Agonist-stimulated reactive oxygen species formation regulates beta2-adrenergic receptor signal transduction

ROS-mediated regulation of β2AR function: Does oxidation play a meaningful role towards β2-agonist tachyphylaxis in airway obstructive diseases?

β2-adrenergic receptor (β2AR) agonists are the clinical gold standard for treatment and prophylaxis of airway constriction in pulmonary obstructive diseases such as asthma and COPD. Inhaled β2-agonists elicit rapid bronchorelaxation of the airway smooth muscle, yet, clinical tachyphylaxis to this response can occur over repeated and chronic use, which reduces the bronchodilatory effectiveness. Several mechanisms have been proposed to impart β2-agonist tachyphylaxis, most notably β2AR desensitization. However, airway tissue is known to be highly oxidative, particularly in obstructive disease states where reactive oxygen species (ROS) generation is upregulated and ROS degradation is suboptimal yielding a large oxidative burden. Recent evidence demonstrates that β2AR can regulate ROS generation and that ROS can post-translationally alter β2AR cysteine residues via oxidation, leading to distinct functional receptor outcomes. Herein, we discuss the growing evidence for β2AR mediated ROS generation in airway cells and the role of ROS in regulating β2AR via cysteine-oxidation of the receptor. Given the functional consequence of the β2AR-ROS signaling axis in the airways, we also discuss the potential role of ROS in mediating β2-agonist tachyphylaxis.

Agonists and hydrogen peroxide mediate hyperoxidation of β2-adrenergic receptor in airway epithelial cells: Implications for tachyphylaxis to β2-agonists in constrictive airway disorders

Asthma and other airway obstructive disorders are characterized by heightened inflammation and excessive airway epithelial cell reactive oxygen species (ROS), which give rise to a highly oxidative environment. After decades of use, β2-adrenergic receptor (β2AR) agonists remain at the forefront of treatment options for asthma, however, chronic use of β2-agonists leads to tachyphylaxis to the bronchorelaxant effects, a phenomenon that remains mechanistically unexplained. We have previously demonstrated that β2AR agonism increases ROS generation in airway epithelial cells, which upholds proper receptor function via feedback oxidation of β2AR cysteine thiolates to Cys-S-sulfenic acids (Cys-SOH). Our previous results also demonstrate that prevention of normal redox cycling of this post-translational oxi-modification back to the thiol prevents proper receptor function. Given that Cys-S-sulfenic acids can be irreversibly overoxidized to Cys-S-sulfinic (Cys-SO2H) or S-sulfonic (Cys-SO3H) acids, which are incapable of further participation in redox reactions, we hypothesized that β2-agonist tachyphylaxis may be explained by hyperoxidation of β2AR to S-sulfinic acids. Here, using airway epithelial cell lines and primary small airway epithelial cells from healthy and asthma-diseased donors, we show that β2AR agonism generates H2O2 in a receptor and NAPDH oxidase-dependent manner. We also demonstrate that acute and chronic receptor agonism can facilitate β2AR S-sulfination, and that millimolar H2O2 concentrations are deleterious to β2AR-mediated cAMP formation, an effect that can be rescued to a degree in the presence of the cysteine-donating antioxidant N-acetyl-L-cysteine. Our results reveal that the oxidative state of β2AR may contribute to receptor functionality and may, at least in part, explain β2-agonist tachyphylaxis.

Role of canagliflozin in ameliorating isoprenaline induced cardiomyocyte oxidative stress via the heme oxygenase-1 mediated pathway

Canagliflozin (CZ) is commonly prescribed for management of type-2 diabetes mellitus (T2DM); it also can reduce the risk of myocardial infarction. We used 80 albino Wistar rats to investigate the cardioprotective potential of CZ against oxidative stress caused by administration of isoprenaline (ISO). We found that ISO stimulates production of reactive oxygen species and that CZ administration caused up-regulation of antioxidants and down-regulation of oxidants due to nuclear factor erythroid-2 related factor-2, as well as by enhancement of the heme oxygenase-1 mediated cascade. CZ monotherapy may play a cardioprotective role in diabetic patients. CZ possesses strong antioxidant potential that ameliorates cardiac damage induced by ISO administration.

H2S regulates redox signaling downstream of cardiac β-adrenergic receptors in a G6PD-dependent manner

Stimulating β-adrenergic receptors (β-AR) culminates in pathological hypertrophy - a condition underlying multiple cardiovascular diseases (CVDs). The ensuing signal transduction network appears to involve mutually communicating phosphorylation-cascades and redox signaling modules, although the regulators of redox signaling processes remain largely unknown. We previously showed that H₂S-induced Glucose-6-phosphate dehydrogenase (G6PD) activity is critical for suppressing cardiac hypertrophy in response to adrenergic stimulation. Here, we extended our findings and identified novel H₂S-dependent pathways constraining β-AR-induced pathological hypertrophy. We demonstrated that H₂S regulated early redox signal transduction processes - including suppression of cue-dependent production of reactive oxygen species (ROS) and oxidation of cysteine thiols (R-SOH) on critical signaling intermediates (including AKT1/2/3 & ERK1/2). Consistently, the maintenance of intracellular levels of H₂S dampened the transcriptional signature associated with pathological hypertrophy upon β-AR-stimulation, as demonstrated by RNA-seq analysis. We further prove that H₂S remodels cell metabolism by promoting G6PD activity to enforce changes in the redox state that favor physiological cardiomyocyte growth over pathological hypertrophy. Thus, our data suggest that G6PD is an effector of H₂S-mediated suppression of pathological hypertrophy and that the accumulation of ROS in the G6PD-deficient background can drive maladaptive remodeling. Our study reveals an adaptive role for H₂S relevant to basic and translational studies. Identifying adaptive signaling mediators of the β-AR-induced hypertrophy may reveal new therapeutic targets and routes for CVD therapy optimization.

The Skeletal Muscle Relaxer Cyclobenzaprine Is a Potent Non-Competitive Antagonist of Histamine H1 Receptors

Cyclobenzaprine is a tricyclic dimethylpropanamine skeletal muscle relaxant, which is used clinically to decrease muscle spasm and hypercontractility, as well as acute musculoskeletal pain. Although the absolute mechanism of action of cyclobenzaprine remains elusive, it is known to mediate its effects centrally via inhibition of tonic somatic motor function, likely through modulation of noradrenergic and serotonergic systems. While cyclobenzaprine is effective as a muscle relaxant, greater than 30% of patients experience drowsiness and sedative-hypnotic effects, yet the mechanisms that cause this adverse effect are also undescribed. Based on this common adverse effect profile and the structural similarity of cyclobenzaprine to tricyclic antidepressants, as well as ethanolamine first-generation antihistamines, we hypothesized that cyclobenzaprine facilitates sedative effects via off-target antagonism of central histamine H1 receptors (H1Rs). Here, for the first time, we present data that demonstrate that cyclobenzaprine exhibits low nanomolar affinity for the cloned human H1R, as well as that expressed in both rat and mouse brain. Using saturation radioligand binding, we also demonstrate that cyclobenzaprine binds to the H1R in a noncompetitive manner. Similarly, functional assays measuring both Ca+2 influx and novel TRUPATH G-protein subunit bioluminescence resonance energy transfer biosensors reveal that cyclobenzaprine also blocks histamine-mediated H1R functional activity in a noncompetitive manner, whereas the classical H1R antagonist diphenhydramine does so competitively. Given that cyclobenzaprine readily crosses the blood-brain barrier and its muscle relaxant effects occur centrally, our data suggest that off-target central antagonism of H1R by cyclobenzaprine facilitates the significant sedative effect of this agent seen in patients. SIGNIFICANCE STATEMENT: Cyclobenzaprine, a clinically used muscle relaxant that is strongly linked to sedation, demonstrates high-affinity noncompetitive antagonism at the histamine H1 receptor. This effect likely modulates the high degree of sedation that patients experience.

[Covalent drug discovery targeting G protein-coupled receptors]

G protein-coupled receptors (GPCRs) play pivotal roles in converting physicochemical stimuli due to environmental changes to intracellular responses. After ligand stimulation, many GPCRs are desensitized and then recycled or degraded through phosphorylation and β-arrestin-dependent internalization, an important process to maintain protein quality control of GPCRs. However, it is unknown how GPCRs with low β-arrestin sensitivity are controlled. Here we unmasked a β-arrestin-independent GPCR internalization, named Redox-dependent Alternative Internalization (REDAI), focusing on β-arrestin-resistant purinergic P2Y₆ receptor (P2Y₆R). P2Y₆R is highly expressed in macrophage and pathologically contributes to the development of colitis in mice. Natural electrophiles including in functional foods induce REDAI-mediated P2Y₆R degradation leading to anti-inflammation in macrophages. Prevention of Cys220 modification on P2Y₆R resulted in aggravation of the colitis. These results strongly suggest that targeting REDAI on GPCRs will be a breakthrough strategy for the prevention and treatment of inflammatory diseases.

Molecular mechanisms of oxidative stress in asthma

The lungs are exposed to reactive oxygen species oxygen (ROS) produced as a result of inhalation of oxygen, as well as smoke and other air pollutants. Cell metabolism and the NADPH oxidases (Nox) generate low levels of intracellular ROS that act as signal transduction mediators by inducing oxidative modifications of histones, enzymes and transcription factors. Redox signalling is also regulated by localised production and sensing of ROS in mitochondria, the endoplasmic reticulum (ER) and inside the nucleus. Intracellular ROS are maintained at low levels through the action of a battery of enzymatic and non-enzymatic antioxidants. Asthma is a heterogeneous airway inflammatory disease with different immune endotypes; these include atopic or non-atopic Th2 type immune response associated with eosinophilia, or a non-Th2 response associated with neutrophilia. Airway remodelling and hyperresponsiveness accompany the inflammatory response in asthma. Over-production of ROS resulting from infiltrating immune cells, particularly eosinophils and neutrophils, and a concomitant impairment of antioxidant responses lead to development of oxidative stress in asthma. Oxidative stress is augmented in severe asthma and during exacerbations, as well as by air pollution and obesity, and causes oxidative damage of tissues promoting airway inflammation and hyperresponsiveness. Furthermore, deregulated Nox activity, mitochondrial dysfunction, ER stress and/or oxidative DNA damage, resulting from exposure to irritants, inflammatory mediators or obesity, may lead to redox-dependent changes in cell signalling. ROS play a central role in airway epithelium-mediated sensing, development of innate and adaptive immune responses, and airway remodelling and hyperresponsiveness. Nonetheless, antioxidant compounds have proven clinically ineffective as therapeutic agents for asthma, partly due to issues with stability and in vivo metabolism of these compounds. The compartmentalised nature of ROS production and sensing, and the role of ROS in homeostatic responses and in the action of corticosteroids and β2-adrenergic receptor agonists, adds another layer of complexity to antioxidant therapy development. Nox inhibitors and mitochondrial-targeted antioxidants are in clinical development for a number of diseases but they have not yet been investigated in asthma. A better understanding of the complex role of ROS in the pathogenesis of asthma will highlight new opportunities for more targeted and effective redox therapies.

Flacourtia indica fruit extract modulated antioxidant gene expression, prevented oxidative stress and ameliorated kidney dysfunction in isoprenaline administered rats

This study evaluated the effect of Flacourtia indica fruit extract against isoprenaline (ISO) induced renal damage in rats. This investigation showed that ISO administration in rats increased the level oxidative stress biomarkers such as malondialdehyde (MDA), nitric oxide (NO), advanced protein oxidation product (APOP) in kidneys followed by a decrease in antioxidant enzymes functions. Flacourtia indica fruit extract, which is rich in strong antioxidants, also reduced the MDA, NO and APOP level in kidney of ISO administered rats. Inflammation and necrosis was also visible in kidney section of ISO administered rats which was significantly prevented by atenolol and Flacourtia indica fruit extract. Moreover, atenolol and Flacourtia indica fruit extract also modulated the genes expressions related to inflammation and oxidative stress in kidneys. The beneficial effects could be attributed to the presence of a number of phenolic antioxidants. This study suggests that Flacourtia indica fruit extract may prevent kidney dysfunction in ISO administered rats, probably by preventing oxidative stress and inflammation.

Canagliflozin ameliorates renal oxidative stress and inflammation by stimulating AMPK-Akt-eNOS pathway in the isoprenaline-induced oxidative stress model

Diabetes is a leading cause of chronic kidney disease, and the high prevalence of sympathetic nervous system (SNS) hyperactivity in diabetic patients makes them further susceptible to SNS-mediated oxidative stress and accelerated kidney damage. Here, we investigated if canagliflozin can reverse isoprenaline (ISO)-induced renal oxidative damage in rats, a model that mimics SNS overstimulation-induced organ injuries in humans. We found that ISO administration elevates renal oxidative stress markers including malondialdehyde (MDA), advanced protein oxidation product (APOP), myeloperoxidase (MPO) and nitric oxide (NO), while depleting levels of endogenous antioxidants such as catalase (CAT), superoxide dismutase (SOD) and glutathione (GSH). Strikingly, canagliflozin treatment of ISO-treated rats not only prevents elevation of oxidative stress markers but also rescues levels of depleted antioxidants. Our results also show that canagliflozin stimulates antioxidant/anti-inflammatory signaling pathways involving AMP-activated protein kinase (AMPK), Akt and eNOS, and inhibits iNOS and NADPH oxidase isoform 4 (NOX4), all of which are associated with oxidative stress and inflammation. Further, canagliflozin prevents ISO-induced apoptosis of kidney cells by inhibiting Bax protein upregulation and caspase-3 activation. Histological examination of kidney sections reveal that canagliflozin attenuates ISO-mediated increases in inflammatory cell infiltration, collagen deposition and fibrosis. Finally, consistent with these findings, canagliflozin treatment improves kidney function in ISO-treated rats, suggesting that the antioxidant effects may be clinically translatable.

Canagliflozin attenuates isoprenaline-induced cardiac oxidative stress by stimulating multiple antioxidant and anti-inflammatory signaling pathways

The antidiabetic drug canagliflozin is reported to possess several cardioprotective effects. However, no studies have investigated protective effects of canagliflozin in isoprenaline (ISO)-induced cardiac oxidative damage-a model mimicking sympathetic nervous system (SNS) overstimulation-evoked cardiac injuries in humans. Therefore, we investigated protective effects of canagliflozin in ISO-induced cardiac oxidative stress, and their underlying molecular mechanisms in Long-Evans rat heart and in HL-1 cardiomyocyte cell line. Our data showed that ISO administration inflicts pro-oxidative changes in heart by stimulating production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). In contrast, canagliflozin treatment in ISO rats not only preserves endogenous antioxidants but also reduces cardiac oxidative stress markers, fibrosis and apoptosis. Our Western blotting and messenger RNA expression data demonstrated that canagliflozin augments antioxidant and anti-inflammatory signaling involving AMP-activated protein kinase (AMPK), Akt, endothelial nitric oxide synthase (eNOS), nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). In addition, canagliflozin treatment attenuates pro-oxidative, pro-inflammatory and pro-apoptotic signaling mediated by inducible nitric oxide synthase (iNOS), transforming growth factor beta (TGF-β), NADPH oxidase isoform 4 (Nox4), caspase-3 and Bax. Consistently, canagliflozin treatment improves heart function marker in ISO-treated rats. In summary, we demonstrated that canagliflozin produces cardioprotective actions by promoting multiple antioxidant and anti-inflammatory signaling.

Aquaporin 8 is involved in H2 O2 -mediated differential regulation of metabolic signaling by α1 - and β-adrenoceptors in hepatocytes

Reactive oxygen species participate in regulating intracellular signaling pathways. Herein, we investigated the reported opposite effects of hydrogen peroxide (H₂ O₂ ) on metabolic signaling mediated by activated α₁ - and β-adrenoceptors (ARs) in hepatocytes. In isolated rat hepatocytes, stimulation of α₁ -AR increases H₂ O₂ production via NADPH oxidase 2 (NOX2) activation. We find that the H₂ O₂ thus produced is essential for α₁ -AR-mediated activation of the classical hepatic glycogenolytic, gluconeogenic, and ureagenic responses. However, H₂ O₂ inhibits β-AR-mediated activation of these metabolic responses. We show that H₂ O₂ mediates its effects on α₁ -AR and β-AR by permeating cells through aquaporin 8 (AQP8) channels and promoting Ca²⁺ mobilization. Thus, our findings reveal a novel NOX2-H₂ O₂ -AQP8-Ca²⁺ signaling cascade acting downstream of α₁ -AR in hepatocytes, which, by negatively regulating β-AR signaling, establishes negative crosstalk between the two pathways.

Carboxy-Terminal Phosphoregulation of the Long Splice Isoform of Free-Fatty Acid Receptor-4 Mediates β-Arrestin Recruitment and Signaling to ERK1/2

Free-fatty acid receptor-4 (FFA4), previously termed GPR120, is a G protein-coupled receptor (GPCR) for medium and long-chained fatty acids, agonism of which can regulate a myriad of metabolic, sensory, inflammatory, and proliferatory signals. Two alternative splice isoforms of FFA4 exist that differ by the presence of an additional 16 amino acids in the longer (FFA4-L) transcript, which has been suggested to be an intrinsically β-arrestin-biased GPCR. Although the shorter isoform (FFA4-S) has been studied more extensively, very little is known about mechanisms of regulation or signaling of the longer isoform. Because β-arrestin recruitment is dependent on receptor phosphorylation, in the current study, we used the endogenous agonist docosahexaenoic acid (DHA) to examine the mechanisms of FFA4-L phosphorylation, as well as DHA-dependent β-arrestin recruitment and DHA-dependent extracellular-signal regulated kinase-1/2 (ERK1/2) signaling in human embryonic kidney 293 cells. Our results reveal differences in basal phosphorylation of the two FFA4 isoforms, and we show that DHA-mediated phosphorylation of FFA4-L is primarily regulated by G protein-coupled receptor kinase 6, whereas protein kinase-C can also contribute to agonist-induced and heterologous phosphorylation. Moreover, our data demonstrate that FFA4-L phosphorylation occurs on the distal C terminus and is directly responsible for recruitment and interactions with β-arrestin-2. Finally, using CRISPR/Cas9 genome-edited cells, our data reveal that unlike FFA4-S, the longer isoform is unable to facilitate phosphorylation of ERK1/2 in cells that are devoid of β-arrestin-1/2. Together, these results are the first to demonstrate phosphoregulation of FFA4-L as well as the effects of loss of phosphorylation sites on β-arrestin recruitment and ERK1/2 activation. SIGNIFICANCE STATEMENT: Free-fatty acid receptor-4 (FFA4) is a cell-surface G protein-coupled receptor for medium and long-chained fatty acids that can be expressed as distinct short (FFA4-S) or long (FFA4-L) isoforms. Although much is known about FFA4-S, the longer isoform remains virtually unstudied. Here, we reveal the mechanisms of docosahexaenoic acid-induced phosphorylation of FFA4-L and subsequent β-arrestin-2 recruitment and extracellular-signal regulated kinase-1/2 activity.

Cysteine redox state regulates human β2-adrenergic receptor binding and function

Bronchoconstrictive airway disorders such as asthma are characterized by inflammation and increases in reactive oxygen species (ROS), which produce a highly oxidative environment. β2-adrenergic receptor (β2AR) agonists are a mainstay of clinical therapy for asthma and provide bronchorelaxation upon inhalation. We have previously shown that β2AR agonism generates intracellular ROS, an effect that is required for receptor function, and which post-translationally oxidizes β2AR cysteine thiols to Cys-S-sulfenic acids (Cys-S-OH). Furthermore, highly oxidative environments can irreversibly oxidize Cys-S-OH to Cys-S-sulfinic (Cys-SO₂H) or S-sulfonic (Cys-SO₃H) acids, which are incapable of further participating in homeostatic redox reactions (i.e., redox-deficient). The aim of this study was to examine the vitality of β2AR-ROS interplay and the resultant functional consequences of β2AR Cys-redox in the receptors native, oxidized, and redox-deficient states. Here, we show for the first time that β2AR can be oxidized to Cys-S-OH in situ, moreover, using both clonal cells and a human airway epithelial cell line endogenously expressing β2AR, we show that receptor redox state profoundly influences β2AR orthosteric ligand binding and downstream function. Specifically, homeostatic β2AR redox states are vital toward agonist-induced cAMP formation and subsequent CREB and G-protein-dependent ERK1/2 phosphorylation, in addition to β-arrestin-2 recruitment and downstream arrestin-dependent ERK1/2 phosphorylation and internalization. On the contrary, redox-deficient β2AR states exhibit decreased ability to signal via either Gαs or β-arrestin. Together, our results demonstrate a β2AR-ROS redox axis, which if disturbed, interferes with proper receptor function.

Evolving concepts in the pathogenesis of uraemic cardiomyopathy

The term uraemic cardiomyopathy refers to the cardiac abnormalities that are seen in patients with chronic kidney disease (CKD). Historically, this term was used to describe a severe cardiomyopathy that was associated with end-stage renal disease and characterized by severe functional abnormalities that could be reversed following renal transplantation. In a modern context, uraemic cardiomyopathy describes the clinical phenotype of cardiac disease that accompanies CKD and is perhaps best characterized as diastolic dysfunction seen in conjunction with left ventricular hypertrophy and fibrosis. A multitude of factors may contribute to the pathogenesis of uraemic cardiomyopathy, and current treatments only modestly improve outcomes. In this Review, we focus on evolving concepts regarding the roles of fibroblast growth factor 23 (FGF23), inflammation and systemic oxidant stress and their interactions with more established mechanisms such as pressure and volume overload resulting from hypertension and anaemia, respectively, activation of the renin-angiotensin and sympathetic nervous systems, activation of the transforming growth factor-β (TGFβ) pathway, abnormal mineral metabolism and increased levels of endogenous cardiotonic steroids.

The β2-adrenergic receptor-ROS signaling axis: An overlooked component of β2AR function?

β2-Adrenergic receptor (β2AR) agonists are clinically used to elicit rapid bronchodilation for the treatment of bronchospasms in pulmonary diseases such as asthma and COPD, both of which exhibit characteristically high levels of reactive oxygen species (ROS); likely secondary to over-expression of ROS generating enzymes and chronically heightened inflammation. Interestingly, β2AR has long-been linked to ROS, yet the involvement of ROS in β2AR function has not been as vigorously studied as other aspects of β2AR signaling. Herein, we discuss the existing body of evidence linking β2AR activation to intracellular ROS generation and importantly, the role of ROS in regulating β2AR function. The reciprocal interplay of the β2AR and ROS appear to endow this receptor with the ability to self-regulate signaling efficacy and ligand binding, hereby unveiling a redox-axis that may be unfavorably altered in pathological states contributing to both disease progression and therapeutic drug responses.

The adrenergic receptor antagonist carvedilol interacts with serotonin 2A receptors both in vitro and in vivo

There is increasing support for the potential clinical use of compounds that interact with serotonin 2A (5-HT_2A) receptors. It is therefore of interest to discover novel compounds that interact with 5-HT_2A receptors. In the present study, we used computational chemistry to identify critical ligand structural features of 5-HT_2A receptor binding and function. Query of compound databases using those ligand features revealed the adrenergic receptor antagonist carvedilol as a high priority match. As carvedilol is used clinically for cardiovascular diseases, we conducted experiments to assess whether it has any interactions with 5-HT_2A receptors. In vitro experiments demonstrated that carvedilol has high nanomolar affinity for 5-HT_2A receptors. In vivo experiments demonstrated that carvedilol increases the ethanol-induced loss of the righting reflex and suppresses operant responding in mice, and that these effects are attenuated by pretreatment with the selective 5-HT_2A receptor antagonist M100907. Moreover, carvedilol did not induce the head-twitch response in mice, suggesting a lack of psychedelic effects. However, carvedilol did not activate canonical 5-HT_2A receptor signaling pathways and antagonized serotonin-mediated signaling. It also reduced the head-twitch response induced by 2,5-Dimethoxy-4-iodoamphetamine, suggesting potential in vivo antagonism, allosteric modulation, or functional bias. These data suggest that carvedilol has functionally relevant interactions with 5-HT_2A receptors, providing a novel mechanism of action for a clinically used compound. However, our findings do not clearly delineate the precise mechanism of action of carvedilol at 5-HT_2A receptors, and additional experiments are needed to elucidate the role of 5-HT_2A receptors in the behavioral and clinical effects of carvedilol.

The Role of β-Adrenergic Overstimulation in the Early Stages of Renal Injury

BACKGROUND/AIMS

To assess the possible contribution of the β-adrenergic overstimulation in early stages of renal injury, the present study evaluated, in rats, the effects of the β-adrenoceptor agonist isoproterenol (ISO) on renal function and morphology, as well as the renal mRNA and protein expression of the NADPH oxidase isoform 4 (Nox 4) and subunit p22phox, endoplasmic reticulum (ER) stress, pro-inflammatory, pro-apoptotic and renin-angiotensin system (RAS) components.

METHODS

Wistar rats received ISO (0.3 mg.kg-1.day-1 s.c.) or vehicle (control) for eight days. At the end of the treatment, food and water intake, urine output and body weight gain were evaluated and renal function studies were performed. Renal tissue was used for the morphological, quantitative PCR and immunohistochemical studies.

RESULTS

ISO did not change metabolic parameters or urine output. However it induced a decrease in renal blood flow and an increase in the filtration fraction. These changes were accompanied by increased cortical mRNA and protein expression for the renal oxidative stress components including Nox 4 and p22phox; ER stress, pro-inflamatory, pro-apoptotic as well as RAS components. ISO also induced a significant increase in medullar renin protein expression.

CONCLUSION

These findings support relevant information regarding the contribution of specific β-adrenergic hyperactivity in early stage of renal injury, indicating the reactive oxygen species, ER stress and intrarenal RAS as important factors in this process.

Different roles of β-arrestin and the PKA pathway in mitochondrial ROS production induced by acute β-adrenergic receptor stimulation in neonatal mouse cardiomyocytes

Reactive oxygen species (ROS) play a crucial role in various physiological and pathological processes mediated by β-adrenergic receptors (β-ARs) in cardiomyocytes. However, the sources and signaling pathways involved in ROS production induced by acute β-AR activation have not yet been fully defined. In primary neonatal mouse cardiomyocytes (NMCMs), the β-AR agonist isoproterenol (ISO) induced a rapid increase in mitochondrial ROS and total ROS production. Both the expression and activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2/4 (NOX 2/4) remained unchanged after 2 h of ISO treatment, suggesting that acute ISO stimulation mainly induces mitochondrial ROS production in NMCMs. Knockdown of β-arrestin1, but not β-arrestin2, inhibited ISO-induced mitochondrial ROS production within 1-2 h after ISO treatment. Moreover, forskolin, an adenylyl cyclase (AC) activator, rapidly increased mitochondrial ROS as early as 15 min after ISO treatment. Inhibition of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway abolished the mitochondrial ROS production within 15-60 min after ISO treatment. In conclusion, mitochondria are the major source of ROS production upon acute ISO stimulation. β-arrestin1, but not β-arrestin2, is involved in ISO-induced mitochondrial ROS production. Upon acute β-AR stimulation in NMCMs, the classical cAMP/PKA pathway is responsible for faster mitochondrial ROS production, whereas β-arrestin1 signaling is responsible for slower mitochondrial ROS production.

Spironolactone Prevents Endothelial Nitric Oxide Synthase Uncoupling and Vascular Dysfunction Induced by β-Adrenergic Overstimulation: Role of Perivascular Adipose Tissue

Supplemental Digital Content is available in the text.

Sustained stimulation of β-adrenoceptors (β-ARs) and activation of renin–angiotensin–aldosterone system are common features of cardiovascular diseases with rising sympathetic activation, including essential hypertension, myocardial infarction, and heart failure. In this study, we investigated the role of AT1 receptor and mineralocorticoid receptor (MR) in the vascular alterations caused by β-AR overstimulation. β-AR overstimulation with associated cardiac hypertrophy and increased vasoconstrictor response to phenylephrine in aorta were modeled in rats by 7-day isoproterenol treatment. The increased vasoconstrictor response to phenylephrine in this model was blunted by the MR antagonist spironolactone, but not by the AT1 receptor antagonist losartan, despite the blunting of cardiac hypertrophy with both drugs. Spironolactone, but not losartan, restored NO bioavailability in association with lower endothelial nitric oxide synthase–derived superoxide production, increased endothelial nitric oxide synthase dimerization, and aortic HSP90 upregulation. MR genomic and nongenomic functions were activated in aortas from isoproterenol-treated rats. Isoproterenol did not modify plasma levels of MR ligands aldosterone and corticosterone but rather increased perivascular adipose tissue–derived corticosterone in association with increased expression of 11β-hydroxysteroid dehydrogenase type 1. The anticontractile effect of aortic perivascular adipose tissue was impaired by β-AR overstimulation and restored by MR blockade. These results suggest that activation of vascular MR signaling contributes to the vascular dysfunction induced by β-AR overstimulation associated with endothelial nitric oxide synthase uncoupling. These findings reveal an additional explanation for the protective effects of MR antagonists in cardiovascular disorders with sympathetic activation.

TGR5 is essential for bile acid-dependent cholangiocyte proliferation in vivo and in vitro

OBJECTIVE

Cholestatic liver diseases in humans as well as bile acid (BA)-feeding and common bile duct ligation (CBDL) in rodents trigger hyperplasia of cholangiocytes within the portal fields. Furthermore, elevation of BA levels enhances proliferation and invasiveness of cholangiocarcinoma (CCA) cells in animal models, thus promoting tumour progression. TGR5 is a G-protein coupled BA receptor, which is highly expressed in cholangiocytes and postulated to mediate the proliferative effects of BA.

DESIGN

BA-dependent cholangiocyte proliferation was examined in TGR5-knockout and wild type mice following cholic acid (CA)-feeding and CBDL. TGR5-dependent proliferation and protection from apoptosis was studied in isolated cholangiocytes and CCA cell lines following stimulation with TGR5 ligands and kinase inhibitors. TGR5 expression was analysed in human CCA tissue.

RESULTS

Cholangiocyte proliferation was significantly reduced in TGR5-knockout mice in response to CA-feeding and CBDL. Taurolithocholic acid and TGR5-selective agonists induced cholangiocyte proliferation through elevation of reactive oxygen species and cSrc mediated epidermal growth factor receptor transactivation and subsequent Erk1/2 phosphorylation only in wild type but not in TGR5-knockout-derived cells. In human CCA tissue TGR5 was overexpressed and the pathway of TGR5-dependent proliferation via epidermal growth factor receptor and extracellular signal-regulated kinase (ERK)1/2 activation also translated to CCA cell lines. Furthermore, apoptosis was inhibited by TGR5-dependent CD95 receptor serine phosphorylation.

CONCLUSIONS

TGR5 is an important mediator of BA-induced cholangiocyte proliferation in vivo and in vitro. Furthermore, TGR5 protects cholangiocytes from death receptor-mediated apoptosis. These mechanisms may protect cholangiocytes from BA toxicity under cholestatic conditions, however, they may trigger proliferation and apoptosis resistance in malignantly transformed cholangiocytes, thus promoting CCA progression.

Different effects of prolonged β-adrenergic stimulation on heart and cerebral artery

The aim of this review was to understand the effects of β-adrenergic stimulation on oxidative stress, structural remodeling, and functional alterations in the heart and cerebral artery. Diverse stimuli activate the sympathetic nervous system, leading to increased levels of catecholamines. Long-term overstimulation of the β-adrenergic receptor (βAR) in response to catecholamines causes cardiovascular diseases, including cardiac hypertrophy, stroke, coronary artery disease, and heart failure. Although catecholamines have identical sites of action in the heart and cerebral artery, the structural and functional modifications differentially activate intracellular signaling cascades. βAR-stimulation can increase oxidative stress in the heart and cerebral artery, but has also been shown to induce different cytoskeletal and functional modifications by modulating various components of the βAR signal transduction pathways. Stimulation of βAR leads to cardiac dysfunction due to an overload of intracellular Ca²⁺ in cardiomyocytes. However, this stimulation induces vascular dysfunction through disruption of actin cytoskeleton in vascular smooth muscle cells. Many studies have shown that excessive concentrations of catecholamines during stressful conditions can produce coronary spasms or arrhythmias by inducing Ca²⁺-handling abnormalities and impairing energy production in mitochondria, In this article, we highlight the different fates caused by excessive oxidative stress and disruptions in the cytoskeletal proteome network in the heart and the cerebral artery in responsed to prolonged βAR-stimulation.

Quercetin-3-O-glucuronide inhibits noradrenaline-promoted invasion of MDA-MB-231 human breast cancer cells by blocking β₂-adrenergic signaling

Endogenous catecholamines such as adrenaline (A) and noradrenaline (NA) are released from the adrenal gland and sympathetic nervous system during exposure to stress. The adrenergic system plays a central role in stress signaling, and excessive stress was found to be associated with increased production of reactive oxygen species (ROS). Overproduction of ROS induces oxidative damage in tissues and causes the development of diseases such as cancer. In this study, we investigated the effects of quercetin-3-O-glucuronide (Q3G), a circulating metabolite of quercetin, which is a type of natural flavonoid, on the catecholamine-induced β2-adrenergic receptor (β2-AR)-mediated response in MDA-MB-231 human breast cancer cells expressing β2-AR. Treatment with A or NA at concentrations above 1μM generated significant levels of ROS, and NA treatment induced the gene expression of heme oxygenase-1 (HMOX1), and matrix metalloproteinase-2 (MMP-2) and -9 (MMP9). Inhibitors of p38 MAP kinase (SB203580), cAMP-dependent protein kinase (PKA) (H-89), activator protein-1 (AP-1) transcription factor (SR11302), and NF-κB and AP-1 (Tanshinone IIA) decreased MMP2 and MMP9 gene expression. NA also enhanced cAMP induction, RAS activation and phosphorylation of ERK1/2. These results suggested that the cAMP-PKA, MAPK, and ROS-NF-κB pathways are involved in β2-AR signaling. Treatment with 0.1μM Q3G suppressed ROS generation, cAMP and RAS activation, phosphorylation of ERK1/2 and the expression of HMOX1, MMP2, and MMP9 genes. Furthermore, Q3G (0.1μM) suppressed invasion of MDA-MB-231 breast cancer cells and MMP-9 induction, and inhibited the binding of [(3)H]-NA to β2-AR. These results suggest that Q3G may function to suppress invasion of breast cancer cells by controlling β2-adrenergic signaling, and may be a dietary chemopreventive factor for stress-related breast cancer.

Tocopherol inhibits the relaxing effect of terbutaline in the respiratory and reproductive tracts of the rat: the role of the oxidative stress index

AIMS

Reactive oxygen species play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (tocopherol) can reduce the effect of terbutaline in beta-2-adrenergic receptor (β2-AR)-regulated smooth muscles.

MAIN METHODS

Contractility of the tissues from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats was investigated in an isolated organ bath. The tracheal and uterine β2-AR expressions were increased by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The accumulation of cyclic-AMP (cAMP), and the total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio of TOS and TAS.

KEY FINDINGS

Terbutaline (10(-10)-10(-5)M) decreased the contractions in the nontreated and the P4-pretreated myometria, but tocopherol (10(-7)M) did not alter these actions. Terbutaline (10(-6)M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while tocopherol reduced this action only in the P4-treated cervices. Terbutaline (10(-9)-10(-4)M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while tocopherol reduced these effects. The changes in the intracellular cAMP levels of the tissues were in harmony with the isolated organ results. The OSI was highest in the trachea and lowest in the pregnant myometrium.

SIGNIFICANCE

A higher OSI is linked to a higher tocopherol sensitivity of beta-mimetic-induced relaxation. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen, while their tocolytic effect may remain unchanged during parallel tocopherol administration.

βArrestin1 regulates the guanine nucleotide exchange factor RasGRF2 expression and the small GTPase Rac-mediated formation of membrane protrusion and cell motility

βArrestin proteins shuttle between the cytosol and nucleus and have been shown to regulate G protein-coupled receptor signaling, actin remodeling, and gene expression. Here, we tested the hypothesis that βarrestin1 regulates actin remodeling and cell migration through the small GTPase Rac. Depletion of βarrestin1 promotes Rac activation, leading to the formation of multipolar protrusions and increased cell circularity, and overexpression of a dominant negative form of Rac reverses these morphological changes. Small interfering RNA library screen identifies RasGRF2 as a target of βarrestin1. RasGRF2 gene and protein expression levels are elevated following depletion of βarrestin1, and the consequent activation of Rac results in dephosphorylation of cofilin that can promote actin polymerization and formation of multipolar protrusions, thereby retarding cell migration and invasion. Together, these results suggest that βarrestin1 regulates rasgrf2 gene expression and Rac activation to affect membrane protrusion and cell migration and invasion.

Central role for hydrogen peroxide in P2Y1 ADP receptor-mediated cellular responses in vascular endothelium

ADP activates a family of cell surface receptors that modulate signaling pathways in a broad range of cells. ADP receptor antagonists are widely used to treat cardiovascular disease states. These studies identify a critical role for the stable reactive oxygen species hydrogen peroxide (H2O2) in mediating cellular responses activated by the G protein-coupled P2Y1 receptor for ADP. We found that ADP-dependent phosphorylation of key endothelial signaling proteins--including endothelial nitric oxide synthase, AMP-activated protein kinase, and the actin-binding MARCKS protein--was blocked by preincubation with PEG-catalase, which degrades H2O2. ADP treatment promoted the H2O2-dependent phosphorylation of c-Abl, a nonreceptor tyrosine kinase that modulates the actin cytoskeleton. Cellular imaging experiments using fluorescence resonance energy transfer-based biosensors revealed that ADP-stimulated activation of the cytoskeleton-associated small GTPase Rac1 was independent of H2O2. However, Rac1-dependent activation of AMP-activated protein kinase, the signaling phospholipid phosphatidylinositol-(4, 5)-bisphosphate, and the c-Abl-interacting protein CrkII are mediated by H2O2. We transfected endothelial cells with differentially targeted HyPer2 H2O2 biosensors and found that ADP promoted a marked increase in H2O2 levels in the cytosol and caveolae, and a smaller increase in mitochondria. We performed a screen for P2Y1 receptor-mediated receptor tyrosine kinase transactivation and discovered that ADP transactivates Fms-like tyrosine kinase 3 (Flt3), a receptor tyrosine kinase expressed in these cells. Our observation that P2Y1 receptor-mediated responses involve Flt3 transactivation may identify a unique mechanism whereby cancer chemotherapy with receptor tyrosine kinase inhibitors promotes vascular dysfunction. Taken together, these findings establish a critical role for endogenous H2O2 in control of ADP-mediated signaling responses in the vascular wall.

The Arf GAP AGAP2 interacts with β-arrestin2 and regulates β2-adrenergic receptor recycling and ERK activation

AGAP2 [Arf (ADP-ribosylation factor) GAP (GTPase-activating protein) with GTP-binding-protein-like, ankyrin repeat and PH (pleckstrin homology) domains] is a multidomain Arf GAP that was shown to promote the fast recycling of transferrin receptors. In the present study we tested the hypothesis that AGAP2 regulates the trafficking of β2-adrenergic receptors. We found that AGAP2 formed a complex with β-arrestin1 and β-arrestin2, proteins that are known to regulate β2-adrenergic receptor signalling and trafficking. AGAP2 co-localized with β-arrestin2 on the plasma membrane, and knockdown of AGAP2 expression reduced plasma membrane association of β-arrestin2 upon β2-adrenergic receptor activation. AGAP2 also co-localized with internalized β2-adrenergic receptors on endosomes, and overexpression of AGAP2 slowed accumulation of β2-adrenergic receptor in the perinuclear recycling endosomes. In contrast, knockdown of AGAP2 expression prevented the recycling of the β2-adrenergic receptor back to the plasma membrane. In addition, AGAP2 formed a complex with endogenous ERK (extracellular-signal-regulated kinase) and overexpression of AGAP2 potentiated ERK phosphorylation induced by β2-adrenergic receptors. Taken together, these results support the hypothesis that AGAP2 plays a role in the signalling and recycling of β2-adrenergic receptors.

β-Adrenergic signaling stimulates osteoclastogenesis via reactive oxygen species

Sympathetic signaling regulates bone resorption through receptor activator of nuclear factor-κB ligand (RANKL) expression via the β-adrenergic receptor (β-AR) on osteoblasts. Reactive oxygen species (ROS) are known as one type of osteoclast regulatory molecule. Here we show that an antioxidant, α-lipoic acid (α-LA), treatment prevent the β-adrenergic signaling-induced bone loss by suppressing osteoclastogenesis, and sympathetic signaling directly regulates osteoclastogenesis through β2-AR expressed on osteoclasts via intracellular ROS generation. In an in vitro study, the β-AR agonist isoprenaline increased intracellular ROS generation in osteoclasts prepared from bone marrow macrophages (BBMs) and RAW 264.7 cells. Isoprenaline enhanced osteoclastogenesis through β2-AR expressed on BMMs and RAW 264.7 cells. The antioxidant α-LA inhibited isoprenaline-enhanced osteoclastogenesis. Isoprenaline increased the expression of osteoclast-related genes such as nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1, tartrate-resistant acid phosphatase, and cathepsin K on osteoclasts. α-LA also inhibited isoprenaline-induced increases of these gene expressions. These in vitro results led to the hypothesis that β-adrenergic signaling directly stimulates osteoclastogenesis via ROS generation. In an in vivo study, isoprenaline treatment alone caused oxidative damage in local bone and reduced bone mass because of an increase in bone resorption, and, in α-LA-treated mice, isoprenaline did not increase tibial osteoclast number even though the RANKL-to-osteoprotegerin ratio increased. These in vitro and in vivo results indicate that β-adrenergic signaling, at least in part, directly stimulates osteoclastogenesis through β2-AR on osteoclasts via ROS generation.

Pharmacological blockade of a β(2)AR-β-arrestin-1 signaling cascade prevents the accumulation of DNA damage in a behavioral stress model

Chronic stress is known to have a profound negative impact on human health and has been suggested to influence a number of disease states. However, the mechanisms underlying the deleterious effects of stress remain largely unknown. Stress is known to promote the release of epinephrine, a catecholamine stress hormone that binds to β(2)-adrenergic receptors (β(2)ARs) with high affinity. Our previous work has demonstrated that chronic stimulation of a β(2)AR-β-arrestin-1-mediated signaling pathway by infusion of isoproterenol suppresses p53 levels and impairs genomic integrity. In this pathway, β-arrestin-1, which is activated via β(2)ARs, facilitates the AKT-mediated activation of Mdm2 and functions as a molecular scaffold to promote the binding and degradation of p53 by the E3-ubiquitin ligase, Mdm2. Here, we show that chronic restraint stress in mice recapitulates the effects of isoproterenol infusion to reduce p53 levels and results in the accumulation of DNA damage in the frontal cortex of the brain, two effects that are abrogated by the β-blocker, propranolol and by genetic deletion of β-arrestin-1. These data suggest that the β(2)AR-β-arrestin-1 signaling pathway may represent an attractive therapeutic target to prevent some of the negative consequences of stress in the treatment of stress-related disorders.

Beta adrenergic overstimulation impaired vascular contractility via actin-cytoskeleton disorganization in rabbit cerebral artery

Background and Purpose

Beta adrenergic overstimulation may increase the vascular damage and stroke. However, the underlying mechanisms of beta adrenergic overstimulation in cerebrovascular dysfunctions are not well known. We investigated the possible cerebrovascular dysfunction response to isoproterenol induced beta-adrenergic overstimulation (ISO) in rabbit cerebral arteries (CAs).

Methods

ISO was induced in six weeks aged male New Zealand white rabbit (0.8–1.0 kg) by 7-days isoproterenol injection (300 μg/kg/day). We investigated the alteration of protein expression in ISO treated CAs using 2DE proteomics and western blot analysis. Systemic properties of 2DE proteomics result were analyzed using bioinformatics software. ROS generation and following DNA damage were assessed to evaluate deteriorative effect of ISO on CAs. Intracellular Ca²⁺ level change and vascular contractile response to vasoactive drug, angiotensin II (Ang II), were assessed to evaluate functional alteration of ISO treated CAs. Ang II-induced ROS generation was assessed to evaluated involvement of ROS generation in CA contractility.

Results

Proteomic analysis revealed remarkably decreased expression of cytoskeleton organizing proteins (e.g. actin related protein 1A and 2, α-actin, capping protein Z beta, and vimentin) and anti-oxidative stress proteins (e.g. heat shock protein 9A and stress-induced-phosphoprotein 1) in ISO-CAs. As a cause of dysregulation of actin-cytoskeleton organization, we found decreased level of RhoA and ROCK1, which are major regulators of actin-cytoskeleton organization. As functional consequences of proteomic alteration, we found the decreased transient Ca²⁺ efflux and constriction response to angiotensin II and high K⁺ in ISO-CAs. ISO also increased basal ROS generation and induced oxidative damage in CA; however, it decreased the Ang II-induced ROS generation rate. These results indicate that ISO disrupted actin cytoskeleton proteome network through down-regulation of RhoA/ROCK1 proteins and increased oxidative damage, which consequently led to contractile dysfunction in CA.

The mechanism of beta-adrenergic preconditioning: roles for adenosine and ROS during triggering and mediation

The aim of this study was to investigate the mechanism of beta-adrenergic preconditioning (BPC). The roles of adenosine and its receptor subtypes, the generation of oxygen free radicals (ROS) and activation of the K(ATP) channels as well as the phosphoinositide-3-kinase (PI(3)K)/PKB/Akt and extracellular signal-regulated kinase (ERK) signal transduction pathways during the triggering and mediation phases were evaluated. Using the isolated working rat heart, BPC was elicited by administration of denopamine (beta1 adrenergic receptor agonist, 10(-7) M), isoproterenol (beta1/beta2 adrenergic receptor agonist, 10(-7) M) or formoterol (beta2 adrenergic receptor agonist, 10(-9) M) for 5 min followed by 5 min washout. Index ischaemia was 35 min regional ischaemia and infarct size determined using the tetrazolium method. The role of adenosine was studied using adenosine deaminase and selective antagonists as well as the PI(3)K and ERK inhibitors, wortmannin and PD98,059, bracketing the triggering and mediating phases. Involvement of ROS, PKC, the mitochondrial K(ATP) channels, release of endogenous opioids and bradykinin was studied by administration of N-acetyl cysteine (NAC), bisindolylmaleimide, the K(ATP) channel blocker 5-hydroxydecanoate (5-HD), naloxone or HOE140, respectively. Activation of PKB/Akt and ERKp44/p42 during triggering and reperfusion was determined by Western blot. Preconditioning with all three beta-adrenergic receptor agonists caused a reduction in infarct size and an improvement in postischaemic function. BPC preconditioning with isoproterenol, denopamine or formoterol was abolished by the adenosine A3 receptor antagonist MRS1191 during both the triggering and mediation phases. Isoproterenol-induced preconditioning (beta1/beta2 PC) was attenuated by MRS1754, an adenosine A(2B) receptor antagonist, during the triggering phase and abolished during reperfusion. The mediation phase of beta1/beta2 PC was also abolished by ZM241385, an adenosine A(2A) antagonist. The free radical scavenger NAC caused a significant attenuation of cardioprotection induced by isoproterenol when administered during both trigger and mediation phases, while being effective during the trigger phase with denopamine and during reperfusion in formoterol preconditioned hearts. The mitochondrial K(ATP) channel blocker, 5-HD, was without effect on beta1/beta2 PC during both triggering and mediation phases. BPC in rat hearts is dependent on activation of the A(3) adenosine receptors by endogenously produced adenosine and production of free radicals during the triggering and mediation phases while the A(2A) and A(2B) adenosine receptors participate mainly during reperfusion. The mitochondrial K(ATP) channels do not contribute to cardioprotection at any stage. Activation of ERK and PI3K/PKB/Akt during the triggering and reperfusion phases is associated with cardioprotection.

Reactive oxygen species are required for β2 adrenergic receptor-β-arrestin interactions and signaling to ERK1/2

The β2-adrenergic receptor (β2AR) is the prototypical member of the heptahelical G protein-coupled receptor (GPCR) superfamily and is well-known to elicit biological effects through both G protein-dependent and G protein-independent signaling cascades. Agonism of β2AR has been described to promote phosphorylation and activation of extracellular signal-regulated kinases (ERK1/2) via a G-protein/PKA pathway that transpires rapidly upon receptor agonism, as well as by a distinct β-arrestin-mediated pathway that occurs at later time points. We have previously shown that β2AR agonism promotes generation of intracellular reactive oxygen species (ROS) and that β2AR-associated G protein signaling is dependent on ROS formation. It has also been suggested that β2AR-mediated ROS generation occurs via recruitment of β-arrestins. In this study, we confirm the effects of β-arrestin on β2AR-induced ROS generation, and investigate the ROS-dependency of β-arrestin-linked β2AR signaling. In HEK293 cells, both coimmunoprecipitation and BRET studies reveal that ROS are vital for the physical interaction of β2AR with β-arrestin partner proteins. Using phosphorylation of ERK1/2 as a functional endpoint to assess the role of ROS in β2AR-β-arrestin signaling, our results show that inhibition of intracellular ROS abrogates both the β-arrestin and G protein-mediated phosphorylation of ERK1/2 upon agonism of β2AR. Importantly, both the G protein and β-arrestin components were reversed upon exogenous administration of ROS, suggesting a critical role for oxidants in stabilization of β2AR. Taken together, our data signify that ROS serve purposeful roles in stabilizing both G protein- and β-arrestin-mediated β2AR signaling in HEK293 cells.

β2-adrenergic receptor antagonist butoxamine partly abolishes the protection of 100% oxygen treatment against zymosan-induced generalized inflammation in mice

We have demonstrated that 100% oxygen inhalation is beneficial to zymosan-induced generalized inflammation, and reactive oxygen species may be involved in the protection of oxygen treatment. Other investigators suggest that reactive oxygen species may modulate the sympathetic nervous system activity and β2-adrenergic receptor (β2AR)-mediated pathway. Moreover, studies have demonstrated that β2AR agonists are beneficial to sepsis. Therefore, we assessed the effects of β2AR antagonist butoxamine on the protection of oxygen treatment against zymosan-induced generalized inflammation in mice. Mice were given oxygen treatment by exposure to 100% oxygen for 3 h starting at 4 and 12 h after zymosan injection, respectively. In the mortality study, survival was monitored for 7 days after zymosan injection in mice. At 24 h after zymosan injection, mice were killed, and blood sample and organs were harvested for analysis. We observed that 100% oxygen treatment prevented the abnormal changes in organ histopathology, lactate dehydrogenase and C-reactive protein in serum, inflammatory cytokines in serum and tissue, and arterial blood gas analysis and improved the survival rate in zymosan-challenged mice. We found that pretreatment with β2AR antagonist butoxamine partly abolished the protection of 100% oxygen inhalation. We also showed that zymosan induced the increase in serum 3'-5'-cyclic adenosine monophosphate (cAMP) and the decrease in tissue cAMP. However, oxygen treatment increased the cAMP levels in both serum and tissue, which were partly abolished by pretreatment with butoxamine. Thus, 100% oxygen inhalation may protect against zymosan-induced generalized inflammation in mice partly through activation of β2AR pathway and subsequently enhance cAMP levels in both serum and tissue.

Agonist- and hydrogen peroxide-mediated oxidation of the β2 adrenergic receptor: evidence of receptor s-sulfenation as detected by a modified biotin-switch assay

Reactive oxygen species (ROS), including hydrogen peroxide (H(2)O(2)), have recently been shown to be generated upon agonism of several members of the G protein-coupled receptor (GPCR) superfamily, including β(2)-adrenergic receptors (β(2)ARs). Previously, we have demonstrated that inhibition of intracellular ROS generation mitigates β(2)AR signaling, suggesting that β(2)AR-mediated ROS generation is capable of feeding back to regulate receptor function. Given that ROS, specifically H(2)O(2), are able to post-translationally oxidize protein cysteine sulfhydryls to cysteine-sulfenic acids, the goal of the current study was to assess whether ROS are capable of S-sulfenating β(2)AR. Using a modified biotin-switch assay that is selective for cysteine-sulfenic acids, our results demonstrate for the first time that H(2)O(2) treatment facilitates S-sulfenation of transiently overexpressed β(2)AR in human embryonic kidney 293 cells. It is noteworthy that stimulation of cells with the β-agonist isoproterenol produces both dose- and time-dependent S-sulfenation of β(2)AR, an effect that is receptor-dependent, and demonstrates that receptor-generated ROS are also capable of oxidizing the β(2)AR. Receptor-dependent S-sulfenation was inhibited by the chemoselective sulfenic acid alkylator dimedone and the cysteine antioxidant N-acetyl-l-cysteine. Moreover, our results reveal that receptor oxidation occurs in cells that endogenously express physiologically relevant levels of β(2)AR, because treatment of human alveolar epithelial A549 cells with either H(2)O(2) or the β(2)-selective agonist formoterol promoted receptor S-sulfenation. These findings provide the first evidence, to our knowledge, that a mammalian GPCR can be oxidized by S-sulfenation and signify an important first step toward shedding light on the overlooked role of ROS in the regulation of β(2)AR function.

Mutations in cytoplasmic dynein lead to a Huntington's disease-like defect in energy metabolism of brown and white adipose tissues

The molecular motor dynein is regulated by the huntingtin protein, and Huntington's disease (HD) mutations of huntingtin disrupt dynein motor activity. Besides abnormalities in the central nervous system, HD animal models develop prominent peripheral pathology, with defective brown tissue thermogenesis and dysfunctional white adipocytes, but whether this peripheral phenotype is recapitulated by dynein dysfunction is unknown. Here, we observed prominently increased adiposity in mice harboring the legs at odd angles (Loa/+) or the Cramping mutations (Cra/+) in the dynein heavy chain gene. In Cra/+ mice, hyperadiposity occurred in the absence of energy imbalance and was the result of impaired norepinephrine-stimulated lipolysis. A similar phenotype was observed in 3T3L1 adipocytes upon chemical inhibition of dynein showing that loss of functional dynein leads to impairment of lipolysis. Ex vivo, dynein mutant adipose tissue displayed increased reactive oxygen species production that was, at least partially, responsible for the decreased cellular responses to norepinephrine and subsequent defect in stimulated lipolysis. Dynein mutation also affected norepinephrine efficacy to elicit a thermogenic response and led to morphological abnormalities in brown adipose tissue and cold intolerance in dynein mutant mice. Interestingly, protein levels of huntingtin were decreased in dynein mutant adipose tissue. Collectively, our results provide genetic evidence that dynein plays a key role in lipid metabolism and thermogenesis through a modulation of oxidative stress elicited by norepinephrine. This peripheral phenotype of dynein mutant mice is similar to that observed in various animal models of HD, lending further support for a functional link between huntingtin and dynein.

beta2- but not beta1-adrenoceptor activation modulates intracellular oxygen availability

beta-Adrenoceptors (beta-ARs) play a critical role in the regulation of cardiovascular function. Intracellular oxygen homeostasis is crucial for the survival of cardiomyocytes. However, it is still unclear whether beta-AR activation can modulate intracellular oxygen. Here we used mitochondrial and cytosolic target Renilla luciferase to detect intracellular oxygen concentration. Pharmacological experiments revealed that beta2-AR activation specifically regulates intracellular oxygen in cardiomyocytes and COS7 cells. This effect was abrogated by inhibitory G protein (Gi) inhibition, endothelial nitric oxide synthase (eNOS) blockade, and NO scavenging, implicating that the beta2-AR-Gi-eNOS pathway is involved in this regulation. beta2-AR activation increased the AMP/ATP ratio, AMPK activity, ROS production and prolyl hydroxylase activity. These effects also contribute to the regulation of beta2-AR signalling, thus providing an additional layer of complexity to enforce the specificity of beta1-AR and beta2-AR signalling. Collectively, the study provides novel insight into the modulation of oxygen homeostasis, broadens the scope of beta2-AR function, and may have crucial implications for beta2-AR signalling regulation.

Agonism with the omega-3 fatty acids alpha-linolenic acid and docosahexaenoic acid mediates phosphorylation of both the short and long isoforms of the human GPR120 receptor

The newly discovered G protein-coupled receptor GPR120 has recently been shown to stimulate secretion of the gut hormones glucagon-like peptide-1 and cholecystokinin upon binding of free fatty acids, thrusting it to the forefront of drug discovery efforts for treatment of type 2 diabetes as well as satiety and obesity. Although sequences for two alternative splice variants of the human GPR120 receptor have been reported, there have been no studies which directly compare the signaling of these isoforms. We have identified an additional 16 amino acid gap containing four phospho-labile serine/threonine residues which is localized to the third intracellular loop of the GPR120-long (GPR120-L) isoform. Based on this finding, we hypothesized that the agonist-stimulated phosphorylation profiles of this isoform would be distinct from that of the short isoform (GPR120-S). Using a clonal HEK293 cell model, we examined agonist-mediated phosphorylation of GPR120-S and GPR120-L with the omega-3 fatty acids alpha-linolenic acid (ALA) and docosahexaenoic acid (DHA). Our results show rapid phosphorylation of both isoforms following agonism by either ALA or DHA. Moreover, we show no significant difference in the degree or rate of phosphorylation of both isoforms upon agonism with either ALA or DHA, suggesting that the additional gap in the longer variant is not phosphorylated. Importantly, our results demonstrate that the shorter variant exhibits significantly more pronounced basal phosphorylation in the absence of agonist, suggesting that the additional gap in the long variant may contribute to masking of constitutive phosphorylation sites. These are the first results which demonstrate specific phosphorylation of GPR120 isoforms upon agonism by free fatty acids and the first which distinguish the phosphorylation profiles of the two GPR120 isoforms.

Acute adrenergic stress inhibits proliferation of murine hematopoietic progenitor cells via p38/MAPK signaling

Acute adrenergic stress is a cause of hematopoietic failure that accompanies severe injury. Although the communication between neuronal and immune system is well documented and catecholamines are known as important regulators of homeostasis, the molecular mechanisms of hematopoietic failure are not well understood. To study the influence of adrenergic stress on hematopoietic progenitor cells (HPCs), which recently have been found to express adrenergic receptors, Lin(-),Sca(+), cells were isolated and treated with alpha- and beta-adrenergic agonists in vitro. Indeed, this stimulation resulted in significantly decreased colony formation capacity using granulocyte/macrophage colony-forming unit assays. This decline was dependent on the formation of reactive oxygen species (ROS) and activation of the p38/mitogen-activated protein kinase (MAPK) pathway, since the addition of antioxidants or a p38 inhibitor restored CFU formation. DNA damage by adrenergically induced ROS, however, does not seem to account for the reduction of colonies. Thus, catecholamine/p38/MAPK is identified as a key signal transduction pathway in HPCs besides those dependent on Wnt, Notch, and sonic hedgehog. Furthermore, a well-known target of p38 signaling, p16 is transcriptionally activated after adrenergic stimulation, suggesting that cell cycle arrest might importantly contribute to hematopoietic failure and immune dysfunctions after severe injury. Since increased levels of catecholamines are also observed in other conditions, such as during aging which is linked with decline of immune functions, adrenergic stress might as well contribute to the lowered immune defence in the elderly.

A novel protein kinase A-independent, beta-arrestin-1-dependent signaling pathway for p38 mitogen-activated protein kinase activation by beta2-adrenergic receptors

A growing body of evidence has demonstrated that p38 mitogen-activated protein kinase (MAPK) has a crucial role in various physiological and pathological processes mediated by beta(2)-adrenergic receptors (beta(2)-ARs). However, the detailed mechanism of beta(2)-ARs-induced p38 MAPK activation has not yet been fully defined. The present study demonstrates a novel kinetic model of p38 MAPK activation induced by beta(2)-ARs in human embryonic kidney 293A cells. The beta(2)-AR agonist isoproterenol induced a time-dependent biphasic phosphorylation of p38 MAPK: the early phase peaked at 10 min, and was followed by a delayed phase that appeared at 90 min and was sustained for 6 h. Interestingly, inhibition of the cAMP/protein kinase A (PKA) pathway failed to affect the early phosphorylation but abolished the delayed activation. By contrast, silencing of beta-arrestin-1 expression by small interfering RNA inhibited the early phase activation of p38 MAPK. Furthermore, the NADPH oxidase complex is a downstream target of beta-arrestin-1, as evidenced by the fact that isoproterenol-induced Rac1 activation was also suppressed by beta-arrestin-1 knockdown. In addition, early phase activation of p38 MAPK was prevented by inactivation of Rac1 and NADPH oxidase by pharmacological inhibitors, overexpression of a dominant negative mutant of Rac1, and p47(phox) knockdown by RNA interference. Of note, we demonstrated that only early activation of p38 MAPK is involved in isoproterenol-induced F-actin rearrangement. Collectively, these data suggest that the classic cAMP/PKA pathway is responsible for the delayed activation, whereas a beta-arrestin-1/Rac1/NADPH oxidase-dependent signaling is a heretofore unrecognized mechanism for beta(2)-AR-mediated early activation of p38 MAPK.