Role Of Β-adrenergic Signaling Research Articles

β3-Adrenoreceptor Blockade Induces Stem Cells Differentiation in Melanoma Microenvironment.

Although there is an increasing evidence that cancer stem cell (CSC) niches in the tumor microenvironment (TME) plays a crucial role in sustaining solid tumors progression, several molecular players involved in this regulation still remain unknown. The role of β-adrenergic signaling in enhancing tumor growth through β2-adrenoreceptors (β2-ARs) has been confirmed in different cancer models, but the role played by the β3-adrenergic receptor (β3-AR) has recently emerged. Previous studies showed that β3-AR promotes cancer growth through the activation of different stromal cells in the TME, and leads to melanoma malignancy progression through inflammation, angiogenesis, and immunotolerance. Here we show that in B16 melanoma-bearing mice, the pharmacological β3-AR blockade is able to reduce the expression of CSC markers, and to induce a differentiated phenotype of hematopoietic subpopulations in TME. In particular, cytofluorimetric analysis (FACS) of the tumor mass shows that β3-AR antagonist SR59230A promotes hematopoietic differentiation as indicated by increased ratios of lymphoid/hematopoietic stem cells (HSCs) and of myeloid progenitor cells/HSCs, and increases the number of Ter119 and natural killer (NK) precursor cells, and of granulocyte precursors, indicating active hematopoiesis within the tumor tissue. Moreover, pharmacological antagonism of β3-AR induces mesenchymal stem cell (MSC) differentiation into adipocytes subtracting a potential renewal of the stem compartment by these cells. Here we demonstrate that β3-AR blockade in the TME by inducing the differentiation of different stromal cells at the expense of stemness traits could possibly have a favorable effect on the control of melanoma progression.

Role of β-adrenergic signaling in masseter muscle.

In skeletal muscle, the major isoform of β-adrenergic receptor (β-AR) is β2-AR and the minor isoform is β1-AR, which is opposite to the situation in cardiac muscle. Despite extensive studies in cardiac muscle, the physiological roles of the β-AR subtypes in skeletal muscle are not fully understood. Therefore, in this work, we compared the effects of chronic β1- or β2-AR activation with a specific β1-AR agonist, dobutamine (DOB), or a specific β2-AR agonist, clenbuterol (CB), on masseter and cardiac muscles in mice. In cardiac muscle, chronic β1-AR stimulation induced cardiac hypertrophy, fibrosis and myocyte apoptosis, whereas chronic β2-AR stimulation induced cardiac hypertrophy without histological abnormalities. In masseter muscle, however, chronic β1-AR stimulation did not induce muscle hypertrophy, but did induce fibrosis and apoptosis concomitantly with increased levels of p44/42 MAPK (ERK1/2) (Thr-202/Tyr-204), calmodulin kinase II (Thr-286) and mammalian target of rapamycin (mTOR) (Ser-2481) phosphorylation. On the other hand, chronic β2-AR stimulation in masseter muscle induced muscle hypertrophy without histological abnormalities, as in the case of cardiac muscle, concomitantly with phosphorylation of Akt (Ser-473) and mTOR (Ser-2448) and increased expression of microtubule-associated protein light chain 3-II, an autophagosome marker. These results suggest that the β1-AR pathway is deleterious and the β2-AR is protective in masseter muscle. These data should be helpful in developing pharmacological approaches for the treatment of skeletal muscle wasting and weakness.

β-adrenergic receptors and cardiac progenitor cell biology: What is the real connection?

Resident cardiac progenitor cells (CPCs) isolated from small animal models may not always be representative of their human counterparts, especially when significant differences in isolation protocols are considered. Nonetheless, multiple evidences support an important role of β-adrenergic signaling in human CPC survival and commitment, which will need appropriate consideration for future developments of human CPCs as regenerative medicine tools.

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

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. 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. 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.

Biological Pacemaker Engineered by Nonviral Gene Transfer in a Mouse Model of Complete Atrioventricular Block

We hypothesized that a nonviral gene delivery of the hyperpolarization-activated HCN2 channel combined with the beta(2)-adrenergic receptor (ADRB2) would generate a functional pacemaker in a mouse model of complete atrioventricular block (CAVB) induced by radiofrequency ablation of the His bundle. Plasmids encoding HCN2 and ADRB2 mixed with tetronic 304, a poloxamine block copolymer, were injected in the left ventricular free wall (HCN2-ADRB2 mice). Sham mice received a noncoding plasmid. CAVB was induced 5 days later. Ventricular escape rhythms in HCN2-ADRB2 mice were significantly faster than in sham mice at day 15 after ablation and later. In HCN2-ADRB2 mice, QRS complexes were larger than in sham mice and characterized by abnormal axes. Immunostaining of GFP-HCN2 fusion protein showed an expression of HCN2 channel in left ventricular myocardium for at least 45 days after injection. In the mouse, CAVB induces progressive hypertrophy and heart failure leading to 50% mortality after 110 days. HCN2-ADRB2 mice survived 3 weeks longer than sham mice. Finally, beta-adrenergic input increased ventricular escape rhythms significantly more in HCN2-ADRB2 mice than in sham mice. In conclusion, nonviral gene transfer can produce a functional cardiac biological pacemaker regulated by sympathetic input, which improves life expectancy in a mouse model of CAVB.

Activation of AP-1 Contributes to the β-Adrenoceptor-Mediated Myocardial Induction of Interleukin-6

The induction of proinflammatory cytokines in stressed myocardium is considered an innate immune response, but the role of beta-adrenergic signaling in this proinflammatory response and the mechanisms of cardioprotection by beta-blockers are not fully understood. In the present study, we analyzed interleukin-6 (IL-6) formation and promoter activation in beta-adrenoceptor-stimulated neonatal rat cardiomyocytes, in transgenic mice with cardiac overexpression of beta1-adrenoceptors, and in failing human myocardium. IL-6 formation and release in cultured cardiomyocytes under beta-adrenoceptor stimulation requires the activation of activating protein-1 (AP-1) binding sites and of cAMP response elements (CRE) in the IL-6 promoter, but this release (140 +/- 6 pg/mL medium under 10(-6) M isoproterenol vs. 81 +/- 3 pg/mL unstimulated, P < 0.05) is moderate compared with that under inflammatory stimulation (855 +/- 44 pg/mL, endotoxin 0.1microg/mL). Similarly, IL-6 is induced together with CRE- and AP-1 activation in the left ventricle (LV) of beta1-transgenic mice before the onset of failure. However, we observed IL-6 induction with activation of NF-kappaB in addition to CRE and AP-1 in beta1-transgenic mice at the age of 22 weeks and in explanted human LV after full development of failure. Treatment with beta-blockers lowered myocardial IL-6 as well as AP-1, NF-kappaB, and CRE activation. Therefore, the activation of AP-1 and CRE is part of beta-adrenergic signal transduction for IL-6 induction in nonfailing and failing cardiomyocytes, whereas NF-kappaB activation contributes only in overloaded failing myocardium.

Gene Therapy in Congestive Heart Failure

Although research and development of gene therapy have encountered several difficulties in recent years, they have also begun to show potential for the treatment of acquired and inherited human diseases. Gene therapy may have wide applicability for the treatment of numerous cardiovascular diseases, including congestive heart failure (CHF), ischemic heart disease, and cardiomyopathy. CHF remains a leading cause of death and morbidity in industrialized nations, and the number of patients with CHF continues to increase as the population ages. Pharmacological therapies control symptoms, reduce left ventricular (LV) dilation, improve function, and reduce mortality. These therapies control the disease but do not cure it. Currently, however, the growing knowledge of molecular mechanisms involved in myocardial dysfunction has allowed the identification of potential therapeutic targets designed with the aim of curing CHF. Several studies in animal models have provided hope that gene therapy may be one of the future strategies for the treatment of clinical CHF. In these studies, myocardial gene transfer has been used to target at least 3 different biological pathways that play a crucial role in the pathophysiology of CHF: Intracellular calcium signaling, β1-adrenergic receptor (β1-AR) signaling, and antiapoptotic signaling. The activity of sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) is decreased in failing myocardium, and this results in abnormal Ca2+ handling.1 In an animal model of heart failure, Miyamoto et al2 showed that in vivo overexpression of SERCA2a, achieved by catheter injection of an adenovirus carrying the SERCA2a gene into the aortic root, restored systolic and diastolic function to normal levels. In another study, Muller et al3 analyzed the chronic overexpression of SERCA2a in both normal and pressure-overloaded hearts (induced by abdominal aortic banding of transgenic rats). Overexpression of SERCA2a resulted in a …

Protein Kinase A Transgenes

The β-adrenergic receptor/adenylyl cyclase/protein kinase A (PKA) axis is the central signaling pathway that serves to stimulate cardiac function. It is classically perceived as a linear signaling cascade (Figure), and cAMP is thought to be the second messenger responsible for the positive inotropic, chronotropic, and lusitropic effects of catecholamines. New data gained from a series of transgenic animals overexpressing various elements of this axis show that this system has a far more complex makeup than previously thought. Transgenic models of the cardiac β-adrenergic receptor/PKA system. The signaling cascade is represented as a simple linear chain. Proteins that are detrimental when overexpressed are shown in black; those causing beneficial effects upon overexpression are depicted in white. PLB indicates phospholamban. It has been known for about two decades that the β-adrenergic receptor system is dysfunctional in heart failure.1 The loss of receptor responsiveness has been attributed to a reduced β-receptor number, particularly of the β1-subtype, plus a functional desensitization of the remaining receptors—presumably mediated via increased activity of G protein–coupled receptor kinases.2 The extent of the receptor downregulation and the functional loss correlate with the severity of the disease.3,4 This phenomenon has long been regarded as detrimental to the compromised function of the failing heart, and it has been proposed that restoration of β-adrenergic receptor responsiveness might be a strategy to improve cardiac function. However, recent clinical studies and observations on a panel of transgenic animals suggest that the opposite is the case. Sustained stimulation or overexpression of cardiac β1-adrenergic receptors leads to hypertrophy, fibrosis, and heart failure,5–7 and blockade of β-adrenergic receptors with several antagonists—bisoprolol, carvedilol, and metoprolol—improves survival in heart failure patients.8 Thus, the loss of β-adrenergic receptor responsiveness in heart failure is more likely to represent a protective mechanism than …

Role of β-Adrenergic Signaling in Exercise Conditioning in Mice

Role of β-Adrenergic Signaling in Exercise Conditioning in Mice