β3AR-Dependent Brain-Derived Neurotrophic Factor (BDNF) Generation Limits Chronic Postischemic Heart Failure

BACKGROUND

Loss of brain-derived neurotrophic factor (BDNF)/TrkB (tropomyosin kinase receptor B) signaling accounts for brain and cardiac disorders. In neurons, β-adrenergic receptor stimulation enhances local BDNF expression. It is unclear if this occurs in a pathophysiological relevant manner in the heart, especially in the β-adrenergic receptor-desensitized postischemic myocardium. Nor is it fully understood whether and how TrkB agonists counter chronic postischemic left ventricle (LV) decompensation, a significant unmet clinical milestone.

METHODS

We conducted in vitro studies using neonatal rat and adult murine cardiomyocytes, SH-SY5Y neuronal cells, and umbilical vein endothelial cells. We assessed myocardial ischemia (MI) impact in wild type, β3AR knockout, or myocyte-selective BDNF knockout (myoBDNF KO) mice in vivo (via coronary ligation [MI]) or in isolated hearts with global ischemia-reperfusion (I/R).

RESULTS

In wild type hearts, BDNF levels rose early after MI (<24 hours), plummeting at 4 weeks when LV dysfunction, adrenergic denervation, and impaired angiogenesis ensued. The TrkB agonist, LM22A-4, countered all these adverse effects. Compared with wild type, isolated myoBDNF KO hearts displayed worse infarct size/LV dysfunction after I/R injury and modest benefits from LM22A-4. In vitro, LM22A-4 promoted neurite outgrowth and neovascularization, boosting myocyte function, effects reproduced by 7,8-dihydroxyflavone, a chemically unrelated TrkB agonist. Superfusing myocytes with the β3AR-agonist, BRL-37344, increased myocyte BDNF content, while β3AR signaling underscored BDNF generation/protection in post-MI hearts. Accordingly, the β1AR blocker, metoprolol, via upregulated β3ARs, improved chronic post-MI LV dysfunction, enriching the myocardium with BDNF. Last, BRL-37344-imparted benefits were nearly abolished in isolated I/R injured myoBDNF KO hearts.

CONCLUSIONS

BDNF loss underscores chronic postischemic heart failure. TrkB agonists can improve ischemic LV dysfunction via replenished myocardial BDNF content. Direct cardiac β3AR stimulation, or β-blockers (via upregulated β3AR), is another BDNF-based means to fend off chronic postischemic heart failure.

Targeting Cardiac Myocyte Na+-K+ Pump Function With β3 Adrenergic Agonist in Rabbit Model of Severe Congestive Heart Failure

BACKGROUND

Abnormally high cytosolic Na⁺ concentrations in advanced heart failure impair myocardial contractility. Stimulation of the membrane Na⁺-K⁺ pump should lower Na⁺ concentrations, and the β3 adrenoceptor (β3 AR) mediates pump stimulation in myocytes. We examined if β3 AR-selective agonists given in vivo increase myocyte Na⁺-K⁺ pump activity and reverse organ congestion in severe heart failure (HF).

METHODS

Indices for HF were lung-, heart-, and liver: body weight ratios and ascites after circumflex coronary artery ligation in rabbits. Na⁺-K⁺ pump current, I_p, was measured in voltage-clamped myocytes from noninfarct myocardium. Rabbits were treated with the β3 AR agonists CL316,243 or ASP9531, starting 2 weeks after coronary ligation.

RESULTS

Coronary ligation caused ascites in most rabbits, significantly increased lung-, heart-, and liver: body weight ratios, and decreased I_p relative to that for 10 sham-operated rabbits. Treatment with CL316,243 for 3 days significantly reduced lung-, heart-, and liver: body weight ratios and prevalence of ascites in 8 rabbits with HF relative to indices for 13 untreated rabbits with HF. It also increased I_p significantly to levels of myocytes from sham-operated rabbits. Treatment with ASP9531 for 14 days significantly reduced indices of organ congestion in 6 rabbits with HF relative to indices of 6 untreated rabbits, and it eliminated ascites. β3 AR agonists did not significantly change heart rates or blood pressures.

CONCLUSIONS

Parallel β3 AR agonists-induced reversal of Na⁺-K⁺ pump inhibition and indices of congestion suggest pump inhibition is a useful target for treatment with β3 AR agonists in congestive HF.

Long-Term Caloric Restriction Improves Cardiac Function, Remodeling, Adrenergic Responsiveness, and Sympathetic Innervation in a Model of Postischemic Heart Failure

BACKGROUND

Caloric restriction (CR) has been described to have cardioprotective effects and improve functional outcomes in animal models and humans. Chronic ischemic heart failure (HF) is associated with reduced cardiac sympathetic innervation, dysfunctional β-adrenergic receptor signaling, and decreased cardiac inotropic reserve. We tested the effects of a long-term CR diet, started late after myocardial infarction on cardiac function, sympathetic innervation, and β-adrenergic receptor responsiveness in a rat model of postischemic HF.

METHODS AND RESULTS

Adult male rats were randomly assigned to myocardial infarction or sham operation and 4 weeks later were further randomized to a 1-year CR or normal diet. One year of CR resulted in a significant reduction in body weight, heart weight, and heart weight/tibia length ratio when compared with normal diet in HF groups. At the end of the study period, echocardiography and histology revealed that HF animals under the CR diet had ameliorated left ventricular remodeling compared with HF rats fed with normal diet. Invasive hemodynamic showed a significant improvement of cardiac inotropic reserve in CR HF rats compared with HF-normal diet animals. Importantly, CR dietary regimen was associated with a significant increase of cardiac sympathetic innervation and with normalized cardiac β-adrenergic receptor levels in HF rats when compared with HF rats on the standard diet.

CONCLUSIONS

We demonstrate, for the first time, that chronic CR, when started after HF established, can ameliorate cardiac dysfunction and improve inotropic reserve. At the molecular level, we find that chronic CR diet significantly improves sympathetic cardiac innervation and β-adrenergic receptor levels in failing myocardium.

Dose Response of β-Blockers in Adrenergic Receptor Polymorphism Genotypes

Background In heart failure (HF) with reduced ejection fraction, 2 clinical trials, the BEST (β-Blocker Evaluation of Survival Trial) and HF-ACTION (Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training), have reported an effectiveness interaction between the ADRB1 (β-1 adrenergic receptor) Arg389Gly polymorphism and β-blockers (BBs). HF-ACTION additionally reported a dose-related interaction of unclear origin. If confirmed and pharmacogenetically resolved, these findings may have important implications for HF with reduced ejection fraction precision therapy. We used uniform methodology to investigate BB dose-ADRB1 Arg389Gly polymorphism interaction with major clinical end points in BEST/bucindolol and HF-ACTION/other BB databases. Methods This was a retrospective analysis of prospectively designed DNA substudies from BEST (N=1040) and HF-ACTION (N=957). Subjects were genotyped for ADRB1 Arg389Gly and ADRA2C (α2C adrenergic receptor) Ins322-325Del. BB dose was defined as either no/low dose or high dose, according to total daily dose of either bucindolol (BEST subjects) or other BB (HF-ACTION subjects) standardized to carvedilol equivalents. The main outcome of interest was all-cause mortality, and CV mortality/HF hospitalization was a secondary outcome. Results Subjects in each trial had less all-cause mortality with high- versus no/low-dose BB if they had ADRB1 Arg389Arg (BEST: hazard ratio [HR]=0.40, P=0.002; HF-ACTION: HR=0.45, P=0.005) but not Arg389Gly genotype (both P>0.2). Among gene-dose groups, there was a differential favorable treatment effect of 46% for high-dose bucindolol with ADRB1 Arg389Arg versus Gly carrier genotype (HR, 0.54; P=0.018), but not for no/low-dose bucindolol. In contrast, HF-ACTION Arg389Arg genotype subjects taking no/low-dose BB had greater all-cause mortality compared with 389Gly carriers (HR, 1.83; P=0.015), whereas all-cause mortality did not vary by genotype among subjects taking high-dose BB (HR, 0.84; P=0.55). Conclusions The enhanced HF with reduced ejection fraction efficacy of bucindolol in the ADRB1 Arg389Arg versus 389Gly carrier genotypes occurs at high dose. Other BBs taken at low dose have reduced efficacy for Arg389Arg genotype subjects compared with 389Gly carriers, suggesting a greater relative treatment effect at high dose. These data support guideline recommendations to use high, clinical trial target doses of all BBs to treat HF with reduced ejection fraction.

Physiological Mitochondrial Fragmentation Is a Normal Cardiac Adaptation to Increased Energy Demand

RATIONALE

Mitochondria play a dual role in the heart, responsible for meeting energetic demands and regulating cell death. Paradigms have held that mitochondrial fission and fragmentation are the result of pathological stresses, such as ischemia, are an indicator of poor mitochondrial health, and lead to mitophagy and cell death. However, recent studies demonstrate that inhibiting fission also results in decreased mitochondrial function and cardiac impairment, suggesting that fission is important for maintaining cardiac and mitochondrial bioenergetic homeostasis.

OBJECTIVE

The purpose of this study is to determine whether mitochondrial fission and fragmentation can be an adaptive mechanism used by the heart to augment mitochondrial and cardiac function during a normal physiological stress, such as exercise.

METHODS AND RESULTS

We demonstrate a novel role for cardiac mitochondrial fission as a normal adaptation to increased energetic demand. During submaximal exercise, physiological mitochondrial fragmentation results in enhanced, rather than impaired, mitochondrial function and is mediated, in part, by β1-adrenergic receptor signaling. Similar to pathological fragmentation, physiological fragmentation is induced by activation of dynamin-related protein 1; however, unlike pathological fragmentation, membrane potential is maintained and regulators of mitophagy are downregulated. Inhibition of fission with P110, Mdivi-1 (mitochondrial division inhibitor), or in mice with cardiac-specific dynamin-related protein 1 ablation significantly decreases exercise capacity.

CONCLUSIONS

These findings demonstrate the requirement for physiological mitochondrial fragmentation to meet the energetic demands of exercise, as well as providing additional support for the evolving conceptual framework, where mitochondrial fission and fragmentation play a role in the balance between mitochondrial maintenance of normal physiology and response to disease.

Adrenergic Receptors in Individual Ventricular Myocytes: The Beta-1 and Alpha-1B Are in All Cells, the Alpha-1A Is in a Subpopulation, and the Beta-2 and Beta-3 Are Mostly Absent

RATIONALE

It is unknown whether every ventricular myocyte expresses all 5 of the cardiac adrenergic receptors (ARs), β1, β2, β3, α1A, and α1B. The β1 and β2 are thought to be the dominant myocyte ARs.

OBJECTIVE

Quantify the 5 cardiac ARs in individual ventricular myocytes.

METHODS AND RESULTS

We studied ventricular myocytes from wild-type mice, mice with α1A and α1B knockin reporters, and β1 and β2 knockout mice. Using individual isolated cells, we measured knockin reporters, mRNAs, signaling (phosphorylation of extracellular signal-regulated kinase and phospholamban), and contraction. We found that the β1 and α1B were present in all myocytes. The α1A was present in 60%, with high levels in 20%. The β2 and β3 were detected in only ≈5% of myocytes, mostly in different cells. In intact heart, 30% of total β-ARs were β2 and 20% were β3, both mainly in nonmyocytes.

CONCLUSION

The dominant ventricular myocyte ARs present in all cells are the β1 and α1B. The β2 and β3 are mostly absent in myocytes but are abundant in nonmyocytes. The α1A is in just over half of cells, but only 20% have high levels. Four distinct myocyte AR phenotypes are defined: 30% of cells with β1 and α1B only; 60% that also have the α1A; and 5% each that also have the β2 or β3. The results raise cautions in experimental design, such as receptor overexpression in myocytes that do not express the AR normally. The data suggest new paradigms in cardiac adrenergic signaling mechanisms.

Critical Roles of STAT3 in β-Adrenergic Functions in the Heart

BACKGROUND

β-Adrenergic receptors (βARs) play paradoxical roles in the heart. On one hand, βARs augment cardiac performance to fulfill the physiological demands, but on the other hand, prolonged activations of βARs exert deleterious effects that result in heart failure. The signal transducer and activator of transcription 3 (STAT3) plays a dynamic role in integrating multiple cytokine signaling pathways in a number of tissues. Altered activation of STAT3 has been observed in failing hearts in both human patients and animal models. Our objective is to determine the potential regulatory roles of STAT3 in cardiac βAR-mediated signaling and function.

METHODS AND RESULTS

We observed that STAT3 can be directly activated in cardiomyocytes by β-adrenergic agonists. To follow up this finding, we analyzed βAR function in cardiomyocyte-restricted STAT3 knockouts and discovered that the conditional loss of STAT3 in cardiomyocytes markedly reduced the cardiac contractile response to acute βAR stimulation, and caused disengagement of calcium coupling and muscle contraction. Under chronic β-adrenergic stimulation, Stat3cKO hearts exhibited pronounced cardiomyocyte hypertrophy, cell death, and subsequent cardiac fibrosis. Biochemical and genetic data supported that Gαs and Src kinases are required for βAR-mediated activation of STAT3. Finally, we demonstrated that STAT3 transcriptionally regulates several key components of βAR pathway, including β1AR, protein kinase A, and T-type Ca(2+) channels.

CONCLUSIONS

Our data demonstrate for the first time that STAT3 has a fundamental role in βAR signaling and functions in the heart. STAT3 serves as a critical transcriptional regulator for βAR-mediated cardiac stress adaption, pathological remodeling, and heart failure.

Adrenergic Repression of the Epigenetic Reader MeCP2 Facilitates Cardiac Adaptation in Chronic Heart Failure

Supplemental Digital Content is available in the text.

In chronic heart failure, increased adrenergic activation contributes to structural remodeling and altered gene expression. Although adrenergic signaling alters histone modifications, it is unknown, whether it also affects other epigenetic processes, including DNA methylation and its recognition.

Microdomain switch of cGMP-regulated phosphodiesterases leads to ANP-induced augmentation of β-adrenoceptor-stimulated contractility in early cardiac hypertrophy

RATIONALE

Cyclic nucleotides are second messengers that regulate cardiomyocyte function through compartmentalized signaling in discrete subcellular microdomains. However, the role of different microdomains and their changes in cardiac disease are not well understood.

OBJECTIVE

To directly visualize alterations in β-adrenergic receptor-associated cAMP and cGMP microdomain signaling in early cardiac disease.

METHODS AND RESULTS

Unexpectedly, measurements of cell shortening revealed augmented β-adrenergic receptor-stimulated cardiomyocyte contractility by atrial natriuretic peptide/cGMP signaling in early cardiac hypertrophy after transverse aortic constriction, which was in sharp contrast to well-documented β-adrenergic and natriuretic peptide signaling desensitization during chronic disease. Real-time cAMP analysis in β1- and β2-adrenergic receptor-associated membrane microdomains using a novel membrane-targeted Förster resonance energy transfer-based biosensor transgenically expressed in mice revealed that this unexpected atrial natriuretic peptide effect is brought about by spatial redistribution of cGMP-sensitive phosphodiesterases 2 and 3 between both receptor compartments. Functionally, this led to a significant shift in cGMP/cAMP cross-talk and, in particular, to cGMP-driven augmentation of contractility in vitro and in vivo.

CONCLUSIONS

Redistribution of cGMP-regulated phosphodiesterases and functional reorganization of receptor-associated microdomains occurs in early cardiac hypertrophy, affects cGMP-mediated contractility, and might represent a previously not recognized therapeutically relevant compensatory mechanism to sustain normal heart function.

Arrhythmogenic remodeling of β2 versus β1 adrenergic signaling in the human failing heart

BACKGROUND

Arrhythmia is the major cause of death in patients with heart failure, for which β-adrenergic receptor blockers are a mainstay therapy. But the role of β-adrenergic signaling in electrophysiology and arrhythmias has never been studied in human ventricles.

METHODS AND RESULTS

We used optical imaging of action potentials and [Ca(2+)]i transients to compare the β1- and β2-adrenergic responses in left ventricular wedge preparations of human donor and failing hearts. β1-Stimulation significantly increased conduction velocity, shortened action potential duration, and [Ca(2+)]i transients duration (CaD) in donor but not in failing hearts, because of desensitization of β1-adrenergic receptor in heart failure. In contrast, β2-stimulation increased conduction velocity in both donor and failing hearts but shortened action potential duration only in failing hearts. β2-Stimulation also affected transmural heterogeneity in action potential duration but not in [Ca(2+)]i transients duration. Both β1- and β2-stimulation augmented the vulnerability and frequency of ectopic activity and enhanced substrates for ventricular tachycardia in failing, but not in donor, hearts. Both β1- and β2-stimulation enhanced Purkinje fiber automaticity, whereas only β2-stimulation promoted Ca-mediated premature ventricular contractions in heart failure.

CONCLUSIONS

During end-stage heart failure, β2-stimulation creates arrhythmogenic substrates via conduction velocity regulation and transmurally heterogeneous repolarization. β2-Stimulation is, therefore, more arrhythmogenic than β1-stimulation. In particular, β2-stimulation increases the transmural difference between [Ca(2+)]i transients duration and action potential duration, which facilitates the formation of delayed afterdepolarizations.

The autonomic nervous system and heart failure

The pathophysiology of heart failure (HF) is characterized by hemodynamic abnormalities that result in neurohormonal activation and autonomic imbalance with increase in sympathetic activity and withdrawal of vagal activity. Alterations in receptor activation from this autonomic imbalance may have profound effects on cardiac function and structure. Inhibition of the sympathetic drive to the heart through β-receptor blockade has become a standard component of therapy for HF with a dilated left ventricle because of its effectiveness in inhibiting the ventricular structural remodeling process and in prolonging life. Several devices for selective modulation of sympathetic and vagal activity have recently been developed in an attempt to alter the natural history of HF. The optimal counteraction of the excessive sympathetic activity is still unclear. A profound decrease in adrenergic support with excessive blockade of the sympathetic nervous system may result in adverse outcomes in clinical HF. In this review, we analyze the data supporting a contributory role of the autonomic functional alterations on the course of HF, the techniques used to assess autonomic nervous system activity, the evidence for clinical effectiveness of pharmacological and device interventions, and the potential future role of autonomic nervous system modifiers in the management of this syndrome.

β-adrenergic signaling inhibits Gq-dependent protein kinase D activation by preventing protein kinase D translocation

RATIONALE

Both β-adrenergic receptor (β-AR) and Gq-coupled receptor (GqR) agonist-driven signaling play key roles in the events, leading up to and during cardiac dysfunction. How these stimuli interact at the level of protein kinase D (PKD), a nodal point in cardiac hypertrophic signaling, remains unclear.

OBJECTIVE

To assess the spatiotemporal dynamics of PKD activation in response to β-AR signaling alone and on coactivation with GqR-agonists. This will test our hypothesis that compartmentalized PKD signaling reconciles disparate findings of PKA facilitation and inhibition of PKD activation.

METHODS AND RESULTS

We report on the spatial and temporal profiles of PKD activation using green fluorescent protein-tagged PKD (wildtype or mutant S427E) and targeted fluorescence resonance energy transfer-based biosensors (D-kinase activity reporters) in adult cardiomyocytes. We find that β-AR/PKA signaling drives local nuclear activation of PKD, without preceding sarcolemmal translocation. We also discover pronounced interference of β-AR/cAMP/PKA signaling on GqR-induced translocation and activation of PKD throughout the cardiomyocyte. We attribute these effects to direct, PKA-dependent phosphorylation of PKD-S427. We also show that phosphomimetic substitution of S427 likewise impedes GqR-induced PKD translocation and activation. In neonatal myocytes, S427E inhibits GqR-evoked cell growth and expression of hypertrophic markers. Finally, we show altered S427 phosphorylation in transverse aortic constriction-induced hypertrophy.

CONCLUSIONS

β-AR signaling triggers local nuclear signaling and inhibits GqR-mediated PKD activation by preventing its intracellular translocation. PKA-dependent phosphorylation of PKD-S427 fine-tunes the PKD responsiveness to GqR-agonists, serving as a key integration point for β-adrenergic and Gq-coupled stimuli.

Adrenergic nervous system in heart failure: pathophysiology and therapy

Heart failure (HF), the leading cause of death in the western world, develops when a cardiac injury or insult impairs the ability of the heart to pump blood and maintain tissue perfusion. It is characterized by a complex interplay of several neurohormonal mechanisms that become activated in the syndrome to try and sustain cardiac output in the face of decompensating function. Perhaps the most prominent among these neurohormonal mechanisms is the adrenergic (or sympathetic) nervous system (ANS), whose activity and outflow are enormously elevated in HF. Acutely, and if the heart works properly, this activation of the ANS will promptly restore cardiac function. However, if the cardiac insult persists over time, chances are the ANS will not be able to maintain cardiac function, the heart will progress into a state of chronic decompensated HF, and the hyperactive ANS will continue to push the heart to work at a level much higher than the cardiac muscle can handle. From that point on, ANS hyperactivity becomes a major problem in HF, conferring significant toxicity to the failing heart and markedly increasing its morbidity and mortality. The present review discusses the role of the ANS in cardiac physiology and in HF pathophysiology, the mechanisms of regulation of ANS activity and how they go awry in chronic HF, methods of measuring ANS activity in HF, the molecular alterations in heart physiology that occur in HF, along with their pharmacological and therapeutic implications, and, finally, drugs and other therapeutic modalities used in HF treatment that target or affect the ANS and its effects on the failing heart.

Impact of substance P receptor antagonism on the serotonin and norepinephrine systems: relevance to the antidepressant/anxiolytic response

Substance P (neurokinin-1 [NK1]) receptor antagonists appear to be effective antidepressant and anxiolytic agents, as indicated in 3 double-blind clinical trials. In laboratory animals, they promptly attenuate the responsiveness of serotonin (5-hydroxytryptamine [5-HT]) and norepinephrine (NE) neurons to agonists of their cell-body autoreceptors, as is the case for some antidepressant drugs that are currently in clinical use. Long-term, but not subacute, antagonism of NK1 receptors in rats increases 5-HT transmission in the hippocampus, a property common to all antidepressant treatments tested thus far. This enhancement seems to be mediated by a time-dependent increase in the firing rate of 5-HT neurons. Mice with the NK1 receptor deleted from their genetic code also have an increased firing rate of 5-HT neurons. Taken together, these observations strongly suggest that NK1 antagonists could become a new class of antidepressant and anxiolytic agents.