5037 were further analysed.

KEY RESULTS

CB₁ receptors were induced in samples from patients with liver fibrosis and from mouse models. These receptors promoted activation of HSCs in liver fibrosis via recruiting β-arrestin1 and Akt signalling, while blockage of CB₁ receptors with JD5037 attenuated CB₁ receptor-regulated HSCs activation and liver fibrosis by suppressing β-arrestin1/Akt signalling.

CONCLUSIONS AND IMPLICATIONS

CB₁ receptors promote the activation of HSCs and liver fibrosis via the β-arrestin1/Akt signalling pathway. The peripheral CB₁ receptor antagonist JD5037 blocked this pathway, the activation of HSCs and liver fibrosis. This compound and the associated pathway may be a novel approach to the treatment of liver fibrosis.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Extended Human G-Protein Coupled Receptor Network: Cell-Type-Specific Analysis of G-Protein Coupled Receptor Signaling Pathways

G-protein coupled receptors (GPCRs) mediate crucial physiological functions in humans, have been implicated in an array of diseases, and are therefore prime drug targets. GPCRs signal via a multitude of pathways, mainly through G-proteins and β-arrestins, to regulate effectors responsible for cellular responses. The limited number of transducers results in different GPCRs exerting control on the same pathway, while the availability of signaling proteins in a cell defines the result of GPCR activation. The aim of this study was to construct the extended human GPCR network (hGPCRnet) and examine the effect that cell-type specificity has on GPCR signaling pathways. To achieve this, protein-protein interaction data between GPCRs, G-protein coupled receptor kinases (GRKs), Gα subunits, β-arrestins, and effectors were combined with protein expression data in cell types. This resulted in the hGPCRnet, a very large interconnected network, and similar cell-type-specific networks in which, distinct GPCR signaling pathways were formed. Finally, a user friendly web application, hGPCRnet ( http://bioinformatics.biol.uoa.gr/hGPCRnet ), was created to allow for the visualization and exploration of these networks and of GPCR signaling pathways. This work, and the resulting application, can be useful in further studies of GPCR function and pharmacology.

Mechanisms of Improved Mortality Following Ablation: Does Ablation Restore Beta-Blocker Benefit in Atrial Fibrillation/Heart Failure?

Observational trials have shown that atrial fibrillation ablation favorably impacts long-term outcomes in systolic heart failure. These outcomes have been confirmed by randomized prospective trials highlighting the favorable impact of ablation on left ventricular function and remodeling, risk of heart failure hospitalization, and mortality. Ablation along with established heart failure medications is new and supported conceptually by the value of restoring sinus rhythm, avoiding long-term antiarrhythmic drugs, and minimizing drug-drug interactions. Observational data suggest a potential long-term benefit of beta-blockers with ablation that becomes augmented as follow-up is extended from 1 to 5 years.

Modelling cardiac fibrosis using three-dimensional cardiac microtissues derived from human embryonic stem cells

Background

Cardiac fibrosis is the most common pathway of many cardiac diseases. To date, there has been no suitable in vitro cardiac fibrosis model that could sufficiently mimic the complex environment of the human heart. Here, a three-dimensional (3D) cardiac sphere platform of contractile cardiac microtissue, composed of human embryonic stem cell (hESC)-derived cardiomyocytes (CMs) and mesenchymal stem cells (MSCs), is presented to better recapitulate the human heart.

Results

We hypothesized that MSCs would develop an in vitro fibrotic reaction in response to treatment with transforming growth factor-β1 (TGF-β1), a primary inducer of cardiac fibrosis. The addition of MSCs improved sarcomeric organization, electrophysiological properties, and the expression of cardiac-specific genes, suggesting their physiological relevance in the generation of human cardiac microtissue model in vitro. MSCs could also generate fibroblasts within 3D cardiac microtissues and, subsequently, these fibroblasts were transdifferentiated into myofibroblasts by the exogenous addition of TGF-β1. Cardiac microtissues displayed fibrotic features such as the deposition of collagen, the presence of numerous apoptotic CMs and the dissolution of mitochondrial networks. Furthermore, treatment with pro-fibrotic substances demonstrated that this model could reproduce key molecular and cellular fibrotic events.

Conclusions

This highlights the potential of our 3D cardiac microtissues as a valuable tool for manifesting and evaluating the pro-fibrotic effects of various agents, thereby representing an important step forward towards an in vitro system for the prediction of drug-induced cardiac fibrosis and the study of the pathological changes in human cardiac fibrosis.

Electronic supplementary material

The online version of this article (10.1186/s13036-019-0139-6) contains supplementary material, which is available to authorized users.

Therapeutic Targets for Treatment of Heart Failure: Focus on GRKs and β-Arrestins Affecting βAR Signaling

Heart failure (HF) is a heart disease that is classified into two main types: HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). Both types of HF lead to significant risk of mortality and morbidity. Pharmacological treatment with β-adrenergic receptor (βAR) antagonists (also called β-blockers) has been shown to reduce the overall hospitalization and mortality rates and improve the clinical outcomes in HF patients with HFrEF but not HFpEF. Although, the survival rate of patients suffering from HF continues to drop, the management of HF still faces several limitations and discrepancies highlighting the need to develop new treatment strategies. Overstimulation of the sympathetic nervous system is an adaptive neurohormonal response to acute myocardial injury and heart damage, whereas prolonged exposure to catecholamines causes defects in βAR regulation, including a reduction in the amount of βARs and an increase in βAR desensitization due to the upregulation of G protein-coupled receptor kinases (GRKs) in the heart, contributing in turn to the progression of HF. Several studies show that myocardial GRK2 activity and expression are raised in the failing heart. Furthermore, β-arrestins play a pivotal role in βAR desensitization and, interestingly, can mediate their own signal transduction without any G protein-dependent pathway involved. In this review, we provide new insight into the role of GRKs and β-arrestins on how they affect βAR signaling regarding the molecular and cellular pathophysiology of HF. Additionally, we discuss the therapeutic potential of targeting GRKs and β-arrestins for the treatment of HF.

miR-133: A Suppressor of Cardiac Remodeling?

Cardiac remodeling, which is characterized by mechanical and electrical remodeling, is a significant pathophysiological process involved in almost all forms of heart diseases. MicroRNAs (miRNAs) are a group of non-coding RNAs of 20–25 nucleotides in length that primarily regulate gene expression by promoting mRNA degradation or post-transcriptional repression in a sequence-specific manner. Three miR-133 genes have been identified in the human genome, miR-133a-1, miR-133a-2, and miR-133b, which are located on chromosomes 18, 20, and 6, respectively. These miRNAs are mainly expressed in muscle tissues and appear to repress the expression of non-muscle genes. Based on accumulating evidence, miR-133 participates in the proliferation, differentiation, survival, hypertrophic growth, and electrical conduction of cardiac cells, which are essential for cardiac fibrosis, cardiac hypertrophy, and arrhythmia. Nevertheless, the roles of miR-133 in cardiac remodeling are ambiguous, and the mechanisms are also sophisticated, involving many target genes and signaling pathways, such as RhoA, MAPK, TGFβ/Smad, and PI3K/Akt. Therefore, in this review, we summarize the critical roles of miR-133 and its potential mechanisms in cardiac remodeling.

Biased Ligands of G Protein-Coupled Receptors (GPCRs): Structure-Functional Selectivity Relationships (SFSRs) and Therapeutic Potential

G protein-coupled receptors (GPCRs) signal through both G-protein-dependent and G-protein-independent pathways, and β-arrestin recruitment is the most recognized one of the latter. Biased ligands selective for either pathway are expected to regulate biological functions of GPCRs in a more precise way, therefore providing new drug molecules with superior efficacy and/or reduced side effects. During the past decade, biased ligands have been discovered and developed for many GPCRs, such as the μ opioid receptor, the angiotensin II receptor type 1, the dopamine D₂ receptor, and many others. In this Perspective, recent advances in this field are reviewed by discussing the structure-functional selectivity relationships (SFSRs) of GPCR biased ligands and the therapeutic potential of these molecules. Further understanding of the biological functions associated with each signaling pathway and structural basis for biased signaling will facilitate future drug design in this field.

Biased Agonism/Antagonism of Cardiovascular GPCRs for Heart Failure Therapy

G protein-coupled receptors (GPCRs) are among the most important drug targets currently used in clinic, including drugs for cardiovascular indications. We now know that, in addition to activating heterotrimeric G protein-dependent signaling pathways, GPCRs can also activate G protein-independent signaling, mainly via the βarrestins. The major role of βarrestin1 and -2, also known as arrestin2 or -3, respectively, is to desensitize GPCRs, i.e., uncoupled them from G proteins, and to subsequently internalize the receptor. As the βarrestin-bound GPCR recycles inside the cell, it serves as a signalosome transducing signals in the cytoplasm. Since both G proteins and βarrestins can transduce signals from the same receptor independently of each other, any given GPCR agonist might selectively activate either pathway, which would make it a biased agonist for that receptor. Although this selectivity is always relative (never absolute), in cases where the G protein- and βarrestin-dependent signals emanating from the same GPCR result in different cellular effects, pharmacological exploitation of GPCR-biased agonism might have therapeutic potential. In this chapter, we summarize the GPCR signaling pathways and their biased agonism/antagonism examples discovered so far that can be exploited for heart failure treatment. We also highlight important issues that need to be clarified along the journey of these ligands from bench to the clinic.

microRNA expression profiles of scar and normal tissue from patients with posterior urethral stricture caused by pelvic fracture urethral distraction defects

Pelvic fracture urethral distraction defect (PFUDD) seriously affects the quality of life of patients. At present, there are few effective drug treatments available for PFUDD-induced urethral stricture, which is associated with fibrosis and scar formation in urethra lumen. Emerging evidence suggests that microRNAs (miRNAs/miRs) may be involved in the regulation of fibrosis, and analysis of miRNA expression profiles in urethral scar and normal urethra tissues may therefore benefit the discovery of novel treatments for urethral stricture with micro invasive procedures. In the present study, miRNA sequencing and quantitative polymerase chain reaction (qPCR) validation using paired scar and normal tissues from patients with PFUDD, and functional analysis of the miRNAs involved in the fibrosis associated signaling pathway was performed. A total of 94 differentially expressed miRNAs were identified in the scar tissue of patients with PFUDD. Among them, 26 miRNAs had significantly altered expression in the scar tissue compared with the normal tissue from the same patient. qPCR validation confirmed that miR-129-5p was overexpressed in scar tissue. The TGF-β pathway-associated functions of a total of 5 miRNAs (hsa-miR-129-5p, hsa-miR-135a-5p, hsa-miR-363-3p, hsa-miR-6720-3p and hsa-miR-9-5p) were further analyzed, as well as their key molecular targets and functional mechanisms in signaling regulation. To conclude the miRNA sequencing indicated a significantly altered expression of hsa-miR-129-5p, hsa-miR-135a-5p, hsa-miR-363-3p, hsa-miR-6720-3p and hsa-miR-9-5p in patients with PFUDD. These miRNAs and their potential target genes were associated with fibrosis in several diseases, and the data from the present study may help explore potential miRNA targets for future precision treatments for urethral stricture.

Sustained β-AR stimulation induces synthesis and secretion of growth factors in cardiac myocytes that affect on cardiac fibroblast activation

Paracrine factors, including growth factors and cytokines, released from cardiac myocytes following β-adrenergic receptor (β-AR) stimulation regulate cardiac fibroblasts. Activated cardiac fibroblasts have the ability to increase collagen synthesis, cell proliferation and myofibroblast differentiation, leading to cardiac fibrosis. However, it is unknown which β-AR subtypes and signaling pathways mediate the upregulation of paracrine factors in cardiac myocytes. In this study, we demonstrated that sustained stimulation of β-ARs significantly induced synthesis and secretion of growth factors, including connective tissue growth factor (CTGF) and vascular endothelial growth factor (VEGF), via the cAMP-dependent and protein kinase A (PKA)-dependent pathways. In addition, isoproterenol (ISO)-mediated synthesis and secretion of CTGF and VEGF through the β₁-AR and β₂-AR subtypes. Paracrine factors released by cardiac myocytes following sustained β-AR stimulation are necessary for the induction of cell proliferation and synthesis of collagen I, collagen III and α-smooth muscle actin (α-SMA) in cardiac fibroblasts, confirming that β-AR overstimulation of cardiac myocytes induces cardiac fibrosis by releasing several paracrine factors. These effects can be antagonized by β-blockers, including atenolol, metoprolol, and propranolol. Thus, the use of β-blockers may have beneficial effects on the treatment of myocardial fibrosis in patients with heart failure.

β-Arrestin-biased AT1R stimulation promotes extracellular matrix synthesis in renal fibrosis

The renin-angiotensin system plays a critical role in the progression of renal fibrosis. Angiotensin II type 1 receptor (AT1R) belongs to the B family of the G protein-coupled receptor (GPCR) family. β-Arrestins are known as negative regulators of GPCRs. Recently, β-arrestins have been found to regulate multiple intracellular signaling pathways independent of G proteins. In this study we investigated the role of β-arrestins in regulating extracellular matrix (ECM) synthesis in renal fibrosis. The rat kidney fibroblast cell line (NRK-49F) was treated with the β-arrestin biased agonist [1-sar, 4, 8-ile]angiotensin II (SII), which does not initiate AT1R-G protein signaling. The cells were transfected with recombinant adenoviruses expressing β-arrestin-2 gene or small-interfering RNA (siRNA) targeting β-arrestin-2. The unilateral ureteral obstruction (UUO) model was used in vivo. mRNA and protein levels of β-arrestin-2, not β-arrestin-1, were significantly upregulated in the UUO kidney tissues. SII induced the tight binding of β-arrestin-2 with AT1R. SII increased the synthesis of collagen I and fibronectin in NRK-49F, which were abolished when pretreated with candesartan (AT1R blocker). Transfection of siRNA targeting β-arrestin-2 decreased the effects of SII on ECM synthesis. Overexpression of β-arrestin-2 enhanced SII-stimulated ECM synthesis. SII induced ERK1/2 phosphorylation in NRK-49F. Transfection of siRNA targeting β-arrestin-2 inhibited ERK phosphorylation. Overexpression of β-arrestin-2 increased ERK1/2 phosphorylation. Our study first showed that AT1R-β-arrestin-2 pathway signaling plays an important role in renal fibrosis, although it was previously believed that the AT1R-G protein pathway plays a major role. Targeting β-arrestin-2 may be a potential therapeutic agent for renal fibrosis.

Synthesis and Characterization of Novel Anchorlipids for Tethered Bilayer Lipid Membranes

Tethered bilayer lipid membranes are versatile solid-supported model membrane systems. Core to these systems is an anchorlipid that covalently links a lipid bilayer to a support. The molecular structure of these lipids can have a significant impact on the properties of the resulting bilayer. Here, the synthesis of anchorlipids containing ester groups in the tethering part is described. The lipids are used to form bilayer membranes, and the resulting structures are compared with membranes formed using conventional anchorlipids or sparsely tethered membranes. All membranes showed good electrical sealing properties; the disulphide-terminated anchorlipids could be used in a sparsely tethered system without significantly reducing the sealing properties of the lipid bilayers. The sparsely tethered systems also allowed for higher ion transport across the membrane, which is in good correlation with higher hydration of the spacer region as seen by neutron scattering.

β-Adrenergic Receptor and Insulin Resistance in the Heart

Insulin resistance is characterized by the reduced ability of insulin to stimulate tissue uptake and disposal of glucose including cardiac muscle. These conditions accelerate the progression of heart failure and increase cardiovascular morbidity and mortality in patients with cardiovascular diseases. It is noteworthy that some conditions of insulin resistance are characterized by up-regulation of the sympathetic nervous system, resulting in enhanced stimulation of β-adrenergic receptor (βAR). Overstimulation of βARs leads to the development of heart failure and is associated with the pathogenesis of insulin resistance in the heart. However, pathological consequences of the cross-talk between the βAR and the insulin sensitivity and the mechanism by which βAR overstimulation promotes insulin resistance remain unclear. This review article examines the hypothesis that βARs overstimulation leads to induction of insulin resistance in the heart.

Achievement of a target dose of bisoprolol may not be a preferred option for attenuating pressure overload-induced cardiac hypertrophy and fibrosis

Bisoprolol is a drug that acts via the mechanism of specifically and selectively inhibiting the β1-adrenoreceptor in cardiac myocytes, and provides a pure reduction of heart rate without changing other cardiac parameters. It has long been clinically used to treat cerebrovascular and cardiovascular illnesses. However, there is little information available on whether the role of bisoprolol in the attenuation of ventricular remodeling is dependent upon the achievement of a target dose, and whether it must be used as a preferred option. The aim of the present study was to clarify the underlying benefits of bisoprolol in the attenuation of pressure overload-induced cardiac hypertrophy and fibrosis at different doses. C57BL/6J male mice, aged 6-8 weeks, were treated with saline or one of three different doses of bisoprolol (Biso: 2.5, 5 or 10 mg/kg/day) for 8 weeks from day 1 after aortic banding (AB). A number of mice underwent sham surgery and were treated with saline or bisoprolol. The mice were randomly assigned into the sham (n=24) and AB (n=62) groups. The results revealed that bisoprolol had a protective role against the cardiac hypertrophy, fibrosis and dysfunction caused by AB. This was determined on the basis of heart/body and lung/body weight ratios and heart weight/tibia length ratios, as well as echocardiographic and hemodynamic parameters, histological analysis, and the gene expression levels of hypertrophic and fibrotic markers. The present study revealed that administration of bisoprolol for a long time period may enhance its role in the prevention of cardiac hypertrophy and fibrosis induced by AB, whereas no statistically significant difference was observed between the middle- and high-doses. These observations indicated that the function of bisoprolol in protecting against cardiac hypertrophy, fibrosis and dysfunction is time-dependent. Furthermore, it is proposed that a middle dose of bisoprolol may be a better option for patients with cardiovascular illnesses, particularly those undertaking coronary artery bypass graft and cardiac pacemaker surgeries. These promising results require further clinical investigation.

Chronic β1-adrenoceptor blockade impairs ischaemic tolerance and preconditioning in murine myocardium

β-adrenoceptor antagonists are commonly used in ischaemic heart disease (IHD) patients, yet may impair signalling and efficacy of 'cardioprotective' interventions. We assessed effects of chronic β1-adrenoceptor antagonism on myocardial resistance to ischaemia-reperfusion (IR) injury and the ability of cardioprotective interventions [classic ischaemic preconditioning (IPC); novel sustained ligand-activated preconditioning (SLP)] to reduce IR injury in murine hearts. Young male C57Bl/6 mice were untreated or received atenolol (0.5g/l in drinking water) for 4 weeks. Subsequently, two cardioprotective stimuli were evaluated: morphine pellets implanted (to induce SLP, controls received placebo) 5 days prior to Langendorff heart perfusion, and IPC in perfused hearts (3×1.5min ischaemia/2min reperfusion). Atenolol significantly reduced in vivo heart rate. Untreated control hearts exhibited substantial left ventricular dysfunction (~50% pressure development recovery, ~20mmHg diastolic pressure rise) with significant release of lactate dehydrogenase (LDH, tissue injury indicator) after 25min ischaemia/45min reperfusion. Contractile dysfunction and elevated LDH were reduced >50% with IPC and SLP. While atenolol treatment did not modify baseline contractile function, post-ischaemic function was significantly depressed compared to untreated hearts. Atenolol pre-treatment abolished beneficial effects of IPC, whereas SLP protection was preserved. These data indicate that chronic β1-adrenoceptor blockade can exert negative effects on functional IR tolerance and negate conventional IPC (implicating β1-adrenoceptors in IR injury and IPC signalling). However, novel morphine-induced SLP is resistant to inhibition by β1-adrenoceptor antagonism.

Tethered and Polymer Supported Bilayer Lipid Membranes: Structure and Function

Solid supported bilayer lipid membranes are model systems to mimic natural cell membranes in order to understand structural and functional properties of such systems. The use of a model system allows for the use of a wide variety of analytical tools including atomic force microscopy, impedance spectroscopy, neutron reflectometry, and surface plasmon resonance spectroscopy. Among the large number of different types of model membranes polymer-supported and tethered lipid bilayers have been shown to be versatile and useful systems. Both systems consist of a lipid bilayer, which is de-coupled from an underlying support by a spacer cushion. Both systems will be reviewed, with an emphasis on the effect that the spacer moiety has on the bilayer properties.

Combination Treatment With Antihypertensive Agents Enhances the Effect of Qiliqiangxin on Chronic Pressure Overload-induced Cardiac Hypertrophy and Remodeling in Male Mice

Supplemental Digital Content is Available in the Text.

We previously showed that Qiliqiangxin (QL) capsules could ameliorate cardiac hypertrophy and remodeling in a mouse model of pressure overload. Here, we compared the effects of QL alone with those of QL combined with the following 3 types of antihypertensive drugs on cardiac remodeling and dysfunction induced by pressure overload for 4 weeks in mice: an angiotensin II type 1 receptor (AT₁-R) blocker (ARB), an angiotensin-converting enzyme inhibitor (ACEI), and a β-adrenergic receptor (β-AR) blocker (BB). Adult male mice (C57B/L6) were subjected to either transverse aortic constriction or sham operation for 4 weeks, and the drugs (or saline) were orally administered through gastric tubes. Cardiac function and remodeling were evaluated through echocardiography, catheterization, histology, and analysis of hypertrophic gene expression. Cardiomyocyte apoptosis and autophagy, AT₁-R and β₁-AR expression, and cell proliferation–related molecules were also examined. Although pressure overload–induced cardiac remodeling and dysfunction, hypertrophic gene reprogramming, AT₁-R and β₁-AR expression, and ERK phosphorylation were significantly attenuated by QL alone, QL + ARB, QL + ACEI, and QL + BB, the attenuation was stronger in the combination treatment groups. Moreover, apoptosis was reduced to a larger extent by each combination treatment than by QL alone, whereas autophagy was more strongly attenuated by either QL + ARB or QL + ACEI. None of the treatments significantly upregulated ErbB2 or ErbB4 phosphorylation, and none significantly downregulated C/EBPβ expression. Therefore, the effects of QL on chronic pressure overload–induced cardiac remodeling may be significantly increased when QL is combined with an ARB, an ACEI, or a BB.

The emerging roles of β-arrestins in fibrotic diseases

β-Arrestins and β-arrestin2 are important adaptor proteins and signal transduction proteins that are mainly involved in the desensitization and internalization of G-protein-coupled receptors. Fibrosis is characterized by accumulation of excess extracellular matrix (ECM) molecules caused by chronic tissue injury. If highly progressive, the fibrotic process leads to organ malfunction and, eventually, death. The incurable lung fibrosis, renal fibrosis and liver fibrosis are among the most common fibrotic diseases. Recent studies show that β-arrestins can activate signaling cascades independent of G-protein activation and scaffold many intracellular signaling networks by diverse types of signaling pathways, including the Hedgehog, Wnt, Notch and transforming growth factor-β pathways, as well as downstream kinases such as MAPK and PI3K. These signaling pathways are involved in the pathological process of fibrosis and fibrotic diseases. This β-arrestin-mediated regulation not only affects cell growth and apoptosis, but also the deposition of ECM, activation of inflammatory response and development of fibrotic diseases. In this review, we survey the involvement of β-arrestins in various signaling pathways and highlight different aspects of their regulation of fibrosis. We also discuss the important roles of β-arrestins in the process of fibrotic diseases by regulating the inflammation and deposit of ECM. It is becoming more evident that targeting β-arrestins may offer therapeutic potential for the treatment of fibrotic diseases.

Therapeutic Molecular Phenotype of β-Blocker-Associated Reverse-Remodeling in Nonischemic Dilated Cardiomyopathy

BACKGROUND

When β-blockers produce reverse-remodeling in idiopathic dilated cardiomyopathy, they partially reverse changes in fetal-adult/contractile protein, natriuretic peptide, SR-Ca(2+)-ATPase gene program constituents. The objective of the current study was to further test the hypothesis that reverse-remodeling is associated with favorable changes in myocardial gene expression by measuring additional contractile, signaling, and metabolic genes that exhibit a fetal/adult expression predominance, are thyroid hormone-responsive, and are regulated by β1-adrenergic receptor signaling. A secondary objective was to identify which of these putative regulatory networks is most closely associated with observed changes.

METHODS AND RESULTS

Forty-seven patients with idiopathic dilated cardiomyopathy (left ventricular ejection fraction, 0.24±0.09) were randomized to the adrenergic-receptor blockers metoprolol (β1-selective), metoprolol+doxazosin (β1/α1), or carvedilol (β1/β2/α1). Serial radionuclide ventriculography and endomyocardial biopsies were performed at baseline, 3, and 12 months. Expression of 50 mRNA gene products was measured by quantitative polymerase chain reaction. Thirty-one patients achieved left ventricular ejection fraction reverse-remodeling response defined as improvement by ≥0.08 at 12 months or by ≥0.05 at 3 months (Δ left ventricular ejection fraction, 0.21±0.10). Changes in gene expression in responders versus nonresponders were decreases in NPPA and NPPB and increases in MYH6, ATP2A2, PLN, RYR2, ADRA1A, ADRB1, MYL3, PDFKM, PDHX, and CPT1B. All except PDHX involved increase in adult or decrease in fetal cardiac genes, but 100% were concordant with changes predicted by inhibition of β1-adrenergic signaling.

CONCLUSIONS

In addition to known gene expression changes, additional calcium-handling, sarcomeric, adrenergic signaling, and metabolic genes were associated with reverse-remodeling. The pattern suggests a fetal-adult paradigm but may be because of reversal of gene expression controlled by a β1-adrenergic receptor gene network.

CLINICAL TRIAL REGISTRATION

URL: www.clinicaltrials.gov. Unique Identifier: NCT01798992.

Differential effects of angiotensin II receptor blockers on Aβ generation

Angiotensin II receptor blockers (ARBs) are widely prescribed for the medication of systemic hypertension and congestive heart failure. It has been reported that ARBs can reduce the risk for the onset of Alzheimer's disease (AD) and have beneficial effects on dementia. Neurotoxic amyloid β-protein (Aβ) is believed to play a causative role in the development of AD. However, whether ARBs regulate Aβ generation remains largely unknown. Here, we studied the effect of ARBs on Aβ generation and found that telmisartan significantly increased Aβ40 and Aβ42 generation, but decreased the Aβ42/Aβ40 ratio. However, losartan, valsartan and candesartan did not increase Aβ generation, while olmesartan significantly increased Aβ42 generation. We also found that telmisartan increased the Aβ generation through angiotensin type 1a receptor (AT1a) and the receptor-related phosphotidylinositide 3-kinases (PI3K) pathway. Our findings revealed the different effects of ARBs on Aβ generation and provide new evidence for the relationship between antihypertensive treatment and AD pathogenesis.

Multiple functions of G protein-coupled receptor kinases

Desensitization is a physiological feedback mechanism that blocks detrimental effects of persistent stimulation. G protein-coupled receptor kinase 2 (GRK2) was originally identified as the kinase that mediates G protein-coupled receptor (GPCR) desensitization. Subsequent studies revealed that GRK is a family composed of seven isoforms (GRK1–GRK7). Each GRK shows a differential expression pattern. GRK1, GRK4, and GRK7 are expressed in limited tissues. In contrast, GRK2, GRK3, GRK5, and GRK6 are ubiquitously expressed throughout the body. The roles of GRKs in GPCR desensitization are well established. When GPCRs are activated by their agonists, GRKs phosphorylate serine/threonine residues in the intracellular loops and the carboxyl-termini of GPCRs. Phosphorylation promotes translocation of β-arrestins to the receptors and inhibits further G protein activation by interrupting receptor-G protein coupling. The binding of β-arrestins to the receptors also helps to promote receptor internalization by clathrin-coated pits. Thus, the GRK-catalyzed phosphorylation and subsequent binding of β-arrestin to GPCRs are believed to be the common mechanism of GPCR desensitization and internalization. Recent studies have revealed that GRKs are also involved in the β-arrestin-mediated signaling pathway. The GRK-mediated phosphorylation of the receptors plays opposite roles in conventional G protein- and β-arrestin-mediated signaling. The GRK-catalyzed phosphorylation of the receptors results in decreased G protein-mediated signaling, but it is necessary for β-arrestin-mediated signaling. Agonists that selectively activate GRK/β-arrestin-dependent signaling without affecting G protein signaling are known as β-arrestin-biased agonists. Biased agonists are expected to have potential therapeutic benefits for various diseases due to their selective activation of favorable physiological responses or avoidance of the side effects of drugs. Furthermore, GRKs are recognized as signaling mediators that are independent of either G protein- or β-arrestin-mediated pathways. GRKs can phosphorylate non-GPCR substrates, and this is found to be involved in various physiological responses, such as cell motility, development, and inflammation. In addition to these effects, our group revealed that GRK6 expressed in macrophages mediates the removal of apoptotic cells (engulfment) in a kinase activity-dependent manner. These studies revealed that GRKs block excess stimulus and also induce cellular responses. Here, we summarized the involvement of GRKs in β-arrestin-mediated and G protein-independent signaling pathways.

Quantifying biased β-arrestin signaling

It is now established that agonists do not uniformly activate pleiotropic signaling mechanisms initiated by receptors but rather can bias signals according to the unique receptor conformations they stabilize. One of the important emerging signaling systems where this can occur is through β-arrestin. This chapter discusses biased signaling where emphasis or de-emphasis of β-arrestin signaling is postulated (or been shown) to be beneficial. The chapter specifically focuses on methods to quantify biased effects; these methods furnish scales that can be used in the process of optimizing biased agonism (and antagonism) for therapeutic benefit. Specifically, methods to derive ΔΔLog(τ/K A) or ΔΔLog(Relative Activity) values are described to do this.