Cardiovascular and metabolic alterations in mice lacking both beta1- and beta2-adrenergic receptors

Esmolol improves sepsis outcomes through cardiovascular and immune modulation

Background

Sepsis poses significant mortality risks. Esmolol, a β1-adrenergic blocker, may improve outcomes through cardiovascular and immune modulation. This study aims to evaluate the effects of Esmolol on survival rates, inflammatory markers, and immune function in sepsis patients.

Methods

In this retrospective observational study, data from 268 sepsis patients were reviewed, and 125 met the inclusion criteria. These patients were divided into Esmolol and control groups. Data were collected from electronic health records, including survival rates, inflammatory markers (IL-6, PCT), and immune function markers (CD4+ and CD8+ T-cell counts). Statistical analyses included multivariate regression, Kaplan-Meier survival analysis, and Generalized Estimating Equations.

Results

The Esmolol group demonstrated significantly higher survival rates at both 14 days (80% vs. 41.67%, p < 0.01) and 28 days (75.38% vs. 30.00%, p < 0.01) compared to the control group. The median ICU stay was longer in the Esmolol group (12 days vs. 10 days, P = 0.045). Significant reductions in heart rate (P = 0.002), NE levels (P = 0.036), and inflammatory markers were observed in the Esmolol group. Additionally, Esmolol treatment resulted in bidirectional regulation of T-cell counts, increasing CD4+ and CD8+ T-cell counts in patients with higher baseline immune function and decreasing these counts in patients with lower baseline levels (P < 0.01).

Conclusion

Esmolol improves survival rates and clinical outcomes in sepsis patients, particularly those with higher baseline immune function. The benefits are attributed to early and prolonged administration of Esmolol, highlighting its potential as a valuable addition to sepsis treatment protocols. Future multicenter trials are needed to confirm these findings and refine the use of β1AR in sepsis management. Clinical Trial Registration: clinicaltrials.gov, identifier NCT06390748.

Carvedilol Prevents UV-Induced Immunosuppression and Skin Carcinogenesis through a Mechanism Independent of β-Blockade

Exposure to UVR suppresses the immune system, which plays a primary role in skin cancer etiology. The β-blocker carvedilol prevents UV-induced skin cancer, but the mechanism is unknown. This study examined the effects of carvedilol and its enantiomers on UV-induced immunosuppression using contact hypersensitivity (CHS) response in SKH-1 mice. A single-dose UVR (224 mJ/cm2) strongly suppressed CHS, which was attenuated by intraperitoneal injection of carvedilol before UV exposure. Adoptive transfer of lymphocytes isolated from UV-irradiated mice to naïve mice without UV exposure triggered CHS suppression, which was not observed for lymphocytes isolated from carvedilol-treated mice. Topically applied carvedilol also prevented UV-induced CHS suppression. Both the β-blocking S-carvedilol and non-β-blocking R-carvedilol attenuated UV-induced CHS suppression. To evaluate the role of β2-adrenergic receptor, a knockout mouse model of β2-adrenergic receptor on the SKH-1 background was used. UV suppressed CHS in β2-adrenergic receptor-knockout mice, and carvedilol attenuated UV-induced CHS suppression in both genotypes. Furthermore, wild-type and knockout mice exposed to chronic UVR developed skin tumors with similar incidence, multiplicity, and tumor burden, whereas carvedilol inhibited skin tumor development in both genotypes. These data suggest that carvedilol prevents skin cancer not through β-blocking but through its activity overcoming UV-induced immunosuppression.

Sympathetic Neurons Promote Small Cell Lung Cancer through the β2-Adrenergic Receptor

SIGNIFICANCE

SCLC is highly aggressive, with limited effective treatment options. We show that ablating sympathetic nerves or inhibiting the ADRB2 receptor slows SCLC progression and prolongs survival in mice. Additionally, ADRB2 inhibition reduces the growth of human SCLC organoids and xenografts by disrupting PKA signaling, identifying a new therapeutic target.

Genetic inactivation of the β1 adrenergic receptor prevents cerebral cavernous malformations in zebrafish

Previously, we showed that propranolol reduces experimental murine cerebral cavernous malformations (CCMs) and prevents embryonic caudal venous plexus (CVP) lesions in zebrafish that follow mosaic inactivation of ccm2 (Li et al., 2021). Because morpholino silencing of the β1 adrenergic receptor (adrb1) prevents the embryonic CVP lesion, we proposed that adrb1 plays a role in CCM pathogenesis. Here, we report that adrb1-/- zebrafish exhibited 86% fewer CVP lesions and 87% reduction of CCM lesion volume relative to wild type brood mates at 2dpf and 8-10 weeks stage, respectively. Treatment with metoprolol, a β1 selective antagonist, yielded a similar reduction in CCM lesion volume. Adrb1-/- zebrafish embryos exhibited reduced heart rate and contractility and reduced CVP blood flow. Similarly, slowing the heart and eliminating the blood flow in CVP by administration of 2,3-BDM suppressed the CVP lesion. In sum, our findings provide genetic and pharmacological evidence that the therapeutic effect of propranolol on CCM is achieved through β1 receptor antagonism.

Fluoxetine promotes IL-10-dependent metabolic defenses to protect from sepsis-induced lethality

Selective serotonin reuptake inhibitors (SSRIs) are some of the most prescribed drugs in the world. While they are used for their ability to increase serotonergic signaling in the brain, SSRIs are also known to have a broad range of effects beyond the brain, including immune and metabolic effects. Recent studies have demonstrated that SSRIs are protective in animal models and humans against several infections, including sepsis and COVID-19; however, the mechanisms underlying this protection are largely unknown. Here, we mechanistically link two previously described effects of the SSRI fluoxetine in mediating protection against sepsis. We show that fluoxetine-mediated protection is independent of peripheral serotonin and instead increases levels of circulating interleukin-10 (IL-10). IL-10 is necessary for protection from sepsis-induced hypertriglyceridemia, preventing cardiac effects including impairment of glucose oxidation, ectopic lipid accumulation, ventricular stretch and possibly cardiac failure. Our work reveals a beneficial "off-target" effect of fluoxetine, and reveals a protective immunometabolic defense mechanism with therapeutic potential.

Genetic Inactivation of the β1 adrenergic receptor prevents Cerebral Cavernous Malformations in zebrafish

Propranolol reduces experimental murine cerebral cavernous malformations (CCMs) and prevents embryonic caudal venous plexus (CVP) lesions in zebrafish that follow mosaic inactivation of ccm2. Because morpholino silencing of the β1 adrenergic receptor (adrb1) prevents the embryonic CVP lesion, we proposed that adrb1 plays a role in CCM pathogenesis. Here we report that adrb1 -/- zebrafish exhibited 86% fewer CVP lesions and 87% reduction of CCM lesion volume relative to wild type brood mates at 2dpf and 8-10 weeks stage, respectively. Treatment with metoprolol, a β1 selective antagonist, yielded a similar reduction in CCM lesion volume. Adrb1 -/- zebrafish embryos exhibited reduced heart rate and contractility and reduced CVP blood flow. Similarly, slowing the heart and eliminating the blood flow in CVP by administration of 2,3-BDM suppressed the CVP lesion. In sum, our findings provide genetic and pharmacological evidence that the therapeutic effect of propranolol on CCM is achieved through β1 receptor antagonism.

Clinical Pharmacogenetics Implementation Consortium Guideline (CPIC) for CYP2D6, ADRB1, ADRB2, ADRA2C, GRK4, and GRK5 Genotypes and Beta-Blocker Therapy

Beta-blockers are widely used medications for a variety of indications, including heart failure, myocardial infarction, cardiac arrhythmias, and hypertension. Genetic variability in pharmacokinetic (e.g., CYP2D6) and pharmacodynamic (e.g., ADRB1, ADRB2, ADRA2C, GRK4, GRK5) genes have been studied in relation to beta-blocker exposure and response. We searched and summarized the strength of the evidence linking beta-blocker exposure and response with the six genes listed above. The level of evidence was high for associations between CYP2D6 genetic variation and both metoprolol exposure and heart rate response. Evidence indicates that CYP2D6 poor metabolizers experience clinically significant greater exposure and lower heart rate in response to metoprolol compared with those who are not poor metabolizers. Therefore, we provide therapeutic recommendations regarding genetically predicted CYP2D6 metabolizer status and metoprolol therapy. However, there was insufficient evidence to make therapeutic recommendations for CYP2D6 and other beta-blockers or for any beta-blocker and the other five genes evaluated (updates at www.cpicpgx.org).

Myeloid-derived suppressor cell mitochondrial fitness governs chemotherapeutic efficacy in hematologic malignancies

Myeloid derived suppressor cells (MDSCs) are key regulators of immune responses and correlate with poor outcomes in hematologic malignancies. Here, we identify that MDSC mitochondrial fitness controls the efficacy of doxorubicin chemotherapy in a preclinical lymphoma model. Mechanistically, we show that triggering STAT3 signaling via β2-adrenergic receptor (β2-AR) activation leads to improved MDSC function through metabolic reprograming, marked by sustained mitochondrial respiration and higher ATP generation which reduces AMPK signaling, altering energy metabolism. Furthermore, induced STAT3 signaling in MDSCs enhances glutamine consumption via the TCA cycle. Metabolized glutamine generates itaconate which downregulates mitochondrial reactive oxygen species via regulation of Nrf2 and the oxidative stress response, enhancing MDSC survival. Using β2-AR blockade, we target the STAT3 pathway and ATP and itaconate metabolism, disrupting ATP generation by the electron transport chain and decreasing itaconate generation causing diminished MDSC mitochondrial fitness. This disruption increases the response to doxorubicin and could be tested clinically.

β3-Adrenoceptor as a new player in the sympathetic regulation of the renal acid-base homeostasis

Efferent sympathetic nerve fibers regulate several renal functions activating norepinephrine receptors on tubular epithelial cells. Of the beta-adrenoceptors (β-ARs), we previously demonstrated the renal expression of β3-AR in the thick ascending limb (TAL), the distal convoluted tubule (DCT), and the collecting duct (CD), where it participates in salt and water reabsorption. Here, for the first time, we reported β3-AR expression in the CD intercalated cells (ICCs), where it regulates acid-base homeostasis. Co-localization of β3-AR with either proton pump H+-ATPase or Cl-/HCO3 - exchanger pendrin revealed β3-AR expression in type A, type B, non-A, and non-B ICCs in the mouse kidney. We aimed to unveil the possible regulatory role of β3-AR in renal acid-base homeostasis, in particular in modulating the expression, subcellular localization, and activity of the renal H+-ATPase, a key player in this process. The abundance of H+-ATPase was significantly decreased in the kidneys of β3-AR-/- compared with those of β3-AR+/+ mice. In particular, H+-ATPase reduction was observed not only in the CD but also in the TAL and DCT, which contribute to acid-base transport in the kidney. Interestingly, we found that in in vivo, the absence of β3-AR reduced the kidneys' ability to excrete excess proton in the urine during an acid challenge. Using ex vivo stimulation of mouse kidney slices, we proved that the β3-AR activation promoted H+-ATPase apical expression in the epithelial cells of β3-AR-expressing nephron segments, and this was prevented by β3-AR antagonism or PKA inhibition. Moreover, we assessed the effect of β3-AR stimulation on H+-ATPase activity by measuring the intracellular pH recovery after an acid load in β3-AR-expressing mouse renal cells. Importantly, β3-AR agonism induced a 2.5-fold increase in H+-ATPase activity, and this effect was effectively prevented by β3-AR antagonism or by inhibiting either H+-ATPase or PKA. Of note, in urine samples from patients treated with a β3-AR agonist, we found that β3-AR stimulation increased the urinary excretion of H+-ATPase, likely indicating its apical accumulation in tubular cells. These findings demonstrate that β3-AR activity positively regulates the expression, plasma membrane localization, and activity of H+-ATPase, elucidating a novel physiological role of β3-AR in the sympathetic control of renal acid-base homeostasis.

The alpha-1A adrenergic receptor regulates mitochondrial oxidative metabolism in the mouse heart

AIMS

The sympathetic nervous system regulates numerous critical aspects of mitochondrial function in the heart through activation of adrenergic receptors (ARs) on cardiomyocytes. Mounting evidence suggests that α1-ARs, particularly the α1A subtype, are cardioprotective and may mitigate the deleterious effects of chronic β-AR activation by shared ligands. The mechanisms underlying these adaptive effects remain unclear. Here, we tested the hypothesis that α1A-ARs adaptively regulate cardiomyocyte oxidative metabolism in both the uninjured and infarcted heart.

METHODS

We used high resolution respirometry, fatty acid oxidation (FAO) enzyme assays, substrate-specific electron transport chain (ETC) enzyme assays, transmission electron microscopy (TEM) and proteomics to characterize mitochondrial function comprehensively in the uninjured hearts of wild type and α1A-AR knockout mice and defined the effects of chronic β-AR activation and myocardial infarction on selected mitochondrial functions.

RESULTS

We found that isolated cardiac mitochondria from α1A-KO mice had deficits in fatty acid-dependent respiration, FAO, and ETC enzyme activity. TEM revealed abnormalities of mitochondrial morphology characteristic of these functional deficits. The selective α1A-AR agonist A61603 enhanced fatty-acid dependent respiration, fatty acid oxidation, and ETC enzyme activity in isolated cardiac mitochondria. The β-AR agonist isoproterenol enhanced oxidative stress in vitro and this adverse effect was mitigated by A61603. A61603 enhanced ETC Complex I activity and protected contractile function following myocardial infarction.

CONCLUSIONS

Collectively, these novel findings position α1A-ARs as critical regulators of cardiomyocyte metabolism in the basal state and suggest that metabolic mechanisms may underlie the protective effects of α1A-AR activation in the failing heart.

Leptin receptor+ cells promote bone marrow innervation and regeneration by synthesizing nerve growth factor

The bone marrow contains peripheral nerves that promote haematopoietic regeneration after irradiation or chemotherapy (myeloablation), but little is known about how this is regulated. Here we found that nerve growth factor (NGF) produced by leptin receptor-expressing (LepR+) stromal cells is required to maintain nerve fibres in adult bone marrow. In nerveless bone marrow, steady-state haematopoiesis was normal but haematopoietic and vascular regeneration were impaired after myeloablation. LepR+ cells, and the adipocytes they gave rise to, increased NGF production after myeloablation, promoting nerve sprouting in the bone marrow and haematopoietic and vascular regeneration. Nerves promoted regeneration by activating β2 and β3 adrenergic receptor signalling in LepR+ cells, and potentially in adipocytes, increasing their production of multiple haematopoietic and vascular regeneration growth factors. Peripheral nerves and LepR+ cells thus promote bone marrow regeneration through a reciprocal relationship in which LepR+ cells sustain nerves by synthesizing NGF and nerves increase regeneration by promoting the production of growth factors by LepR+ cells.

Epac1 participates in β1-adrenoreceptor autoantibody-mediated decreased autophagic flux in cardiomyocytes

Decreased autophagic flux in cardiomyocytes is an important mechanism by which the β1-adrenoreceptor (β1-AR) autoantibody (β1-AA) induces heart failure. A previous study found that β1-AA imparts its biological effects via the β1-AR/Gs/AC/cAMP/PKA canonical signaling pathway, but PKA inhibition does not completely reverse β1-AA-induced reduction in autophagy in myocardial tissues, suggesting that other signaling molecules participate in this process. This study confirmed that Epac1 upregulation is indeed involved β1-AA-induced decreased cardiomyocyte autophagy through CE3F4 pretreatment, Epac1 siRNA transfection, western blot and immunofluorescence methods. On this basis, we constructed β1-AR and β2-AR knockout mice, and used receptor knockout mice, β1-AR selective blocker (atenolol), and the β2-AR/Gi-biased agonist ICI 118551 to show that β1-AA upregulated Epac1 expression through β1-AR and β2-AR to inhibit autophagy, and biased activation of β2-AR/Gi signaling downregulated myocardial Epac1 expression to reverse β1-AA-induced myocardial autophagy inhibition. This study aimed to test the hypothesis that Epac1 acts as another effector downstream of cAMP on β1-AA-induced reduction in cardiomyocyte autophagy, and β1-AA upregulates myocardial Epac1 expression through β1-AR and β2-AR, and biased activation of the β2-AR/Gi signaling pathway can reverse β1-AA-induced myocardial autophagy inhibition. This study provides new ideas and therapeutic targets for the prevention and treatment of cardiovascular diseases related to dysregulated autophagy.

GDF15 increases insulin action in the liver and adipose tissue via a β-adrenergic receptor-mediated mechanism

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5 h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the β-adrenergic antagonist propranolol and in β1,β2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases β-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.

Tumour immune rejection triggered by activation of α2-adrenergic receptors

Immunotherapy based on immunecheckpoint blockade (ICB) using antibodies induces rejection of tumours and brings clinical benefit in patients with various cancer types¹. However, tumours often resist immune rejection. Ongoing efforts trying to increase tumour response rates are based on combinations of ICB with compounds that aim to reduce immunosuppression in the tumour microenvironment but usually have little effect when used as monotherapies^2,3. Here we show that agonists of α2-adrenergic receptors (α2-AR) have very strong anti-tumour activity when used as monotherapies in multiple immunocompetent tumour models, including ICB-resistant models, but not in immunodeficient models. We also observed marked effects in human tumour xenografts implanted in mice reconstituted with human lymphocytes. The anti-tumour effects of α2-AR agonists were reverted by α2-AR antagonists, and were absent in Adra2a-knockout (encoding α2a-AR) mice, demonstrating on-target action exerted on host cells, not tumour cells. Tumours from treated mice contained increased infiltrating T lymphocytes and reduced myeloid suppressor cells, which were more apoptotic. Single-cell RNA-sequencing analysis revealed upregulation of innate and adaptive immune response pathways in macrophages and T cells. To exert their anti-tumour effects, α2-AR agonists required CD4⁺ T lymphocytes, CD8⁺ T lymphocytes and macrophages. Reconstitution studies in Adra2a-knockout mice indicated that the agonists acted directly on macrophages, increasing their ability to stimulate T lymphocytes. Our results indicate that α2-AR agonists, some of which are available clinically, could substantially improve the clinical efficacy of cancer immunotherapy.

Pathophysiology and pharmacology of G protein-coupled receptors in the heart

G protein-coupled receptors (GPCRs), comprising the largest superfamily of cell surface receptors, serve as fundamental modulators of cardiac health and disease owing to their key roles in the regulation of heart rate, contractile dynamics, and cardiac function. Accordingly, GPCRs are heavily pursued as drug targets for a wide variety of cardiovascular diseases ranging from heart failure, cardiomyopathy, and arrhythmia to hypertension and coronary artery disease. Recent advancements in understanding the signalling mechanisms, regulation, and pharmacological properties of GPCRs have provided valuable insights that will guide the development of novel therapeutics. Herein, we review the cellular signalling mechanisms, pathophysiological roles, and pharmacological developments of the major GPCRs in the heart, highlighting the β-adrenergic, muscarinic, and angiotensin receptors as exemplar subfamilies.

Overexpression of GRK2 in vascular smooth muscle leads to inappropriate hypertension and acute heart failure as in clinical scenario 1

Clinical scenario 1 (CS1) is acute heart failure (HF) characterized by transient systolic blood pressure (SBP) elevation and pulmonary congestion. Although it is managed by vasodilators, the molecular mechanism remains unclear. The sympathetic nervous system plays a key role in HF, and desensitization of cardiac β-adrenergic receptor (AR) signaling due to G protein-coupled receptor kinase 2 (GRK2) upregulation is known. However, vascular β-AR signaling that regulates cardiac afterload remains unelucidated in HF. We hypothesized that upregulation of vascular GRK2 leads to pathological conditions similar to CS1. GRK2 was overexpressed in vascular smooth muscle (VSM) of normal adult male mice by peritoneally injected adeno-associated viral vectors driven by the myosin heavy chain 11 promoter. Upregulation of GRK2 in VSM of GRK2 overexpressing mice augmented the absolute increase in SBP (+ 22.5 ± 4.3 mmHg vs. + 36.0 ± 4.0 mmHg, P < 0.01) and lung wet weight (4.28 ± 0.05 mg/g vs. 4.76 ± 0.15 mg/g, P < 0.01) by epinephrine as compared to those in control mice. Additionally, the expression of brain natriuretic peptide mRNA was doubled in GRK2 overexpressing mice as compared to that in control mice (P < 0.05). These findings were similar to CS1. GRK2 overexpression in VSM may cause inappropriate hypertension and HF, as in CS1.

Benzodiazepine diazepam regulates cell surface β1-adrenergic receptor density in human monocytes

Downregulation of cell surface β-adrenergic receptors (β-AR) is an important adaptive response that prevents deleterious effects of receptor overstimulation. Various factors including reactive oxygen species cause β-AR downregulation. In this study, we evaluated the effects of ligands of the peripheral benzodiazepine receptor (PBR), a key protein in regulating oxidative stress, on surface density of endogenous β₁-and β₂-ARs in highly differentiated cells such as human monocytes, which express both β-AR subtypes. β-AR expression in human monocytes was evaluated by flow cytometry, qPCR and western blotting. Monocyte treatment with β-AR agonist isoproterenol did not change surface β₁-AR density while downregulating surface β₂-AR density. This effect was antagonized by the β-blocker propranolol. An opposite response was observed with benzodiazepine diazepam that led to a time-dependent reduction in β₁-AR density. In particular, while no significant downregulation was observed after 3 h of treatment, only 63% of β₁-ARs were still present on the cell surface after 48 h of treatment with diazepam at 1 μM. Treatment with the PBR antagonist PK11195, but not with propranolol, antagonized the effects of diazepam. No change in β₁-AR-mRNA or protein levels was observed at any time after diazepam treatment. We also found that diazepam did not affect Gs-protein or β-arrestin-2 recruitment for both β-ARs in engineered fibroblasts, further suggesting that diazepam activity on β₁-AR density is mediated by PBR. Finally, no sex-related differences were found. Collectively, these results indicate that monocyte β₁-ARs are resistant to catecholamine-mediated downregulation and suggest that PBR plays an important role in regulating β₁-AR density.

Data on cardiac and vascular functionality in ex vivo and in vivo models following acute administration of trimethylamine N-oxide

This dataset describes in detail the outcomes of acute trimethylamine N-oxide (TMAO) administration on cardiac, vascular and mitochondrial functionality in ex vivo and in vivo models. The accumulation of TMAO in target tissues was assessed after performing heart perfusion or by incubating aortic tissue in a solution containing TMAO. To evaluate the impact of TMAO on mitochondrial function, the aortic rings and heart homogenates of Wistar rats were incubated in a solution containing [9,10-3H] palmitate (5 µCi/ml) or D-[U-14C] glucose (0.625 µCi/ml) in the presence or absence of TMAO with subsequent measurement of substrate oxidation and uptake. The effects of TMAO on the vascular reactivity of isolated conductance and resistance vessels were tested by measuring their response to acetylcholine and sodium nitroprusside. The impact of elevated TMAO levels on cardiac function and infarct size caused by ischemia-reperfusion injury was evaluated in Langendorff perfused heart model. Normal and forced heart functioning was analyzed by echocardiography in CD-1 mouse acute cardiac stress model induced by isoproterenol (10 µg/mouse) upon single and 7 repeated daily administrations of TMAO (120 mg/kg). The data presented in the manuscript provide valuable information on measurements performed under conditions of acutely elevated TMAO levels in experimental models of cardiac and vascular function and energy metabolism. Furthermore, the data have high reuse potential as they could be applied in the planning of future in vitro, ex vivo, and in vivo studies addressing the molecular mechanisms targeted by elevated levels of TMAO.

β-adrenoreceptor-triggered PKA activation negatively regulates the innate antiviral response

Upon viral infection, cytoplasmic pattern recognition receptors detect viral nucleic acids and activate the adaptor protein VISA/MAVS- or MITA/STING-mediated innate antiviral response. Whether and how the innate antiviral response is regulated by neuronal endocrine functions is unclear. Here, we show that viral infection reduced the serum levels of the β-adrenergic hormones epinephrine and norepinephrine as well as the cellular levels of their receptors ADRB1 and ADRB2. We further show that an increase in epinephrine/norepinephrine level inhibited the innate antiviral response in an ADRB1-/2-dependent manner. Mechanistically, epinephrine/norepinephrine stimulation activated the downstream kinase PKA, which catalyzed the phosphorylation of MITA at S241, S243 and T263, inhibiting MITA activation and suppressing the innate immune response to DNA virus. In addition, phosphorylation of VISA at T54 by PKA antagonized the innate immune response to RNA virus. These findings reveal the regulatory mechanisms of innate antiviral responses by epinephrine/norepinephrine and provide a possible explanation for increased host susceptibility to viral infection in stressful and anxiety-promoting situations.

Propranolol Modulates Cerebellar Circuit Activity and Reduces Tremor

Tremor is the most common movement disorder. Several drugs reduce tremor severity, but no cures are available. Propranolol, a β-adrenergic receptor blocker, is the leading treatment for tremor. However, the in vivo circuit mechanisms by which propranolol decreases tremor remain unclear. Here, we test whether propranolol modulates activity in the cerebellum, a key node in the tremor network. We investigated the effects of propranolol in healthy control mice and Car8^wdl/wdl mice, which exhibit pathophysiological tremor and ataxia due to cerebellar dysfunction. Propranolol reduced physiological tremor in control mice and reduced pathophysiological tremor in Car8^wdl/wdl mice to control levels. Open field and footprinting assays showed that propranolol did not correct ataxia in Car8^wdl/wdl mice. In vivo recordings in awake mice revealed that propranolol modulates the spiking activity of control and Car8^wdl/wdl Purkinje cells. Recordings in cerebellar nuclei neurons, the targets of Purkinje cells, also revealed altered activity in propranolol-treated control and Car8^wdl/wdl mice. Next, we tested whether propranolol reduces tremor through β₁ and β₂ adrenergic receptors. Propranolol did not change tremor amplitude or cerebellar nuclei activity in β₁ and β₂ null mice or Car8^wdl/wdl mice lacking β₁ and β₂ receptor function. These data show that propranolol can modulate cerebellar circuit activity through β-adrenergic receptors and may contribute to tremor therapeutics.

How Carvedilol activates β2-adrenoceptors

Carvedilol is among the most effective β-blockers for improving survival after myocardial infarction. Yet the mechanisms by which carvedilol achieves this superior clinical profile are still unclear. Beyond blockade of β1-adrenoceptors, arrestin-biased signalling via β2-adrenoceptors is a molecular mechanism proposed to explain the survival benefits. Here, we offer an alternative mechanism to rationalize carvedilol's cellular signalling. Using primary and immortalized cells genome-edited by CRISPR/Cas9 to lack either G proteins or arrestins; and combining biological, biochemical, and signalling assays with molecular dynamics simulations, we demonstrate that G proteins drive all detectable carvedilol signalling through β2ARs. Because a clear understanding of how drugs act is imperative to data interpretation in basic and clinical research, to the stratification of clinical trials or to the monitoring of drug effects on the target pathway, the mechanistic insight gained here provides a foundation for the rational development of signalling prototypes that target the β-adrenoceptor system.

Adrenergic signaling controls early transcriptional programs during CD8+ T cell responses to viral infection

Norepinephrine is a key sympathetic neurotransmitter, which acts to suppress CD8 + T cell cytokine secretion and lytic activity by signaling through the β2-adrenergic receptor (ADRB2). Although ADRB2 signaling is considered generally immunosuppressive, its role in regulating the differentiation of effector T cells in response to infection has not been investigated. Using an adoptive transfer approach, we compared the expansion and differentiation of wild type (WT) to Adrb2-/- CD8 + T cells throughout the primary response to vesicular stomatitis virus (VSV) infection in vivo. We measured the dynamic changes in transcriptome profiles of antigen-specific CD8 + T cells as they responded to VSV. Within the first 7 days of infection, WT cells out-paced the expansion of Adrb2-/- cells, which correlated with reduced expression of IL-2 and the IL-2Rα in the absence of ADRB2. RNASeq analysis identified over 300 differentially expressed genes that were both temporally regulated following infection and selectively regulated in WT vs Adrb2-/- cells. These genes contributed to major transcriptional pathways including cytokine receptor activation, signaling in cancer, immune deficiency, and neurotransmitter pathways. By parsing genes within groups that were either induced or repressed over time in response to infection, we identified three main branches of genes that were differentially regulated by the ADRB2. These gene sets were predicted to be regulated by specific transcription factors involved in effector T cell development, such as Tbx21 and Eomes. Collectively, these data demonstrate a significant role for ADRB2 signaling in regulating key transcriptional pathways during CD8 + T cells responses to infection that may dramatically impact their functional capabilities and downstream memory cell development.

A functional circuit formed by the autonomic nerves and myofibroblasts controls mammalian alveolar formation for gas exchange

Alveolar formation increases the surface area for gas exchange. A molecular understanding of alveologenesis remains incomplete. Here, we show that the autonomic nerve and alveolar myofibroblast form a functional unit in mice. Myofibroblasts secrete neurotrophins to promote neurite extension/survival, whereas neurotransmitters released from autonomic terminals are necessary for myofibroblast proliferation and migration, a key step in alveologenesis. This establishes a functional link between autonomic innervation and alveolar formation. We also discover that planar cell polarity (PCP) signaling employs a Wnt-Fz/Ror-Vangl cascade to regulate the cytoskeleton and neurotransmitter trafficking/release from the terminals of autonomic nerves. This represents a new aspect of PCP signaling in conferring cellular properties. Together, these studies offer molecular insight into how autonomic activity controls alveolar formation. Our work also illustrates the fundamental principle of how two tissues (e.g., nerves and lungs) interact to build alveoli at the organismal level.

Expression profiles of GPR21, GPR39, GPR135, and GPR153 orphan receptors in different cancers

Orphan receptors have unknown endogenous ligands, are expressed in different tissues, and participate in various diseases such as diabetes, hypertension and cancer. We studied the expression profiles of GPR21, GPR39, GPR135 and GPR153 orphan receptors in several tumour tissues. Cervical, breast, skin, prostate, and astrocytoma tissues were analysed for orphan receptor gene expression using Real time PCR analysis. GPR39 is over-expressed in cervical and prostate cancer tissues, and GPR21 and GPR135 receptors are significantly decreased in cervical, breast, skin, prostate, and astrocytoma tissues, when compared with healthy human fibroblasts. In conclusion, GPR21 and GPR135 receptor gene expression is reduced in cancerous tissues. GPR39 may have a role in the development and evolution of cervical and prostate cancer. These data suggest these receptors may be alternative molecules for new diagnostic approaches, and the design of novel therapeutics against oncological pathologies.

α-adrenoceptor stimulation attenuates melanoma growth in mice

BACKGROUND AND PURPOSE

Recently, β-adrenoceptor blockade has emerged as a potential strategy to inhibit melanoma growth. However, it remains to be ascertained whether β-adrenoceptor stimulation by circulating catecholamines increases melanoma growth in mice.

EXPERIMENTAL APPROACH

B16F10 melanoma-bearing mice were used to evaluate effects of adrenaline and specific adrenoceptor (AR) ligands on tumor volume. AR expression as well as effects of AR ligands on cell viability, production of mitochondrial reactive oxygen species (mROS) and proliferation activity in B16F10 cells were determined by biochemical analyses.

KEY RESULTS

qPCR analyses revealed that B16F10 cells express both α- (α1B-, α2A- and α2B-AR) and β-ARs (β₂ -AR). We found that treatment with the α- and β-AR agonist adrenaline or with the synthetic catecholamine isoprenaline, that selectively stimulates β-ARs, did not affect melanoma growth. Conversely, adrenaline reduced tumor growth in mice co-treated with propranolol, a β1β2-AR antagonist. Adrenaline had no effect in tumor-bearing β1β2-AR knockout mice, in which β1- and β2-ARs are lacking, but it reduced tumor growth when co-administered with propranolol suggesting that tumor β2-ARs negatively regulate adrenaline antitumor activity. Additionally, we found that α1-AR stimulation with cirazoline yielded a decrease in B16F10 melanoma size. These effects on melanoma growth were paralleled by reduced cell viability and proliferation activity as well as increased mROS production in α1-AR-stimulated B16F10 cells. Decreased viability, proliferation and mitochondrial function in B16F10 cells also occurred after α2-AR stimulation by α2-AR agonist ST-91.

CONCLUSIONS AND IMPLICATIONS

In B16F10 melanoma model, stimulation of α-AR subtypes yields in vivo and in vitro anticancer activity.

Activation of the Thiazide-Sensitive Sodium-Chloride Cotransporter by Beta3-Adrenoreceptor in the Distal Convoluted Tubule

We previously showed that the beta-3 adrenergic receptor (BAR3) is expressed in most segments of the nephron where its agonism promotes a potent antidiuretic effect. We localized BAR3 in distal convoluted tubule (DCT) cells expressing the thiazide-sensitive sodium-chloride cotransporter (NCC). Aim of this study is to investigate the possible functional role of BAR3 on NCC modulation in DCT cells. Here, we found that, in mice, the knockout of BAR3 was paralleled by a significant attenuation of NCC phosphorylation, paralleled by reduced expression and activation of STE-20/SPS1-related proline-alanine-rich kinase (SPAK) and WNKs the main kinases involved in NCC activation. Conversely, in BAR1/2 knockout mice, we found reduced NCC abundance with no changes in the phosphorylation state of NCC. Moreover, selective BAR3 agonism promotes both SPAK and NCC activation in wild-type mouse kidney slices. In conclusion, our findings suggest a novel role for BAR3 in the regulation of NCC in DCT.

L-type channel inactivation balances the increased peak calcium current due to absence of Rad in cardiomyocytes

The L-type Ca²⁺ channel (LTCC) provides trigger calcium to initiate cardiac contraction in a graded fashion that is regulated by L-type calcium current (I_Ca,L) amplitude and kinetics. Inactivation of LTCC is controlled to fine-tune calcium flux and is governed by voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). Rad is a monomeric G protein that regulates I_Ca,L and has recently been shown to be critical to β-adrenergic receptor (β-AR) modulation of I_Ca,L. Our previous work showed that cardiomyocyte-specific Rad knockout (cRadKO) resulted in elevated systolic function, underpinned by an increase in peak I_Ca,L, but without pathological remodeling. Here, we sought to test whether Rad-depleted LTCC contributes to the fight-or-flight response independently of β-AR function, resulting in I_Ca,L kinetic modifications to homeostatically balance cardiomyocyte function. We recorded whole-cell I_Ca,L from ventricular cardiomyocytes from inducible cRadKO and control (CTRL) mice. The kinetics of I_Ca,L stimulated with isoproterenol in CTRL cardiomyocytes were indistinguishable from those of unstimulated cRadKO cardiomyocytes. CDI and VDI are both enhanced in cRadKO cardiomyocytes without differences in action potential duration or QT interval. To confirm that Rad loss modulates LTCC independently of β-AR stimulation, we crossed a β₁,β₂-AR double-knockout mouse with cRadKO, resulting in a Rad-inducible triple-knockout mouse. Deletion of Rad in cardiomyocytes that do not express β₁,β₂-AR still yielded modulated I_Ca,L and elevated basal heart function. Thus, in the absence of Rad, increased Ca²⁺ influx is homeostatically balanced by accelerated CDI and VDI. Our results indicate that the absence of Rad can modulate the LTCC without contribution of β₁,β₂-AR signaling and that Rad deletion supersedes β-AR signaling to the LTCC to enhance in vivo heart function.

Role of PI3K/Akt signaling pathway in cardiac fibrosis

Heart failure (HF) is considered as a severe health problem worldwide, while cardiac fibrosis is one of the main driving factors for the progress of HF. Cardiac fibrosis was characterized by changes in cardiomyocytes, cardiac fibroblasts, ratio of collagen (COL) I/III, and the excessive production and deposition of extracellular matrix (ECM), thus forming a scar tissue, which leads to pathological process of cardiac structural changes and systolic as well as diastolic dysfunction. Cardiac fibrosis is a common pathological change of many advanced cardiovascular diseases including ischemic heart disease, hypertension, and HF. Accumulated studies have proven that phosphoinositol-3 kinase (PI3K)/Akt signaling pathway is involved in regulating the occurrence, progression and pathological formation of cardiac fibrosis via regulating cell survival, apoptosis, growth, cardiac contractility and even the transcription of related genes through a series of molecules including mammalian target of rapamycin (mTOR), glycogen synthase kinase 3 (GSK-3), forkhead box proteins O1/3 (FoxO1/3), and nitric oxide synthase (NOS). Thus, the review focuses on the role of PI3K/Akt signaling pathway in the cardiac fibrosis. The information reviewed here should be significant in understanding the role of PI3K/Akt in cardiac fibrosis and contribute to the design of further studies related to PI3K/Akt and the cardiac fibrotic response, as well as sought to shed light on a potential treatment for cardiac fibrosis.

Visualization of β-adrenergic receptor dynamics and differential localization in cardiomyocytes

A key question in receptor signaling is how specificity is realized, particularly when different receptors trigger the same biochemical pathway(s). A notable case is the two β-adrenergic receptor (β-AR) subtypes, β1 and β2, in cardiomyocytes. They are both coupled to stimulatory Gs proteins, mediate an increase in cyclic adenosine monophosphate (cAMP), and stimulate cardiac contractility; however, other effects, such as changes in gene transcription leading to cardiac hypertrophy, are prominent only for β1-AR but not for β2-AR. Here, we employ highly sensitive fluorescence spectroscopy approaches, in combination with a fluorescent β-AR antagonist, to determine the presence and dynamics of the endogenous receptors on the outer plasma membrane as well as on the T-tubular network of intact adult cardiomyocytes. These techniques allow us to visualize that the β2-AR is confined to and diffuses within the T-tubular network, as opposed to the β1-AR, which is found to diffuse both on the outer plasma membrane as well as on the T-tubules. Upon overexpression of the β2-AR, this compartmentalization is lost, and the receptors are also seen on the cell surface. Such receptor segregation depends on the development of the T-tubular network in adult cardiomyocytes since both the cardiomyoblast cell line H9c2 and the cardiomyocyte-differentiated human-induced pluripotent stem cells express the β2-AR on the outer plasma membrane. These data support the notion that specific cell surface targeting of receptor subtypes can be the basis for distinct signaling and functional effects.

Effect of β1 /β2 -adrenoceptor blockade on β3 -adrenoceptor activity in the rat cremaster muscle artery

BACKGROUND AND PURPOSE

The physiological role of vascular β₃ -adrenoceptors is not fully understood. Recent evidence suggests cardiac β₃ -adrenoceptors are functionally effective after down-regulation of β₁ /β₂ -adrenoceptors. The functional interaction between the β₃ -adrenoceptor and other β-adrenoceptor subtypes in rat striated muscle arteries was investigated.

EXPERIMENTAL APPROACH

Studies were performed in cremaster muscle arteries isolated from male Sprague-Dawley rats. β-adrenoceptor expression was assessed through RT-PCR and immunofluorescence. Functional effects of β₃ -adrenoceptor agonists and antagonists and other β-adrenoceptor ligands were measured using pressure myography.

KEY RESULTS

All three β-adrenoceptor subtypes were present in the endothelium of the cremaster muscle artery. The β₃ -adrenoceptor agonists mirabegron and CL 316,243 had no effect on the diameter of pressurized (70 mmHg) cremaster muscle arterioles with myogenic tone, while the β₃ -adrenoceptor agonist SR 58611A and the nonselective β-adrenoceptor agonist isoprenaline caused concentration-dependent dilation. In the presence of β_1/2 -adrenoceptor antagonists nadolol (10 μM), atenolol (1 μM) and ICI 118,551 (0.1 μM) both mirabegron and CL 316,243 were effective in causing vasodilation and the potency of SR 58611A was enhanced, while responses to isoprenaline were inhibited. The β₃ -adrenoceptor antagonist L 748,337 (1 μM) inhibited vasodilation caused by β₃ -adrenoceptor agonists (in the presence of β_1/2 -adrenoceptor blockade), but L 748,337 had no effect on isoprenaline-induced vasodilation.

CONCLUSION AND IMPLICATIONS

All three β-adrenoceptor subtypes were present in the endothelium of the rat cremaster muscle artery, but β₃ -adrenoceptor mediated vasodilation was only evident after blockade of β_1/2 -adrenoceptors. This suggests constitutive β_1/2 -adrenoceptor activity inhibits β₃ -adrenoceptor function in the endothelium of skeletal muscle resistance arteries.

Thermogenic recruitment of brown and brite/beige adipose tissues is not obligatorily associated with macrophage accretion or attrition

Cold- and diet-induced recruitment of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT) are dynamic processes, and the recruited state attained is a state of dynamic equilibrium, demanding continuous stimulation to be maintained. An involvement of macrophages, classical proinflammatory (M1) or alternatively activated anti-inflammatory (M2), is presently discussed as being an integral part of these processes. If these macrophages play a mediatory role in the recruitment process, such an involvement would have to be maintained in the recruited state. We have, therefore, investigated whether the recruited state of these tissues is associated with macrophage accretion or attrition. We found no correlation (positive or negative) between total UCP1 mRNA levels (as a measure of recruitment) and proinflammatory macrophages in any adipose depot. We found that in young chow-fed mice, cold-induced recruitment correlated with accretion of anti-inflammatory macrophages; however, such a correlation was not seen when cold-induced recruitment was studied in diet-induced obese mice. Furthermore, the anti-inflammatory macrophage accretion was mediated via β₁/β₂-adrenergic receptors; yet, in their absence, and thus in the absence of macrophage accretion, recruitment proceeded normally. We thus conclude that the classical recruited state in BAT and inguinal (brite/beige) WAT is not paralleled by macrophage accretion or attrition. Our results make mediatory roles for macrophages in the recruitment process less likely.NEW & NOTEWORTHY A regulatory or mediatory role-positive or negative-for macrophages in the recruitment of brown adipose tissue is presently discussed. As the recruited state in the tissue is a dynamic process, maintenance of the recruited state would need persistent alterations in macrophage complement. Contrary to this expectation, we demonstrate here an absence of alterations in macrophage complement in thermogenically recruited brown-or brite/beige-adipose tissues. Macrophage regulation of thermogenic capacity is thus less likely.

GRKs and Epac1 Interaction in Cardiac Remodeling and Heart Failure

β-adrenergic receptors (β-ARs) play a major role in the physiological regulation of cardiac function through signaling routes tightly controlled by G protein-coupled receptor kinases (GRKs). Although the acute stimulation of β-ARs and the subsequent production of cyclic AMP (cAMP) have beneficial effects on cardiac function, chronic stimulation of β-ARs as observed under sympathetic overdrive promotes the development of pathological cardiac remodeling and heart failure (HF), a leading cause of mortality worldwide. This is accompanied by an alteration in cAMP compartmentalization and the activation of the exchange protein directly activated by cAMP 1 (Epac1) signaling. Among downstream signals of β-ARs, compelling evidence indicates that GRK2, GRK5, and Epac1 represent attractive therapeutic targets for cardiac disease. Here, we summarize the pathophysiological roles of GRK2, GRK5, and Epac1 in the heart. We focus on their signalosome and describe how under pathological settings, these proteins can cross-talk and are part of scaffolded nodal signaling systems that contribute to a decreased cardiac function and HF development.

The metabolic effects of mirabegron are mediated primarily by β3 -adrenoceptors

The β3 -adrenoceptor agonist mirabegron is approved for use for overactive bladder and has been purported to be useful in the treatment of obesity-related metabolic diseases in humans, including those involving disturbances of glucose homeostasis. We investigated the effect of mirabegron on glucose homeostasis with in vitro and in vivo models, focusing on its selectivity at β-adrenoceptors, ability to cause browning of white adipocytes, and the role of UCP1 in glucose homeostasis. In mouse brown, white, and brite adipocytes, mirabegron-mediated effects were examined on cyclic AMP, UCP1 mRNA, [3 H]-2-deoxyglucose uptake, cellular glycolysis, and O2 consumption. Mirabegron increased cyclic AMP levels, UCP1 mRNA content, glucose uptake, and cellular glycolysis in brown adipocytes, and these effects were either absent or reduced in white adipocytes. In brite adipocytes, mirabegron increased cyclic AMP levels and UCP1 mRNA content resulting in increased UCP1-mediated oxygen consumption, glucose uptake, and cellular glycolysis. The metabolic effects of mirabegron in both brown and brite adipocytes were primarily due to actions at β3 -adrenoceptors as they were largely absent in adipocytes derived from β3 -adrenoceptor knockout mice. In vivo, mirabegron increased whole body oxygen consumption, glucose uptake into brown and inguinal white adipose tissue, and improved glucose tolerance, all effects that required the presence of the β3 -adrenoceptor. Furthermore, in UCP1 knockout mice, the effects of mirabegron on glucose tolerance were attenuated. Thus, mirabegron had effects on cellular metabolism in adipocytes that improved glucose handling in vivo, and were primarily due to actions at the β3 -adrenoceptor.

Cardiac Overexpression of PDE4B Blunts β-Adrenergic Response and Maladaptive Remodeling in Heart Failure

BACKGROUND

The cyclic AMP (adenosine monophosphate; cAMP)-hydrolyzing protein PDE4B (phosphodiesterase 4B) is a key negative regulator of cardiac β-adrenergic receptor stimulation. PDE4B deficiency leads to abnormal Ca²⁺ handling and PDE4B is decreased in pressure overload hypertrophy, suggesting that increasing PDE4B in the heart is beneficial in heart failure.

METHODS

We measured PDE4B expression in human cardiac tissues and developed 2 transgenic mouse lines with cardiomyocyte-specific overexpression of PDE4B and an adeno-associated virus serotype 9 encoding PDE4B. Myocardial structure and function were evaluated by echocardiography, ECG, and in Langendorff-perfused hearts. Also, cAMP and PKA (cAMP dependent protein kinase) activity were monitored by Förster resonance energy transfer, L-type Ca²⁺ current by whole-cell patch-clamp, and cardiomyocyte shortening and Ca²⁺ transients with an Ionoptix system. Heart failure was induced by 2 weeks infusion of isoproterenol or transverse aortic constriction. Cardiac remodeling was evaluated by serial echocardiography, morphometric analysis, and histology.

RESULTS

PDE4B protein was decreased in human failing hearts. The first PDE4B-transgenic mouse line (TG15) had a ≈15-fold increase in cardiac cAMP-PDE activity and a ≈30% decrease in cAMP content and fractional shortening associated with a mild cardiac hypertrophy that resorbed with age. Basal ex vivo myocardial function was unchanged, but β-adrenergic receptor stimulation of cardiac inotropy, cAMP, PKA, L-type Ca²⁺ current, Ca²⁺ transients, and cell contraction were blunted. Endurance capacity and life expectancy were normal. Moreover, these mice were protected from systolic dysfunction, hypertrophy, lung congestion, and fibrosis induced by chronic isoproterenol treatment. In the second PDE4B-transgenic mouse line (TG50), markedly higher PDE4B overexpression, resulting in a ≈50-fold increase in cardiac cAMP-PDE activity caused a ≈50% decrease in fractional shortening, hypertrophy, dilatation, and premature death. In contrast, mice injected with adeno-associated virus serotype 9 encoding PDE4B (10¹² viral particles/mouse) had a ≈50% increase in cardiac cAMP-PDE activity, which did not modify basal cardiac function but efficiently prevented systolic dysfunction, apoptosis, and fibrosis, while attenuating hypertrophy induced by chronic isoproterenol infusion. Similarly, adeno-associated virus serotype 9 encoding PDE4B slowed contractile deterioration, attenuated hypertrophy and lung congestion, and prevented apoptosis and fibrotic remodeling in transverse aortic constriction.

CONCLUSIONS

Our results indicate that a moderate increase in PDE4B is cardioprotective and suggest that cardiac gene therapy with PDE4B might constitute a new promising approach to treat heart failure.

Thyrotoxicosis Involves β2-Adrenoceptor Signaling to Negatively Affect Microarchitecture and Biomechanical Properties of the Femur

Background: Thyrotoxicosis increases bone turnover, resulting in net bone loss. Sympathetic nervous system (SNS) activation, via β2-adrenoceptor (β2-AR) signaling, also has osteopenic effects. Because thyroid hormones (TH) interact with the SNS to regulate several physiological processes, we hypothesized that this interaction also occurs to regulate bone mass. Previous studies support this hypothesis, as α2-AR knockout (KO) mice are less susceptible to thyrotoxicosis-induced osteopenia. Here, we evaluated whether TH-SNS interactions in bone involve β2-AR signaling. Methods: Thyrotoxicosis was induced in 120-day-old female and male mice with β2-AR gene inactivation (β2-AR^-/-) by daily treatment with supraphysiological doses of triiodothyronine (T3) for 12 weeks. The impact of thyrotoxicosis on femoral bone microarchitecture, remodeling, fracture risk, and gene expression of the receptor activator of nuclear factor-kappa-B (RANK)-RANK ligand (RANKL)-osteoprotegerin (OPG) pathway was evaluated. In addition, the effect of the β2-AR-specific agonist clenbuterol (CL) on cAMP accumulation was determined in osteoblastic (MC3T3-E1) cells treated with T3 and/or 17β-estradiol (E2). Results: Thyrotoxicosis negatively affected trabecular bone microarchitecture in wild-type (WT) females, but this effect was milder or nonexistent in β2-AR^-/- animals, whereas the opposite was seen in males. T3 treatment increased the femoral RANKL/OPG mRNA ratio and the endosteal perimeter and medullary area of the diaphysis in WT females and males, but not in β2-AR^-/- mice, suggesting that T3 promotes endosteal resorption in cortical bone, in a mechanism that involves β2-AR signaling. T3 treatment increased endocortical mineral apposition rate only in WT females but not in β2-AR^-/- mice, suggesting that TH also induce bone formation in a β2-AR signaling-dependent mechanism. T3 treatment decreased femoral resistance to fracture only in WT females, but not in KO mice. E2 and CL similarly increased cAMP accumulation in MC3T3-E1 cells; whereas T3 alone had no effect, but it completely blocked E2-stimulated cAMP accumulation, suggesting that some T3 effects on bone may involve E2/cAMP signaling in osteoblasts. Conclusions: These findings sustain the hypothesis that T3 interacts with the SNS to regulate bone morphophysiology in a β2-AR signaling-dependent mechanism. The data also reveal sex as an important modifier of skeletal manifestations of thyrotoxicosis, as well as a modifier of the TH-SNS interactions to control bone microarchitecture, remodeling, and resistance to fracture.

Low-Dose Adrenaline Reduces Blood Pressure Acutely in Anesthetized Pigs Through a β2-Adrenergic Pathway

Adrenaline (epinephrine) is one of the prime messengers of the fight-or-flight response, favoring the activation of β-adrenergic receptors. Although general vasoconstriction to nonessential tissues is imperative, the vasodilatory effect of β-adrenergic receptor activation contends with this. We aimed to determine the dose-dependent effects of adrenaline on hemodynamics and to test whether adrenaline could lower blood pressure (BP) through a β2-adrenergic pathway. Nineteen Danish landrace pigs were used to pharmacologically probe the hemodynamic effect of adrenaline. Pigs were anesthetized, intubated, and electrocardiogram, systolic BP (SBP), diastolic BP (DBP), and left ventricular pressure (LVP) were monitored continuously. First, we tested the dose-dependent effects of adrenaline (0.01-10 µg/kg). Second, we determined the response to adrenaline (0.3 µg/kg) after atropine, prazosin, and propranolol pretreatment. Finally, we tested the hemodynamic effect of salbutamol in a subset of pigs. All doses of adrenaline increased heart rate, while BP showed a biphasic response: At low doses, adrenaline decreased SBP from 118 ± 3 to 106 ± 4 mm Hg (n = 15; P < 0.05) and DBP from 86 ± 3 to 71 ± 3 (n = 15; P < 0.05), while at high doses, SBP and DBP increased. LVP showed a similar pattern, with a tendency of decreased pressure at low doses, and an increased pressure at high doses (P < 0.05). Pretreatment with autonomic blockers revealed that the increase in BP was due to α-adrenergic activity, while the decrease was due to β-adrenergic activity. In confirmation, β-adrenergic activation through salbutamol showed a similar decrease in SBP, DBP, and LVP. We conclude that adrenaline dose-dependently increases heart rate, while producing a biphasic response in BP with a decrease at low doses and an increase at high doses in an anesthetized, large-animal model.

Vascular phenotype of amyloid precursor protein-deficient mice

The amyloid precursor protein (APP) is expressed in the blood vessel wall, but the physiological function of APP is not completely understood. Previous studies established that APP has amine oxidase activity responsible for degradation of catecholamines. In the present study, we characterized the vascular phenotype of APP-knockout (APP-/-) mice. We demonstrate that circulating levels of catecholamines are significantly increased in male as compared with female APP-/- mice. Studies of vasomotor function in isolated aortas revealed that contractions to the α1-receptor agonist phenylephrine were significantly reduced in male APP-/- mice but not in females. In addition, contractions to G protein activation with sodium fluoride were reduced exclusively in male APP-/- mice aortas. The endothelium-dependent relaxations to acetylcholine were not affected by the loss of APP in mice of both sexes. Further analysis of the mechanisms underlying endothelium-dependent relaxations revealed that inhibition of cyclooxygenase by indomethacin significantly impaired relaxations to acetylcholine exclusively in male APP-/- mice. Furthermore, acetylcholine-induced production of cyclic guanosine monophosphate (cGMP) was significantly reduced in male APP-/- mice aortas while acetylcholine-induced production of cyclic adenosine monophosphate (cAMP) was enhanced. We concluded that altered vascular reactivity to phenylephrine appears to be in part the result of chronic exposure of male APP-/- aorta to high circulating levels of catecholamines. The mechanisms responsible for the impairment of endothelium-dependent cGMP signaling and adaptive enhancement of endothelium-dependent production of cAMP remain to be defined. NEW & NOTEWORTHY Male amyloid precursor protein (APP)-deficient mice have higher circulating levels of catecholamines as compared with female APP-deficient mice. As a consequence, endothelium-dependent and endothelium-independent vasomotor functions of male APP-deficient mice are significantly altered. Under physiological conditions, expression of APP appears to play an important role in vascular function.

Carvedilol inhibits EGF-mediated JB6 P+ colony formation through a mechanism independent of adrenoceptors

Carvedilol is reported to prevent cancers in humans and animal models. However, a molecular mechanism has yet to be established, and the extent to which other β-blockers are chemopreventive remains relatively unknown. A comparative pharmacological approach was utilized with the expectation that a mechanism of action could be devised. JB6 Cl 41-5a (JB6 P+) murine epidermal cells were used to elucidate the chemopreventative properties of β-blockers, as JB6 P+ cells recapitulate in vivo tumor promotion and chemoprevention. The initial hypothesis was that β-blockers that are GRK/β-arrestin biased agonists, like carvedilol, are chemopreventive. Sixteen β-blockers of different classes, isoproterenol, and HEAT HCl were individually co-administered with epidermal growth factor (EGF) to JB6 P+ cells to examine the chemopreventative properties of each ligand. Cytotoxicity was examined to ensure that the anti-transformation effects of each ligand were not due to cellular growth inhibition. Many of the examined β-blockers suppressed EGF-induced JB6 P+ cell transformation in a non-cytotoxic and concentration-dependent manner. However, the IC₅₀ values are high for the most potent inhibitors (243, 326, and 431 nM for carvedilol, labetalol, and alprenolol, respectively) and there is no correlation between pharmacological properties and inhibition of transformation. Therefore, the role of α1- and β2-adrenergic receptors (AR) was examined by standard competition assays and shRNA targeting β2-ARs, the only β-AR expressed in JB6 P+ cells. The results reveal that pharmacological inhibition of α1- and β2-ARs and genetic knockdown of β2-ARs did not abrogate carvedilol-mediated inhibition of EGF-induced JB6 P+ cell transformation. Furthermore, topical administration of carvedilol protected mice from UV-induced skin damage, while genetic ablation of β2-ARs increased carvedilol-mediated effects. Therefore, the prevailing hypothesis that the chemopreventive property of carvedilol is mediated through β-ARs is not supported by this data.

Pharmacological Characterization of a Novel 5-Hydroxybenzothiazolone-Derived β 2-Adrenoceptor Agonist with Functional Selectivity for Anabolic Effects on Skeletal Muscle Resulting in a Wider Cardiovascular Safety Window in Preclinical Studies

The anabolic effects of β 2-adrenoceptor (β 2-AR) agonists on skeletal muscle have been demonstrated in various species. However, the clinical use of β 2-AR agonists for skeletal muscle wasting conditions has been limited by their undesired cardiovascular effects. Here, we describe the preclinical pharmacological profile of a novel 5-hydroxybenzothiazolone (5-HOB) derived β 2-AR agonist in comparison with formoterol as a representative β 2-AR agonist that have been well characterized. In vitro, 5-HOB has nanomolar affinity for the human β 2-AR and selectivity over the β 1-AR and β 3-AR. 5-HOB also shows potent agonistic activity at the β 2-AR in primary skeletal muscle myotubes and induces hypertrophy of skeletal muscle myotubes. Compared with formoterol, 5-HOB demonstrates comparable full-agonist activity on cAMP production in skeletal muscle cells and skeletal muscle tissue-derived membranes. In contrast, a greatly reduced intrinsic activity was determined in cardiomyocytes and cell membranes prepared from the rat heart. In addition, 5-HOB shows weak effects on chronotropy, inotropy, and vascular relaxation compared with formoterol. In vivo, 5-HOB significantly increases hind limb muscle weight in rats with attenuated effects on heart weight and ejection fraction, unlike formoterol. Furthermore, changes in cardiovascular parameters after bolus subcutaneous treatment in rats and rhesus monkeys are significantly lower with 5-HOB compared with formoterol. In conclusion, the pharmacological profile of 5-HOB indicates superior tissue selectivity compared with the conventional β 2-AR agonist formoterol in preclinical studies and supports the notion that such tissue-selective agonists should be investigated for the safe treatment of muscle-wasting conditions without cardiovascular limiting effects.

Biased Receptor Signaling in Drug Discovery

A great deal of experimental evidence suggests that ligands can stabilize different receptor active states that go on to interact with cellular signaling proteins to form a range of different complexes in varying quantities. In pleiotropically linked receptor systems, this leads to selective activation of some signaling pathways at the expense of others (biased signaling). This article summarizes the current knowledge about the complex components of receptor systems, the evidence that biased signaling is used in natural physiology to fine-tune signaling, and the current thoughts on how this mechanism may be applied to the design of better drugs. Although this is a fairly newly discovered phenomenon, theoretical and experimental data suggest that it is a ubiquitous behavior of ligands and receptors and to be expected. Biased signaling is simple to detect in vitro and there are numerous methods to quantify the effect with scales that can be used to optimize this activity in structure-activity medicinal chemistry studies. At present, the major hurdle in the application of this mechanism to therapeutics is the translation of in vitro bias to in vivo effect; this is because of the numerous factors that can modify measures of bias in natural physiologic systems. In spite of this, biased signaling still has the potential to justify revisiting of receptor targets previously thought to be intractable and also furnishes the means to pursue targets previously thought to be forbidden due to deleterious physiology (as these may be eliminated through biased signaling).

Emergent Concepts of Receptor Pharmacology

Pharmacology, the chemical control of physiology, emerged as an offshoot of physiology when the physiologists using chemicals to probe physiological systems became more interested in the probes than the systems. Pharmacologists were always, and in many ways still are, bound to study drugs in systems they do not fully understand. Under these circumstances, null methods were the main ways in which conclusions about biologically active molecules were made. However, as understanding of the basic mechanisms of cellular function and biochemical systems were elucidated, so too did the understanding of how drugs affected these systems. Over the past 20 years, new ideas have emerged in the field that have completely changed and revitalized it; these are described herein. It will be seen how null methods in isolated tissues gave way to, first biochemical radioligand binding studies, and then to a wide array of functional assay technologies that can measure the effects of molecules on drug targets. In addition, the introduction of molecular dynamics, the appreciation of the allosteric nature of receptors, protein X-ray crystal structures, genetic manipulations in the form of knock-out and knock-in systems and Designer Receptors Exclusively Activated by Designer Drugs have revolutionized pharmacology.

The deubiquitinase ubiquitin-specific protease 20 is a positive modulator of myocardial β1-adrenergic receptor expression and signaling

Reversible ubiquitination of G protein-coupled receptors regulates their trafficking and signaling; whether deubiquitinases regulate myocardial β₁-adrenergic receptors (β₁ARs) is unknown. We report that ubiquitin-specific protease 20 (USP20) deubiquitinates and attenuates lysosomal trafficking of the β₁AR. β₁AR-induced phosphorylation of USP20 Ser-333 by protein kinase A-α (PKAα) was required for optimal USP20-mediated regulation of β₁AR lysosomal trafficking. Both phosphomimetic (S333D) and phosphorylation-impaired (S333A) USP20 possess intrinsic deubiquitinase activity equivalent to WT activity. However, unlike USP20 WT and S333D, the S333A mutant associated poorly with the β₁AR and failed to deubiquitinate the β₁AR. USP20-KO mice showed normal baseline systolic function but impaired β₁AR-induced contractility and relaxation. Dobutamine stimulation did not increase cAMP in USP20-KO left ventricles (LVs), whereas NKH477-induced adenylyl cyclase activity was equivalent to WT. The USP20 homolog USP33, which shares redundant roles with USP20, had no effect on β₁AR ubiquitination, but USP33 was up-regulated in USP20-KO hearts suggesting compensatory regulation. Myocardial β₁AR expression in USP20-KO was drastically reduced, whereas β₂AR expression was maintained as determined by radioligand binding in LV sarcolemmal membranes. Phospho-USP20 was significantly increased in LVs of wildtype (WT) mice after a 1-week catecholamine infusion and a 2-week chronic pressure overload induced by transverse aortic constriction (TAC). Phospho-USP20 was undetectable in β₁AR KO mice subjected to TAC, suggesting a role for USP20 phosphorylation in cardiac response to pressure overload. We conclude that USP20 regulates β₁AR signaling in vitro and in vivo Additionally, β₁AR-induced USP20 phosphorylation may serve as a feed-forward mechanism to stabilize β₁AR expression and signaling during pathological insults to the myocardium.

Increased Abundance of Lactobacillales in the Colon of Beta-Adrenergic Receptor Knock Out Mouse Is Associated With Increased Gut Bacterial Production of Short Chain Fatty Acids and Reduced IL17 Expression in Circulating CD4+ Immune Cells

Emerging evidence suggests an associative link between gut dysbiosis, the autonomic nervous system (ANS) and the immune system in pathophysiology of neurogenic hypertension (HTN). However, the close interplay between these three systems presents us with difficulties in deciphering the cause-effect relationship in disease. The present study utilized beta 1 and 2 adrenergic receptor knock out (AdrB1^tm1BkkAdrB2^tm1Bkk/J KO) mice to isolate the effects of reduced overall sympathetic drive on gut microbiota and systemic immune system. We observed the following: (i) Diminished beta adrenergic signaling mainly reflects in shifts in the Firmicutes phyla, with a significant increase in abundance of largely beneficial Bacilli Lactobacillales in the KO mice; (ii) This was associated with increased colonic production of beneficial short chain fatty acids (SCFAs) butyrate, acetate and propionate, confirming functional microbiota shifts in the KO mice; (iii) Dampened systemic immune responses in the KO mice reflected in reduction on circulating CD4⁺.IL17⁺ T cells and increase in young neutrophils, both previously associated with shifts in the gut microbiota. Taken together, these observations demonstrate that reduced expression of beta adrenergic receptors may lead to beneficial shifts in the gut microbiota and dampened systemic immune responses. Considering the role of both in hypertension, this suggests that dietary intervention may be a viable option for manipulation of blood pressure via correcting gut dysbiosis.

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

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

Increasing T-type calcium channel activity by β-adrenergic stimulation contributes to β-adrenergic regulation of heart rates

KEY POINTS

Cav3.1 T-type Ca2+ channel current (ICa-T ) contributes to heart rate genesis but is not known to contribute to heart rate regulation by the sympathetic/β-adrenergic system (SAS). We show that the loss of Cav3.1 makes the beating rates of the heart in vivo and perfused hearts ex vivo, as well as sinoatrial node cells, less sensitive to β-adrenergic stimulation; it also renders less conduction acceleration through the atrioventricular node by β-adrenergic stimulation. Increasing Cav3.1 in cardiomyocytes has the opposite effects. ICa-T in sinoatrial nodal cells can be upregulated by β-adrenergic stimulation. The results of the present study add a new contribution to heart rate regulation by the SAS system and provide potential new mechanisms for the dysregulation of heart rate and conduction by the SAS in the heart. T-type Ca2+ channel can be a target for heart disease treatments that aim to slow down the heart rate ABSTRACT: Cav3.1 (α1G ) T-type Ca2+ channel (TTCC) is expressed in mouse sinoatrial node cells (SANCs) and atrioventricular (AV) nodal cells and contributes to heart rate (HR) genesis and AV conduction. However, its role in HR regulation and AV conduction acceleration by the β-adrenergic system (SAS) is unclear. In the present study, L- (ICa-L ) and T-type (ICa-T ) Ca2+ currents were recorded in SANCs from Cav3.1 transgenic (TG) and knockout (KO), and control mice. ICa-T was absent in KO SANCs but enhanced in TG SANCs. In anaesthetized animals, different doses of isoproterenol (ISO) were infused via the jugular vein and the HR was recorded. The EC50 of the HR response to ISO was lower in TG mice but higher in KO mice, and the maximal percentage of HR increase by ISO was greater in TG mice but less in KO mice. In Langendorff-perfused hearts, ISO increased HR and shortened PR intervals to a greater extent in TG but to a less extent in KO hearts. KO SANCs had significantly slower spontaneous beating rates than control SANCs before and after ISO; TG SANCs had similar basal beating rates as control SANCs probably as a result of decreased ICa-L but a greater response to ISO than control SANCs. ICa-T in SANCs was significantly increased by ISO. ICa-T upregulation by β-adrenergic stimulation contributes to HR and conduction regulation by the SAS. TTCC can be a target for slowing the HR.

Moderate Continuous Aerobic Exercise Training Improves Cardiomyocyte Contractility in Β1 Adrenergic Receptor Knockout Mice

Background

The lack of cardiac β₁-adrenergic receptors (β₁-AR) negatively affects the regulation of both cardiac inotropy and lusitropy, leading, in the long term, to heart failure (HF). Moderate-intensity aerobic exercise (MCAE) is recommended as an adjunctive therapy for patients with HF.

Objective

We tested the effects of MCAE on the contractile properties of left ventricular (LV) myocytes from β₁ adrenergic receptor knockout (β₁ARKO) mice.

Methods

Four- to five-month-old male wild type (WT) and β₁ARKO mice were divided into groups: WT control (WTc) and trained (WTt); and β₁ARKO control (β₁ARKOc) and trained (β₁ARKOt). Animals from trained groups were submitted to a MCAE regimen (60 min/day; 60% of maximal speed, 5 days/week) on a treadmill, for 8 weeks. P ≤ 0.05 was considered significant in all comparisons.

Results

The β₁ARKO and exercised mice exhibited a higher (p < 0.05) running capacity than WT and sedentary ones, respectively. The β₁ARKO mice showed higher body (BW), heart (HW) and left ventricle (LVW) weights, as well as the HW/BW and LVW/BW than WT mice. However, the MCAE did not affect these parameters. Left ventricular myocytes from β₁ARKO mice showed increased (p < 0.05) amplitude and velocities of contraction and relaxation than those from WT. In addition, MCAE increased (p < 0.05) amplitude and velocities of contraction and relaxation in β₁ARKO mice.

Conclusion

MCAE improves myocyte contractility in the left ventricle of β₁ARKO mice. This is evidence to support the therapeutic value of this type of exercise training in the treatment of heart diseases involving β₁-AR desensitization or reduction.

Genetic background dominates the susceptibility to ventricular arrhythmias in a murine model of β-adrenergic stimulation

In cardiovascular research, several mouse strains with differing genetic backgrounds are used to investigate mechanisms leading to and sustaining ventricular arrhythmias. The genetic background has been shown to affect the studied phenotype in other research fields. Surprisingly little is known about potential strain-specific susceptibilities towards ventricular arrhythmias in vivo. Here, we hypothesized that inter-strain differences reported in the responsiveness of the β-adrenergic pathway, which is relevant for the development of arrhythmias, translate into a strain-specific vulnerability. To test this hypothesis, we characterized responses to β-adrenergic blockade (metoprolol) and β-adrenergic stimulation (isoproterenol) in 4 mouse strains commonly employed in cardiovascular research (Balb/c, BS, C57Bl/6 and FVB) using telemetric ECG recordings. We report pronounced differences in the electrical vulnerability following isoproterenol: Balb/c mice developed the highest number and the most complex arrhythmias while BS mice were protected. Balb/c mice, therefore, seem to be the background of choice for experiments requiring the occurrence of arrhythmias while BS mice may give insight into electrical stability. Arrhythmias did not correlate with the basal β-adrenergic tone, with the response to β-adrenergic stimulation or with the absolute heart rates during β-adrenergic stimulation. Thus, genetic factors dominate the susceptibility to ventricular arrhythmias in this model of β-adrenergic stimulation.

Gαi is required for carvedilol-induced β1 adrenergic receptor β-arrestin biased signaling

The β₁ adrenergic receptor (β₁AR) is recognized as a classical Gα_s-coupled receptor. Agonist binding not only initiates G protein-mediated signaling but also signaling through the multifunctional adapter protein β-arrestin. Some βAR ligands, such as carvedilol, stimulate βAR signaling preferentially through β-arrestin, a concept known as β-arrestin-biased agonism. Here, we identify a signaling mechanism, unlike that previously known for any Gα_s-coupled receptor, whereby carvedilol induces the transition of the β₁AR from a classical Gα_s-coupled receptor to a Gα_i-coupled receptor stabilizing a distinct receptor conformation to initiate β-arrestin-mediated signaling. Recruitment of Gα_i is not induced by any other βAR ligand screened, nor is it required for β-arrestin-bias activated by the β₂AR subtype of the βAR family. Our findings demonstrate a previously unrecognized role for Gα_i in β₁AR signaling and suggest that the concept of β-arrestin-bias may need to be refined to incorporate the selective bias of receptors towards distinct G protein subtypes.

Model of Murine Ventricular Cardiac Tissue for In Vitro Kinematic-Dynamic Studies of Electromagnetic and β-Adrenergic Stimulation

In a model of murine ventricular cardiac tissue in vitro, we have studied the inotropic effects of electromagnetic stimulation (frequency, 75 Hz), isoproterenol administration (10 μM), and their combination. In particular, we have performed an image processing analysis to evaluate the kinematics and the dynamics of beating cardiac syncytia starting from the video registration of their contraction movement. We have found that the electromagnetic stimulation is able to counteract the β-adrenergic effect of isoproterenol and to elicit an antihypertrophic response.