The adrenergic pathway and heart failure

β-Caryophyllene, a natural bicyclic sesquiterpene attenuates β-adrenergic agonist-induced myocardial injury in a cannabinoid receptor-2 dependent and independent manner

The downregulation of cannabinoid type-2 receptors (CB2R) have been reported in numerous diseases including cardiovascular diseases (CVDs). The activation of CB2R has recently emerged as an important therapeutic target to mitigate myocardial injury. We examined whether CB2R activation can protect against isoproterenol (ISO)-induced myocardial injury (MI) in rats. In the present study, we investigated the cardioprotective effect of β-caryophyllene (BCP), a naturally occurring dietary cannabinoid in rat model of MI. Rats were pre- and co-treated with BCP (50 mg/kg, orally) twice daily for 10 days along with subcutaneous injection of ISO (85 mg/kg) at an interval of 24 h for two days (9th and 10th days). AM630 (1 mg/kg), a CB2 receptor antagonist, was injected intraperitoneal as a pharmacological challenge prior to BCP treatment to reveal CB2R-mediated cardioprotective mechanisms of BCP. Desensitization of beta-adrenergic receptor (β-AR) signaling, receptor phosphorylation and recruitment of adapter β-arrestins were observed in ISO-induced MI in rats. ISO injections caused impaired cardiac function, elevated the levels of serum cardiac marker enzymes, and enhanced oxidative stress markers along with altered PI3K/Akt and NrF2/Keap1/HO-1 signaling pathways. ISO also promoted lysosomal dysfunction along with activation of NLRP3 inflammasomes and TLR4-NFκB/MAPK signaling and triggered rise in proinflammatory cytokines. There was a concomitant mitochondrial dysfunction followed by the activation of endoplasmic reticulum (ER) stress-mediated Hippo signaling and intrinsic pathway of apoptosis as well as altered autophagic flux/mTOR signaling in ISO-induced MI. Furthermore, ISO also triggered dyslipidemia evidenced by altered lipids, lipoproteins and lipid marker enzymes along with ionic homeostasis malfunction. However, treatment with BCP resulted in significant protective effects on all biochemical and molecular parameters analyzed. The cardioprotective effects were further strengthened by preservation of cardiomyocytes and cell organelles as observed in histopathological and ultrastructural studies. Interestingly, treatment with AM630, a CB2R antagonist was observed to abrogate the protective effects of BCP on the biochemical and molecular parameters except hyperlipidemia and ionic homeostasis in ISO-induced MI in rats. The present study findings demonstrate that BCP possess the potential to protect myocardium against ISO-induced MI in a CB2-dependent and independent manner.

Novel Paradigms Governing β1-Adrenergic Receptor Trafficking in Primary Adult Rat Cardiac Myocytes

The β₁-adrenergic receptor (β₁-AR) is a major cardiac G protein-coupled receptor, which mediates cardiac actions of catecholamines and is involved in genesis and treatment of numerous cardiovascular disorders. In mammalian cells, catecholamines induce the internalization of the β₁-AR into endosomes and their removal promotes the recycling of the endosomal β₁-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the β₁-AR in response to β-agonists and antagonists was determined by confocal microscopy in primary adult rat ventricular myocytes (ARVMs), which are terminally differentiated myocytes with unique structures such as transverse tubules (T-tubules) and contractile sarcomeres. In unstimulated ARVMs, the fluorescently labeled β₁-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface β₁-ARs into small (∼225-250 nm) regularly spaced internal punctate structures that overlapped with puncta stained by Di-8 ANEPPS, a membrane-impermeant T-tubule-specific dye. Replacing the β-agonist with the β-blocker alprenolol, induced the translocation of the wild-type β₁-AR from these punctate structures back to the plasma membrane. This step was dependent on two barcodes, namely, the type-1 PDZ binding motif and serine at position 312 of the β₁-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the β₁-AR. These data show that redistribution of the β₁-AR in ARVMs from internal structures back to the plasma membrane was mediated by a novel sorting mechanism, which might explain unique aspects of cardiac β₁-AR signaling under normal or pathologic conditions.

Targeting cardiac β-adrenergic signaling via GRK2 inhibition for heart failure therapy

Cardiac cells, like those of the other tissues, undergo regulation through membrane-bound proteins known as G protein-coupled receptors (GPCRs). β-adrenergic receptors (βARs) are key GPCRs expressed on cardiomyocytes and their role is crucial in cardiac physiology since they regulate inotropic and chronotropic responses of the sympathetic nervous system (SNS). In compromised conditions such as heart failure (HF), chronic βAR hyperstimulation occurs via SNS activation resulting in receptor dysregulation and down-regulation and consequently there is a marked reduction of myocardial inotropic reserve and continued loss of pump function. Data accumulated over the last two decades indicates that a primary culprit in initiating and maintain βAR dysfunction in the injured and stressed heart is GPCR kinase 2 (GRK2), which was originally known as βARK1 (for βAR kinase). GRK2 is up-regulated in the failing heart due to chronic SNS activity and targeting this kinase has emerged as a novel therapeutic strategy in HF. Indeed, its inhibition or genetic deletion in several disparate animal models of HF including a pre-clinical pig model has shown that GRK2 targeting improves functional and morphological parameters of the failing heart. Moreover, non-βAR properties of GRK2 appear to also contribute to its pathological effects and thus, its inhibition will likely complement existing therapies such as βAR blockade. This review will explore recent research regarding GRK2 inhibition; in particular it will focus on the GRK2 inhibitor peptide known as βARKct, which represents new hope in the treatment against HF progression.

Protein kinase A and phosphodiesterase-4D3 binding to coding polymorphisms of cardiac muscle anchoring protein (mAKAP)

Protein kinase A (PKA) substrate phosphorylation is facilitated through its co-localization with its signaling partner by A-kinase anchoring proteins (AKAPs). mAKAP (muscle-selective AKAP) localizes PKA and its substrates such as phosphodiesterase-4D3 (PDE4D3), ryanodine receptor, and protein phosphatase 2A (PP2A) to the sarcoplasmic reticulum and perinuclear space. The genetic role of mAKAP, in modulating PKA/PDE4D3 molecular signaling during cardiac diseases, remains unclear. The purpose of this study was to examine the effects of naturally occurring mutations in human mAKAP on PKA and PDE4D3 signaling. We have recently identified potentially important human mAKAP coding non-synonymous polymorphisms located within or near key protein binding sites critical to β-adrenergic receptor signaling. Three mutations (P1400S, S2195F, and L717V) were cloned and transfected into a mammalian cell line for the purpose of comparing whether those substitutions disrupt mAKAP binding to PKA or PDE4D3. Immunoprecipitation study of mAKAP-P1400S, a mutation located in the mAKAP-PDE4D3 binding site, displayed a significant reduction in binding to PDE4D3, with no significant changes in PKA binding or PKA activity. Conversely, mAKAP-S2195F, a mutation located in mAKAP-PP2A binding site, showed significant increase in both binding propensity to PKA and PKA activity. Additionally, mAKAP-L717V, a mutation flanking the mAKAP-spectrin repeat domain, exhibited a significant increase in PKA binding compared to wild type, but there was no change in PKA activity. We also demonstrate specific binding of wild-type mAKAP to PDE4D3. Binding results were demonstrated using immunoprecipitation and confirmed with surface plasmon resonance (Biacore-2000); functional results were demonstrated using activity assays, Ca(2+) measurements, and Western blot. Comparative analysis of the binding responses of mutations to mAKAP could provide important information about how these mutations modulate signaling.

Evidence for a critical role of catecholamines for cardiomyocyte lineage commitment in murine embryonic stem cells

Catecholamine release is known to modulate cardiac output by increasing heart rate. Although much is known about catecholamine function and regulation in adults, little is known about the presence and role of catecholamines during heart development. The present study aimed therefore to evaluate the effects of different catecholamines on early heart development in an in vitro setting using embryonic stem (ES) cell-derived cardiomyocytes. Effects of catecholamine depletion induced by reserpine were examined in murine ES cells (line D3, αPIG44) during differentiation. Cardiac differentiation was assessed by immunocytochemistry, qRT-PCR, quantification of beating clusters, flow cytometry and pharmacological approaches. Proliferation was analyzed by EB cross-section measurements, while functionality of cardiomyocytes was studied by extracellular field potential (FP) measurements using microelectrode arrays (MEAs). To further differentiate between substance-specific effects of reserpine and catecholamine action via α- and β-receptors we proved the involvement of adrenergic receptors by application of unspecific α- and β-receptor antagonists. Reserpine treatment led to remarkable down-regulation of cardiac-specific genes, proteins and mesodermal marker genes. In more detail, the average ratio of ∼40% spontaneously beating control clusters was significantly reduced by 100%, 91.1% and 20.0% on days 10, 12, and 14, respectively. Flow cytometry revealed a significant reduction (by 71.6%, n = 11) of eGFP positive CMs after reserpine treatment. By contrast, reserpine did not reduce EB growth while number of neuronal cells in reserpine-treated EBs was significantly increased. MEA measurements of reserpine-treated EBs showed lower FP frequencies and weak responsiveness to adrenergic and muscarinic stimulation. Interestingly we found that developmental inhibition after α- and β-adrenergic blocker application mimicked developmental changes with reserpine. Using several methodological approaches our data suggest that reserpine inhibits cardiac differentiation. Thus catecholamines play a critical role during development.

Protein kinase A and phosphodiesterase-4D3 binding to coding polymorphisms of cardiac muscle anchoring protein (mAKAP)

Protein kinase A (PKA) substrate phosphorylation is facilitated through its co-localization with its signaling partner by A-kinase anchoring proteins (AKAPs). mAKAP (muscle-selective AKAP) localizes PKA and its substrates such as phosphodiesterase-4D3 (PDE4D3), ryanodine receptor, and protein phosphatase 2A (PP2A) to the sarcoplasmic reticulum and perinuclear space. The genetic role of mAKAP, in modulating PKA/PDE4D3 molecular signaling during cardiac diseases, remains unclear. The purpose of this study was to examine the effects of naturally occurring mutations in human mAKAP on PKA and PDE4D3 signaling. We have recently identified potentially important human mAKAP coding non-synonymous polymorphisms located within or near key protein binding sites critical to β-adrenergic receptor signaling. Three mutations (P1400S, S2195F, and L717V) were cloned and transfected into a mammalian cell line for the purpose of comparing whether those substitutions disrupt mAKAP binding to PKA or PDE4D3. Immunoprecipitation study of mAKAP-P1400S, a mutation located in the mAKAP-PDE4D3 binding site, displayed a significant reduction in binding to PDE4D3, with no significant changes in PKA binding or PKA activity. Conversely, mAKAP-S2195F, a mutation located in mAKAP-PP2A binding site, showed significant increase in both binding propensity to PKA and PKA activity. Additionally, mAKAP-L717V, a mutation flanking the mAKAP-spectrin repeat domain, exhibited a significant increase in PKA binding compared to wild type, but there was no change in PKA activity. We also demonstrate specific binding of wild-type mAKAP to PDE4D3. Binding results were demonstrated using immunoprecipitation and confirmed with surface plasmon resonance (Biacore-2000); functional results were demonstrated using activity assays, Ca(2+) measurements, and Western blot. Comparative analysis of the binding responses of mutations to mAKAP could provide important information about how these mutations modulate signaling.

Garlic extracts prevent oxidative stress, hypertrophy and apoptosis in cardiomyocytes: a role for nitric oxide and hydrogen sulfide

Background

In ancient times, plants were recognized for their medicinal properties. Later, the arrival of synthetic drugs pushed it to the backstage. However, from being merely used for food, plants are now been widely explored for their therapeutic value. The current study explores the potential of skin and flesh extracts from a hard-necked Rocambole variety of purple garlic in preventing cardiomyocyte hypertrophy and cell death.

Methods

Norepinephrine (NE) was used to induce hypertrophy in adult rat cardiomyocytes pretreated with garlic skin and flesh extracts. Cell death was measured as ratio of rod to round shaped cardiomyocytes. Fluorescent probes were used to measure apoptosis and oxidative stress in cardiomyocytes treated with and without extracts and NE. Pharmacological blockade of nitric oxide (NO) and hydrogen sulfide (H₂S) were used to elucidate the mechanism of action of garlic extracts. Garlic extract samples were also tested for alliin and allicin concentrations.

Results

Exposure of cardiomyocytes to NE induced an increase in cell size and cell death; this increase was significantly prevented upon treatment with garlic skin and flesh extracts. Norepinephrine increased apoptosis and oxidative stress in cardiomyocytes which was prevented upon pretreatment with skin and flesh extracts; NO, and H₂S blockers significantly inhibited this beneficial effect. Allicin and alliin concentration were significantly higher in garlic flesh extract when compared to the skin extract.

Conclusion

These results suggest that both skin and flesh garlic extracts are effective in preventing NE induced cardiomyocyte hypertrophy and cell death. Reduction in oxidative stress may also play an important role in the anti-hypertrophic and anti-apoptotic properties of garlic extracts. These beneficial effects may in part be mediated by NO and H₂S.

Merits of non-invasive rat models of left ventricular heart failure

Heart failure (HF) is characterized as a limitation to cardiac output that prevents the heart from supplying tissues with adequate oxygen and predisposes individuals to pulmonary edema. Impaired cardiac function is secondary to either decreased contractility reducing ejection (systolic failure), diminished ventricular compliance preventing filling (diastolic failure), or both. To study HF etiology, many different techniques have been developed to elicit this condition in experimental animals, with varying degrees of success. Among rats, surgically induced HF models are the most prevalent, but they bear several shortcomings, including high mortality rates and limited recapitulation of the pathophysiology, etiology, and progression of human HF. Alternatively, a number of non-invasive HF induction methods avoid many of these pitfalls, and their merits in technical simplicity, reliability, survivability, and comparability to the pathophysiologic and pathogenic characteristics of HF are reviewed herein. In particular, this review focuses on the primary pathogenic mechanisms common to genetic strains (spontaneously hypertensive and spontaneously hypertensive heart failure), pharmacological models of toxic cardiomyopathy (doxorubicin and isoproterenol), and dietary salt models, all of which have been shown to induce left ventricular HF in the rat. Additional non-invasive techniques that may potentially enable the development of new HF models are also discussed.

Lifestyle modification in metabolic syndrome and associated changes in plasma amino acid profiles

BACKGROUND

Although lifestyle modification is the key treatment of metabolic syndrome (MetS), clinical data on the dynamical relationship between metabolic state and MetS has been limited. This study investigated the mutual correlations between demographic and biochemical variables, and the metabolic state based on the plasma amino acid (AA) concentrations, during a lifestyle modification for MetS.

METHODS AND RESULTS

Japanese subjects, consisting of 54 patients with MetS [MetS(+)] and 35 persons without MetS [MetS(-)] were included in the study. Before a lifestyle modification program, the levels of glutamate metabolism-related AA (Glu-mAA), aromatic AA metabolism-related AA (Aromatic-mAA) and alanine metabolism-related AA (Ala-mAA) were significantly higher, while those of glycine-serine-threonine metabolism-related AA (Gly-Ser-Thr-mAA) were significantly lower compared to those in MetS(-). After a lifestyle modification, significant reductions (P<0.05) in the BMI (-1.4 kg/m(2)), mean blood pressure (-7.9 mmHg), hemoglobin A(1c) (-0.4%), and triglycerides (-30.6 mg/dl) were observed, and significant differences in the plasma AA levels between MetS(+) and MetS(-) were resolved. In addition, the diagnostic items of MetS were positively correlated with the levels of Glu-mAA, Ala-mAA, branched chain AA (BCAA)-mAA, Aromatic-mAA, and negatively correlated with the levels of Gly-Ser-Thr-mAA.

CONCLUSIONS

As MetS subsided, the abnormality of mean plasma AA levels of the MetS(+) group returned to similar values as those in the MetS(-) group, suggesting a novel viewpoint regarding the metabolic mechanism of lifestyle modification.

Neurohormonal regulation of cardiac ion channels in chronic heart failure

Alteration of neurohormonal homeostasis is a hallmark of the pathophysiology of chronic heart failure (CHF). In particular, overactivation of the renin-angiotensin-aldosterone system and the sympathetic catecholaminergic system is consistently observed. Chronic overactivation of these hormonal pathways leads to a detrimental arrhythmogenic remodeling of cardiac tissue due to dysregulation of cardiac ion channels. Sudden cardiac death resulting from ventricular arrhythmias is a major cause of mortality in patients with CHF. All the drug classes known to reduce mortality in patients with CHF are neurohormonal blockers. The aim of this review was to provide an overview of how cardiac ion channels are regulated by hormones known to play a central role in the pathogenesis of CHF.

Involvement of the beta-adrenergic system in the cardiac chronic form of experimental Trypanosoma cruzi infection

Changes in the cardiac beta-adrenergic system in early stages of Trypanosoma cruzi infection have been described. Here, we studied an early (135 days post-infection-p.i.) and a late stage (365 days p.i.) of the cardiac chronic form of the experimental infection (Tulahuen or SGO-Z12 strains), determining plasma epinephrine and norepinephrine levels, beta-receptor density, affinity and function, cardiac cAMP concentration and phosphodiesterase activity, cardiac contractility, and the presence of beta-receptor autoantibodies. Tulahuen-infected mice presented lower epinephrine and norepinephrine levels; lower beta-receptor affinity and density; a diminished norepinephrine response and higher cAMP levels in the early stage, and a basal contractility similar to non-infected controls in the early and augmented in the late stage. The Tulahuen strain induced autoantibodies with weak beta-receptor interaction. SGO-Z12-infected mice presented lower norepinephrine levels and epinephrine levels that diminished with the evolution of the infection; lower beta-receptor affinity and an increased density; unchanged epinephrine and norepinephrine response in the early and a diminished response in the late stage; higher cAMP levels and unchanged basal contractility. The SGO-Z12 isolate induced beta-receptor autoantibodies with strong interaction with the beta-receptors. None of the antibodies, however, acted a as beta-receptor agonist. The present results demonstrate that this system is seriously compromised in the cardiac chronic stage of T. cruzi infection.

Inhibition of vascular smooth muscle G protein-coupled receptor kinase 2 enhances alpha1D-adrenergic receptor constriction

G protein-coupled receptor kinase 2 (GRK2) is a serine/theorinine kinase that phosphorylates and desensitizes agonist-bound G protein-coupled receptors. GRK2 is increased in expression and activity in lymphocytes and vascular smooth muscle (VSM) in human hypertension and animal models of the disease. Inhibition of GRK2 using the carboxyl-terminal portion of the protein (GRK2ct) has been an effective tool to restore compromised beta-adrenergic receptor (AR) function in heart failure and improve outcome. A well-characterized dysfunction in hypertension is attenuation of betaAR-mediated vasodilation. Therefore, we tested the role of inhibition of GRK2 using GRK2ct or VSM-selective GRK2 gene ablation in a renal artery stenosis model of elevated blood pressure (BP) [the two-kidney, one-clip (2K1C) model]. Use of the 2K1C model resulted in a 30% increase in conscious BP, a threefold increase in plasma norepinephrine levels, and a 50% increase in VSM GRK2 mRNA levels. BP remained increased despite VSM-specific GRK2 inhibition by either GRK2 knockout (GRK2KO) or peptide inhibition (GRK2ct). Although betaAR-mediated dilation in vivo and in situ was enhanced, alpha(1)AR-mediated vasoconstriction was also increased. Further pharmacological experiments using alpha(1)AR antagonists revealed that GRK2 inhibition of expression (GRK2KO) or activity (GRK2ct) enhanced alpha(1D)AR vasoconstriction. This is the first study to suggest that VSM alpha(1D)ARs are a GRK2 substrate in vivo.

G protein-coupled receptor kinase 2 ablation in cardiac myocytes before or after myocardial infarction prevents heart failure

Myocardial G protein-coupled receptor kinase (GRK)2 is a critical regulator of cardiac beta-adrenergic receptor (betaAR) signaling and cardiac function. Its upregulation in heart failure may further depress cardiac function and contribute to mortality in this syndrome. Preventing GRK2 translocation to activated betaAR with a GRK2-derived peptide that binds G(beta)gamma (betaARKct) has benefited some models of heart failure, but the precise mechanism is uncertain, because GRK2 is still present and betaARKct has other potential effects. We generated mice in which cardiac myocyte GRK2 expression was normal during embryonic development but was ablated after birth (alphaMHC-Cre x GRK2 fl/fl) or only after administration of tamoxifen (alphaMHC-MerCreMer x GRK2 fl/fl) and examined the consequences of GRK2 ablation before and after surgical coronary artery ligation on cardiac adaptation after myocardial infarction. Absence of GRK2 before coronary artery ligation prevented maladaptive postinfarction remodeling and preserved betaAR responsiveness. Strikingly, GRK2 ablation initiated 10 days after infarction increased survival, enhanced cardiac contractile performance, and halted ventricular remodeling. These results demonstrate a specific causal role for GRK2 in postinfarction cardiac remodeling and heart failure and support therapeutic approaches of targeting GRK2 or restoring betaAR signaling by other means to improve outcomes in heart failure.

The prevalence and significance of periodic leg movements during sleep in patients with congestive heart failure

PURPOSE

The aim of this study was to evaluate (1) the prevalence of periodic leg movements during sleep (PLMs) in a consecutive sample of congestive heart failure (CHF) outpatients; (2) the presence of correlation between PLMs, subjective daytime sleepiness, and sleep architecture; and (3) the heart rate response to PLMs in CHF.

MATERIALS AND METHODS

Seventy-nine [50 men, age 59 +/- 11 years, body mass index (BMI) 26 +/- 5 kg/m(2)] consecutive adult stable outpatients with CHF [left ventricular ejection fraction (LVEF) 36 +/- 6%] were prospectively evaluated. The patients underwent assessment of echocardiography, sleepiness (Epworth Scale), and overnight in-lab polysomnography.

RESULTS

Fifteen patients (19%) had PLM index >5. These subjects were similar in sex distribution, BMI, subjective somnolence, LVEF, and apnea-hypopnea index (AHI), but were significantly older than subjects without PLMs. Sleep architecture was similar in subjects with and without PLMs. There was a small but significant elevation of heart rate after PLMs (80.1 +/- 9.4 vs. 81.5 +/- 9.2; p < 0.001). The cardiac acceleration was also present in absence of electroencephalogram activation.

CONCLUSION

The prevalence of PLMs in consecutive sample of adult CHF outpatients was 19%. There were no differences in subjective daytime sleepiness, sleep architecture, AHI, and severity of CHF in subjects with and without PLMs. PLMs caused a small but statistically significant cardiac acceleration.

G-protein coupled receptor signaling in myocardium: not for the faint of heart

Catecholamines, endothelin-1 and angiotensin II are among a diverse group of diffusible extracellular signals that regulate pump function of the heart by binding to G-protein coupled receptors (GPCR). When the body demands a temporary boost of power output or if temporary budgeting of resources is required, these signals can adjust heart rate and contractile strength to maintain continuous perfusion of all vascular beds with nutrient- and oxygen-rich blood. Given adequate time in the face of prolonged challenges, activation of GPCRs can also promote "remodeling of the heart" by increasing cell size, organ size, and chamber dimensions, or by varying tissue composition and altering the expression of protein isoforms controlling excitability and contractility. A common feature of heart disease is the state of chronic activation of GPCR signaling systems. Paradoxically, whereas acute activation is beneficial, chronic activation often contributes to further deterioration of cardiac performance. A better understanding of how chronic GPCR activation contributes to the development of heart disease is needed so that it can be translated into better prevention and therapeutic strategies in the clinic.

Targeting myocardial beta-adrenergic receptor signaling and calcium cycling for heart failure gene therapy

Heart failure (HF) is a leading cause of morbidity and mortality in Western countries and projections reveal that HF incidence in the coming years will rise significantly because of an aging population. Pharmacologic therapy has considerably improved HF treatment during the last 2 decades, but fails to rescue failing myocardium and to increase global cardiac function. Therefore, novel therapeutic approaches to target the underlying molecular defects of ventricular dysfunction and to increase the outcome of patients in HF are needed. Failing myocardium generally exhibits distinct changes in beta-adrenergic receptor (betaAR) signaling and intracellular Ca2+-handling providing opportunities for research. Recent advances in transgenic and gene therapy techniques have presented novel therapeutic strategies to alter myocardial function and to target both betaAR signaling and Ca2+-cycling. In this review, we will discuss functional alterations of the betaAR system and Ca2+-handling in HF as well as corresponding therapeutic strategies. We will then focus on recent in vivo gene therapy strategies using the targeted inhibition of the betaAR kinase (betaARK1 or GRK2) and the restoration of S100A1 protein expression to support the injured heart and to reverse or prevent HF.

New insights into the regulation of cAMP synthesis beyond GPCR/G protein activation: implications in cardiovascular regulation

Regulation of intracellular concentrations of cyclic AMP is one of the most ubiquitous mechanisms for regulating cellular functions. Further, the manner in which cAMP production is regulated via G proteins at the level of adenylyl cyclase activation has been studied extensively. This review focuses instead on the recently identified mechanisms and roles for regulation of adenylyl cyclase functions beyond G protein activation. These mechanisms include: a) the coupling of particular isoforms of adenylyl cyclase to function within a single cell type b) regulation of membrane trafficking of higher order enzyme aggregates and c) raf kinase-dependent phosphorylation and sensitization of adenylyl cyclases--an important pathway for crosstalk between tyrosine kinase signaling cascades with regulation of cAMP-mediated responses.

Abnormal muscle and hematopoietic gene expression may be important for clinical morbidity in primary hyperparathyroidism

In primary hyperparathyroidism (PHPT), excess PTH secretion by adenomatous or hyperplastic parathyroid glands leads to elevated serum [Ca(2+)]. Patients present complex symptoms of muscular fatigue, various neuropsychiatric, neuromuscular, and cardiovascular manifestations, and, in advanced disease, kidney stones and metabolic bone disease. Our objective was to characterize changes in muscle and hematopoietic gene expression in patients with reversible mild PHPT after parathyroidectomy and possibly link molecular pathology to symptoms. Global mRNA profiling using Affymetrix gene chips was carried out in biopsies obtained before and 1 yr after parathyroidectomy in seven patients discovered by routine blood [Ca(2+)] screening. The tissue distribution of PTH receptor (PTHR1 and PTHR2) mRNAs were quantitated using real-time RT-PCR in unrelated persons to define PTH target tissues. Of about 10,000 expressed genes, 175 muscle, 169 hematological, and 99 bone-associated mRNAs were affected. Notably, the major part of muscle-related mRNAs was increased whereas hematological mRNAs were predominantly decreased during disease. Functional and molecular network analysis demonstrated major alterations of several tissue characteristic groups of mRNAs as well as those belonging to common cell signaling and major metabolic pathways. PTHR1 and PTHR2 mRNAs were more abundantly expressed in muscle and brain than in hematopoietic cells. We suggest that sustained stimulation of PTH receptors present in brain, muscle, and hematopoietic cells have to be considered as one independent, important cause of molecular disease in PHPT leading to profound alterations in gene expression that may help explain symptoms like muscle fatigue, cardiovascular pathology, and precipitation of psychiatric illness.

Beta-adrenergic receptor antagonism preserves myocardial function after brain death in a porcine model

BACKGROUND

Cardiac dysfunction after brain death decreases the already limited number of potential donors for cardiac transplantation. Acute beta-adrenergic receptor (betaAR) desensitization after the brain death-associated catecholamine surge is an important mechanism. We hypothesized that acute betaAR antagonism could improve myocardial function after brain death by preserving betaAR signaling.

METHODS

Pigs were randomly assigned to three study groups (n = 5): sham; brain death; and brain death with betaAR antagonist (200 microg/kg/min esmolol), 30 minutes before brain death until 45 minutes after brain death. Functional data were collected for 6 hours after brain death and tissues procured.

RESULTS

Compared with baseline, pre-load recruitable stroke work (PRSW), a pre-load-independent measure of systolic function (21.4 +/- 7.5 vs 43.3 +/- 6.8, slope of regression line during vena caval occlusion, p < 0.001), diastolic function (Tau, 101 +/- 54.7 vs 36.4 +/- 5.4 ms, p = 0.03) and systemic oxygen delivery (151 +/- 79.7 vs 298 +/- 78.7 ml/min, p < 0.001) deteriorated in untreated animals at 6 hours after brain death. In contrast, betaAR antagonist maintained baseline systolic function (PRSW, 37.8 +/- 5.6 vs 38.2 +/- 4.7, slope of regression line during vena caval occlusion, p = 0.92), diastolic function (Tau, 32.6 +/- 5.1 vs 48.5 +/- 28.3 ms, p = 0.57) and oxygen delivery (427 +/- 116 vs 397 +/- 98.8 ml/min, p = 0.36) at 6 hours after brain death. betaAR antagonist preserved betaAR signaling, as demonstrated by similar left ventricular (LV) basal (55.4 +/- 32.8 vs 58.8 +/- 10.9 pmol/mg/min, p = 0.40) and isoproterenol-stimulated (125 +/- 70.5 vs 124 +/- 52.0 pmol/mg/min, p = 0.49) adenylate cyclase activity at 6 hours after brain death, upon comparing betaAR antagonist and sham treatment groups. Both LV basal and isoproterenol-stimulated adenyl cyclase activity were higher with betaAR antagonist (25.9 +/- 4.8 pmol/mg/min, p = 0.03) than with untreated brain death (55.6 +/- 17.3 pmol/mg/min, p = 0.02).

CONCLUSIONS

Beta-adrenergic receptor antagonism before brain death preserves cardiac function by preventing betaAR desensitization. This therapy in potential donors might increase the number of organs available for transplantation.

Mechanisms of sympathetic activation in heart failure

1. Heart Failure (HF) is a serious, debilitating condition with poor survival rates and an increasing level of prevalence. A characteristic of HF is a compensatory neurohumoral activation that increases with the severity of the condition. 2. The increase in sympathetic activity may be beneficial initially, providing inotropic support to the heart and peripheral vasoconstriction, but in the longer term it promotes disease progression and worsens prognosis. This is particularly true for the increase in cardiac sympathetic nerve activity, as shown by the strong inverse correlation between cardiac noradrenaline spillover and prognosis and by the beneficial effect of beta-adrenoceptor antagonists. 3. Possible causes for the raised level of sympathetic activity in HF include altered neural reflexes, such as those from baroreceptors and chemoreceptors, raised levels of hormones, such as angiotensin II, acting on circumventricular organs, and changes in central mechanisms that may amplify the responses to these inputs. 4. The control of sympathetic activity to different organs is regionally heterogeneous, as demonstrated by a lack of concordance in burst patterns, different responses to reflexes, opposite responses of cardiac and renal sympathetic nerves to central angiotensin and organ-specific increases in sympathetic activity in HF. These observations indicate that, in HF, it is essential to study the factors causing sympathetic activation in individual outflows, in particular those that powerfully, and perhaps preferentially, increase cardiac sympathetic nerve activity.

Protein kinase A-mediated phosphorylation contributes to enhanced contraction observed in mice that overexpress beta-adrenergic receptor kinase-1

Transgenic mice with cardiac specific overexpression of beta-adrenergic receptor kinase-1 (betaARK-1) exhibit reduced contractility in the presence of adrenergic stimulation. However, whether contractility is altered in the absence of exogenous agonist is not clear. Effects of betaARK-1 overexpression on contraction were examined in mouse ventricular myocytes, studied at 37 degrees C, in the absence of adrenergic stimulation. In myocytes voltage-clamped with microelectrodes (18-26 MOmega; 2.7 M KCl) to minimize intracellular dialysis, contractions were significantly larger in betaARK-1 cells than in wild-type myocytes. In contrast, when cells were dialyzed with patch pipette solution (1-3 MOmega; 0 mM NaCl, 70 mM KCl, 70 mM potassium aspartate, 4 mM MgATP, 1 mM MgCl(2), 2.5 mM KH(2)PO(4), 0.12 mM CaCl(2), 0.5 mM EGTA, and 10 mM HEPES), the extent of cell shortening was similar in wild-type and betaARK-1 myocytes. Furthermore, when cells were dialyzed with solutions that contained phosphodiesterase-sensitive sodium-cAMP (50 microM), the extent of cell shortening was similar in wild-type and betaARK-1 myocytes. However, when patch solutions were supplemented with phosphodiesterase-resistant 8-bromo-cAMP (50 muM), contractions were larger in betaARK-1 than wild-type cells. This difference was eliminated by the protein kinase A inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89). Interestingly, Ca(2+) current amplitudes and inactivation rates were similar in betaARK-1 and wild-type cells in all experiments. These results suggest components of the adenylyl cyclase-protein kinase A pathway are sensitized by chronically increased betaARK-1 activity, which may augment contractile function in the absence of exogenous agonist. Thus, changes in contractile function in myocytes from failing hearts may reflect, in part, effects of chronic up-regulation of betaARK-1 on the cAMP-protein kinase A pathway.

Improved myocardial beta-adrenergic responsiveness and signaling with exercise training in hypertension

BACKGROUND

Cardiac responses to beta-adrenergic receptor stimulation are depressed with pressure overload-induced cardiac hypertrophy. We investigated whether exercise training could modify beta-adrenergic receptor responsiveness in a model of spontaneous hypertension by modifying the beta-adrenergic receptor desensitizing kinase GRK2 and the abundance and phosphorylation of some key Ca2+ cycling proteins.

METHODS AND RESULTS

Female spontaneously hypertensive rats (SHR; age, 4 months) were placed into a treadmill running (SHR-TRD; 20 m/min, 1 h/d, 5 d/wk, 12 weeks) or sedentary group (SHR-SED). Age-matched Wistar Kyoto (WKY) rats were controls. Mean blood pressure was higher in SHR versus WKY (P<0.01) and unaltered with exercise. Left ventricular (LV) diastolic anterior and posterior wall thicknesses were greater in SHR than WKY (P<0.001) and augmented with training (P<0.01). Langendorff LV performance was examined during isoproterenol (ISO) infusions (1x10(-10) to 1x10(-7) mol/L) and pacing stress (8.5 Hz). The peak LV developed pressure/ISO dose response was shifted rightward 100-fold in SHR relative to WKY. The peak ISO LV developed pressure response was similar between WKY and SHR-SED and increased in SHR-TRD (P<0.05). SHR-TRD showed the greatest lusitropic response to ISO (P<0.05) and offset the pacing-induced increase in LV end-diastolic pressure and the time constant of isovolumic relaxation (tau) observed in WKY and SHR-SED. Improved cardiac responses to ISO in SHR-TRD were associated with normalized myocardial levels of GRK2 (P<0.05). SHR displayed increased L-type Ca2+ channel and sodium calcium exchanger abundance compared with WKY (P<0.001). Training increased ryanodine receptor phosphorylation and phospholamban phosphorylation at both the Ser16 and Thr17 residues (P<0.05).

CONCLUSIONS

Exercise training in hypertension improves the inotropic and lusitropic responsiveness to beta-adrenergic receptor stimulation despite augmenting LV wall thickness. A lower GRK2 abundance and an increased phosphorylation of key Ca2+ cycling proteins may be responsible for the above putative effects.

Diabetic cardiomyopathy: do women differ from men?

Although many aspects of cardiovascular disease are similar between women and men, it is becoming increasingly obvious that there are significant differences as well. Premenopausal women usually have a lower risk of cardiovascular diseases than age-matched men and postmenopausal women. However, the "female advantage" disappears once women are afflicted with diabetes mellitus. Heart diseases are twice as common in diabetic men and five times as common in diabetic women. It is believed that differences in sex hormones and intrinsic myocardial and endothelial functions between men and women may be responsible for this female "advantage" and "disadvantage" in normal and diabetic conditions. Most experimental and clinical studies on diabetes only included male subjects and failed to address this important gender difference in diabetic heart complications. Although female hearts may be better tolerated to stress (such as ischemia) insults than their male counterparts, female sex hormone such as estrogen may interact with certain risk factors under diabetes which may compromise the overall cardiac function. The benefit versus risk of estrogen replacement therapy on cardiac function and overall cardiovascular health in diabetes remains controversial. This review will focus on gender-related difference in diabetic heart complication--diabetic cardiomyopathy--and if gender differences in intrinsic myocardial contraction, polyol pathway metabolism, and advanced glycation endproduct formation and other neuroendocrinal regulatory mechanisms to the heart may contribute to disparity in diabetic cardiomyopathy between men and women.