Role of β-adrenergic receptor signaling and desensitization in heart failure: new concepts and prospects for treatment

Cellular forgetting, desensitisation, stress and ageing in signalling networks. When do cells refuse to learn more?

Recent findings show that single, non-neuronal cells are also able to learn signalling responses developing cellular memory. In cellular learning nodes of signalling networks strengthen their interactions e.g. by the conformational memory of intrinsically disordered proteins, protein translocation, miRNAs, lncRNAs, chromatin memory and signalling cascades. This can be described by a generalized, unicellular Hebbian learning process, where those signalling connections, which participate in learning, become stronger. Here we review those scenarios, where cellular signalling is not only repeated in a few times (when learning occurs), but becomes too frequent, too large, or too complex and overloads the cell. This leads to desensitisation of signalling networks by decoupling signalling components, receptor internalization, and consequent downregulation. These molecular processes are examples of anti-Hebbian learning and 'forgetting' of signalling networks. Stress can be perceived as signalling overload inducing the desensitisation of signalling pathways. Ageing occurs by the summative effects of cumulative stress downregulating signalling. We propose that cellular learning desensitisation, stress and ageing may be placed along the same axis of more and more intensive (prolonged or repeated) signalling. We discuss how cells might discriminate between repeated and unexpected signals, and highlight the Hebbian and anti-Hebbian mechanisms behind the fold-change detection in the NF-κB signalling pathway. We list drug design methods using Hebbian learning (such as chemically-induced proximity) and clinical treatment modalities inducing (cancer, drug allergies) desensitisation or avoiding drug-induced desensitisation. A better discrimination between cellular learning, desensitisation and stress may open novel directions in drug design, e.g. helping to overcome drug resistance.

Association between dose of catecholamines and markers of organ injury early after out-of-hospital cardiac arrest

BACKGROUND

Catecholamines are recommended as first-line drugs to treat hemodynamic instability after out-of-hospital cardiac arrest (OHCA). The benefit-to-risk ratio of catecholamines is dose dependent, however, their effect on metabolism and organ function early after OHCA has not been investigated.

METHODS

The Post-Cardiac Arrest Syndrome (PCAS) pilot study was a prospective, observational, multicenter study. The primary outcomes of this analysis were association between norepinephrine/cumulative catecholamines doses and neuron specific enolase (NSE)/lactate concentration over the first 72 hours after resuscitation. The association was adjusted for proven OHCA mortality predictors and verified with propensity score matching (PSM).

RESULTS

Overall 148 consecutive OHCA patients; aged 18-91 (62.9 ± 15.27), 41 (27.7%) being female, were included. Increasing norepinephrine and cumulative catecholamines doses were significantly associated with higher NSE concentration on admission (r = 0.477, p < 0.001; r = 0.418, p < 0.001) and at 24 hours after OHCA (r = 0.339, p < 0.01; r = 0.441, p < 0.001) as well as with higher lactate concentration on admission (r = 0.404, p < 0.001; r = 0.280, p < 0.01), at 24 hours (r = 0.476, p < 0.00; r = 0.487, p < 0.001) and 48 hours (r = 0.433, p < 0.01; r = 0.318, p = 0.01) after OHCA. The associations remained significant up to 48 hours in non-survivors after PSM.

CONCLUSIONS

Increasing the dose of catecholamines is associated with higher lactate and NSE concentration, which may suggest their importance for tissue oxygen delivery, anaerobic metabolism, and organ function early after OHCA.

Unique Positive Cooperativity Between the β-Arrestin-Biased β-Blocker Carvedilol and a Small Molecule Positive Allosteric Modulator of the β2-Adrenergic Receptor

Among β-blockers that are clinically prescribed for heart failure, carvedilol is a first-choice agent with unique pharmacological properties. Carvedilol is distinct from other β-blockers in its ability to elicit β-arrestin–biased agonism, which has been suggested to underlie its cardioprotective effects. Augmenting the pharmacologic properties of carvedilol thus holds the promise of developing more efficacious and/or biased β-blockers. We recently identified compound-6 (cmpd-6), the first small molecule positive allosteric modulator of the β2-adrenergic receptor (β2AR). Cmpd-6 is positively cooperative with orthosteric agonists at the β2AR and enhances agonist-mediated transducer (G-protein and β-arrestin) signaling in an unbiased manner. Here, we report that cmpd-6, quite unexpectedly, displays strong positive cooperativity only with carvedilol among a panel of structurally diverse β-blockers. Cmpd-6 enhances the binding affinity of carvedilol for the β2AR and augments its ability to competitively antagonize agonist-induced cAMP generation. Cmpd-6 potentiates β-arrestin1– but not Gs-protein–mediated high-affinity binding of carvedilol at the β2AR and β-arrestin–mediated cellular functions in response to carvedilol including extracellular signal-regulated kinase phosphorylation, receptor endocytosis, and trafficking into lysosomes. Importantly, an analog of cmpd-6 that selectively retains positive cooperativity with carvedilol acts as a negative modulator of agonist-stimulated β2AR signaling. These unprecedented cooperative properties of carvedilol and cmpd-6 have implications for fundamental understanding of G-protein–coupled receptor (GPCR) allosteric modulation, as well as for the development of more effective biased beta blockers and other GPCR therapeutics.

Targeted inhibition of GRK2 kinase domain by CP-25 to reverse fibroblast-like synoviocytes dysfunction and improve collagen-induced arthritis in rats

Rheumatoid arthritis (RA) is an autoimmune disease and is mainly characterized by abnormal proliferation of fibroblast-like synoviocytes (FLS). The up-regulated cellular membrane expression of G protein coupled receptor kinase 2 (GRK2) of FLS plays a critical role in RA progression, the increase of GRK2 translocation activity promotes dysfunctional prostaglandin E4 receptor (EP4) signaling and FLS abnormal proliferation. Recently, although our group found that paeoniflorin-6ʹ-O-benzene sulfonate (CP-25), a novel compound, could reverse FLS dysfunction via GRK2, little is known as to how GRK2 translocation activity is suppressed. Our findings revealed that GRK2 expression up-regulated and EP4 expression down-regulated in synovial tissues of RA patients and collagen-induced arthritis (CIA) rats, and prostaglandin E2 (PGE2) level increased in arthritis. CP-25 could down-regulate GRK2 expression, up-regulate EP4 expression, and improve synovitis of CIA rats. CP-25 and GRK2 inhibitors (paroxetine or GSK180736A) inhibited the abnormal proliferation of FLS in RA patients and CIA rats by down-regulating GRK2 translocation to EP4 receptor. The results of microscale thermophoresis (MST), cellular thermal shift assay, and inhibition of kinase activity assay indicated that CP-25 could directly target GRK2, increase the protein stability of GRK2 in cells, and inhibit GRK2 kinase activity. The docking of CP-25 and GRK2 suggested that the kinase domain of GRK2 might be an important active pocket for CP-25. G201, K220, K230, A321, and D335 in kinase domain of GRK2 might form hydrogen bonds with CP-25. Site-directed mutagenesis and co-immunoprecipitation assay further revealed that CP-25 down-regulated the interaction of GRK2 and EP4 via controlling the key amino acid residue of Ala321 of GRK2. Our data demonstrate that FLS proliferation is regulated by GRK2 translocation to EP4. Targeted inhibition of GRK2 kinase domain by CP-25 improves FLS function and represents an innovative drug for the treatment of RA by targeting GRK2.

Functional Characterization of the Obesity-Linked Variant of the β3-Adrenergic Receptor

Adrenergic receptor β₃ (ADRβ₃) is a member of the rhodopsin-like G protein-coupled receptor family. The binding of the ligand to ADRβ₃ activates adenylate cyclase and increases cAMP in the cells. ADRβ₃ is highly expressed in white and brown adipocytes and controls key regulatory pathways of lipid metabolism. Trp64Arg (W64R) polymorphism in the ADRβ₃ is associated with the early development of type 2 diabetes mellitus, lower resting metabolic rate, abdominal obesity, and insulin resistance. It is unclear how the substitution of W64R affects the functioning of ADRβ₃. This study was initiated to functionally characterize this obesity-linked variant of ADRβ₃. We evaluated in detail the expression, subcellular distribution, and post-activation behavior of the WT and W64R ADRβ₃ using single cell quantitative fluorescence microscopy. When expressed in HEK 293 cells, ADRβ₃ shows a typical distribution displayed by other GPCRs with a predominant localization at the cell surface. Unlike adrenergic receptor β₂ (ADRβ₂), agonist-induced desensitization of ADRβ₃ does not involve loss of cell surface expression. WT and W64R variant of ADRβ₃ displayed comparable biochemical properties, and there was no significant impact of the substitution of tryptophan with arginine on the expression, cellular distribution, signaling, and post-activation behavior of ADRβ₃. The obesity-linked W64R variant of ADRβ₃ is indistinguishable from the WT ADRβ₃ in terms of expression, cellular distribution, signaling, and post-activation behavior.

G proteins: binary switches in health and disease

Cell signaling plays critical role in health and disease. The normal functioning of body depends on the homeostasis of immunity players. One of the very important cell signaling participants is G protein-coupled receptor (GPCR). GPCRs transduce extracellular signals into target cell by binding to and activating different G proteins (G αβγ, families Gi, Gs, Gq/11, G12/13) leading to range of different functions. Abnormal GPCRs signaling leads to various abnormalities, including but not limited to, cancer, pain, cardiac problems, and asthma. Mutations, which lead to activation or inactivation of GPCR pathways, permanently alter the pathways controlled by these receptors. A large number of human cancer incidence is a consequence of genetic abnormalities in signaling pathways, which influence cell division. Some bacteria and pathogens may interfere with the GPCR signaling pathways for their survival and immune evasion. Inhibition of GPCR signaling by small inhibitors is a novel way to treat various pathological conditions. There are several types of GPCRs in human genome, which due to their central role in health and disease, are the target of many commercially available drugs. Importantly, GPCRs have huge impact on drug discovery and approximately 30% of current drug targets are GPCRs. There is a need of further studies to explore more the role of G protein and the GPCRs in human health and how certain mutations can lead to disease state. Such studies may be important to adjust the signaling pathways for health improvement.

The Potential Role of Protein Tyrosine Phosphatase, Receptor Type C (CD45) in the Intestinal Ischemia-Reperfusion Injury

This study was designed to identify several key genes and their functions in preventing or ameliorating intestinal ischemia-reperfusion (IR) injury, which could provide rationale for further exploring the regulatory mechanisms or clinical treatment for intestinal IR injury. The microarray GSE37013 of human intestinal IR injury was downloaded from Gene Expression Omnibus database. The differentially expressed genes (DEGs) with changes of reperfusion time were screened using Short Time-series Expression Miner, followed by function enrichment analysis, protein-protein interaction (PPI) network, and module construction. Subsequently, the key DEGs were identified with VEEN analysis based on the significant results of function enrichment analysis and PPI module. Finally, the gene-drug interactions were predicted using DGIdb 2.0. The DEGs of intestinal IR injury were significantly divided into three clusters with changes of reperfusion time. The genes in the three clusters were mainly enriched in transmembrane transport, defense responses, and cellular component assembly related pathways, respectively. There were 121 nodes and 281 interactions in PPI network, including one significant submodule. Protein tyrosine phosphatase, receptor type C (PTPRC) was a hub code both in PPI network and in submodule. A total of eight key DEGs were identified but only PTPRC was predicted to be interacted with eight drugs, such as infliximab. Totally, eight key genes associated with intestinal IR were identified; PTPRC especially was the most prominent potential drug target. These findings provided several potential therapeutic targets or potential breakthrough area in the study of intestinal IR injury.

Shock - Classification and Pathophysiological Principles of Therapeutics

The management of patients with shock is extremely challenging because of the myriad of possible clinical presentations in cardiogenic shock, septic shock and hypovolemic shock and the limitations of contemporary therapeutic options. The treatment of shock includes the administration of endogenous catecholamines (epinephrine, norepinephrine, and dopamine) as well as various vasopressor agents that have shown efficacy in the treatment of the various types of shock. In addition to the endogenous catecholamines, dobutamine, isoproterenol, phenylephrine, and milrinone have served as the mainstays of shock therapy for several decades. Recently, experimental studies have suggested that newer agents such as vasopressin, selepressin, calcium-sensitizing agents like levosimendan, cardiac-specific myosin activators like omecamtiv mecarbil (OM), istaroxime, and natriuretic peptides like nesiritide can enhance shock therapy, especially when shock presents a more complex clinical picture than normal. However, their ability to improve clinical outcomes remains to be proven. It is the purpose of this review to describe the mechanism of action, dosage requirements, advantages and disadvantages, and specific indications and contraindications for the use of each of these catecholamines and vasopressors, as well as to elucidate the most important clinical trials that serve as the basis of contemporary shock therapy.

Statins Perturb Gβγ Signaling and Cell Behavior in a Gγ Subtype Dependent Manner

Guanine nucleotide-binding proteins (G proteins) facilitate the transduction of external signals to the cell interior, regulate most eukaryotic signaling, and thus have become crucial disease drivers. G proteins largely function at the inner leaflet of the plasma membrane (PM) using covalently attached lipid anchors. Both small monomeric and heterotrimeric G proteins are primarily prenylated, either with a 15-carbon farnesyl or a 20-carbon geranylgeranyl polyunsaturated lipid. The mevalonate [3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase] pathway synthesizes lipids for G-protein prenylation. It is also the source of the precursor lipids for many biomolecules, including cholesterol. Consequently, the rate-limiting enzymes of the mevalonate pathway are major targets for cholesterol-lowering medications and anticancer drug development. Although prenylated G protein γ (Gγ) is essential for G protein-coupled receptor (GPCR)-mediated signaling, how mevalonate pathway inhibitors, statins, influence subcellular distribution of Gβγ dimer and Gαβγ heterotrimer, as well as their signaling upon GPCR activation, is poorly understood. The present study shows that clinically used statins not only significantly disrupt PM localization of Gβγ but also perturb GPCR-G protein signaling and associated cell behaviors. The results also demonstrate that the efficiency of prenylation inhibition by statins is Gγ subtype-dependent and is more effective toward farnesylated Gγ types. Since Gγ is required for Gβγ signaling and shows a cell- and tissue-specific subtype distribution, the present study can help understand the mechanisms underlying clinical outcomes of statin use in patients. This work also reveals the potential of statins as clinically usable drugs to control selected GPCR-G protein signaling.

AT-RvD1 combined with DEX is highly effective in treating TNF-α-mediated disruption of the salivary gland epithelium

Sjögren's syndrome (SS) is an autoimmune disorder characterized by chronic inflammation and destruction of salivary and lacrimal glands leading to dry mouth and dry eyes, respectively. Currently, the etiology of SS is unknown and the current therapies have no permanent benefit; therefore, new approaches are necessary to effectively treat this condition. Resolvins are highly potent endogenous lipid mediators that are synthesized during the resolution of inflammation to restore tissue homeostasis. Previous studies indicate that the resolvin family member, RvD1, binds to the ALX/FPR2 receptor to block inflammatory signals caused by tumor necrosis factor-alpha (TNF-α) in the salivary epithelium. More recently, the corticosteroid, dexamethasone (DEX), was shown to be effective in reducing salivary gland inflammation. However, DEX, as with other corticosteroids, elicits adverse secondary effects that could be ameliorated when used in smaller doses. Therefore, we investigated whether the more stable aspirin-triggered (AT) epimer, AT-RvD1, combined with reduced doses of DEX is effective in treating TNF-α-mediated disruption of polarized rat parotid gland (Par-C10) epithelial cell clusters. Our results indicate that AT-RvD1 and DEX individually reduced TNF-α-mediated alteration in the salivary epithelium (i.e, maintained cell cluster formation, increased lumen size, reduced apoptosis, and preserved cell survival signaling responses) as compared to untreated cells. Furthermore, AT-RvD1 combined with a reduced dose of DEX produced stronger responses (i.e., robust salivary cell cluster formation, larger lumen sizes, further reduced apoptosis, and sustained survival signaling responses) as compared to those observed with individual treatments. These studies demonstrate that AT-RvD1 combined with DEX is highly effective in treating TNF-α-mediated disruption of salivary gland epithelium.

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.

Phosphodiesterase 2 Protects Against Catecholamine-Induced Arrhythmia and Preserves Contractile Function After Myocardial Infarction

Rationale:

Phosphodiesterase 2 is a dual substrate esterase, which has the unique property to be stimulated by cGMP, but primarily hydrolyzes cAMP. Myocardial phosphodiesterase 2 is upregulated in human heart failure, but its role in the heart is unknown.

Objective:

To explore the role of phosphodiesterase 2 in cardiac function, propensity to arrhythmia, and myocardial infarction.

Methods and Results:

Pharmacological inhibition of phosphodiesterase 2 (BAY 60–7550, BAY) led to a significant positive chronotropic effect on top of maximal β-adrenoceptor activation in healthy mice. Under pathological conditions induced by chronic catecholamine infusions, BAY reversed both the attenuated β-adrenoceptor–mediated inotropy and chronotropy. Conversely, ECG telemetry in heart-specific phosphodiesterase 2-transgenic (TG) mice showed a marked reduction in resting and in maximal heart rate, whereas cardiac output was completely preserved because of greater cardiac contraction. This well-tolerated phenotype persisted in elderly TG with no indications of cardiac pathology or premature death. During arrhythmia provocation induced by catecholamine injections, TG animals were resistant to triggered ventricular arrhythmias. Accordingly, Ca 2+ -spark analysis in isolated TG cardiomyocytes revealed remarkably reduced Ca 2+ leakage and lower basal phosphorylation levels of Ca 2+ -cycling proteins including ryanodine receptor type 2. Moreover, TG demonstrated improved cardiac function after myocardial infarction.

Conclusions:

Endogenous phosphodiesterase 2 contributes to heart rate regulation. Greater phosphodiesterase 2 abundance protects against arrhythmias and improves contraction force after severe ischemic insult. Activating myocardial phosphodiesterase 2 may, thus, represent a novel intracellular antiadrenergic therapeutic strategy protecting the heart from arrhythmia and contractile dysfunction.

Phospholamban Inhibition by a Single Dose of Locked Nucleic Acid Antisense Oligonucleotide Improves Cardiac Contractility in Pressure Overload-Induced Systolic Dysfunction in Mice

BACKGROUND

Phospholamban (PLN) inhibition enhances calcium cycling and is a potential novel therapy for heart failure (HF). Antisense oligonucleotides (ASOs) are a promising tool for unmet medical needs. Nonviral vector use of locked nucleic acid (LNA)-modified ASOs (LNA-ASOs), which shows strong binding to target RNAs and is resistant to nuclease, is considered to have a potential for use in novel therapeutics in the next decades. Thus, the efficacy of a single-dose injection of LNA-ASO for cardiac disease needs to be elucidated. We assessed the therapeutic efficacy of a single-dose LNA-ASO injection targeting PLN in pressure overload-induced cardiac dysfunction.

METHODS AND RESULTS

Mice intravenously injected with Cy3-labeled LNA-ASO displayed Cy3 fluorescence in the liver and heart 24 hours after injection. Subsequently, male C57BL/6 mice were subjected to sham or transverse aortic constriction surgery; after 3 weeks, these were treated with PLN-targeting LNA-ASO (0.3 mg/kg) or scrambled LNA-ASO. Cardiac function was measured by echocardiography before and 1 week after injection. Phospholamban-targeting LNA-ASO treatment significantly improved fractional shortening (FS) by 6.5%, whereas administration of the scrambled LNA-ASO decreased FS by 4.0%.

CONCLUSION

Our study revealed that a single-dose injection of PLN-targeting LNA-ASO improved contractility in pressure overload-induced cardiac dysfunction, suggesting that LNA-ASO is a promising tool for hypertensive HF treatment.

The oxoglutarate receptor 1 (OXGR1) modulates pressure overload-induced cardiac hypertrophy in mice

The G-protein-coupled receptors (GPCRs) family of proteins play essential roles in the heart, including in the regulation of cardiac hypertrophy. One member of this family, the oxoglutarate receptor 1 (OXGR1), may have a crucial role in the heart because it acts as a receptor for α-ketoglutarate, a metabolite that is elevated in heart failure patients. OXGR1 is expressed in the heart but its precise function during cardiac pathophysiological process is unknown. Here we used both in vivo and in vitro approaches to investigate the role of OXGR1 in cardiac hypertrophy. Genetic ablation of Oxgr1 in mice (OXGR1^-/-) resulted in a significant increase in hypertrophy following transverse aortic constriction (TAC). This was accompanied by reduction in contractile function as indicated by cardiac fractional shortening and ejection fraction. Conversely, adenoviral mediated overexpression of OXGR1 in neonatal rat cardiomyocytes significantly reduced phenylephrine-induced cardiomyocyte hypertrophy, a result that was consistent with the in vivo data. Using a combination of yeast two hybrid screening and phospho-antibody array analysis we identified novel interacting partner and downstream signalling pathway that might be regulated by the OXGR1. First, we found that OXGR1 forms a molecular complex with the COP9 signalosome complex subunit 5 (CSN5). Secondly, we observed that the STAT3 signalling pathway was upregulated in OXGR1^-/- hearts. Since CSN5 interacts with TYK2, a major upstream regulator of STAT3, OXGR1 might regulate the pro-hypertrophic STAT3 pathway via interaction with the CSN5-TYK2 complex. In conclusion, our study has identified OXGR1 as a novel regulator of pathological hypertrophy via the regulation of the STAT3. Identification of molecules that can specifically activate or inhibit this receptor may be very useful in the development of novel therapeutic approach for pathological cardiac hypertrophy.

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.

Prognostic Value of Lymphocyte G Protein-Coupled Receptor Kinase-2 Protein Levels in Patients With Heart Failure

RATIONALE

Sympathetic nervous system hyperactivity is associated with poor prognosis in patients with heart failure (HF), yet routine assessment of sympathetic nervous system activation is not recommended for clinical practice. Myocardial G protein-coupled receptor kinase-2 (GRK2) is upregulated in HF patients, causing dysfunctional β-adrenergic receptor signaling. Importantly, myocardial GRK2 levels correlate with levels found in peripheral lymphocytes of HF patients.

OBJECTIVE

The independent prognostic value of blood GRK2 measurements in HF patients has never been investigated; thus, the purpose of this study was to evaluate whether lymphocyte GRK2 levels predict clinical outcome in HF patients.

METHODS AND RESULTS

We prospectively studied 257 HF patients with mean left ventricular ejection fraction of 31.4±8.5%. At the time of enrollment, plasma norepinephrine, serum NT-proBNP, and lymphocyte GRK2 levels, as well as clinical and instrumental variables were measured. The prognostic value of GRK2 to predict cardiovascular (CV) death and all-cause mortality was assessed using the Cox proportional hazard model including demographic, clinical, instrumental, and laboratory data. Over a mean follow-up period of 37.5±20.2 months (range, 3-60 months), there were 102 CV deaths. Age, left ventricular ejection fraction, New York Heart Association class, chronic obstructive pulmonary disease, chronic kidney disease, N-terminal-pro brain natriuretic peptide, and lymphocyte GRK2 protein levels were independent predictors of CV mortality in HF patients. GRK2 levels showed an additional prognostic and clinical value over demographic and clinical variables. The independent prognostic value of lymphocyte GRK2 levels was also confirmed for all-cause mortality.

CONCLUSIONS

Lymphocyte GRK2 protein levels can independently predict prognosis in patients with HF.

Decreased polycystin 2 expression alters calcium-contraction coupling and changes β-adrenergic signaling pathways

Cardiac disorders are the main cause of mortality in autosomal-dominant polycystic kidney disease (ADPKD). However, how mutated polycystins predispose patients with ADPKD to cardiac pathologies before development of renal dysfunction is unknown. We investigate the effect of decreased levels of polycystin 2 (PC2), a calcium channel that interacts with the ryanodine receptor, on myocardial function. We hypothesize that heterozygous PC2 mice (Pkd2(+/-)) undergo cardiac remodeling as a result of changes in calcium handling, separate from renal complications. We found that Pkd2(+/-) cardiomyocytes have altered calcium handling, independent of desensitized calcium-contraction coupling. Paradoxically, in Pkd2(+/-) mice, protein kinase A (PKA) phosphorylation of phospholamban (PLB) was decreased, whereas PKA phosphorylation of troponin I was increased, explaining the decoupling between calcium signaling and contractility. In silico modeling supported this relationship. Echocardiography measurements showed that Pkd2(+/-) mice have increased left ventricular ejection fraction after stimulation with isoproterenol (ISO), a β-adrenergic receptor (βAR) agonist. Blockers of βAR-1 and βAR-2 inhibited the ISO response in Pkd2(+/-) mice, suggesting that the dephosphorylated state of PLB is primarily by βAR-2 signaling. Importantly, the Pkd2(+/-) mice were normotensive and had no evidence of renal cysts. Our results showed that decreased PC2 levels shifted the βAR pathway balance and changed expression of calcium handling proteins, which resulted in altered cardiac contractility. We propose that PC2 levels in the heart may directly contribute to cardiac remodeling in patients with ADPKD in the absence of renal dysfunction.

Modeling the effects of β1-adrenergic receptor blockers and polymorphisms on cardiac myocyte Ca2+ handling

β-Adrenergic receptor blockers (β-blockers) are commonly used to treat heart failure, but the biologic mechanisms governing their efficacy are still poorly understood. The complexity of β-adrenergic signaling coupled with the influence of receptor polymorphisms makes it difficult to intuit the effect of β-blockers on cardiac physiology. While some studies indicate that β-blockers are efficacious by inhibiting β-adrenergic signaling, other studies suggest that they work by maintaining β-adrenergic responsiveness. Here, we use a systems pharmacology approach to test the hypothesis that in ventricular myocytes, these two apparently conflicting mechanisms for β-blocker efficacy can occur concurrently. We extended a computational model of the β(1)-adrenergic pathway and excitation-contraction coupling to include detailed receptor interactions for 19 ligands. Model predictions, validated with Ca(2+) and Förster resonance energy transfer imaging of adult rat ventricular myocytes, surprisingly suggest that β-blockers can both inhibit and maintain signaling depending on the magnitude of receptor stimulation. The balance of inhibition and maintenance of β(1)-adrenergic signaling is predicted to depend on the specific β-blocker (with greater responsiveness for metoprolol than carvedilol) and β(1)-adrenergic receptor Arg389Gly polymorphisms.

miR-145 inhibits isoproterenol-induced cardiomyocyte hypertrophy by targeting the expression and localization of GATA6

Excessive βAR stimulation is an independent factor in inducing pathological cardiac hypertrophy. Here, we report miR-145 regulates both expression and localization of GATA6, thereby protecting the heart against cardiomyocyte hypertrophy induced by isoproterenol (ISO). The protective activity of miR-145 was associated with down-regulation of ANF, BNP and β-MHC expression, a decreased rate of protein synthesis, inhibited cardiomyocyte growth and the modulation of several signaling pathways including ERK1/2, JNK and Akt-GSK3β. The anti-hypertrophic effect was abrogated by exogenous over-expression of transcription factor GATA6 which was further identified as a direct target of miR-145. In addition, GSK3β antagonists, LiCl and TDZD8, restored the nuclear accumulation of GATA6, which was attenuated by miR-145 Finally, we observed a dynamic pattern of miR-145 expression in ISO-treated NRCMs and in the hearts of TAC mice. Together, our results identify miR-145 as an important regulator in cardiac hypertrophy.

Cardiac fibroblasts inhibit β-adrenoceptor-dependent connexin43 expression in neonatal rat cardiomyocytes

Cardiac fibroblasts play an important role in adverse cardiac remodelling. As in many cardiac diseases connexin43 (Cx43) is altered, we wanted to elucidate whether fibroblasts may influence cardiac Cx43 expression. We used four different cell culture systems of neonatal rat cardiomyocytes (CM) and fibroblasts (FB): type 1, pure CM culture; type 2, co-culture of CM/FB; type 3, pure FB culture; type 4, Transwell® system: CM/FB co-cultured but separated by a microporous membrane. Stimulation of types 1-3 cell culture models with isoprenaline significantly enhanced Cx43-protein and Cx43-mRNA expression as well as phosphorylation of ERK and translocation of AP1 and CREB only in the CM cultures; whereas, the CM/FB co-cultures and the FB cultures did not respond to isoprenaline. Similarly, if CM and FB were separated by a microporous membrane (Transwell® system) the isoprenaline-induced increase in CM Cx43 was completely suppressed, suggesting the existence of a soluble factor responsible for the suppressant effect of FB. Angiotensin II determination in types 1 and 2 cell culture supernatants revealed that the CM/FB co-cultures exhibited a significant higher angiotensin II release than the CM cultures. Furthermore, we aimed to inhibit angiotensin II signal transduction pathway: blockade of AT1 receptors or PKC inhibition restored the responsiveness of CM/FB co-cultures to isoprenaline. Moreover, external addition of angiotensin II to CM cultures also resulted in suppression of isoprenaline-stimulated Cx43 expression in an AT1-receptor- and PKC-dependent manner. Thus, our study indicates that cardiac fibroblasts inhibit β-adrenoceptor-dependent Cx43 signalling in CM involving angiotensin II.

The functional activity of inhibitory G protein (G(i)) is not increased in failing heart ventricle

Beta-adrenergic receptor (βAR) inotropic effects are attenuated and muscarinic receptor-mediated inhibition thereof is enhanced in heart failure. We investigated if increased G(i) activity contributes to attenuated βAR-inotropic effects and potentiates muscarinic accentuated antagonism in failing rat ventricle. Contractility was measured in ventricular strips and adenylyl cyclase (AC) activity in ventricular membranes from rats with post-infarction heart failure (HF) or Sham-operated controls (Sham). The maximal βAR-mediated inotropic effect of isoproterenol was reduced by ~70% and basal, βAR- & forskolin-stimulated AC activity was significantly lower in HF vs. Sham. Carbachol-evoked antagonism of the βAR-mediated inotropic response was complete only in HF despite a ~40% reduction in the ability of carbachol to inhibit βAR-stimulated AC. However, neither the relative efficacy (contractility decreased by ~46%) nor the potency of carbachol to inhibit the βAR inotropic response differed between Sham and HF ventricle. Pertussis toxin (PTX) inactivation of G(i) did not increase the maximal βAR inotropic effect or the attenuated basal, βAR- & forskolin-stimulated AC activity in HF, but increased the potency of isoproterenol only in Sham (~0.5 log unit). In HF ventricle pretreated with PTX, simultaneous inhibition of phosphodiesterases 3,4 (PDE3,4) alone produced a larger inotropic response than isoproterenol in ventricle untreated with PTX (84% and 48% above basal respectively). In the absence of PTX, PDE3,4 inhibition evoked negligible inotropic effects in HF. These data are not consistent with the hypothesis that increased G(i) activity contributes to the reduced βAR-mediated inotropic response and AC activity in failing ventricle. The data, however, support the hypothesis that G(i), through chronic receptor independent inhibition of AC, together with PDE3,4 activity, is necessary to maintain a low basal level of contractility.

Altered sarcoplasmic reticulum calcium cycling--targets for heart failure therapy

Cardiac myocyte function is dependent on the synchronized movements of Ca(2+) into and out of the cell, as well as between the cytosol and sarcoplasmic reticulum. These movements determine cardiac rhythm and regulate excitation-contraction coupling. Ca(2+) cycling is mediated by a number of critical Ca(2+)-handling proteins and transporters, such as L-type Ca(2+) channels (LTCCs) and sodium/calcium exchangers in the sarcolemma, and sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), ryanodine receptors, and cardiac phospholamban in the sarcoplasmic reticulum. The entry of Ca(2+) into the cytosol through LTCCs activates the release of Ca(2+) from the sarcoplasmic reticulum through ryanodine receptor channels and initiates myocyte contraction, whereas SERCA2a and cardiac phospholamban have a key role in sarcoplasmic reticulum Ca(2+) sequesteration and myocyte relaxation. Excitation-contraction coupling is regulated by phosphorylation of Ca(2+)-handling proteins. Abnormalities in sarcoplasmic reticulum Ca(2+) cycling are hallmarks of heart failure and contribute to the pathophysiology and progression of this disease. Correcting impaired intracellular Ca(2+) cycling is a promising new approach for the treatment of heart failure. Novel therapeutic strategies that enhance myocyte Ca(2+) homeostasis could prevent and reverse adverse cardiac remodeling and improve clinical outcomes in patients with heart failure.

Blockade of β-adrenoceptors restores the GRK2-mediated adrenal α(2) -adrenoceptor-catecholamine production axis in heart failure

BACKGROUND AND PURPOSE

Sympathetic nervous system (SNS) hyperactivity is characteristic of chronic heart failure (HF) and significantly worsens prognosis. The success of β-adrenoceptor antagonist (β-blockers) therapy in HF is primarily attributed to protection of the heart from the noxious effects of augmented catecholamine levels. β-Blockers have been shown to reduce SNS hyperactivity in HF, but the underlying molecular mechanisms are not understood. The GPCR kinase-2 (GRK2)-α(2) adrenoceptor-catecholamine production axis is up-regulated in the adrenal medulla during HF causing α(2) -adrenoceptor dysfunction and elevated catecholamine levels. Here, we sought to investigate if β-blocker treatment in HF could lower SNS activation by directly altering adrenal GRK2 levels.

EXPERIMENTAL APPROACH

Four weeks after myocardial infarction-induced HF, adult rats were randomized to 10-week treatment with vehicle (HF/C) or bisoprolol (HF/B). Cardiac function and dimensions were measured. In heart and adrenal gland, GRK2 levels were assessed by RT-PCR and Western blotting and adrenoceptors studied with radioligand binding. Catecholamines and α(2) adrenoceptors in adrenal medulla chromaffin cell cultures were also measured.

KEY RESULTS

Bisoprolol treatment ameliorated HF-related adverse cardiac remodelling and reduced plasma catecholamine levels, compared with HF/C rats. Bisoprolol also attenuated adrenal GRK2 overexpression as observed in HF/C rats and increased α(2) adrenoceptor density. In cultures of adrenal medulla chromaffin cells from all study groups, bisoprolol reversed HF-related α(2) adrenoceptor dysfunction. This effect was reversed by GRK2 overexpression.

CONCLUSION AND IMPLICATIONS

Blockade of β-adrenoceptors normalized the adrenal α(2) adrenoceptor-catecholamine production axis by reducing GRK2 levels. This effect may contribute significantly to the decrease of HF-related sympathetic overdrive by β-blockers.

Differential regulation of EHD3 in human and mammalian heart failure

Electrical and structural remodeling during the progression of cardiovascular disease is associated with adverse outcomes subjecting affected patients to overt heart failure (HF) and/or sudden death. Dysfunction in integral membrane protein trafficking has long been linked with maladaptive electrical remodeling. However, little is known regarding the molecular identity or function of these intracellular targeting pathways in the heart. Eps15 homology domain-containing (EHD) gene products (EHD1-4) are polypeptides linked with endosomal trafficking, membrane protein recycling, and lipid homeostasis in a wide variety of cell types. EHD3 was recently established as a critical mediator of membrane protein trafficking in the heart. Here, we investigate the potential link between EHD3 function and heart disease. Using four different HF models including ischemic rat heart, pressure overloaded mouse heart, chronic pacing-induced canine heart, and non-ischemic failing human myocardium we provide the first evidence that EHD3 levels are consistently increased in HF. Notably, the expression of the Na/Ca exchanger (NCX1), targeted by EHD3 in heart is similarly elevated in HF. Finally, we identify a molecular pathway for EHD3 regulation in heart failure downstream of reactive oxygen species and angiotensin II signaling. Together, our new data identify EHD3 as a previously unrecognized component of the cardiac remodeling pathway.

Functional relevance of biased signaling at the angiotensin II type 1 receptor

Angiotensin II type 1 receptor antagonists (AT1R blockers, or ARBs) are used commonly in the treatment of cardiovascular disorders such as heart failure and hypertension. Their clinical success arises from their ability to prevent deleterious Gα(q) protein activation downstream of AT1R, which leads to a decrease in morbidity and mortality. Recent studies have identified AT1R ligands that concurrently inhibit Gα(q) protein-dependent signaling and activate Gα(q) protein-independent/β-arrestin-dependent signaling downstream of AT1R, events that may actually improve cardiovascular performance more than conventional ARBs. The ability of such ligands to induce intracellular signaling events in an AT1R-β-arrestin-dependent manner while preventing AT1R-Gα(q) protein activity defines them as biased AT1R ligands. This mini-review will highlight recent studies that have defined biased signaling at the AT1R and discuss the possible clinical relevance of β-arrestin-biased AT1R ligands in the cardiovascular system.

G protein-dependent and G protein-independent signaling pathways and their impact on cardiac function

G protein-coupled receptors signal through a variety of mechanisms that impact cardiac function, including contractility and hypertrophy. G protein-dependent and G protein-independent pathways each have the capacity to initiate numerous intracellular signaling cascades to mediate these effects. G protein-dependent signaling has been studied for decades and great strides continue to be made in defining the intricate pathways and effectors regulated by G proteins and their impact on cardiac function. G protein-independent signaling is a relatively newer concept that is being explored more frequently in the cardiovascular system. Recent studies have begun to reveal how cardiac function may be regulated via G protein-independent signaling, especially with respect to the ever-expanding cohort of β-arrestin-mediated processes. This review primarily focuses on the impact of both G protein-dependent and β-arrestin-dependent signaling pathways on cardiac function, highlighting the most recent data that illustrate the comprehensive nature of these mechanisms of G protein-coupled receptor signaling.

G protein coupled receptor kinases as therapeutic targets in cardiovascular disease

G protein-coupled receptors (GPCRs) represent the largest family of membrane receptors and are responsible for regulating a wide variety of physiological processes. This is accomplished via ligand binding to GPCRs, activating associated heterotrimeric G proteins and intracellular signaling pathways. G protein-coupled receptor kinases (GRKs), in concert with β-arrestins, classically desensitize receptor signal transduction, thus preventing hyperactivation of GPCR second-messenger cascades. As changes in GRK expression have featured prominently in many cardiovascular pathologies, including heart failure, myocardial infarction, hypertension, and cardiac hypertrophy, GRKs have been intensively studied as potential diagnostic or therapeutic targets. Herein, we review our evolving understanding of the role of GRKs in cardiovascular pathophysiology.

Biased Ligands for Better Cardiovascular Drugs

Drug discovery efforts targeting G-protein-coupled receptors (GPCR) have been immensely successful in creating new cardiovascular medicines. Currently marketed GPCR drugs are broadly classified as either agonists that activate receptors or antagonists that prevent receptor activation by endogenous stimuli. However, GPCR couple to a multitude of intracellular signaling pathways beyond classical G-protein signals, and these signals can be independently activated by biased ligands to vastly expand the potential for new drugs at these classic targets. By selectively engaging only a subset of a receptor's potential intracellular partners, biased ligands may deliver more precise therapeutic benefit with fewer side effects than current GPCR-targeted drugs. In this review, we discuss the history of biased ligand research, the current understanding of how biased ligands exert their unique pharmacology, and how research into GPCR signaling has uncovered previously unappreciated capabilities of receptor pharmacology. We focus on several receptors to illustrate the approaches taken and discoveries made, and how these are steadily illuminating the intricacies of GPCR pharmacology. Discoveries of biased ligands targeting the angiotensin II type 1 receptor and of separable pharmacology suggesting the potential value of biased ligands targeting the β-adrenergic receptors and nicotinic acid receptor GPR109a highlight the powerful clinical promise of this new category of potential therapeutics.

Vasoactive support in the optimization of post-cardiac arrest hemodynamic status: from pharmacology to clinical practice

As a critical component of post-resuscitation care, prompt optimization of hemodynamic status by means of targeted interventions is vital in order to maximize the likelihood of good outcome. Vasoactive agents play an essential role in the supportive care of post cardiac arrest patients. The administration of these agents is associated with serious side-effects and therefore they should be used in the minimal dose necessary to achieve low-normal mean arterial pressure and adequate systematic perfusion. Careful and frequent serial evaluation of the patient is important primarily to assess volume status and adequacy of circulatory support. Continuous monitoring of blood pressure and laboratory parameters is essential both to accurately titrate therapy and because inotropes and vasopressors have the potential to induce life-threatening side-effects. The clinical efficacy of inotropes and vasopressors has been largely investigated through examination of their impact on hemodynamic end points, and clinical practice has been driven in part by expert opinion, extrapolation from animal studies, and physician preference. Clearly these agents should all be considered as supportive measures to stabilize the patient prior to some form of definitive therapy.

In vitro studies of early cardiac remodeling: impact on contraction and calcium handling

Cardiac remodeling, hypertrophy, and alterations in calcium signaling are changes of the heart that often lead to failure. After a hypertrophic stimulus, the heart progresses through a state of compensated hypertrophy which over time leads to decompensated hypertrophy or failure. It is at this point that a cardiac transplant is required for survival making early detection imperative. Current experimental systems used to study the remodeling of the heart include in vivo systems (the whole body), isolated organ and sub-organ tissue, and the individual cardiac muscle cells and organelles.. During pathological remodeling there is a derangement in the intracellular calcium handling processes. These derangements are thought to lead to a dysregulation of contractile output. Hence, understanding the mechanism between remodeling and dysregulation is of great interest in the cardiac field and will ultimately help in the development of future treatment and early detection. This review will center on changes in contraction and calcium handling in early cardiac remodeling, with a specific focus on findings in two different in vitro model systems: multicellular and individual cell preparations.

β-Adrenergic Receptor-Stimulated Cardiac Myocyte Apoptosis: Role of β1 Integrins

Increased sympathetic nerve activity to the myocardium is a central feature in patients with heart failure. Accumulation of catecholamines plays an important role in the pathogenesis of heart disease. Acting via β-adrenergic receptors (β-AR), catecholamines (norepinephrine and isoproterenol) increase cardiac myocyte apoptosis in vitro and in vivo. Specifically, β₁-AR and β₂-AR coupled to Gαs exert a proapoptotic action, while β₂-AR coupled to Gi exerts an antiapoptotic action. β1 integrin signaling protects cardiac myocytes against β-AR-stimulated apoptosis in vitro and in vivo. Interaction of matrix metalloproteinase-2 (MMP-2) with β1 integrins interferes with the survival signals initiated by β1 integrins. This paper will discuss background information on β-AR and integrin signaling and summarize the role of β1 integrins in β-AR-stimulated cardiac myocyte apoptosis.

Cyclic AMP-dependent inotropic effects are differentially regulated by muscarinic G(i)-dependent constitutive inhibition of adenylyl cyclase in failing rat ventricle

BACKGROUND AND PURPOSE

β-Adrenoceptor (β-AR)-mediated inotropic effects are attenuated and G(i) proteins are up-regulated in heart failure (HF). Muscarinic receptors constitutively inhibit cAMP formation in normal rat cardiomyocytes. We determined whether constitutive activity of muscarinic receptors to inhibit adenylyl cyclase (AC) increases in HF and if so, whether it modifies the reduced β-AR- or emergent 5-HT₄-mediated cAMP-dependent inotropic effects.

EXPERIMENTAL APPROACH

Contractility and AC activity were measured and related to each other in rat ventricle with post-infarction HF and sham-operated (Sham) controls with or without blockade of muscarinic receptors by atropine and inactivation of G(i) protein by pertussis toxin (PTX).

KEY RESULTS

Isoprenaline-mediated inotropic effects were attenuated and basal, isoprenaline- and forskolin-stimulated AC activity was reduced in HF compared with Sham. Atropine or PTX pretreatment increased forskolin-stimulated AC activity in HF hearts. β-AR-stimulated AC and maximal inotropic response were unaffected by atropine in Sham and HF. In HF, the potency of serotonin (5-HT) to evoke an inotropic response was increased in the presence of atropine with no change in the maximal inotropic response. Interestingly, PTX pretreatment reduced the potency of 5-HT to evoke inotropic responses while increasing the maximal inotropic response.

CONCLUSIONS AND IMPLICATIONS

Although muscarinic constitutive inhibition of AC is increased in HF, it does not contribute to the reduced β-AR-mediated inotropic effects in rat ventricle in HF. The data support the hypothesis that there are differences in the functional compartmentation of 5-HT₄ and β-AR AC signalling in myocardium during HF.

Exercise preconditioning initiates late cardioprotection against isoproterenol-induced myocardial injury in rats independent of protein kinase C

The objective of this study was to investigate the late cardioprotective effect of exercise preconditioning (EP) on isoproterenol (ISO)-induced myocardial injury in rats and the role of protein kinase C (PKC) in EP. Rats were injected with ISO 24 h after running on a treadmill for four periods of 10 min each at 28-30 m/min with intervening periods of rest of 10 min. Nonselective PKC inhibitor chelerythrine (CHE) was injected before EP. The myocardial injury was evaluated quantitatively in terms of the serum cardiac troponin I (cTnI) levels, the myocardial ischemia/hypoxia area, and the integral optical density (IOD) of haematoxylin-basic fuchsin-picric acid (HBFP) staining, and qualitatively in terms of the myocardial ultrastructure. EP markedly attenuated the ISO-induced myocardial ischemia/hypoxia and ultrastructural damage with lower serum cTnI levels. CHE injection before EP did not block the protective effect of EP, displaying a mild myocardial ischemia/hypoxia and well-preserved ultrastructure with even lower serum cTnI levels. The results indicate that EP can exert a late cardioprotection against ISO-induced myocardial injury, and that an injection of the nonselective PKC inhibitor CHE before EP may have a different effect on ISO-induced myocardial injury. Further investigation needs to be conducted to define the role of different PKC isozymes in EP by using isozyme-selective inhibitors.

Decreased beta-adrenergic responsiveness following hypertrophy occurs only in cardiomyocytes that also re-express beta-myosin heavy chain

AIMS

Cardiac hypertrophy is associated with a reduction in the contractile response to beta-adrenergic stimulation, and with re-expression of foetal genes such as beta-myosin heavy chain (MHC). However, whether these two markers of pathology develop concordantly in the same individual cells or independently in different cells is not known.

METHODS AND RESULTS

To answer this question, we examined the beta-adrenergic response of individual beta-MHC expressing and non-expressing myocytes from hypertrophic hearts, using a previously generated mouse model (YFP/beta-MHC) in which a yellow fluorescent protein (YFP) is fused to the native beta-MHC protein allowing easy identification of beta-MHC expressing cells. Yellow fluorescent protein/beta-MHC mice were submitted to 4 weeks of transverse aortic constriction (TAC), and the contractile parameters of isolated individual myocytes in response to the beta-adrenergic agonist isoproterenol were assessed. Our results demonstrate that the decrease in isoproterenol-induced cell shortening that develops in TAC hearts occurs only in those hypertrophic myocytes that re-express beta-MHC. Hypertrophic myocytes that do not express beta-MHC have contractility indices indistinguishable from non-TAC controls.

CONCLUSION

These data show that the reduction of beta-adrenergic response occurs only in subsets, rather than in all myocytes, and is coincident with re-expression of beta-MHC.

Level of G protein-coupled receptor kinase-2 determines myocardial ischemia/reperfusion injury via pro- and anti-apoptotic mechanisms

RATIONALE

Activation of prosurvival kinases and subsequent nitric oxide (NO) production by certain G protein-coupled receptors (GPCRs) protects myocardium in ischemia/reperfusion injury (I/R) models. GPCR signaling pathways are regulated by GPCR kinases (GRKs), and GRK2 has been shown to be a critical molecule in normal and pathological cardiac function.

OBJECTIVE

A loss of cardiac GRK2 activity is known to arrest progression of heart failure (HF), at least in part by normalization of cardiac β-adrenergic receptor (βAR) signaling. Chronic HF studies have been performed with GRK2 knockout mice, as well as expression of the βARKct, a peptide inhibitor of GRK2 activity. This study was conducted to examine the role of GRK2 and its activity during acute myocardial ischemic injury using an I/R model.

METHODS AND RESULTS

We demonstrate, using cardiac-specific GRK2 and βARKct-expressing transgenic mice, a deleterious effect of GRK2 on in vivo myocardial I/R injury with βARKct imparting cardioprotection. Post-I/R infarct size was greater in GRK2-overexpressing mice (45.0±2.8% versus 31.3±2.3% in controls) and significantly smaller in βARKct mice (16.8±1.3%, P<0.05). Importantly, in vivo apoptosis was found to be consistent with these reciprocal effects on post-I/R myocardial injury when levels of GRK2 activity were altered. Moreover, these results were reflected by higher Akt activation and induction of NO production via βARKct, and these antiapoptotic/survival effects could be recapitulated in vitro. Interestingly, selective antagonism of β(2)ARs abolished βARKct-mediated cardioprotection, suggesting that enhanced GRK2 activity on this GPCR is deleterious to cardiac myocyte survival.

CONCLUSION

The novel effect of reducing acute ischemic myocardial injury via increased Akt activity and NO production adds significantly to the therapeutic potential of GRK2 inhibition with the βARKct not only in chronic HF but also potentially in acute ischemic injury conditions.

Reduction of sympathetic activity via adrenal-targeted GRK2 gene deletion attenuates heart failure progression and improves cardiac function after myocardial infarction

Chronic heart failure (HF) is characterized by sympathetic overactivity and enhanced circulating catecholamines (CAs), which significantly increase HF morbidity and mortality. We recently reported that adrenal G protein-coupled receptor kinase 2 (GRK2) is up-regulated in chronic HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell alpha(2)-adrenergic receptors that normally inhibit CA secretion. We also showed that adrenal GRK2 inhibition decreases circulating CAs and improves cardiac inotropic reserve and function. Herein, we hypothesized that adrenal-targeted GRK2 gene deletion before the onset of HF might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we crossed PNMTCre mice, expressing Cre recombinase under the chromaffin cell-specific phenylethanolamine N-methyltransferase (PNMT) gene promoter, with floxedGRK2 mice. After confirming a significant ( approximately 50%) reduction of adrenal GRK2 mRNA and protein levels, the PNMT-driven GRK2 knock-out (KO) offspring underwent myocardial infarction (MI) to induce HF. At 4 weeks post-MI, plasma levels of both norepinephrine and epinephrine were reduced in PNMT-driven GRK2 KO, compared with control mice, suggesting markedly reduced post-MI sympathetic activation. This translated in PNMT-driven GRK2 KO mice into improved cardiac function and dimensions as well as amelioration of abnormal cardiac beta-adrenergic receptor signaling at 4 weeks post-MI. Thus, adrenal-targeted GRK2 gene KO decreases circulating CAs, leading to improved cardiac function and beta-adrenergic reserve in post-MI HF. GRK2 inhibition in the adrenal gland might represent a novel sympatholytic strategy that can aid in blocking HF progression.

Cross-regulation between beta 1- and beta 3-adrenoceptors following chronic beta-adrenergic stimulation in neonatal rat cardiomyocytes

BACKGROUND AND PURPOSE

We have previously shown that beta-adrenoceptors continuously stimulated with noradrenaline induces an increase in beta(3)-adrenoceptors (G alpha(i)PCRs) and a decrease in beta(1)-adrenoceptors (G alpha(s)PCRs) at functional, genomic and protein levels. This compensatory modification induced by noradrenaline is probably one of the consequences of cardiac depression observed in heart disease. Therefore, we investigated further the interaction between beta(1)- and beta(3)-adrenoceptors in neonatal rat cardiomyocytes.

EXPERIMENTAL APPROACH

Functional studies were performed by cyclic adenosine monophosphate (cAMP) accumulation assays in cells untreated or treated with dobutamine and ICI 118551 (beta(1)-adrenoceptor) or CL-3162436243 (beta(3)-adrenoceptor) for 24 h in the presence or absence of protein kinase inhibitors. Beta-adrenoceptor and protein kinase expression was monitored by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and by Western blotting, respectively.

KEY RESULTS

Chronic beta(1)- or beta(3)-adrenoceptor stimulation reduced beta(1)-adrenoceptor-mediated cAMP accumulation in association with a decrease in beta(1)-adrenoceptor mRNA and protein levels through protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and p38 mitogen-activated protein kinase (p38MAPK) activation. In contrast, both treatments induced an increase in beta(3)-adrenoceptor expression and beta(3)-adrenoceptor-inhibited forskolin response through PKC, extracellular-signal-regulated kinases 1 and 2 (ERK1/2) and p38MAPK phosphorylation, although no beta(3)-adrenoceptor response was observed in untreated cells. ERK1/2 and p38MAPK were activated by both treatments. The modulation of beta(1)- or beta(3)-adrenoceptor function did not require stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) although chronic beta(1)-adrenoceptor stimulation activated SAPK/JNK. Beta(3)-adrenoceptor treatment activated Akt although PI3K was not involved in beta(3)-adrenoceptor up-regulation.

CONCLUSION AND IMPLICATIONS

We show for the first time that chronic beta(1)- or beta(3)-adrenoceptor stimulation leads to the modulation of beta(1)- and beta(3)-adrenoceptors by a cross-regulation involving PKC, PI3K p38MAPK and MEK/ERK1/2 pathway, and through protein kinase A when beta(1)-adrenoceptors are chronically activated.

Adrenal GRK2 lowering is an underlying mechanism for the beneficial sympathetic effects of exercise training in heart failure

Exercise training has been reported to exert beneficial effects on cardiac function and to reduce morbidity and mortality of chronic heart failure (HF). Augmented sympathetic nervous system (SNS) activity, leading to elevated circulating catecholamine (CA) levels, is a hallmark of chronic HF that significantly aggravates this disease. Exercise training has been shown to also reduce SNS overactivity in HF, but the underlying molecular mechanism(s) remain unidentified. We recently reported that adrenal G protein-coupled receptor kinase-2 (GRK2), an enzyme that regulates the sympathoinhibitory alpha(2)-adrenoceptors (alpha(2)-ARs) present in the CA-producing adrenal medulla, is upregulated in HF, contributing to the chronically elevated CA levels and SNS activity of the disease. In the present study, we tested whether exercise training can affect the adrenal GRK2-alpha(2)-AR-CA production system in the context of HF. For this purpose, a 10-wk-long exercise training regimen of adult male Sprague-Dawley rats starting at 4 wk postmyocardial infarction (post-MI) was employed, and examination at the end of this treatment period revealed significant amelioration of beta-AR-stimulated contractility in response to exercise training, accompanied by cardiac GRK2 reduction and restoration of circulating plasma CA levels. Importantly, adrenal GRK2 expression (72 + or - 5% reduction vs. post-MI untrained) and alpha(2)-AR number were also restored after exercise training in post-MI animals. These results suggest that exercise training restores the adrenal GRK2-alpha(2)-AR-CA production axis, and this might be part of the mechanism whereby this therapeutic modality normalizes sympathetic overdrive and impedes worsening of the failing heart.

Electrophysiological remodeling in heart failure

Heart failure affects nearly 6 million Americans, with a half-million new cases emerging each year. Whereas up to 50% of heart failure patients die of arrhythmia, the diverse mechanisms underlying heart failure-associated arrhythmia are poorly understood. As a consequence, effectiveness of antiarrhythmic pharmacotherapy remains elusive. Here, we review recent advances in our understanding of heart failure-associated molecular events impacting the electrical function of the myocardium. We approach this from an anatomical standpoint, summarizing recent insights gleaned from pre-clinical models and discussing their relevance to human heart failure.

Transgenic simulation of human heart failure-like L-type Ca2+-channels: implications for fibrosis and heart rate in mice

AIMS

Cardiac L-type Ca(2+)-currents show distinct alterations in chronic heart failure, including increased single-channel activity and blunted adrenergic stimulation, but minor changes of whole-cell currents. Expression of L-type Ca(2+)-channel beta(2)-subunits is enhanced in human failing hearts. In order to determine whether prolonged alteration of Ca(2+)-channel gating by beta(2)-subunits contributes to heart failure pathogenesis, we generated and characterized transgenic mice with cardiac overexpression of a beta(2a)-subunit or the pore Ca(v)1.2 or both, respectively.

METHODS AND RESULTS

Four weeks induction of cardiac-specific overexpression of rat beta(2a)-subunits shifted steady-state activation and inactivation of whole-cell currents towards more negative potentials, leading to increased Ca(2+)-current density at more negative test potentials. Activity of single Ca(2+)-channels was increased in myocytes isolated from beta(2a)-transgenic mice. Ca(2+)-current stimulation by 8-Br-cAMP and okadaic acid was blunted in beta(2a)-transgenic myocytes. In vivo investigation revealed hypotension and bradycardia upon Ca(v)1.2-transgene expression but not in mice only overexpressing beta(2a). Double-transgenics showed cardiac arrhythmia. Interstitial fibrosis was aggravated by the beta(2a)-transgene compared with Ca(v)1.2-transgene expression alone. Overt cardiac hypertrophy was not observed in any model.

CONCLUSION

Cardiac overexpression of a Ca(2+)-channel beta(2a)-subunit alone is sufficient to induce Ca(2+)-channel properties characteristic of chronic human heart failure. beta(2a)-overexpression by itself did not induce cardiac hypertrophy or contractile dysfunction, but aggravated the development of arrhythmia and fibrosis in Ca(v)1.2-transgenic mice.

Mechanisms of enhanced beta-adrenergic reserve from cardiac resynchronization therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) is the first clinical heart failure treatment that improves chamber systolic function in both the short-term and long-term yet also reduces mortality. The mechanical impact of CRT is immediate and well documented, yet its long-term influences on myocyte function and adrenergic modulation that may contribute to its sustained benefits are largely unknown.

METHODS AND RESULTS

We used a canine model of dyssynchronous heart failure (DHF; left bundle ablation, atrial tachypacing for 6 weeks) and CRT (DHF for 3 weeks, biventricular tachypacing for subsequent 3 weeks), contrasting both to nonfailing controls. CRT restored contractile synchrony and improved systolic function compared with DHF. Myocyte sarcomere shortening and calcium transients were markedly depressed at rest and after isoproterenol stimulation in DHF (both anterior and lateral walls), and CRT substantially improved both. In addition, beta(1) and beta(2) stimulation was enhanced, coupled to increased beta(1) receptor abundance but no change in binding affinity. CRT also augmented adenylate cyclase activity over DHF. Inhibitory G-protein (Galpha(i)) suppression of beta-adrenergic stimulation was greater in DHF and reversed by CRT. Galpha(i) expression itself was unaltered; however, expression of negative regulators of Galpha(i) signaling (particularly RGS3) rose uniquely with CRT over DHF and controls. CRT blunted elevated myocardial catecholamines in DHF, restoring levels toward control.

CONCLUSIONS

CRT improves rest and beta-adrenergic-stimulated myocyte function and calcium handling, upregulating beta(1) receptors and adenylate cyclase activity and suppressing G(i)-coupled signaling associated with novel RGS upregulation. The result is greater rest and sympathetic reserve despite reduced myocardial neurostimulation as components underlying its net benefit.

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

BACKGROUND

The upregulation of G protein-coupled receptor kinase 2 in failing myocardium appears to contribute to dysfunctional beta-adrenergic receptor (betaAR) signaling and cardiac function. The peptide betaARKct, which can inhibit the activation of G protein-coupled receptor kinase 2 and improve betaAR signaling, has been shown in transgenic models and short-term gene transfer experiments to rescue heart failure (HF). This study was designed to evaluate long-term betaARKct expression in HF with the use of stable myocardial gene delivery with adeno-associated virus serotype 6 (AAV6).

METHODS AND RESULTS

In HF rats, we delivered betaARKct or green fluorescent protein as a control via AAV6-mediated direct intramyocardial injection. We also treated groups with concurrent administration of the beta-blocker metoprolol. We found robust and long-term transgene expression in the left ventricle at least 12 weeks after delivery. betaARKct significantly improved cardiac contractility and reversed left ventricular remodeling, which was accompanied by a normalization of the neurohormonal (catecholamines and aldosterone) status of the chronic HF animals, including normalization of cardiac betaAR signaling. Addition of metoprolol neither enhanced nor decreased betaARKct-mediated beneficial effects, although metoprolol alone, despite not improving contractility, prevented further deterioration of the left ventricle.

CONCLUSIONS

Long-term cardiac AAV6-betaARKct gene therapy in HF results in sustained improvement of global cardiac function and reversal of remodeling at least in part as a result of a normalization of the neurohormonal signaling axis. In addition, betaARKct alone improves outcomes more than a beta-blocker alone, whereas both treatments are compatible. These findings show that betaARKct gene therapy can be of long-term therapeutic value in HF.

Epidermal growth factor-induced esophageal cancer cell proliferation requires transactivation of beta-adrenoceptors

Unchecked mitogenic signals due to the overexpression of epidermal growth factor (EGF) and its receptor (EGFR) is implicated in the promotion and progression of cancer. In addition, beta-adrenoceptor is involved in the control of cancer cell proliferation. This study sought to elucidate whether a functional connection exists between these two disparate receptor systems. EGF was used to stimulate HKESC-1 cells, an esophageal squamous cancer cell line, in which beta-adrenoceptor activity was monitored by measuring intracellular cAMP levels in the absence or presence of beta-adrenoceptor antagonists. Results showed that EGF significantly increased cAMP levels and cell proliferation, both of which were attenuated by atenolol [(+)-4-[2-hydroxy-3-[(1-methylethyl)amino]propoxy]benzeneacetamide] or ICI 118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol], which are antagonists for the beta-adrenoceptor. Further mechanistic investigation revealed that the cellular release of epinephrine and the expression of its synthesizing enzyme tyrosine hydroxylase were induced by EGF. The expression of beta(1)-adrenoceptor and the downstream signal transducer protein kinase A were also up-regulated. In this connection, AG1478 [4-(3-chloroanilino)-6,7-dimethoxyquinazoline], an EGFR tyrosine kinase inhibitor, abrogated all these EGF-elicited alteration. Collectively, this study demonstrates that beta-adrenergic signaling could be up-regulated at multiple levels upon EGFR activation to mediate the mitogenic signals in esophageal cancer cells. This novel finding not only unveils the sinister liaison between EGFR and beta-adrenoceptors but also sheds new light on the purported therapeutic use of beta-adrenoceptor antagonists in the treatment of esophageal cancer.