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de Moura AL, Brum PC, de Carvalho AETS, Spadari RC. Effect of stress on the chronotropic and inotropic responses to β-adrenergic agonists in isolated atria of KOβ2 mice. Life Sci 2023; 322:121644. [PMID: 37004731 DOI: 10.1016/j.lfs.2023.121644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 03/06/2023] [Accepted: 03/26/2023] [Indexed: 04/03/2023]
Abstract
Altered sensitivity to the chronotropic and inotropic effects of catecholamines and reduction in β1/β2-adrenoceptor (β1/β2-AR) ratio were reported in failing and in senescent human heart, as well as in isolated atria and ventricle of rats submitted to stress. This was due to downregulation of β1-AR with or without up-regulation of β2-AR. AIMS To investigate the stress-induced behavior of β1-AR in the heart of mice expressing a non-functional β2-AR subtype. The guiding hypothesis is that the absence of β2-AR signaling will not affect the behavior of β1-AR during stress and that those are independent processes. MATERIALS AND METHODS The chronotropic and inotropic responses to β-AR agonists in isolated atria of stressed mice expressing a non-functional β2-AR were analyzed. The mRNA and protein expressions of β1- and β2-AR were also determined. KEY FINDINGS No deaths were observed in mice under stress protocol. Atria of stressed mice displayed reduced sensitivity to isoprenaline compared to the controls, an effect that was abolished by the β2- and β1-AR antagonists 50 nM ICI118,551 and 300 nM CGP20712A, respectively. Sensitivity and maximum response to the β-agonists dobutamine and salbutamol were not altered by stress or ICI118,551. The responses to dobutamine and salbutamol were prevented by CGP20712A. The expression of β1-AR was reduced at protein levels. SIGNIFICANCE Collectively, our data provide evidence that the cardiac β2-AR is not essential for survival in a stressful situation and that the stress-induced reduction of β1-AR expression was independent of the β2-AR presence.
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Cheng M, Chen C, Yu K, Lv X, Zeng Q, Dong N, Zhu F. Ablation of CXCR4 expression in cardiomyocytes exacerbates isoproterenol‑induced cell death and heart failure. Int J Mol Med 2022; 51:13. [PMID: 36579657 PMCID: PMC9869727 DOI: 10.3892/ijmm.2022.5216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 11/21/2022] [Indexed: 12/30/2022] Open
Abstract
CXCR4 is a seven‑transmembrane‑spanning Gi‑coupled receptor for the SDF‑1 chemokine and plays a critical role in cardiovascular development and post‑injury repair. However, the specific role of CXCR4 in cardiomyocytes is incompletely understood. It was hypothesized that CXCR4 activation in cardiomyocytes antagonizes β‑adrenoceptor/Gs signaling‑induced cardiac dysfunction. Cardiomyocyte‑specific CXCR4 knockout (CXCR4‑CMKO) mice were generated by crossing CXCR4fl/fl and MHC‑Cre+/‑ mice. Their cardiac structure and function in the basal state are equivalent to that of the control MHC‑Cre+/‑ littermates until at least 4 months old. However, following continuous subcutaneous administration of isoproterenol (Iso) via an osmotic mini‑pump, the ventricular myocardial contractility, dilation, cardiomyocyte apoptosis, and interstitial fibrosis are worse in CXCR4‑CMKO mice than in MHC‑Cre+/‑ littermates. In the cultured H9C2 cardiomyocytes, SDF‑1 treatment markedly attenuated Iso‑induced apoptosis and reduction in phospho‑Akt, and this protective effect was lost by knockdown of CXCR4 or by co‑treatment with Gi inhibitors. In conclusion, CXCR4 promotes cardiomyocyte survival and heart function during β‑adrenergic stress.
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Affiliation(s)
- Min Cheng
- Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China,Correspondence to: Dr Min Cheng or Dr Feng Zhu, Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1377 Jiefang Avenue, Wuhan, Hubei 430022, P.R. China, E-mail: , E-mail:
| | - Can Chen
- Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
| | - Kunwu Yu
- Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
| | - Xiao Lv
- Department of Orthopedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
| | - Qiutang Zeng
- Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
| | - Nianguo Dong
- Department of Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
| | - Feng Zhu
- Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China,Correspondence to: Dr Min Cheng or Dr Feng Zhu, Department of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1377 Jiefang Avenue, Wuhan, Hubei 430022, P.R. China, E-mail: , E-mail:
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3
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Yang D, Dai X, Xing Y, Tang X, Yang G, Harrison AG, Cahoon J, Li H, Lv X, Yu X, Wang P, Wang H. Intrinsic cardiac adrenergic cells contribute to LPS-induced myocardial dysfunction. Commun Biol 2022; 5:96. [PMID: 35079095 PMCID: PMC8789803 DOI: 10.1038/s42003-022-03007-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 12/23/2021] [Indexed: 02/08/2023] Open
Abstract
Intrinsic cardiac adrenergic (ICA) cells regulate both developing and adult cardiac physiological and pathological processes. However, the role of ICA cells in septic cardiomyopathy is unknown. Here we show that norepinephrine (NE) secretion from ICA cells is increased through activation of Toll-like receptor 4 (TLR4) to aggravate myocardial TNF-α production and dysfunction by lipopolysaccharide (LPS). In ICA cells, LPS activated TLR4-MyD88/TRIF-AP-1 signaling that promoted NE biosynthesis through expression of tyrosine hydroxylase, but did not trigger TNF-α production due to impairment of p65 translocation. In a co-culture consisting of LPS-treated ICA cells and cardiomyocytes, the upregulation and secretion of NE from ICA cells activated cardiomyocyte β1-adrenergic receptor driving Ca2+/calmodulin-dependent protein kinase II (CaMKII) to crosstalk with NF-κB and mitogen-activated protein kinase pathways. Importantly, blockade of ICA cell-derived NE prevented LPS-induced myocardial dysfunction. Our findings suggest that ICA cells may be a potential therapeutic target for septic cardiomyopathy.
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Affiliation(s)
- Duomeng Yang
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Xiaomeng Dai
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Yun Xing
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Xiangxu Tang
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Guang Yang
- Department of Pathogen biology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Andrew G Harrison
- Department of Immunology, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT, 06030, USA
| | - Jason Cahoon
- Department of Immunology, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT, 06030, USA
| | - Hongmei Li
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Xiuxiu Lv
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Xiaohui Yu
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China
| | - Penghua Wang
- Department of Immunology, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT, 06030, USA
| | - Huadong Wang
- Department of Pathophysiology, Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China.
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Colombe AS, Pidoux G. Cardiac cAMP-PKA Signaling Compartmentalization in Myocardial Infarction. Cells 2021; 10:cells10040922. [PMID: 33923648 PMCID: PMC8073060 DOI: 10.3390/cells10040922] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/02/2021] [Accepted: 04/13/2021] [Indexed: 02/07/2023] Open
Abstract
Under physiological conditions, cAMP signaling plays a key role in the regulation of cardiac function. Activation of this intracellular signaling pathway mirrors cardiomyocyte adaptation to various extracellular stimuli. Extracellular ligand binding to seven-transmembrane receptors (also known as GPCRs) with G proteins and adenylyl cyclases (ACs) modulate the intracellular cAMP content. Subsequently, this second messenger triggers activation of specific intracellular downstream effectors that ensure a proper cellular response. Therefore, it is essential for the cell to keep the cAMP signaling highly regulated in space and time. The temporal regulation depends on the activity of ACs and phosphodiesterases. By scaffolding key components of the cAMP signaling machinery, A-kinase anchoring proteins (AKAPs) coordinate both the spatial and temporal regulation. Myocardial infarction is one of the major causes of death in industrialized countries and is characterized by a prolonged cardiac ischemia. This leads to irreversible cardiomyocyte death and impairs cardiac function. Regardless of its causes, a chronic activation of cardiac cAMP signaling is established to compensate this loss. While this adaptation is primarily beneficial for contractile function, it turns out, in the long run, to be deleterious. This review compiles current knowledge about cardiac cAMP compartmentalization under physiological conditions and post-myocardial infarction when it appears to be profoundly impaired.
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Nashawi M, Sheikh O, Battisha A, Ghali A, Chilton R. Neural tone and cardio-renal outcomes in patients with type 2 diabetes mellitus: a review of the literature with a focus on SGLT2 inhibitors. Heart Fail Rev 2020; 26:643-652. [PMID: 33169337 DOI: 10.1007/s10741-020-10046-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/19/2020] [Indexed: 12/18/2022]
Abstract
Recent clinical trials involving the systemic effects of sodium-glucose cotransporter 2 inhibitors (SGLT2i) have revealed beneficial outcomes pertaining to the microvascular sequelae of type 2 diabetes mellitus (T2DM) such as nephropathy, as well as macrovascular effects such as major adverse cardiovascular effects (MACE). Such findings have spurred the elevation of these agents to level A-tiers of recommendation within clinical guidelines addressing the management of complicated T2DM. While the mechanisms of SGLTi (-flozin drugs) are still being elucidated, a paucity of data exists within the literature appraising the role of neuromodulation and associated mechanisms in the aforementioned outcome studies. Given the role of the nervous system in orchestrating the pathologic processes that hamper cardio-renal status, insight into this topic offers an expanded perspective on T2DM. In this review we investigate the mechanisms by which SGLTi improve cardio-renal function in T2DM patients with emphases on neural tone and nervous system physiology.
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Affiliation(s)
- Mouhamed Nashawi
- Division of Medicine-Cardiology, UT Health San Antonio, 7872, 7703 Floyd Curl Drive, San Antonio, TX, 78229, USA.
| | - Omar Sheikh
- Division of Medicine-Cardiology, UT Health San Antonio, 7872, 7703 Floyd Curl Drive, San Antonio, TX, 78229, USA
| | - Ayman Battisha
- Department of Internal Medicine, University of Massachusetts Medical School-Bay State, 759 Chestnut Street, Springfield, MA, 01199, USA
| | - Abdullah Ghali
- Division of Medicine-Cardiology, UT Health San Antonio, 7872, 7703 Floyd Curl Drive, San Antonio, TX, 78229, USA
| | - Robert Chilton
- Division of Medicine-Cardiology, UT Health San Antonio, 7872, 7703 Floyd Curl Drive, San Antonio, TX, 78229, USA
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Bernardo BC, Ooi JYY, Weeks KL, Patterson NL, McMullen JR. Understanding Key Mechanisms of Exercise-Induced Cardiac Protection to Mitigate Disease: Current Knowledge and Emerging Concepts. Physiol Rev 2018; 98:419-475. [PMID: 29351515 DOI: 10.1152/physrev.00043.2016] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The benefits of exercise on the heart are well recognized, and clinical studies have demonstrated that exercise is an intervention that can improve cardiac function in heart failure patients. This has led to significant research into understanding the key mechanisms responsible for exercise-induced cardiac protection. Here, we summarize molecular mechanisms that regulate exercise-induced cardiac myocyte growth and proliferation. We discuss in detail the effects of exercise on other cardiac cells, organelles, and systems that have received less or little attention and require further investigation. This includes cardiac excitation and contraction, mitochondrial adaptations, cellular stress responses to promote survival (heat shock response, ubiquitin-proteasome system, autophagy-lysosomal system, endoplasmic reticulum unfolded protein response, DNA damage response), extracellular matrix, inflammatory response, and organ-to-organ crosstalk. We summarize therapeutic strategies targeting known regulators of exercise-induced protection and the challenges translating findings from bench to bedside. We conclude that technological advancements that allow for in-depth profiling of the genome, transcriptome, proteome and metabolome, combined with animal and human studies, provide new opportunities for comprehensively defining the signaling and regulatory aspects of cell/organelle functions that underpin the protective properties of exercise. This is likely to lead to the identification of novel biomarkers and therapeutic targets for heart disease.
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Affiliation(s)
- Bianca C Bernardo
- Baker Heart and Diabetes Institute , Melbourne , Australia ; Department of Paediatrics, University of Melbourne , Victoria , Australia ; Department of Diabetes, Central Clinical School, Monash University , Victoria , Australia ; Department of Medicine, Central Clinical School, Monash University , Victoria , Australia ; and Department of Physiology, School of Biomedical Sciences , Victoria , Australia
| | - Jenny Y Y Ooi
- Baker Heart and Diabetes Institute , Melbourne , Australia ; Department of Paediatrics, University of Melbourne , Victoria , Australia ; Department of Diabetes, Central Clinical School, Monash University , Victoria , Australia ; Department of Medicine, Central Clinical School, Monash University , Victoria , Australia ; and Department of Physiology, School of Biomedical Sciences , Victoria , Australia
| | - Kate L Weeks
- Baker Heart and Diabetes Institute , Melbourne , Australia ; Department of Paediatrics, University of Melbourne , Victoria , Australia ; Department of Diabetes, Central Clinical School, Monash University , Victoria , Australia ; Department of Medicine, Central Clinical School, Monash University , Victoria , Australia ; and Department of Physiology, School of Biomedical Sciences , Victoria , Australia
| | - Natalie L Patterson
- Baker Heart and Diabetes Institute , Melbourne , Australia ; Department of Paediatrics, University of Melbourne , Victoria , Australia ; Department of Diabetes, Central Clinical School, Monash University , Victoria , Australia ; Department of Medicine, Central Clinical School, Monash University , Victoria , Australia ; and Department of Physiology, School of Biomedical Sciences , Victoria , Australia
| | - Julie R McMullen
- Baker Heart and Diabetes Institute , Melbourne , Australia ; Department of Paediatrics, University of Melbourne , Victoria , Australia ; Department of Diabetes, Central Clinical School, Monash University , Victoria , Australia ; Department of Medicine, Central Clinical School, Monash University , Victoria , Australia ; and Department of Physiology, School of Biomedical Sciences , Victoria , Australia
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Abstract
β-arrestin1 (or arrestin2) and β-arrestin2 (or arrestin3) are ubiquitously expressed cytosolic adaptor proteins that were originally discovered for their inhibitory role in G protein-coupled receptor (GPCR) signaling through heterotrimeric G proteins. However, further biochemical characterization revealed that β-arrestins do not just "block" the activated GPCRs, but trigger endocytosis and kinase activation leading to specific signaling pathways that can be localized on endosomes. The signaling pathways initiated by β-arrestins were also found to be independent of G protein activation by GPCRs. The discovery of ligands that blocked G protein activation but promoted β-arrestin binding, or vice-versa, suggested the exciting possibility of selectively activating intracellular signaling pathways. In addition, it is becoming increasingly evident that β-arrestin-dependent signaling is extremely diverse and provokes distinct cellular responses through different GPCRs even when the same effector kinase is involved. In this review, we summarize various signaling pathways mediated by β-arrestins and highlight the physiologic effects of β-arrestin-dependent signaling.
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Postinfarct Left Ventricular Remodelling: A Prevailing Cause of Heart Failure. Cardiol Res Pract 2016; 2016:2579832. [PMID: 26989555 PMCID: PMC4775793 DOI: 10.1155/2016/2579832] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 01/13/2016] [Accepted: 01/17/2016] [Indexed: 12/11/2022] Open
Abstract
Heart failure is a chronic disease with high morbidity and mortality, which represents a growing challenge in medicine. A major risk factor for heart failure with reduced ejection fraction is a history of myocardial infarction. The expansion of a large infarct scar and subsequent regional ventricular dilatation can cause postinfarct remodelling, leading to significant enlargement of the left ventricular chamber. It has a negative prognostic value, because it precedes the clinical manifestations of heart failure. The characteristics of the infarcted myocardium predicting postinfarct remodelling can be studied with cardiac magnetic resonance and experimental imaging modalities such as diffusion tensor imaging can identify the changes in the architecture of myocardial fibers. This review discusses all the aspects related to postinfarct left ventricular remodelling: definition, pathogenesis, diagnosis, consequences, and available therapies, together with experimental interventions that show promising results against postinfarct remodelling and heart failure.
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Palmitoyl acyltransferase Aph2 in cardiac function and the development of cardiomyopathy. Proc Natl Acad Sci U S A 2015; 112:15666-71. [PMID: 26644582 DOI: 10.1073/pnas.1518368112] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Protein palmitoylation regulates many aspects of cell function and is carried out by acyl transferases that contain zf-DHHC motifs. The in vivo physiological function of protein palmitoylation is largely unknown. Here we generated mice deficient in the acyl transferase Aph2 (Ablphilin 2 or zf-DHHC16) and demonstrated an essential role for Aph2 in embryonic/postnatal survival, eye development, and heart development. Aph2(-/-) embryos and pups showed cardiomyopathy and cardiac defects including bradycardia. We identified phospholamban, a protein often associated with human cardiomyopathy, as an interacting partner and a substrate of Aph2. Aph2-mediated palmitoylation of phospholamban on cysteine 36 differentially alters its interaction with PKA and protein phosphatase 1 α, augmenting serine 16 phosphorylation, and regulates phospholamban pentamer formation. Aph2 deficiency results in phospholamban hypophosphorylation, a hyperinhibitory form. Ablation of phospholamban in Aph2(-/-) mice histologically and functionally alleviated the heart defects. These findings establish Aph2 as a critical in vivo regulator of cardiac function and reveal roles for protein palmitoylation in the development of other organs including eyes.
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Affiliation(s)
- Paul C Simpson
- From the VA Medical Center, San Francisco, CA; and University of California, Department of Medicine and CVRI, San Francisco.
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11
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Baker AJ. Adrenergic signaling in heart failure: a balance of toxic and protective effects. Pflugers Arch 2014; 466:1139-50. [PMID: 24623099 DOI: 10.1007/s00424-014-1491-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Revised: 02/24/2014] [Accepted: 02/26/2014] [Indexed: 10/25/2022]
Abstract
Heart failure with reduced ejection fraction involves activation of the sympathetic nervous system and chronic hyperactivation of the sympatho-adrenergic receptors (ARs) β-ARs and α1-ARs, which are thought to be cardiotoxic and worsen pathological remodeling and function. Concurrently, the failing heart manifests significant decreases in sympathetic nerve terminal density, decreased cardiac norepinephrine levels, and marked downregulation of β-AR abundance and signaling. Thus, a state of both feast and famine coexist with respect to the adrenergic state in heart failure. For the failing heart, the hyperadrenergic state is toxic. However, the role of hypoadrenergic mechanisms in the pathophysiology of heart failure is less clear. Cardiotoxic effects are known to arise from the β1-AR subtype, and use of β-AR blockers is a cornerstone of current heart failure therapy. However, cardioprotective effects arise from the β2-AR subtype that counteract hyperactive β1-AR signaling, but unfortunately, β2-AR cardioprotective signaling in heart failure is inhibited by β-AR blocker therapy. In contrast to current dogma, recent research shows β1-AR signaling can also be cardioprotective. Moreover, for some forms of heart failure, β2-AR signaling is cardiotoxic. Thus for both β-AR subtypes, there is a balance between cardiotoxic versus cardioprotective effects. In heart failure, stimulation of α1-ARs is widely thought to be cardiotoxic. However, also contrary to current dogma, recent research shows that α1-AR signaling is cardioprotective. Taken together, recent research identifies cardioprotective signaling arising from β1-AR, β2-AR, and α1-ARs. A goal for future therapies will to harness the protective effects of AR signaling while minimizing cardiotoxic effects. The trajectory of heart failure therapy changed radically from the previous and intuitive use of sympathetic agonists, which unfortunately resulted in greater mortality, to the current use of β-AR blockers, which initially seemed counterintuitive. As a cautionary note, if the slow adoption of beta-blocker therapy in heart failure is any guide, then new treatment strategies, especially counterintuitive therapies involving stimulating β-AR and α1-AR signaling, may take considerable time to develop and gain acceptance.
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Affiliation(s)
- Anthony J Baker
- Veterans Affairs Medical Center, San Francisco and Department of Medicine, University of California, Cardiology Division (111C), 4150 Clement St, San Francisco, CA, 94121, USA,
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