Pflugers Arch - Eur J Physiol DOI 10.1007/s00424-014-1491-5

INVITED REVIEW

Adrenergic signaling in heart failure: a balance of toxic and protective effects Anthony J. Baker

Received: 3 January 2014 / Revised: 24 February 2014 / Accepted: 26 February 2014 # Springer-Verlag Berlin Heidelberg (outside the USA) 2014

Abstract Heart failure with reduced ejection fraction involves activation of the sympathetic nervous system and chronic hyperactivation of the sympatho-adrenergic receptors (ARs) β-ARs and α1-ARs, which are thought to be cardiotoxic and worsen pathological remodeling and function. Concurrently, the failing heart manifests significant decreases in sympathetic nerve terminal density, decreased cardiac norepinephrine levels, and marked downregulation of β-AR abundance and signaling. Thus, a state of both feast and famine coexist with respect to the adrenergic state in heart failure. For the failing heart, the hyperadrenergic state is toxic. However, the role of hypoadrenergic mechanisms in the pathophysiology of heart failure is less clear. Cardiotoxic effects are known to arise from the β1-AR subtype, and use of β-AR blockers is a cornerstone of current heart failure therapy. However, cardioprotective effects arise from the β2-AR subtype that counteract hyperactive β1-AR signaling, but unfortunately, β2-AR cardioprotective signaling in heart failure is inhibited by β-AR blocker therapy. In contrast to current dogma, recent research shows β1-AR signaling can also be cardioprotective. Moreover, for some forms of heart failure, β2-AR signaling is cardiotoxic. Thus for both β-AR subtypes, there is a balance between cardiotoxic versus cardioprotective effects. In heart failure, stimulation of α1-ARs is widely thought to be cardiotoxic. However, also contrary to current dogma, recent research shows that α1-AR signaling is cardioprotective. Taken together, recent research identifies cardioprotective signaling arising from β1-AR, β2-AR, and α1-ARs. A goal for future therapies will to harness the protective effects of AR signaling while minimizing cardiotoxic effects. The trajectory of heart failure therapy changed radically from the previous and intuitive use of sympathetic A. J. Baker (*) Veterans Affairs Medical Center, San Francisco and Department of Medicine, University of California, Cardiology Division (111C), 4150 Clement St, San Francisco, CA 94121, USA e-mail: [email protected]

agonists, which unfortunately resulted in greater mortality, to the current use of β-AR blockers, which initially seemed counterintuitive. As a cautionary note, if the slow adoption of beta-blocker therapy in heart failure is any guide, then new treatment strategies, especially counterintuitive therapies involving stimulating β-AR and α1-AR signaling, may take considerable time to develop and gain acceptance. Keywords Sympathetic . Adrenergic receptor . Heat failure . Catecholamine . Beta-blocker . Cardiac denervation . G protein . Beta-arrestin . Inotropic . Calcium . Myofilament . Contraction

Heart failure—the neuroendocrine model Heart failure has been defined as a complex clinical syndrome that can result from any structural or functional cardiac disorder that impairs the ability of the ventricle to fill with or eject blood [49]. Heart failure is a serious condition with a 50 % mortality within 5 years after diagnosis [91]. The prevalence of heart failure ranges from 1–12 % based on data from the US and Europe [91]. Heart failure is predominantly a condition of the elderly, with an incidence approximately doubling during each decade of life after the age of 55 years [56]. Heart failure is a clinical syndrome with multiple etiologies such as an acute event (myocardial infarction) or a chronic condition (e.g., heritable or chronic forms of cardiomyopathy). The resulting decline in cardiac output prompts multiple neuroendocrine compensatory mechanisms to preserve cardiac output. These include activation of the sympathetic nervous system (SNS) and the hormones renin, angiotensin, and aldosterone (Fig. 1). In this review, the term “heart failure” is applied to the historically most prevalent form of heart failure with reduced left ventricular (LV) ejection fraction (HFrEF). However, another class of heart failure with preserved LV ejection

Pflugers Arch - Eur J Physiol Fig. 1 Pathogenesis of heart failure. Cardiac injury produces a decline in pump function. Compensatory mechanisms are activated including activation of the sympathetic nervous system (SNS) and the renin, angiotensin, and aldosterone systems. Acutely, these mechanisms stabilize pump function. However, chronic SNS activation is toxic and leads to myocardial damage and worsening of pump function. This viscous cycle leads to cardiac decompensation and symptomatic heart failure

injury

cardiac output

further injury

vicious cycle

Force Frequency Relaxation

Acute improvement

chronic SNS activation

Apoptosis Hypertrophy Arrhythmia

fraction (HFpEF) has been growing in prevalence over the past two decades [60], such that HFpEF now accounts for approximately half of all heart failure patients [59, 91]. HFpEF is reviewed by Gladden et. al. in this series [41]. In heart failure patients with reduced LV ejection fraction, a decline in pump function prompts increased SNS activation to bolster cardiac function. Increased SNS activation is compensatory in the short term, but chronic SNS activation eventually becomes toxic and actually contributes to further deterioration of cardiac function in the later stages of heart failure (Fig. 1). In summary, toxic effects due to SNS hyperactivation in heart failure have been a foundation of thinking in the field for the last 30 years [67, 68, 106]. This review will focus on newly emerging data showing both cardiotoxic and cardioprotective effects of SNS activation in heart failure. A challenge for future therapies of heart failure will be to harness the protective effects while minimizing the toxic effects.

Sympathetic nervous system (SNS) in heart failure: a balance of hyperactivation and downregulation The SNS is a potent stimulator of cardiac performance. For example, during exercise, activation of the SNS can increase cardiac output fivefold in a matter of seconds [110]. SNS activation augments cardiac output by causing acceleration of heart rate, increased cardiac contractility, and faster cardiac relaxation, along with decreased venous capacitance and constriction of resistance and cutaneous vessels. Sympathetic nerves increase cardiac output by releasing the catecholamine norepinephrine (NE) from cardiac nerve terminals. Sympathetic hyperactivation in HF is evidenced by increased central sympathetic outflow, spillover of NE to the plasma from activated sympathetic nerve fibers, and increased plasma NE levels [86]. In HF patients, spillover of NE from the heart to the circulation is increased five to sixfold 1

Acute SNS activation

compared to healthy controls, as assessed using tritiated NE infusion techniques [44, 75]. Consistent with this, the plasma NE level in HF patients is elevated up to fivefold and is increased in direct proportion to the degree of LV dysfunction [103]. Importantly, elevated plasma NE levels are significant predictors of mortality among patients with moderate to severe congestive heart failure [25]. Paradoxically, in heart failure, there is also evidence suggesting significant SNS downregulation at multiple levels downstream from NE release. For heart failure patients, it has long been known that there is marked depletion of cardiac abundance of NE, with a reduction of NE level in heart failure to approximately 30 % of nonfailing controls [21, 22]. In experimental heart failure models, the density of sympathetic nerve endings is markedly reduced, and the reduction is quantitatively similar to the large decrease in cardiac NE level [47, 58, 61]. The majority of NE in the heart is located in intraneuronal storage vesicles. Thus, the similar reductions in both NE content and density of sympathetic nerve endings in heart failure suggest that cardiac denervation is a major factor contributing to the decreased NE content of the failing heart [58]. Furthermore, impaired neuronal reuptake of NE via the NE transporter, which exhibits reduced abundance/activity in heart failure, may also contribute to the decreased NE content in this syndrome [47, 58, 61]. Noninvasive imaging of cardiac NE abundance and NE release kinetics in human heart failure is possible using the radioiodinated analog of NE metaiodobenzylguanidine (mIBG). The neuronal uptake and release characteristics of mIBG are similar to NE (reviewed in [18]). Thus, mIBG allows imaging of sympathetic nerve function. Clinical studies using mIBG suggest that heart failure patients have low cardiac mIBG levels and enhanced mIBG release kinetics compared to nonfailing controls. These findings are consistent with the biochemical studies described above showing low cardiac NE levels and increased NE spillover in heart failure.

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Importantly, low cardiac mIBG abundance (as a measure of low cardiac NE levels), is an independent predictor of adverse clinical outcomes, including mortality in patients with heart failure [51]. Low cardiac levels of mIBG are thought to reflect decreased nerve density; furthermore, decreased density/ activity of the NE transporter may also play a role. Thus, partial sympathetic denervation and impaired NE storage occur in heart failure, and could even be involved in the pathogenesis of this disorder. The postsynaptic abundance of β-adrenergic receptors (ARs) is decreased in heart failure patients by approximately 50 % [12, 13, 108]. Moreover, compared to healthy controls, for myocardium from heart failure patients, the content of cAMP (a key downstream β-AR signaling molecule) is similar [8] or even reduced [89]. In summary, these findings create a complex picture of both feast and famine coexisting in heart failure with respect to the sympatho-adrenergic state. The failing heart manifests a hyperadrenergic state with respect to sympathetic nerve activity, NE release and NE spillover. However, these changes are effectively countered by decreased nerve terminal density, decreased NE storage, and downregulation of β-AR receptor abundance and signaling, such that cardiac myocyte cAMP levels are normalized. Thus, the adrenergic state of the failing heart is difficult to define because both hyperadrenergic and hypoadrenergic components coexist. For the failing heart, the hyperadrenergic state is thought to be cardiotoxic (see below). However, the role of hypoadrenergic mechanisms in the pathophysiology of heart failure is less clear.

Cardiac adrenergic receptors Modulation of cardiac function by the sympathetic nervous system is mediated by cardiac adrenergic receptors (ARs) that are responsive to the endogenous adrenergic catecholamines epinephrine (or adrenaline) and norepinephrine (or noradrenaline). Norepinephrine (NE) released from cardiac sympathetic

nerves is the primary signaling molecule for cardiac ARs. Epinephrine released from the adrenal gland into the circulation plays a minor role in stimulating cardiac ARs [11]. The family of adrenergic receptors (ARs) has been defined [16] and divided into two subfamilies based on pharmacological properties: α-ARs and β-ARs [2] (Fig. 2). In the human heart, β-ARs represent about 90 % of ARs and α1-ARs about 10 %. α-ARs are further subdivided based on anatomic location and pharmacological properties into α1-ARs and α2-ARs [63]. Of the α-ARs, α1-ARs are by far the most abundant in the heart and are located in cardiac myocytes and in the coronary vasculature; α2-ARs are of much lower abundance and are located within the coronary microvasculature [46, 55] and on nerve terminals to mediate presynaptic inhibition of noradrenaline release [16]. For α1-ARs, α2-ARs, and β-ARs, three distinct subtypes exist (see Fig. 2). It is generally believed that ARs are localized to the plasma membrane. However, recent studies challenge this assumption by demonstrating that a fraction of β-ARs [9, 109] and perhaps all α1-ARs [48, 120, 121] localize to and can signal at the nucleus in cardiac myocytes [80].

Adrenergic receptor signaling Cardiac ARs are G protein-coupled receptors (GPCRs). Receptor activation results from an adrenergic agonist-induced conformational switch [97] that facilitates the association of the receptor with cognate heterotrimer G proteins on the inner surface of the plasma membrane. This interaction accelerates the exchange of GTP for GDP on the nucleotide-binding site of the G protein α-subunit. GTP binding to leads to dissociation of the GTP-α-subunit from the βγ-dimer, resulting in effector activation [90]. While receptor specificity appears to be primarily conferred by the nature of the G protein α-subunit, both the αsubunit and the βγ-dimer contribute to activation of specific effectors. The classical biochemical effects of Gi, Gs, and Gq

Fig. 2 The family of adrenergic receptors (ARs) and the major AR subtypes (based on [16])

Adrenergic Receptors

α

α1

α1A α1B α1D

β

α2

α2A α2B

α2C

β1

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are to inhibit adenylyl cyclase, activate adenylyl cyclase, and stimulate phospholipase C, respectively. These effects are largely due to the activated α-subunits of these G proteins. In addition to classical G protein signaling, GPCRs can activate G protein-independent signaling via two β-arrestin isoforms [57, 84, 117], which were originally known for their roles in the desensitization and internalization of GPCRs in response to sustained agonist stimulation. Moreover, a significant advance in understanding of the complexity of GPRC signaling was the discovery of biased ligand signaling, where only a subset of potential signaling pathways for a particular GPCR are activated or blocked by a biased ligand [111]. For example, carvedilol, a β-AR antagonist used extensively to treat cardiovascular disease, is a biased ligand that both inhibits β-AR G protein signaling and activates β-arrestin-mediated cardioprotective EGFRERK signaling [57, 77, 84]. Cardioprotective biased ligand signaling mediated by carvedilol may contribute to the finding that carvedilol has superior clinical efficacy compared to other β-AR blockers that are not biased ligands and inhibit β-AR G protein signaling without activating β-arrestinmediated cardioprotective signaling [32]. Development of novel biased ligands to selectively activate or inhibit a subset of GPCR signaling may be promising therapeutic strategy to treat cardiovascular disease [32].

binding protein C [52], which increases crossbridge kinetics [100] and titin [62, 125], which reduces sarcomeric passive stiffness and thus may improve diastolic ventricular filling. In addition, β-ARs activate an exchange protein directly activated by cAMP (Epac) independently of PKA [10]. The Epac1 isoform, which is the main isoform expressed in human heart, is increased in heart failure and contributes to β-ARmediated myocyte hypertrophy [71]. Moreover, β1-ARs also activate a second isoform, Epac2, resulting in CaMKIIdependent sarcoplasmic reticulum Ca2+ leak and arrhythmia [87]. Despite these cardiotoxic effects, Epac may also promote survival signaling in heart failure (see below) [128].

Cardiac β-AR signaling in heart failure—toxic and protective effects (Fig. 3)

Acute stimulation of β-ARs augments cardiac contraction. In contrast, chronic β-AR signaling in heart failure is cardiotoxic. Previous heart failure therapies based on inotropic stimulation via β-ARs found that sustained β-AR stimulation is toxic [64], as exemplified by the greater mortality of heart failure patients treated with dobutamine [39, 81]. Toxic effects

NE

Cardiac β-AR signaling and inotropic responses Activation of β-ARs is the most powerful mechanism to acutely increase cardiac performance. For example, the normal heart is able to rapidly increase its output nearly fivefold, primarily by the SNS acting on β-ARs to cause increases of heart rate, myocardial contractility, and faster relaxation [110]. In the human heart, β-ARs are composed predominantly of β1-ARs and β2-ARs in a ratio of approximately 80:20 [13, 15]. β1-ARs and β2-ARs couple to the Gs signaling pathway to mediate a powerful positive inotropic response. However, with sustained activation, coupling of the β2-AR switches from Gs to Gi which opposes the positive inotropic effect [28, 123]. In the human heart, β-ARs mediate robust positive inotropic responses by activating the classical signaling cascade involving activation of Gs proteins, leading to stimulation of adenylyl cyclase, which catalyzes the formation of cAMP from ATP, resulting in cAMP-dependent activation of protein kinase A (PKA), and PKA-dependent protein phosphorylation of key Ca2+ handling proteins and myofilament proteins [122, 124]. These include L-type Ca2+ channels and ryanodine receptors, which increases Ca2+ entry into the cytosol; phospholamban, which accelerates Ca2+ removal from the cytosol; troponin I, which reduces myofilament Ca2+ sensitivity and thus accelerates relaxation of the myofilaments [124]; myosin1

β1-AR

Plasma membrane

cAMP

PKA

Epac

Ca2+ ERK CAMKII

Death

Survival

Fig. 3 Cardiotoxic and cardioprotective signaling by β1-ARs. NE stimulation of β1-ARs results in increased cAMP levels. Increased cAMP stimulates cardiotoxic signaling via PKA, which results in Ca2+ influx to the cell by L-type calcium channels, activation of Ca2+/calmodulin-dependent kinase II (CaMKII) which leads to sarcoplasmic reticulum Ca2+ overload and cell death. In contrast, increased cAMP also stimulates cardioprotective signaling involving exchange protein directly activated by cAMP (Epac) and ERK (extracellular signal-related kinases)

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of sustained β-AR stimulation are consistent with the finding that in heart failure patients, elevated plasma NE levels correlated with the degree of LV dysfunction and mortality [25, 103]. Animal models revealed that excessive β-AR stimulation caused myocardial contraction bands and myocardial necrosis [104, 105]. Mechanistically, chronic β-AR stimulation with NE caused cardiac cell death due to cellular Ca2+ overload [27, 69]. Conversely, β-AR blockers improve cardiac function and decrease mortality in patients with chronic heart failure [83, 113]. This finding is also consistent with the observed toxicity of chronic β-AR activation in heart failure. In heart failure, the abundance of cardiac β-ARs is decreased by 50 % [12, 13, 108]. Moreover, β-ARs become desensitized to chronic catecholamine stimulation [12, 45]. These changes may be adaptive responses to lessen the toxic effects of chronic β-AR signaling. The toxic effects from β-AR activation in heart failure appear to arise from the β1-AR subtype. Overexpression of human β1-ARs in mice causes early hypertrophy and interstitial fibrosis followed by marked cardiac dysfunction [6, 36]. Consistent with this, β1-AR selective antagonism (but not β2AR antagonism) effectively inhibits NE-induced apoptosis in adult rat ventricular myocytes [127]. β1-ARs mediate proapoptotic signaling by activation of PKA and calcium/ calmodulin-dependent protein kinase [128], although the role of PKA in apoptosis is still controversial [118, 129]. A mouse model lacking β1-ARs [92] is an ideal tool for a more definitive determination of the toxic role of β1-ARs in heart failure. Surprisingly, few studies have used this model in the context of heart failure. With heart failure induced by myocardial infarction, the relative decline in fractional shortening was less in β1-AR knockout failing hearts compared to wild-type failing hearts, consistent with a toxic effect of β1ARs in wild-type failing hearts [126]. However, this study also noted that prior to the infarct, the β1-AR knockout hearts had lower fractional shortening than wild type. Moreover, after the infarct, the fractional shortening was similar in failing hearts from β1-AR knockout versus wild-type mice [126]. Thus, the observed smaller decline in fractional shortening in the β1-AR knockout failing hearts is qualified by being dependent on the β1-AR knockout hearts having lower fractional shortening prior to the infarct [126]. In marked contrast, in a genetic, nonischemic cardiomyopathy model, the muscle LIM protein knockout mouse, knockout of β1-ARs resulted in a drastically more severe phenotype, suggesting that in this cardiomyopathy model, β1-ARs have a major positive effect on survival and function [37]. Thus, whether chronic β1-AR signaling has a toxic or protective effect depends on the underlying disease [37]. Additional support for a cardioprotective role of chronic β1-AR signaling comes from recent studies by Zhang et. al. [128]. By inhibiting β1-AR/PKA signaling, these authors found that β1-AR/Epac signaling is cardioprotective

(Fig. 3). Importantly, in a mouse myocardial infarction model, PKA inhibition was more effective than a β-AR blocker for preserving cardiac function. This suggests that targeted inhibition of the PKA death-signaling pathway, while preserving the Epac survival-signaling pathway, is a superior therapy than ablating both β-AR signaling pathways using a β-AR blocker [128]. In failing human hearts, β1-ARs are downregulated by up to 50 %, but the abundance of β2-AR remains unchanged; accordingly, the ratio of β1-:β2-ARs changes from ≈80:20 in nonfailing hearts to ≈60:40 in failing hearts [13, 53]. As a result, in the failing human heart, the responses of β2-ARs to nonselective β-AR stimulation become relatively more important. Numerous studies indicate a cardioprotective role for β2ARs in heart failure. In mice lacking β2-ARs, chronic stimulation with the β-AR agonist isoproterenol results in enhanced myocyte apoptosis and increased mortality compared with wild-type mice treated with isoproterenol [85]. In isolated myocytes, β2-AR stimulation protects against stress-induced apoptosis [20, 127]. In a rat model of myocardial infarctioninduced heart failure, selective activation with a β2-AR agonist improves cardiac performance and reduces apoptosis [3]. In heart failure, there is enhanced signaling of β2-ARs via the inhibitory G protein Gi, which attenuates the positive inotropi c effec ts o f β 1-AR stim ulat ion a nd activates cardioprotective signaling pathways [7, 20, 38, 130]. In contrast to these well established protective effects mediated by β2-ARs, recent studies suggest that chronic β2-AR signaling in heart failure can be cardiotoxic [37]. In both a genetic MLP knockout cardiomyopathy model and a transaortic constriction pressure-overload model, knockout of β2-ARs resulted in an improved phenotype compared to mice expressing β2-ARs. These findings suggest that in wildtype mice, β2-ARs mediate toxic effects in these heart failure models [37]. In summary, in heart failure, chronic β1-AR signaling is thought to be cardiotoxic and chronic β2-AR signaling cardioprotective. However, for both β-AR subtypes, the balance between toxic versus protective effects depends on the underlying disease and/or the specific model used to study βAR effects [37].

Cardiac α1-AR signaling and inotropic responses α1-ARs are found in vascular beds throughout the body where they function to increase vascular smooth muscle contractility and hence blood pressure. α1-ARs are also found in the heart. In human heart, α1-ARs are of lower abundance (10 %) than β-ARs [16, 53]. For human myocardium, acute α1-AR stimulation in vitro elicits a positive inotropic response that is 15–35 % of that produced by β-AR stimulation

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[16]. There are three distinct subtypes of α1-ARs (α1A-AR, α1B-AR, and α1D-AR) [23] with about 60 % α1B-AR and 40 % α1A-AR in human [53, 54] and similar levels in mouse heart [79, 93]. Studies in α1-AR knockout mice demonstrate that cardiac myocytes express only the α1A and α1B subtypes, based on lack of functional responses in hearts from α1AB-double knockout mice [70, 107]. The α1D-AR subtype is not expressed on cardiac myocytes in mouse [79] or human heart [53, 54], but is expressed in coronary artery smooth muscle cells [53, 54] and mediates vasoconstriction based a report of α1-AR-mediated reduction in coronary flow in isolated α1-AR knockout hearts [107]. The function of α1-ARs is less well studied compared to βARs. In contrast to β-ARs, the inotropic response to α1-AR stimulation has remained uncertain because it has varied considerably among studies and might be influenced by experimental conditions, vary among species [99] and even differ between the right ventricle versus left ventricle [115]. The inotropic response mediated by α1-ARs tends to develop slowly over many minutes, unlike the rapid onset response to β-ARs. Moreover, the inotropic response tends to be multiphasic, with an early negative inotropic phase followed by a later positive inotropic phase [4, 115]. These characteristics seem more suitable for fine tuning of cardiac contractility, as opposed to the rapid “flight or fight” augmentation of contractility that is typically ascribed to β-AR stimulation. Previous studies suggest that the three cardiac α1-AR subtypes mediate different inotropic responses, with the α1A-AR subtype linked with positive inotropy [66], the α1B-AR subtype linked with negative inotropy [43, 95], and the α1D-AR subtype linked with vasoconstriction [107]. In rat myocardium, there is evidence of functional antagonism between receptor subtypes: stimulation of α1A-ARs causes increases of contractions, Ca2+ transients, myofilament response to Ca2+, and intracellular pH [40]; however, α1B-AR stimulation decreases contractions, Ca2+ transients, and pH [40]. Consistent with this, inactivation of the α1B-AR subtype potentiates the effect of α1A-AR agonists in rat neonatal myocytes [31]. Stimulation of α1-ARs activates the guanine nucleotidebinding protein Gq which stimulates the hydrolysis of phosphatidylinositol 4,5 bisphosphate by phospholipase C (PLC) to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) [17, 82, 88]. DAG then stimulates protein kinase C (PKC) [101] which mediates a variety of effects in the heart, including potentiation of L-type Ca2+ channel currents [119], Na+/Ca2+ exchange [50, 76], and phosphorylation of the contractile proteins [73, 74]. IP3 binds to the IP3 receptor to release Ca2+ from intracellular stores. Interestingly, recent studies suggest that α1-ARs are not localized to the plasma membrane but instead localize to and signal at the nucleus in cardiac myocytes [48, 120, 121] (Fig. 4). This new α1-AR signaling paradigm was recently 1

reviewed in detail [80]. Recent experiments identify nuclear localization protein sequences in the α1A and α1B subtypes, and mutation of these sequences results in loss of nuclear localization for each subtype in adult mouse cardiac myocytes [121]. Moreover, the α1-AR signaling molecules Gαq and PLCβ1 are detected in nuclei isolated by biochemical fractionation of adult mouse cardiac myocytes [120]. Signaling molecules downstream of PLCβ1 are also present at the nucleus in adult cardiac myocytes including the type II IP3 receptor, the subtype predominantly expressed in myocytes [5], and PKCs α, δ, and ε, the subtypes activated by α1-ARs. Finally, in order for NE to access the nucleus, the NE transporter EMT/OCT3 (extraneuronal monoamine transporter/ organic cation transporter 3) is expressed on both the plasma and nuclear membranes in adult cardiac myocytes [120]. Figure 4 shows a schematic of this novel “inside-out” nuclear α1-AR signaling hypothesis [80]. In this model, the fact that extracellular agonist does not get direct access to α1ARs, but must first be imported into the cell, may contribute to the relatively slow onset of the contractile response mediated by α1-ARs. Recent studies have identified nuclear α1-AR-mediated activation of PKC isoforms in isolated nuclei (O’Connell, TD. Personal communication). Furthermore, as the majority of α1-ARs (≥80 %) localize to the nucleus [120], and α1-ARs do influence transcription, it is likely that α1-AR nuclear transcriptional regulation occurs. These concepts are consistent with studies demonstrating that a fraction of β-ARs also localize to the nucleus and mediate β-AR nuclear signaling and nuclear transcriptional regulation [9, 109].

Cardiac α1-AR signaling in heart failure—toxic and protective effects In heart failure, β1-ARs are downregulated; in contrast, α1AR levels are not decreased [16]. Consequently, α1-ARs which normally represent ≈10 % of all ARs are increased to ≈25 % of ARs in heart failure [80]. Thus, α1-ARs may play a relatively greater role in heart failure. Indeed, α1-ARmediated inotropy can equal β-AR-mediated inotropy in trabeculae isolated from failing human hearts [98]. It is generally believed that α1-ARs, along with all Gqcoupled GPCRs that signal through Gαq, such as endothelin receptors and angiotensin receptors play a pathogenic role in heart failure. Hallmarks of cardiomyopathy with heart failure include contractile dysfunction, myocyte hypertrophy, fibrosis, and increased cardiac cell death, which can all be worsened by Gq-coupled receptors [96]. Consistent with this, expression of a constitutively active mutant α1B-AR resulted in hypertrophy and worsened cardiomyopathy after pressure overload [72, 114]. Long-term expression of α1A-ARs and α1B-ARs led to pathological remodeling [19, 65].

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Fig. 4 Schematic of “inside-out” nuclear α1-AR signaling hypothesis [80]. In adult cardiac myocytes, catecholamine α1-AR agonists (e.g., NE) are actively transported into the myocyte via organic cation transporter 3 (OCT). This model suggests that active α1-ARs localize to the inner nuclear membrane with the ligand-binding domain facing the space between the outer and inner nuclear membranes. On the basis of this orientation, binding of agonist to α1-ARs induces signaling inside the

nucleus, possibly through Gαq, although downstream intranuclear signaling pathways remain to be defined. The model proposes that activation of nuclear α1-ARs can induce intranuclear hypertrophic signaling as well as extranuclear signaling, including activation of ERK in caveolae and survival signaling or phosphorylation of cardiac troponin I (cTnI) at the sarcomere and contractile function. PTP mitochondrial permeability transition pore. Figure generously provided by Timothy D. O’Connell

In contrast, there is also evidence that α1-AR signaling has cardioprotective effects. α1A-AR overexpression enhances contractility without causing hypertrophy [66], protects against pressure-overload-induced dysfunction [34], limits post-infarct cardiomyopathy [35], and protects against ischemic injury [94]. Consistent with α1-ARs having a protective effect, knockout of α1-ARs prevents normal cardiac growth [79] and worsens cardiomyopathy after pressure overload [78]. As noted above, in trabeculae isolated from failing human hearts, α1-AR-mediated inotropy can equal β-AR-mediated inotropy [98]. Moreover, in right ventricular failure, the failing RV has increased α1-AR inotropic responses, which is not observed in failing LV myocardium [116]. Data from human clinical trials also suggest a cardioprotective effect mediated by α1-ARs. A massive clinical trial (ALLHAT) of an α1-AR antagonist was stopped prematurely because of an increase in heart failure in the α1AR antagonist-treated group [1]. These findings suggest that a higher level of α1-AR activation is cardioprotective in heart failure. A small clinical trial (VHeFT) ound that

vasodilator treatment improved mortality in heart failure patients, with the notable exception of the α1-AR antagonist prazosin as the only vasodilator that failed to show any positive outcome [24]. This finding again suggests that α1-AR blockade is harmful to the heart and therefore that α1-AR activation is beneficial. Several clinical trials based on reducing catecholamine levels using sympatholytic agents (MOXSE, MOXCON, and BEST) found sympatholytic therapy increased mortality or adverse events in heart failure patients [14, 26, 102]. The failure of these trials suggests that some catecholamine signaling is beneficial in heart failure. Although the mechanism whereby sympatholysis leads to increased mortality is uncertain, it is possible that decreasing catecholamine levels eliminates the cardioprotective effects of α1-AR signaling [80]. In summary, in heart failure, chronic α1-AR signaling is widely thought to be cardiotoxic. In contrast, experimental and clinical evidence suggest that α1-AR signaling can be protective in heart failure. Thus, α1-ARs may represent novel targets for development of new heart failure therapies.

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Exceptions to the conventional models of heart failure As noted earlier, this review of adrenergic signaling in heart failure applies to heart failure with reduced left ventricular ejection fraction (HFrEF). However, approximately half of current heart failure patients have heart failure with preserved ejection fraction (HFpEF) with functional impairment arising from increased myocardial stiffness and impaired diastolic filling [59, 91]. Moreover, conventional heart failure therapies for HFrEF, including reducing β-AR signaling, are not effective for patients HFpEF [60]. Thus, the disease mechanisms in HFpEF are distinctly different from HFrEF and therefore treatment of HFpEF will require fundamentally different therapeutic strategies. HFpEF is reviewed by Gladden et. al. in this series [41]. Failure of the right ventricle (RV) is a common and serious clinical problem [42]. For example, the presence of RV failure in patients with LV failure causes markedly worse symptoms and a markedly worse prognosis (>50 % mortality at one year) compared to patients with LV failure without RV dysfunction [29, 33]. Moreover, RV failure is the leading cause of death in patients with pulmonary hypertension [112]. Despite clinical significance, RV failure is relatively understudied and poorly understood [112]. It has been assumed that an understanding of RV failure can be extrapolated from studies of LV failure [112]. However, our previous studies suggest that the LV and RV are categorically different. We found that the RV vs. LV have fundamentally different inotropic responses to α1-AR stimulation [115]. Moreover, the failing RV has increased α1-AR inotropic responses, which are not observed in failing LV myocardium [116]. Therapies for the failing RV may need to be tailored to the distinctive RV physiology. Right heart failure is reviewed by de Man in this series [30]. In summary, no single model of heart failure can encompass the many diseases that make up this clinical syndrome. Understanding of adrenergic signaling in the context of HFrEF has accompanied development of therapies which have major benefits on function and survival. For other forms of heart failure, there are challenges to understand their pathophysiological basis and to develop appropriate therapies.

Conclusion Understanding of the role of adrenergic signaling in heart failure has steadily accumulated over many decades. Treatments for heart failure have also evolved from an era in which inotropic adrenergic agents were used and eventually recognized to be toxic, to an era in which anti-adrenergic agents were found to be effective. This sea change in treatment strategies took a long time to be accepted and fully adopted. Indeed, use of an anti-adrenergic therapy in patients with 1

reduced ejection fraction, initially appeared counterintuitive. Recent research suggests that new therapeutic strategies may become available, that may also seem at first counterintuitive. Among these are harnessing the cardioprotective effects of βAR and α1-AR signaling, while avoiding their cardiotoxic effects. If the slow adoption of use of beta-blockers is any guide, new treatment strategies will take considerable time to develop and gain acceptance. Acknowledgements Supported by a VA Merit Award and a grant-inaid from the American Heart Association, Western States Affiliate. Figure 4 generously provided by Timothy D. O’Connell, University of Minnesota. Helpful discussion of the manuscript with Drs. Paul C. Simpson and Joel S. Karliner is gratefully acknowledged.

References 1. ALLHAT Collaborative Research Group (2000) Major cardiovascular events in hypertensive patients randomized to doxazosin vs chlorthalidone: the antihypertensive and lipid-lowering treatment to prevent heart attack trial (ALLHAT). JAMA 283:1967–75 2. Ahlquist RP (1948) A study of the adrenotropic receptors. Am J Physiol 153:586–600 3. Ahmet I, Krawczyk M, Heller P, Moon C, Lakatta EG, Talan MI (2004) Beneficial effects of chronic pharmacological manipulation of beta-adrenoreceptor subtype signaling in rodent dilated ischemic cardiomyopathy. Circulation 110:1083–1090 4. Andersen GG, Qvigstad E, Schiander I, Aass H, Osnes JB, Skomedal T (2002) Alpha(1)-AR-induced positive inotropic response in heart is dependent on myosin light chain phosphorylation. Am J Physiol Heart Circ Physiol 283:H1471–H1480 5. Bare DJ, Kettlun CS, Liang M, Bers DM, Mignery GA (2005) Cardiac type 2 inositol 1,4,5-trisphosphate receptor: interaction and modulation by calcium/calmodulin-dependent protein kinase II. J Biol Chem 280:15912–15920 6. Bisognano JD, Weinberger HD, Bohlmeyer TJ, Pende A, Raynolds MV, Sastravaha A, Roden R, Asano K, Blaxall BC, Wu SC, Communal C, Singh K, Colucci W, Bristow MR, Port DJ (2000) Myocardial-directed overexpression of the human beta(1)-adrenergic receptor in transgenic mice. J Mol Cell Cardiol 32:817–830 7. Bohm M, Eschenhagen T, Gierschik P, Larisch K, Lensche H, Mende U, Schmitz W, Schnabel P, Scholz H, Steinfath M et al (1994) Radioimmunochemical quantification of Gi alpha in right and left ventricles from patients with ischaemic and dilated cardiomyopathy and predominant left ventricular failure. J Mol Cell Cardiol 26:133–149 8. Bohm M, Reiger B, Schwinger RH, Erdmann E (1994) cAMP concentrations, cAMP dependent protein kinase activity, and phospholamban in non-failing and failing myocardium. Cardiovasc Res 28:1713–1719 9. Boivin B, Lavoie C, Vaniotis G, Baragli A, Villeneuve LR, Ethier N, Trieu P, Allen BG, Hebert TE (2006) Functional beta-adrenergic receptor signalling on nuclear membranes in adult rat and mouse ventricular cardiomyocytes. Cardiovasc Res 71:69–78 10. Bos JL (2006) Epac proteins: multi-purpose cAMP targets. Trends Biochem Sci 31:680–686 11. Bristow MR, Feldman AM, Adams KF Jr, Goldstein S (2003) Selective versus nonselective beta-blockade for heart failure therapy: are there lessons to be learned from the COMET trial? J Card Fail 9:444–453

Pflugers Arch - Eur J Physiol 12. Bristow MR, Ginsburg R, Minobe W, Cubicciotti RS, Sageman WS, Lurie K, Billingham ME, Harrison DC, Stinson EB (1982) Decreased catecholamine sensitivity and beta-adrenergic-receptor density in failing human hearts. N Engl J Med 307:205–211 13. Bristow MR, Ginsburg R, Umans V, Fowler M, Minobe W, Rasmussen R, Zera P, Menlove R, Shah P, Jamieson S et al (1986) Beta 1- and beta 2-adrenergic-receptor subpopulations in nonfailing and failing human ventricular myocardium: coupling of both receptor subtypes to muscle contraction and selective beta 1-receptor down-regulation in heart failure. Circ Res 59: 297–309 14. Bristow MR, Krause-Steinrauf H, Nuzzo R, Liang CS, Lindenfeld J, Lowes BD, Hattler B, Abraham WT, Olson L, Krueger S, Thaneemit-Chen S, Hare JM, Loeb HS, Domanski MJ, Eichhorn EJ, Zelis R, Lavori P (2004) Effect of baseline or changes in adrenergic activity on clinical outcomes in the beta-blocker evaluation of survival trial. Circulation 110:1437–1442 15. Brodde OE (1991) Beta 1- and beta 2-adrenoceptors in the human heart: properties, function, and alterations in chronic heart failure. Pharmacol Rev 43:203–242 16. Brodde OE, Michel MC (1999) Adrenergic and muscarinic receptors in the human heart. Pharmacol Rev 51:651–690 17. Brown JH, Buxton IL, Brunton LL (1985) Alpha 1-adrenergic and muscarinic cholinergic stimulation of phosphoinositide hydrolysis in adult rat cardiomyocytes. Circ Res 57:532–537 18. Carrio I, Cowie MR, Yamazaki J, Udelson J, Camici PG (2010) Cardiac sympathetic imaging with mIBG in heart failure. JACC Cardiovasc Imaging 3:92–100 19. Chaulet H, Lin F, Guo J, Owens WA, Michalicek J, Kesteven SH, Guan Z, Prall OW, Mearns BM, Feneley MP, Steinberg SF, Graham RM (2006) Sustained augmentation of cardiac alpha1A-adrenergic drive results in pathological remodeling with contractile dysfunction, progressive fibrosis and reactivation of matricellular protein genes. J Mol Cell Cardiol 40:540–552 20. Chesley A, Lundberg MS, Asai T, Xiao RP, Ohtani S, Lakatta EG, Crow MT (2000) The beta(2)-adrenergic receptor delivers an antiapoptotic signal to cardiac myocytes through G(i)-dependent coupling to phosphatidylinositol 3′-kinase. Circ Res 87: 1172–1179 21. Chidsey CA, Braunwald E, Morrow AG (1965) Catecholamine excretion and cardiac stores of norepinephrine in congestive heart failure. Am J Med 39:442–451 22. Chidsey CA, Braunwald E, Morrow AG, Mason DT (1963) Myocardial norepinephrine concentration in man. Effects of reserpine and of congestive heart failure. N Engl J Med 269:653–658 23. Civantos Calzada B, Aleixandre de Artinano A (2001) Alphaadrenoceptor subtypes. Pharmacol Res 44:195–208 24. Cohn JN (1993) The Vasodilator-Heart Failure Trials (V-HeFT). Mechanistic data from the VA Cooperative Studies. Introduction. Circulation 87:VI1–VI4 25. Cohn JN, Levine TB, Olivari MT, Garberg V, Lura D, Francis GS, Simon AB, Rector T (1984) Plasma norepinephrine as a guide to prognosis in patients with chronic congestive heart failure. N Engl J Med 311:819–823 26. Cohn JN, Pfeffer MA, Rouleau J, Sharpe N, Swedberg K, Straub M, Wiltse C, Wright TJ, Investigators M (2003) Adverse mortality effect of central sympathetic inhibition with sustained-release moxonidine in patients with heart failure (MOXCON). Eur J Heart Fail 5:659–667 27. Communal C, Singh K, Pimentel DR, Colucci WS (1998) Norepinephrine stimulates apoptosis in adult rat ventricular myocytes by activation of the beta-adrenergic pathway. Circulation 98:1329–1334 28. Daaka Y, Luttrell LM, Lefkowitz RJ (1997) Switching of the coupling of the beta2-adrenergic receptor to different G proteins by protein kinase A. Nature 390:88–91

29. de Groote P, Millaire A, Foucher-Hossein C, Nugue O, Marchandise X, Ducloux G, Lablanche JM (1998) Right ventricular ejection fraction is an independent predictor of survival in patients with moderate heart failure. J Am Coll Cardiol 32:948–954 30. de Man F (2014) Right Heart Failure. Pflugers Arch, Eur J Physiol 31. Deng XF, Sculptoreanu A, Mulay S, Peri KG, Li JF, Zheng WH, Chemtob S, Varma DR (1998) Crosstalk between alpha-1A and alpha-1B adrenoceptors in neonatal rat myocardium: implications in cardiac hypertrophy. J Pharmacol Exp Ther 286:489–496 32. DeWire SM, Violin JD (2011) Biased ligands for better cardiovascular drugs: dissecting G-protein-coupled receptor pharmacology. Circ Res 109:205–216 33. Di Salvo TG, Mathier M, Semigran MJ, Dec GW (1995) Preserved right ventricular ejection fraction predicts exercise capacity and survival in advanced heart failure. J Am Coll Cardiol 25:1143–1153 34. Du XJ, Fang L, Gao XM, Kiriazis H, Feng X, Hotchkin E, Finch AM, Chaulet H, Graham RM (2004) Genetic enhancement of ventricular contractility protects against pressure-overload-induced cardiac dysfunction. J Mol Cell Cardiol 37:979–987 35. Du XJ, Gao XM, Kiriazis H, Moore XL, Ming Z, Su Y, Finch AM, Hannan RA, Dart AM, Graham RM (2006) Transgenic alpha1Aadrenergic activation limits post-infarct ventricular remodeling and dysfunction and improves survival. Cardiovasc Res 71:735–743 36. Engelhardt S, Hein L, Wiesmann F, Lohse MJ (1999) Progressive hypertrophy and heart failure in beta1-adrenergic receptor transgenic mice. Proc Natl Acad Sci U S A 96:7059–7064 37. Fajardo G, Zhao M, Urashima T, Farahani S, Hu DQ, Reddy S, Bernstein D (2013) Deletion of the beta2-adrenergic receptor prevents the development of cardiomyopathy in mice. J Mol Cell Cardiol 63:155–164 38. Feldman AM, Cates AE, Veazey WB, Hershberger RE, Bristow MR, Baughman KL, Baumgartner WA, Van Dop C (1988) Increase of the 40,000-mol wt pertussis toxin substrate (G protein) in the failing human heart. J Clin Invest 82:189–197 39. Felker GM, O’Connor CM (2001) Inotropic therapy for heart failure: an evidence-based approach. Am Heart J 142:393–401 40. Gambassi G, Spurgeon HA, Ziman BD, Lakatta EG, Capogrossi MC (1998) Opposing effects of alpha 1-adrenergic receptor subtypes on Ca2+ and pH homeostasis in rat cardiac myocytes. Am J Physiol 274:H1152–H1162 41. Gladden JD, Linke WL, Redfeld M (2014) Diastolic heart failure. Pflugers Arch, Eur J Physiol 42. Greyson CR (2008) Pathophysiology of right ventricular failure. Crit Care Med 36:S57–S65 43. Grupp IL, Lorenz JN, Walsh RA, Boivin GP, Rindt H (1998) Overexpression of alpha1B-adrenergic receptor induces left ventricular dysfunction in the absence of hypertrophy. Am J Physiol 275: H1338–H1350 44. Hasking GJ, Esler MD, Jennings GL, Burton D, Johns JA, Korner PI (1986) Norepinephrine spillover to plasma in patients with congestive heart failure: evidence of increased overall and cardiorenal sympathetic nervous activity. Circulation 73:615–621 45. Hausdorff WP, Caron MG, Lefkowitz RJ (1990) Turning off the signal: desensitization of beta-adrenergic receptor function. FASEB J 4:2881–2889 46. Heusch G, Baumgart D, Camici P, Chilian W, Gregorini L, Hess O, Indolfi C, Rimoldi O (2000) Alpha-adrenergic coronary vasoconstriction and myocardial ischemia in humans. Circulation 101:689– 694 47. Himura Y, Felten SY, Kashiki M, Lewandowski TJ, Delehanty JM, Liang CS (1993) Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure. Circulation 88:1299–1309 48. Huang Y, Wright CD, Merkwan CL, Baye NL, Liang Q, Simpson PC, O’Connell TD (2007) An alpha1A-adrenergic-extracellular

Pflugers Arch - Eur J Physiol signal-regulated kinase survival signaling pathway in cardiac myocytes. Circulation 115:763–772 49. Hunt SA, Abraham WT, Chin MH, Feldman AM, Francis GS, Ganiats TG, Jessup M, Konstam MA, Mancini DM, Michl K, Oates JA, Rahko PS, Silver MA, Stevenson LW, Yancy CW, American College of Cardiology F, American Heart A (2009) 2009 Focused update incorporated into the ACC/AHA 2005 guidelines for the diagnosis and management of heart failure in adults: a report of the American College of Cardiology Foundation/ American Heart Association Task Force on practice guidelines: developed in collaboration with the International Society for Heart and Lung Transplantation. J Am Coll Cardiol 53:e1–e90 50. Iwamoto T, Pan Y, Wakabayashi S, Imagawa T, Yamanaka HI, Shigekawa M (1996) Phosphorylation-dependent regulation of cardiac Na+/Ca2+ exchanger via protein kinase C. J Biol Chem 271: 13609–13615 51. Jacobson AF, Senior R, Cerqueira MD, Wong ND, Thomas GS, Lopez VA, Agostini D, Weiland F, Chandna H, Narula J (2010) Myocardial iodine-123 meta-iodobenzylguanidine imaging and cardiac events in heart failure. Results of the prospective ADMIRE-HF (AdreView myocardial imaging for risk evaluation in heart failure) study. J Am Coll Cardiol 55:2212–2221 52. Jeacocke SA, England PJ (1980) Phosphorylation of a myofibrillar protein of Mr 150 000 in perfused rat heart, and the tentative indentification of this as C-protein. FEBS Lett 122:129–132 53. Jensen BC, Swigart PM, De Marco T, Hoopes C, Simpson PC (2009) {alpha}1-Adrenergic receptor subtypes in nonfailing and failing human myocardium. Circ Heart Fail 2:654–663 54. Jensen B, Swigart PM, Laden M, DeMarco T, Hoopes C, Simpson PC (2009) The alpha-1D is the predominant alpha-1-adrenergic receptor subtype in human epicardial coronary arteries. J Am Coll Cardiol 54:1137–1145 55. Jones CJ, DeFily DV, Patterson JL, Chilian WM (1993) Endothelium-dependent relaxation competes with alpha 1- and alpha 2-adrenergic constriction in the canine epicardial coronary microcirculation. Circulation 87:1264–1274 56. Kannel WB, Belanger AJ (1991) Epidemiology of heart failure. Am Heart J 121:951–957 57. Kim IM, Tilley DG, Chen J, Salazar NC, Whalen EJ, Violin JD, Rockman HA (2008) Beta-blockers alprenolol and carvedilol stimulate beta-arrestin-mediated EGFR transactivation. Proc Natl Acad Sci U S A 105:14555–14560 58. Kimura K, Kanazawa H, Ieda M, Kawaguchi-Manabe H, Miyake Y, Yagi T, Arai T, Sano M, Fukuda K (2010) Norepinephrine-induced nerve growth factor depletion causes cardiac sympathetic denervation in severe heart failure. Auton Neurosci 156:27–35 59. Kitzman DW, Little WC, Brubaker PH, Anderson RT, Hundley WG, Marburger CT, Brosnihan B, Morgan TM, Stewart KP (2002) Pathophysiological characterization of isolated diastolic heart failure in comparison to systolic heart failure. JAMA 288: 2144–2150 60. Konstantinou DM, Chatzizisis YS, Giannoglou GD (2013) Pathophysiology-based novel pharmacotherapy for heart failure with preserved ejection fraction. Pharmacol Ther 140:156–166 61. Kreusser MM, Buss SJ, Krebs J, Kinscherf R, Metz J, Katus HA, Haass M, Backs J (2008) Differential expression of cardiac neurotrophic factors and sympathetic nerve ending abnormalities within the failing heart. J Mol Cell Cardiol 44:380–387 62. Kruger M, Linke WA (2006) Protein kinase-A phosphorylates titin in human heart muscle and reduces myofibrillar passive tension. J Muscle Res Cell Motil 27:435–444 63. Langer SZ (1974) Presynaptic regulation of catecholamine release. Biochem Pharmacol 23:1793–1800 64. Lee GJA, Yan L, Vatner DE, Vatner SF (2013) β-Adrenergic receptor signaling in heart failure cardiac remodeling. Springer, pp. 3-30 1

65. Lemire I, Ducharme A, Tardif JC, Poulin F, Jones LR, Allen BG, Hebert TE, Rindt H (2001) Cardiac-directed overexpression of wild-type alpha1B-adrenergic receptor induces dilated cardiomyopathy. Am J Physiol Heart Circ Physiol 281:H931–H938 66. Lin F, Owens WA, Chen S, Stevens ME, Kesteven S, Arthur JF, Woodcock EA, Feneley MP, Graham RM (2001) Targeted alpha(1A)-adrenergic receptor overexpression induces enhanced cardiac contractility but not hypertrophy. Circ Res 89:343–350 67. Lymperopoulos A, Rengo G, Koch WJ (2013) Adrenergic nervous system in heart failure: pathophysiology and therapy. Circ Res 113: 739–753 68. Mann DL, Bristow MR (2005) Mechanisms and models in heart failure: the biomechanical model and beyond. Circulation 111: 2837–2849 69. Mann DL, Kent RL, Parsons B, Gt C (1992) Adrenergic effects on the biology of the adult mammalian cardiocyte. Circulation 85:790–804 70. McCloskey DT, Turnbull L, Swigart P, O’Connell TD, Simpson PC, Baker AJ (2003) Abnormal myocardial contraction in alpha(1A)and alpha(1B)-adrenoceptor double-knockout mice. J Mol Cell Cardiol 35:1207–1216 71. Metrich M, Lucas A, Gastineau M, Samuel JL, Heymes C, Morel E, Lezoualc’h F (2008) Epac mediates beta-adrenergic receptorinduced cardiomyocyte hypertrophy. Circ Res 102:959–965 72. Milano CA, Dolber PC, Rockman HA, Bond RA, Venable ME, Allen LF, Lefkowitz RJ (1994) Myocardial expression of a constitutively active alpha 1B-adrenergic receptor in transgenic mice induces cardiac hypertrophy. Proc Natl Acad Sci U S A 91: 10109–10113 73. Montgomery DE, Chandra M, Huang Q, Jin J, Solaro RJ (2001) Transgenic incorporation of skeletal TnT into cardiac myofilaments blunts PKC-mediated depression of force. Am J Physiol Heart Circ Physiol 280:H1011–H1018 74. Montgomery DE, Wolska BM, Pyle WG, Roman BB, Dowell JC, Buttrick PM, Koretsky AP, Del Nido P, Solaro RJ (2002) Alphaadrenergic response and myofilament activity in mouse hearts lacking PKC phosphorylation sites on cardiac TnI. Am J Physiol Heart Circ Physiol 282:H2397–H2405 75. Morris MJ, Cox HS, Lambert GW, Kaye DM, Jennings GL, Meredith IT, Esler MD (1997) Region-specific neuropeptide Y overflows at rest and during sympathetic activation in humans. Hypertension 29:137–143 76. Nishimaru K, Kobayashi M, Matsuda T, Tanaka Y, Tanaka H, Shigenobu K (2001) Alpha-adrenoceptor stimulation-mediated negative inotropism and enhanced Na(+)/Ca(2+) exchange in mouse ventricle. Am J Physiol Heart Circ Physiol 280:H132–H141 77. Noma T, Lemaire A, Naga Prasad SV, Barki-Harrington L, Tilley DG, Chen J, Le Corvoisier P, Violin JD, Wei H, Lefkowitz RJ, Rockman HA (2007) Beta-arrestin-mediated beta1-adrenergic receptor transactivation of the EGFR confers cardioprotection. J Clin Invest 117:2445–2458 78. O’Connell TD, Swigart PM, Rodrigo MC, Ishizaka S, Joho S, Turnbull L, Tecott LH, Baker AJ, Foster E, Grossman W, Simpson PC (2006) Alpha(1)-adrenergic receptors prevent a maladaptive cardiac response to pressure overload. J Clin Invest 116: 1005–1015 79. O’Connell TD, Ishizaka S, Nakamura A, Swigart PM, Rodrigo MC, Simpson GL, Cotecchia S, Rokosh DG, Grossman W, Foster E, Simpson PC (2003) The alpha(1A/C)- and alpha(1B)-adrenergic receptors are required for physiological cardiac hypertrophy in the double-knockout mouse. J Clin Invest 111:1783–1791 80. O’Connell TD, Jensen BC, Baker AJ, Simpson PC (2014) Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance. Pharmacol Rev 66:308–333 81. O’Connor CM, Gattis WA, Uretsky BF, Adams KF Jr, McNulty SE, Grossman SH, McKenna WJ, Zannad F, Swedberg K,

Pflugers Arch - Eur J Physiol Gheorghiade M, Califf RM (1999) Continuous intravenous dobutamine is associated with an increased risk of death in patients with advanced heart failure: insights from the Flolan International Randomized Survival Trial (FIRST). Am Heart J 138:78–86 82. Otani H, Das DK (1988) Alpha 1-adrenoceptor-mediated phosphoinositide breakdown and inotropic response in rat left ventricular papillary muscles. Circ Res 62:8–17 83. Packer M, Bristow MR, Cohn JN, Colucci WS, Fowler MB, Gilbert EM, Shusterman NH (1996) The effect of carvedilol on morbidity and mortality in patients with chronic heart failure. U.S. Carvedilol Heart Failure Study Group. N Engl J Med 334:1349–1355 84. Patel CB, Noor N, Rockman HA (2010) Functional selectivity in adrenergic and angiotensin signaling systems. Mol Pharmacol 78: 983–992 85. Patterson AJ, Zhu W, Chow A, Agrawal R, Kosek J, Xiao RP, Kobilka B (2004) Protecting the myocardium: a role for the beta2 adrenergic receptor in the heart. Crit Care Med 32:1041–1048 86. Pepper GS, Lee RW (1999) Sympathetic activation in heart failure and its treatment with beta-blockade. Arch Intern Med 159:225–234 87. Pereira L, Cheng H, Lao DH, Na L, van Oort RJ, Brown JH, Wehrens XH, Chen J, Bers DM (2013) Epac2 mediates cardiac beta1-adrenergic-dependent sarcoplasmic reticulum Ca2+ leak and arrhythmia. Circulation 127:913–922 88. Poggioli J, Sulpice JC, Vassort G (1986) Inositol phosphate production following alpha 1-adrenergic, muscarinic or electrical stimulation in isolated rat heart. FEBS Lett 206:292–298 89. Regitz-Zagrosek V, Hertrampf R, Steffen C, Hildebrandt A, Fleck E (1994) Myocardial cyclic AMP and norepinephrine content in human heart failure. Eur Heart J 15(Suppl D):7–13 90. Rockman HA, Koch WJ, Lefkowitz RJ (2002) Seventransmembrane-spanning receptors and heart function. Nature 415:206–212 91. Roger VL (2013) Epidemiology of heart failure. Circ Res 113:646– 659 92. Rohrer DK, Desai KH, Jasper JR, Stevens ME, Regula DP Jr, Barsh GS, Bernstein D, Kobilka BK (1996) Targeted disruption of the mouse beta1-adrenergic receptor gene: developmental and cardiovascular effects. Proc Natl Acad Sci U S A 93:7375–7380 93. Rokosh DG, Simpson PC (2002) Knockout of the alpha 1A/Cadrenergic receptor subtype: the alpha 1A/C is expressed in resistance arteries and is required to maintain arterial blood pressure. Proc Natl Acad Sci U S A 99:9474–9479 94. Rorabaugh BR, Ross SA, Gaivin RJ, Papay RS, McCune DF, Simpson PC, Perez DM (2005) alpha1A- but not alpha1Badrenergic receptors precondition the ischemic heart by a staurosporine-sensitive, chelerythrine-insensitive mechanism. Cardiovasc Res 65:436–445 95. Ross SA, Rorabaugh BR, Chalothorn D, Yun J, Gonzalez-Cabrera PJ, McCune DF, Piascik MT, Perez DM (2003) The alpha(1B)adrenergic receptor decreases the inotropic response in the mouse Langendorff heart model. Cardiovasc Res 60:598–607 96. Salazar NC, Chen J, Rockman HA (2007) Cardiac GPCRs: GPCR signaling in healthy and failing hearts. Biochim Biophys Acta 1768: 1006–1018 97. Sheikh SP, Vilardarga JP, Baranski TJ, Lichtarge O, Iiri T, Meng EC, Nissenson RA, Bourne HR (1999) Similar structures and shared switch mechanisms of the beta2-adrenoceptor and the parathyroid hormone receptor. Zn(II) bridges between helices III and VI block activation. J Biol Chem 274:17033–17041 98. Skomedal T, Borthne K, Aass H, Geiran O, Osnes JB (1997) Comparison between alpha-1 adrenoceptor-mediated and beta adrenoceptor-mediated inotropic components elicited by norepinephrine in failing human ventricular muscle. J Pharmacol Exp Ther 280:721–729

99. Steinberg SF (2002) Alpha(1)-adrenergic receptor subtype function in cardiomyocytes: lessons from genetic models in mice. J Mol Cell Cardiol 34:1141–1145 100. Stelzer JE, Patel JR, Walker JW, Moss RL (2007) Differential roles of cardiac myosin-binding protein C and cardiac troponin I in the myofibrillar force responses to protein kinase A phosphorylation. Circ Res 101:503–511 101. Sugden PH, Bogoyevitch MA (1995) Intracellular signalling through protein kinases in the heart. Cardiovasc Res 30:478–492 102. Swedberg K, Bristow MR, Cohn JN, Dargie H, Straub M, Wiltse C, Wright TJ, Moxonidine S, Efficacy I (2002) Effects of sustainedrelease moxonidine, an imidazoline agonist, on plasma norepinephrine in patients with chronic heart failure. Circulation 105:1797– 1803 103. Thomas JA, Marks BH (1978) Plasma norepinephrine in congestive heart failure. Am J Cardiol 41:233–243 104. Todd GL, Baroldi G, Pieper GM, Clayton FC, Eliot RS (1985) Experimental catecholamine-induced myocardial necrosis. I. Morphology, quantification and regional distribution of acute contraction band lesions. J Mol Cell Cardiol 17:317–338 105. Todd GL, Baroldi G, Pieper GM, Clayton FC, Eliot RS (1985) Experimental catecholamine-induced myocardial necrosis. II. Temporal development of isoproterenol-induced contraction band lesions correlated with ECG, hemodynamic and biochemical changes. J Mol Cell Cardiol 17:647–656 106. Triposkiadis F, Karayannis G, Giamouzis G, Skoularigis J, Louridas G, Butler J (2009) The sympathetic nervous system in heart failure physiology, pathophysiology, and clinical implications. J Am Coll Cardiol 54:1747–1762 107. Turnbull L, McCloskey DT, O’Connell TD, Simpson PC, Baker AJ (2003) Alpha 1-adrenergic receptor responses in alpha 1AB-AR knockout mouse hearts suggest the presence of alpha 1D-AR. Am J Physiol Heart Circ Physiol 284:H1104–H1109 108. Ungerer M, Bohm M, Elce JS, Erdmann E, Lohse MJ (1993) Altered expression of beta-adrenergic receptor kinase and beta 1adrenergic receptors in the failing human heart. Circulation 87:454– 463 109. Vaniotis G, Del Duca D, Trieu P, Rohlicek CV, Hebert TE, Allen BG (2011) Nuclear beta-adrenergic receptors modulate gene expression in adult rat heart. Cell Signal 23:89–98 110. Vatner SF, Franklin D, Higgins CB, Patrick T, Braunwald E (1972) Left ventricular response to severe exertion in untethered dogs. J Clin Invest 51:3052–3060 111. Violin JD, Lefkowitz RJ (2007) Beta-arrestin-biased ligands at seven-transmembrane receptors. Trends Pharmacol Sci 28:416–422 112. Voelkel NF, Quaife RA, Leinwand LA, Barst RJ, McGoon MD, Meldrum DR, Dupuis J, Long CS, Rubin LJ, Smart FW, Suzuki YJ, Gladwin M, Denholm EM, Gail DB (2006) Right ventricular function and failure: report of a National Heart, Lung, and Blood Institute working group on cellular and molecular mechanisms of right heart failure. Circulation 114:1883–1891 113. Waagstein F, Hjalmarson A, Varnauskas E, Wallentin I (1975) Effect of chronic beta-adrenergic receptor blockade in congestive cardiomyopathy. Br Heart J 37:1022–1036 114. Wang BH, Du XJ, Autelitano DJ, Milano CA, Woodcock EA (2000) Adverse effects of constitutively active alpha(1B)-adrenergic receptors after pressure overload in mouse hearts. Am J Physiol Heart Circ Physiol 279:H1079–H1086 115. Wang GY, McCloskey DT, Turcato S, Swigart PM, Simpson PC, Baker AJ (2006) Contrasting inotropic responses to {alpha}1-adrenergic receptor stimulation in left versus right ventricular myocardium. Am J Physiol Heart Circ Physiol 291:H2013–H2017 116. Wang G, Yeh CC, Jensen BC, Mann MJ, Simpson PC, Baker AJ (2010) Heart failure switches the RV {alpha}1-adrenergic inotropic response from negative to positive. Am J Physiol Heart Circ Physiol 298:H913–H920

Pflugers Arch - Eur J Physiol 117. Wei H, Ahn S, Shenoy SK, Karnik SS, Hunyady L, Luttrell LM, Lefkowitz RJ (2003) Independent beta-arrestin 2 and G proteinmediated pathways for angiotensin II activation of extracellular signal-regulated kinases 1 and 2. Proc Natl Acad Sci U S A 100: 10782–10787 118. Whelan RS, Konstantinidis K, Xiao RP, Kitsis RN (2013) Cardiomyocyte life-death decisions in response to chronic betaadrenergic signaling. Circ Res 112:408–410 119. Woo SH, Lee CO (1999) Role of PKC in the effects of alpha1adrenergic stimulation on Ca2+ transients, contraction and Ca2+ current in guinea-pig ventricular myocytes. Pflugers Arch 437:335– 344 120. Wright CD, Chen Q, Baye NL, Huang Y, Healy CL, Kasinathan S, O’Connell TD (2008) Nuclear alpha1-adrenergic receptors signal activated ERK localization to caveolae in adult cardiac myocytes. Circ Res 103:992–1000 121. Wright CD, Wu SC, Dahl EF, Sazama AJ, O’Connell TD (2012) Nuclear localization drives alpha1-adrenergic receptor oligomerization and signaling in cardiac myocytes. Cell Signal 24:794–802 122. Xiang Y, Kobilka BK (2003) Myocyte adrenoceptor signaling pathways. Science 300:1530–1532 123. Xiao RP, Ji X, Lakatta EG (1995) Functional coupling of the beta 2adrenoceptor to a pertussis toxin-sensitive G protein in cardiac myocytes. Mol Pharmacol 47:322–329 124. Xiao RP, Zhu W, Zheng M, Cao C, Zhang Y, Lakatta EG, Han Q (2006) Subtype-specific alpha1- and beta-adrenoceptor signaling in the heart. Trends Pharmacol Sci 27:330–337

1

125. Yamasaki R, Wu Y, McNabb M, Greaser M, Labeit S, Granzier H (2002) Protein kinase A phosphorylates titin’s cardiac-specific N2B domain and reduces passive tension in rat cardiac myocytes. Circ Res 90:1181–1188 126. Yoo B, Lemaire A, Mangmool S, Wolf MJ, Curcio A, Mao L, Rockman HA (2009) Beta1-adrenergic receptors stimulate cardiac contractility and CaMKII activation in vivo and enhance cardiac dysfunction following myocardial infarction. Am J Physiol Heart Circ Physiol 297:H1377–H1386 127. Zaugg M, Xu W, Lucchinetti E, Shafiq SA, Jamali NZ, Siddiqui MA (2000) Beta-adrenergic receptor subtypes differentially affect apoptosis in adult rat ventricular myocytes. Circulation 102:344– 350 128. Zhang X, Szeto C, Gao E, Tang M, Jin J, Fu Q, Makarewich C, Ai X, Li Y, Tang A, Wang J, Gao H, Wang F, Ge XJ, Kunapuli SP, Zhou L, Zeng C, Xiang KY, Chen X (2013) Cardiotoxic and cardioprotective features of chronic beta-adrenergic signaling. Circ Res 112:498–509 129. Zhu WZ, Wang SQ, Chakir K, Yang D, Zhang T, Brown JH, Devic E, Kobilka BK, Cheng H, Xiao RP (2003) Linkage of beta1adrenergic stimulation to apoptotic heart cell death through protein kinase A-independent activation of Ca2+/calmodulin kinase II. J Clin Invest 111:617–625 130. Zhu WZ, Zheng M, Koch WJ, Lefkowitz RJ, Kobilka BK, Xiao RP (2001) Dual modulation of cell survival and cell death by beta(2)adrenergic signaling in adult mouse cardiac myocytes. Proc Natl Acad Sci U S A 98:1607–1612