Epac is required for exogenous and endogenous stimulation of adenosine A2B receptor for inhibition of angiotensin II-induced collagen synthesis and myofibroblast differentiation

Role of A1 adenosine receptor in cardiovascular diseases: Bridging molecular mechanisms with therapeutic opportunities

Adenosine serves as a critical homeostatic regulator, exerting influence over physiological and pathological conditions in the cardiovascular system. During cellular stress, increased extracellular adenosine levels have been implicated in conferring cardioprotective effects through the activation of adenosine receptors with the A1 adenosine receptor subtype showing the highest expression in the heart. A1 adenosine receptor stimulation inhibits adenylyl cyclase activity via heterotrimeric Gi proteins, leading to the activation of distinct downstream effectors involved in cardiovascular homeostasis. While the comprehensive characterization of the pharmacological functions and intracellular signaling pathways associated with the A1 adenosine receptor subtype is still ongoing, this receptor is widely recognized as a crucial pharmacological target for the treatment of various states of cardiovascular diseases (CVDs). In this review, we focus on elucidating signal transduction of A1 adenosine receptor, particularly Gi protein-dependent and -independent pathways, and their relevance to cardiovascular protective effects as well as pathological consequences during cellular and tissue stresses in the cardiovascular system. Additionally, we provide comprehensive updates and detailed insights into a range of A1 adenosine receptor agonists and antagonists, detailing their development and evaluation through preclinical and clinical studies with a specific focus on their potential for the management of CVDs, especially heart diseases.

Current Understanding of the Role of Adenosine Receptors in Cancer

Cancer, a complex array of diseases, involves the unbridled proliferation and dissemination of aberrant cells in the body, forming tumors that can infiltrate neighboring tissues and metastasize to distant sites. With over 200 types, each cancer has unique attributes, risks, and treatment avenues. Therapeutic options encompass surgery, chemotherapy, radiation therapy, hormone therapy, immunotherapy, targeted therapy, or a blend of these methods. Yet, these treatments face challenges like late-stage diagnoses, tumor diversity, severe side effects, drug resistance, targeted drug delivery hurdles, and cost barriers. Despite these hurdles, advancements in cancer research, encompassing biology, genetics, and treatment, have enhanced early detection methods, treatment options, and survival rates. Adenosine receptors (ARs), including A1, A2A, A2B, and A3 subtypes, exhibit diverse roles in cancer progression, sometimes promoting or inhibiting tumor growth depending on the receptor subtype, cancer type, and tumor microenvironment. Research on AR ligands has revealed promising anticancer effects in lab studies and animal models, hinting at their potential as cancer therapeutics. Understanding the intricate signaling pathways and interactions of adenosine receptors in cancer is pivotal for crafting targeted therapies that optimize benefits while mitigating drawbacks. This review delves into each adenosine receptor subtype's distinct roles and signaling pathways in cancer, shedding light on their potential as targets for improving cancer treatment outcomes.

Targeting G protein-coupled receptors for heart failure treatment

Heart failure remains a leading cause of morbidity and mortality worldwide. Current treatment for patients with heart failure include drugs targeting G protein-coupled receptors such as β-adrenoceptor antagonists (β-blockers) and angiotensin II type 1 receptor antagonists (or angiotensin II receptor blockers). However, many patients progress to advanced heart failure with persistent symptoms, despite treatment with available therapeutics that have been shown to reduce mortality and mortality. GPCR targets currently being explored for the development of novel heart failure therapeutics include adenosine receptor, formyl peptide receptor, relaxin/insulin-like family peptide receptor, vasopressin receptor, endothelin receptor and the glucagon-like peptide 1 receptor. Many GPCR drug candidates are limited by insufficient efficacy and/or dose-limiting unwanted effects. Understanding the current challenges hindering successful clinical translation and the potential to overcome existing limitations will facilitate the future development of novel heart failure therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Gαq protein-biased ligand of angiotensin II type 1 receptor mediates myofibroblast differentiation through TGF-β1/ERK axis in human cardiac fibroblasts

Angiotensin II receptors are members of G protein-coupled receptor superfamily that manifest biased signals toward G protein- and β-arrestin-dependent pathways. However, the role of angiotensin II receptor-biased ligands and the mechanisms underlying myofibroblast differentiation in human cardiac fibroblasts have not been fully elucidated. Our results demonstrated that antagonism of angiotensin II type 1 receptor (AT₁ receptor) and blockade of G_αq protein suppressed angiotensin II (Ang II)-induced fibroblast proliferation, overexpression of collagen I and α-smooth muscle actin (α-SMA), and stress fibre formation, indicating the AT₁ receptor/G_αq axis is necessary for fibrogenic effects of Ang II. Stimulation of AT₁ receptors by their G_αq-biased ligand (TRV120055), but not β-arrestin-biased ligand (TRV120027), substantially exerted fibrogenic effects at a level similar to that of Ang II, suggesting that AT₁ receptor induced cardiac fibrosis in a G_αq-dependent and β-arrestin-independent manner. Valsartan prevents TRV120055-mediated fibroblast activation. TRV120055 mediated the upregulation of transforming growth factor-beta1 (TGF-β1) through the AT₁ receptor/G_αq cascade. In addition, G_αq protein and TGF-β1 were necessary for ERK1/2 activation induced by Ang II and TRV120055. Collectively, TGF-β1 and ERK1/2 are downstream effectors of the G_αq-biased ligand of AT₁ receptor for the induction of cardiac fibrosis.

Dual Blockade of TGF-β Receptor and Endothelin Receptor Synergistically Inhibits Angiotensin II-Induced Myofibroblast Differentiation: Role of AT1R/Gαq-Mediated TGF-β1 and ET-1 Signaling

Angiotensin II (Ang II) upregulates transforming growth factor-beta1 (TGF-β1) and endothelin-1 (ET-1) in various types of cells, and all of them act as profibrotic mediators. However, the signal transduction of angiotensin II receptor (ATR) for upregulation of TGF-β1 and ET-1, and their effectors that play an essential role in myofibroblast differentiation, are not fully understood. Therefore, we investigated the ATR networking with TGF-β1 and ET-1 and identified the signal transduction of these mediators by measuring the mRNA expression of alpha-smooth muscle actin (α-SMA) and collagen I using qRT-PCR. Myofibroblast phenotypes were monitored by α-SMA and stress fiber formation with fluorescence microscopy. Our findings suggested that Ang II induced collagen I and α-SMA synthesis and stress fiber formation through the AT₁R/G_αq axis in adult human cardiac fibroblasts (HCFs). Following AT₁R stimulation, G_αq protein, not G_βγ subunit, was required for upregulation of TGF-β1 and ET-1. Moreover, dual inhibition of TGF-β and ET-1 signaling completely inhibited Ang II-induced myofibroblast differentiation. The AT₁R/G_αq cascade transduced signals to TGF-β1, which in turn upregulated ET-1 via the Smad- and ERK1/2-dependent pathways. ET-1 consecutively bound to and activated endothelin receptor type A (ET_AR), leading to increases in collagen I and α-SMA synthesis and stress fiber formation. Remarkably, dual blockade of TGF-β receptor and ETR exhibited the restorative effects to reverse the myofibroblast phenotype induced by Ang II. Collectively, TGF-β1 and ET-1 are major effectors of AT₁R/G_αq cascade, and therefore, negative regulation of TGF-β and ET-1 signaling represents a targeted therapeutic strategy for the prevention and restoration of cardiac fibrosis.

Endothelin-1 Induces Cell Proliferation and Myofibroblast Differentiation through the ETAR/Gαq/ERK Signaling Pathway in Human Cardiac Fibroblasts

Endothelin-1 (ET-1) has been implicated in the pathogenesis of cardiac fibrosis. Stimulation of endothelin receptors (ETR) with ET-1 leads to fibroblast activation and myofibroblast differentiation, which is mainly characterized by an overexpression of α-smooth muscle actin (α-SMA) and collagens. Although ET-1 is a potent profibrotic mediator, the signal transductions and subtype specificity of ETR contributing to cell proliferation, as well as α-SMA and collagen I synthesis in human cardiac fibroblasts are not well clarified. This study aimed to evaluate the subtype specificity and signal transduction of ETR on fibroblast activation and myofibroblast differentiation. Treatment with ET-1 induced fibroblast proliferation, and synthesis of myofibroblast markers, α-SMA, and collagen I through the ET_AR subtype. Inhibition of G_αq protein, not G_αi or G_βγ, inhibited these effects of ET-1, indicating the essential role of G_αq protein-mediated ET_AR signaling. In addition, ERK1/2 was required for ET_AR/G_αq axis-induced proliferative capacity and overexpression of these myofibroblast markers. Antagonism of ETR with ETR antagonists (ERAs), ambrisentan and bosentan, inhibited ET-1-induced cell proliferation and synthesis of α-SMA and collagen I. Furthermore, ambrisentan and bosentan promoted the reversal of myofibroblasts after day 3 of treatment, with loss of proliferative ability and a reduction in α-SMA synthesis, confirming the restorative effects of ERAs. This novel work reports on the ET_AR/G_αq/ERK signaling pathway for ET-1 actions and blockade of ETR signaling with ERAs, representing a promising therapeutic strategy for prevention and restoration of ET-1-induced cardiac fibrosis.

Adenosine and Adenosine Receptors: Advances in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the world. Because the key to developing innovative therapies that limit the onset and the progression of AF is to fully understand the underlying molecular mechanisms of AF, the aim of the present narrative review is to report the most recent advances in the potential role of the adenosinergic system in the pathophysiology of AF. After a comprehensive approach describing adenosinergic system signaling and the mechanisms of the initiation and maintenance of AF, we address the interactions of the adenosinergic system's signaling with AF. Indeed, adenosine release can activate four G-coupled membrane receptors, named A₁, A_2A, A_2B and A₃. Activation of the A_2A receptors can promote the occurrence of delayed depolarization, while activation of the A₁ receptors can shorten the action potential's duration and induce the resting membrane's potential hyperpolarization, which promote pulmonary vein firing, stabilize the AF rotors and allow for functional reentry. Moreover, the A_2B receptors have been associated with atrial fibrosis homeostasis. Finally, the adenosinergic system can modulate the autonomous nervous system and is associated with AF risk factors. A question remains regarding adenosine release and the adenosine receptors' activation and whether this would be a cause or consequence of AF.

High Glucose-Induced Cardiomyocyte Damage Involves Interplay between Endothelin ET-1/ETA/ETB Receptor and mTOR Pathway

Patients with type two diabetes mellitus (T2DM) are at increased risk for cardiovascular diseases. Impairments of endothelin-1 (ET-1) signaling and mTOR pathway have been implicated in diabetic cardiomyopathies. However, the molecular interplay between the ET-1 and mTOR pathway under high glucose (HG) conditions in H9c2 cardiomyoblasts has not been investigated. We employed MTT assay, qPCR, western blotting, fluorescence assays, and confocal microscopy to assess the oxidative stress and mitochondrial damage under hyperglycemic conditions in H9c2 cells. Our results showed that HG-induced cellular stress leads to a significant decline in cell survival and an impairment in the activation of ETA-R/ETB-R and the mTOR main components, Raptor and Rictor. These changes induced by HG were accompanied by a reactive oxygen species (ROS) level increase and mitochondrial membrane potential (MMP) loss. In addition, the fragmentation of mitochondria and a decrease in mitochondrial size were observed. However, the inhibition of either ETA-R alone by ambrisentan or ETA-R/ETB-R by bosentan or the partial blockage of the mTOR function by silencing Raptor or Rictor counteracted those adverse effects on the cellular function. Altogether, our findings prove that ET-1 signaling under HG conditions leads to a significant mitochondrial dysfunction involving contributions from the mTOR pathway.

Stimulation of adenosine A1 receptor prevents oxidative injury in H9c2 cardiomyoblasts: Role of Gβγ-mediated Akt and ERK1/2 signaling

Oxidative stress causes cellular injury and damage in the heart primarily through apoptosis resulting in cardiac abnormalities such as heart failure and cardiomyopathy. During oxidative stress, stimulation of adenosine receptor (AR) has been shown to protect against oxidative damage due to their cytoprotective properties. However, the subtype specificity and signal transductions of adenosine A₁ receptor (A₁R) on cardiac protection during oxidative stress have remained elusive. In this study, we found that stimulation of A₁Rs with N⁶-cyclopentyladenosine (CPA), a specific A₁R agonist, attenuated the H₂O₂-induced intracellular and mitochondrial reactive oxygen species (ROS) production and apoptosis. In addition, A₁R stimulation upregulated the synthesis of antioxidant enzymes (catalase and GPx-1), antiapoptotic proteins (Bcl-2 and Bcl-xL), and mitochondria-related markers (UCP2 and UCP3). Blockades of Gβγ subunit of heterotrimeric Gα_i protein antagonized A₁R-mediated antioxidant and antiapoptotic effects, confirming the potential role of Gβγ subunit-mediated A₁R signaling. Additionally, cardioprotective effects of CPA mediated through PI3K/Akt- and ERK1/2-dependent signaling pathways. Thus, we propose that A₁R represents a promising therapeutic target for prevention of oxidative injury in the heart.

Cardioprotective Effects of Glucagon-like Peptide-1 (9-36) Against Oxidative Injury in H9c2 Cardiomyoblasts: Potential Role of the PI3K/Akt/NOS Pathway

ABSTRACT

Glucagon-like peptide (GLP)-1(7-36), a major active form of GLP-1 hormone, is rapidly cleaved by dipeptidyl peptidase-4 to generate a truncated metabolite, GLP-1(9-36) which has a low affinity for GLP-1 receptor (GLP-1R). GLP-1(7-36) has been shown to have protective effects on cardiovascular system through GLP-1R-dependent pathway. Nevertheless, the cardioprotective effects of GLP-1(9-36) have not fully understood. The present study investigated the effects of GLP-1(9-36), including its underlying mechanisms against oxidative stress and apoptosis in H9c2 cells. Here, we reported that GLP-1(9-36) protects H9c2 cardiomyoblasts from hydrogen peroxide (H2O2)-induced oxidative stress by promoting the synthesis of antioxidant enzymes, glutathione peroxidase-1, catalase, and heme oxygenase-1. In addition, treatment with GLP-1(9-36) suppressed H2O2-induced apoptosis by attenuating caspase-3 activity and upregulating antiapoptotic proteins, Bcl-2 and Bcl-xL. These protective effects of GLP-1(9-36) are attenuated by blockade of PI3K-mediated Akt phosphorylation and prevention of nitric oxide synthase-induced nitric oxide production. Thus, GLP-1(9-36) represents the potential therapeutic target for prevention of oxidative stress and apoptosis in the heart via PI3K/Akt/nitric oxide synthase signaling pathway.

Pharmacological Tuning of Adenosine Signal Nuances Underlying Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) roughly represents half of the cardiac failure events in developed countries. The proposed 'systemic microvascular paradigm' has been used to explain HFpHF presentation heterogeneity. The lack of effective treatments with few evidence-based therapeutic recommendations makes HFpEF one of the greatest unmet clinical necessities worldwide. The endogenous levels of the purine nucleoside, adenosine, increase significantly following cardiovascular events. Adenosine exerts cardioprotective, neuromodulatory, and immunosuppressive effects by activating plasma membrane-bound P1 receptors that are widely expressed in the cardiovascular system. Its proven benefits have been demonstrated in preclinical animal tests. Here, we provide a comprehensive and up-to-date critical review about the main therapeutic advantages of tuning adenosine signalling pathways in HFpEF, without discounting their side effects and how these can be seized.

Molecular Basis of Atrial Fibrillation Initiation and Maintenance

Atrial fibrillation (AF) is the most common cardiac arrhythmia, largely associated to morbidity and mortality. Over the past decades, research in appearance and progression of this arrhythmia have turned into significant advances in its management. However, the incidence of AF continues to increase with the aging of the population and many important fundamental and translational underlaying mechanisms remain elusive. Here, we review recent advances in molecular and cellular basis for AF initiation, maintenance and progression. We first provide an overview of the basic molecular and electrophysiological mechanisms that lead and characterize AF. Next, we discuss the upstream regulatory factors conducting the underlying mechanisms which drive electrical and structural AF-associated remodeling, including genetic factors (risk variants associated to AF as transcriptional regulators and genetic changes associated to AF), neurohormonal regulation (i.e., cAMP) and oxidative stress imbalance (cGMP and mitochondrial dysfunction). Finally, we discuss the potential therapeutic implications of those findings, the knowledge gaps and consider future approaches to improve clinical management.

Therapeutic Targets for the Treatment of Cardiac Fibrosis and Cancer: Focusing on TGF-β Signaling

Transforming growth factor-β (TGF-β) is a common mediator of cancer progression and fibrosis. Fibrosis can be a significant pathology in multiple organs, including the heart. In this review, we explain how inhibitors of TGF-β signaling can work as antifibrotic therapy. After cardiac injury, profibrotic mediators such as TGF-β, angiotensin II, and endothelin-1 simultaneously activate cardiac fibroblasts, resulting in fibroblast proliferation and migration, deposition of extracellular matrix proteins, and myofibroblast differentiation, which ultimately lead to the development of cardiac fibrosis. The consequences of fibrosis include a wide range of cardiac disorders, including contractile dysfunction, distortion of the cardiac structure, cardiac remodeling, and heart failure. Among various molecular contributors, TGF-β and its signaling pathways which play a major role in carcinogenesis are considered master fibrotic mediators. In fact, recently the inhibition of TGF-β signaling pathways using small molecule inhibitors, antibodies, and gene deletion has shown that the progression of several cancer types was suppressed. Therefore, inhibitors of TGF-β signaling are promising targets for the treatment of tissue fibrosis and cancers. In this review, we discuss the molecular mechanisms of TGF-β in the pathogenesis of cardiac fibrosis and cancer. We will review recent in vitro and in vivo evidence regarding antifibrotic and anticancer actions of TGF-β inhibitors. In addition, we also present available clinical data on therapy based on inhibiting TGF-β signaling for the treatment of cancers and cardiac fibrosis.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Adenosine Receptor Signaling Targets Both PKA and Epac Pathways to Polarize Dendritic Cells to a Suppressive Phenotype

Extracellular adenosine accumulates in tumors and causes suppression of immune cells. Suppressive adenosine signaling is achieved through adenosine A2A and A2B receptors, which are Gs coupled, and their activation elevates cAMP levels. Gs-coupled GPCR signaling causes cAMP accumulation, which plays an anti-inflammatory role in immune cells. Protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) are two intracellular receptors of cAMP. In this study we showed that adenosine receptor signaling polarizes activated murine dendritic cells (DCs) into a tumor-promoting suppressive phenotype. Adenosine receptor signaling activates cAMP pathway and upregulates the negative regulators of NF-κB but does not influence phosphorylation of immediate inflammatory signaling molecules downstream of TLR signaling. Pharmacologic activation of both PKA and Epac pathways by specific cAMP analogues phenocopied the effects of adenosine signaling on murine DCs, such as suppression of proinflammatory cytokines, elevation of anti-inflammatory IL-10, increased expression of regulators of NF-κB pathway, and finally suppression of T cell activation. Inhibition of effector cytokine, IL-12p40 production, and increased immunosuppressive IL-10 production by adenosine signaling is significantly reversed only when both PKA and Epac pathways were inhibited together. Adenosine signaling increased IL-10 secretion while decreasing IL-12p40 secretion in human monocyte-derived DCs. Stimulation of both PKA and Epac pathways also caused combinatorial effects in regulation of IL-12p40 secretion in human monocyte-derived DCs. Interestingly, PKA signaling alone caused similar increase in IL-10 secretion to that of adenosine signaling in human monocyte-derived DCs. Our data suggest adenosine/cAMP signaling targets both PKA/Epac pathways to fully differentiate DCs into a suppressive phenotype.

Elevated cyclic-AMP represses expression of exchange protein activated by cAMP (EPAC1) by inhibiting YAP-TEAD activity and HDAC-mediated histone deacetylation

Ligand-induced activation of Exchange Protein Activated by cAMP-1 (EPAC1) is implicated in numerous physiological and pathological processes, including cardiac fibrosis where changes in EPAC1 expression have been detected. However, little is known about how EPAC1 expression is regulated. Therefore, we investigated regulation of EPAC1 expression by cAMP in cardiac fibroblasts. Elevation of cAMP using forskolin, cAMP-analogues or adenosine A2B-receptor activation significantly reduced EPAC1 mRNA and protein levels and inhibited formation of F-actin stress fibres. Inhibition of actin polymerisation with cytochalasin-D, latrunculin-B or the ROCK inhibitor, Y-27632, mimicked effects of cAMP on EPAC1 mRNA and protein levels. Elevated cAMP also inhibited activity of an EPAC1 promoter-reporter gene, which contained a consensus binding element for TEAD, which is a target for inhibition by cAMP. Inhibition of TEAD activity using siRNA-silencing of its co-factors YAP and TAZ, expression of dominant-negative TEAD or treatment with YAP-TEAD inhibitors, significantly inhibited EPAC1 expression. However, whereas expression of constitutively-active YAP completely reversed forskolin inhibition of EPAC1-promoter activity it did not rescue EPAC1 mRNA levels. Chromatin-immunoprecipitation detected a significant reduction in histone3-lysine27-acetylation at the EPAC1 proximal promoter in response to forskolin stimulation. HDAC1/3 inhibition partially reversed forskolin inhibition of EPAC1 expression, which was completely rescued by simultaneously expressing constitutively active YAP. Taken together, these data demonstrate that cAMP downregulates EPAC1 gene expression via disrupting the actin cytoskeleton, which inhibits YAP/TAZ-TEAD activity in concert with HDAC-mediated histone deacetylation at the EPAC1 proximal promoter. This represents a novel negative feedback mechanism controlling EPAC1 levels in response to cAMP elevation.

The adenosine A2B G protein-coupled receptor: Recent advances and therapeutic implications

The adenosine A_2B receptor (A_2BAR) is one of four adenosine receptor subtypes belonging to the Class A family of G protein-coupled receptors (GPCRs). Until recently, the A_2BAR remained poorly characterised, in part due to its relatively low affinity for the endogenous agonist adenosine and therefore presumed minor physiological significance. However, the substantial increase in extracellular adenosine concentration, the sensitisation of the receptor and the upregulation of A_2BAR expression under conditions of hypoxia and inflammation, suggest the A_2BAR as an exciting therapeutic target in a variety of pathological disease states. Here we discuss the pharmacology of the A_2BAR and outline its role in pathophysiology including ischaemia-reperfusion injury, fibrosis, inflammation and cancer.

Prolonged stimulation of β2-adrenergic receptor with β2-agonists impairs insulin actions in H9c2 cells

Insulin resistance is a condition in which there is a defect in insulin actions to induce glucose uptake into the cells. Overstimulation of β₂-adrenergic receptors (β₂ARs) is associated with the pathogenesis of insulin resistance in the heart. However, the mechanisms by which β₂-agonists affect insulin resistance in the heart are incompletely understood. The β₂-agonists are used for treatment of asthma due to bronchodilating effects. We also investigated the effects of β₂-agonists in human bronchial smooth muscle (HBSM) cells. In this study, we demonstrate that chronic treatment with salbutamol, salmeterol, and formoterol inhibited insulin-induced glucose uptake and GLUT4 synthesis in H9c2 myoblast cells. Sustained β₂AR stimulation also attenuated GLUT4 translocation to the plasma membrane, whereas short-term stimulation had no effect. In HBSM cells, prolonged treatment with β₂-agonists had no effect on insulin-induced glucose uptake and did not alter insulin-induced expressions of GLUT1, GLUT4, and GLUT10. In addition, genetic polymorphisms at amino acid positions 16 and 27 of β₂AR are linked to insulin resistance by significant suppression of GLUT4 translocation compared to wild-type. Thus, prolonged β₂AR stimulation by β₂-agonists impairs insulin actions through suppression of GLUT synthesis and translocation only in H9c2 cells.