Dexmedetomidine activates the PKA/CREB pathway and inhibits proinflammatory factor expression through β2 adrenergic receptors

INTRODUCTION

Dexmedetomidine (DEX) is primarily utilized for sedation in the context of general anesthesia or intensive care. However, the exact regulatory mechanism by which DEX affects cytokines remains unclear. This study aims to investigate the underlying mechanism by which DEX inhibits proinflammatory factors through activation of the β2 adrenergic receptor (β2 AR).

METHODS

The inflammatory cell model of human mononuclear macrophage (THP-1) cells induced by lipopolysaccharide (LPS) was established to study the effect of DEX on the expression of cell-related inflammatory factors. ADRA2A gene knockout THP-1 cells (THP-1KO ) were constructed by CRISPR technology, and the effect of DEX on the expression of inflammatory factors of THP-1KO cells was detected. The target sites of DEX on β2 AR were screened by molecular docking. Reversion experiments were performed using ADRB2-siRNA. Western blot was used to detect the activation of β2 AR/PKA/CREB pathway and NF-κB, and ELISA was used to detect the release level of inflammatory factors.

RESULTS

The results demonstrated a significant reduction in the expression levels of MCP-1, interleukin-06, and IL-8 in both THP-1 and THP-1KO cells when induced by LPS following treatment with DEX. Additionally, DEX treatment led to an increase in IL-10 expression. Immunofluorescence analysis revealed an upregulation of β2 AR expression after DEX treatment. Western blot results indicated that DEX notably enhanced the activation of the β2 AR and PKA/CREB pathways, while concurrently suppressing the activation of NF-κB. Notably, the use of ADRB2 siRNA reversed the effects of DEX treatment and promoted the release of inflammatory cytokines.

CONCLUSION

DEX initiates the activation of the PKA/CREB pathway through the activation of β2 AR. Simultaneously, it exerts an inhibitory effect on the activation of NF-κB, consequently reducing the transcription of proinflammatory factors while increasing the transcription of anti-inflammatory factors.

CP-25 inhibits the hyperactivation of rheumatic synoviocytes by suppressing the switch in Gαs-Gαi coupling to the β2-adrenergic receptor

In essence, the β2 adrenergic receptor (β2AR) plays an antiproliferative role by increasing the intracellular cyclic 3',5'-adenosine monophosphate (cAMP) concentration through Gαs coupling, but interestingly, β2AR antagonists are able to effectively inhibit fibroblast-like synoviocytes (FLSs) proliferation, thus ameliorating experimental RA, indicating that the β2AR signalling pathway is impaired in RA FLSs via unknown mechanisms. The local epinephrine (Epi) level was found to be much higher in inflammatory joints than in normal joints, and high-level stimulation with Epi or isoproterenol (ISO) directly promoted FLSs proliferation and migration due to impaired β2AR signalling and cAMP production. By applying inhibitor of receptor internalization, and small interfering RNA (siRNA) of Gαs and Gαi, and by using fluorescence resonance energy transfer and coimmunoprecipitation assays, a switch in Gαs-Gαi coupling to β2AR was observed in inflammatory FLSs as well as in FLSs with chronic ISO stimulation. This Gαi coupling was then revealed to be initiated by G protein coupled receptor kinase 2 (GRK2) but not β-arrestin2 or protein kinase A-mediated phosphorylation of β2AR. Inhibiting the activity of GRK2 with the novel GRK2 inhibitor paeoniflorin-6'-O-benzene sulfonate (CP-25), a derivative of paeoniflorin, or the accepted GRK2 inhibitor paroxetine effectively reversed the switch in Gαs-Gαi coupling to β2AR during inflammation and restored the intracellular cAMP level in ISO-stimulated FLSs. As expected, CP-25 significantly inhibited the hyperplasia of FLSs in a collagen-induced arthritis (CIA) model (CIA FLSs) and normal FLSs stimulated with ISO and finally ameliorated CIA in rats. Together, our findings revealed the pathological changes in β2AR signalling in CIA FLSs, determined the underlying mechanisms and identified the pharmacological target of the GRK2 inhibitor CP-25 in treating CIA. Video Abstract.

Regulation of the Ca2+ Channel CaV1.2 Supports Spatial Memory and Its Flexibility and LTD

Widespread release of norepinephrine (NE) throughout the forebrain fosters learning and memory via adrenergic receptor (AR) signaling, but the molecular mechanisms are largely unknown. The β2 AR and its downstream effectors, the trimeric stimulatory Gs-protein, adenylyl cyclase (AC), and the cAMP-dependent protein kinase A (PKA), form a unique signaling complex with the L-type Ca2+ channel (LTCC) CaV1.2. Phosphorylation of CaV1.2 by PKA on Ser1928 is required for the upregulation of Ca2+ influx on β2 AR stimulation and long-term potentiation induced by prolonged theta-tetanus (PTT-LTP) but not LTP induced by two 1-s-long 100-Hz tetani. However, the function of Ser1928 phosphorylation in vivo is unknown. Here, we show that S1928A knock-in (KI) mice of both sexes, which lack PTT-LTP, express deficiencies during initial consolidation of spatial memory. Especially striking is the effect of this mutation on cognitive flexibility as tested by reversal learning. Mechanistically, long-term depression (LTD) has been implicated in reversal learning. It is abrogated in male and female S1928A knock-in mice and by β2 AR antagonists and peptides that displace β2 AR from CaV1.2. This work identifies CaV1.2 as a critical molecular locus that regulates synaptic plasticity, spatial memory and its reversal, and LTD.SIGNIFICANCE STATEMENT We show that phosphorylation of the Ca2+ channel CaV1.2 on Ser1928 is important for consolidation of spatial memory and especially its reversal, and long-term depression (LTD). Identification of Ser1928 as critical for LTD and reversal learning supports the model that LTD underlies flexibility of reference memory.

Induction of tetraspanin 13 contributes to the synergistic anti-inflammatory effects of parasympathetic and sympathetic stimulation in macrophages

The autonomic nervous system plays an important role in the regulation of peripheral inflammation. Sympathetic nervous activation stimulates inflammatory gene expression and cytokines, whereas parasympathetic nervous activation suppresses the production of inflammatory cytokines by immune cells. However, most studies on the relationship between the autonomic nervous system and immune processes have analyzed a single branch of the autonomic nerves in isolation. Therefore, this study aimed to examine the effects of sympathetic and parasympathetic stimulation on macrophages, which are controlled by autonomic regulation. Macrophages were stimulated with lipopolysaccharide (LPS) to induce TNF-α. Then, the effects of β2 adrenergic receptor and α7 nicotinic acetylcholine receptor activation on TNF-α production were assessed using concentration-dependent assays. RNA-seq data were also used to identify genes whose expression was enhanced by parasympathetic and sympathetic stimulation. The simultaneous activation of β2 adrenergic receptors and α7 nicotinic acetylcholine receptors suppressed LPS-induced TNF-α production in a concentration-dependent manner. Moreover, simultaneous activation of these receptors had synergistic anti-inflammatory effects and induced Tspan13 expression, thereby contributing to anti-inflammatory mechanisms in macrophages. Our study revealed the synergistic anti-inflammatory effects of the parasympathetic and sympathetic stimulation of macrophages. Our results suggest that targeting both sympathetic and parasympathetic signaling is a promising therapeutic approach for inflammatory diseases.

Design of Drug Efficacy Guided by Free Energy Simulations of the β2-Adrenoceptor

G protein-coupled receptors (GPCR) play important roles in physiological processes and are modulated by drugs that either activate or block signaling. Rational design of the pharmacological efficacy profiles of GPCR ligands could enable the development of more efficient drugs, but is challenging even if high-resolution receptor structures are available. We performed molecular dynamics simulations of the β2 adrenergic receptor (β2R) in active and inactive conformations to assess if binding free energy calculations can predict differences in ligand efficacy for closely related compounds. Previously identified ligands were successfully classified into groups with comparable efficacy profiles based on the calculated shift in ligand affinity upon activation. A series of ligands were then predicted and synthesized, leading to the discovery of partial agonists with nanomolar potencies and novel scaffolds. Our results demonstrate that free energy simulations enable design of ligand efficacy and the same approach can be applied to other GPCR drug targets.

Salutary effects of moderate but not high intensity aerobic exercise training on the frequency of peripheral T-cells associated with immunosenescence in older women at high risk of breast cancer: a randomized controlled trial

Background

Immunosenescence is described as age-associated changes within the immune system that are responsible for decreased immunity and increased cancer risk. Physically active individuals have fewer ‘senescent’ and more naïve T-cells compared to their sedentary counterparts, but it is not known if exercise training can rejuvenate ‘older looking’ T-cell profiles. We determined the effects of 12-weeks supervised exercise training on the frequency of T-cell subtypes in peripheral blood and their relationships with circulating levels of the muscle-derived cytokines (i.e. ‘myokines’) IL-6, IL-7, IL-15 and osteonectin in older women at high risk of breast cancer. The intervention involved 3 sessions/week of either high intensity interval exercise (HIIT) or moderate intensity continuous exercise (MICT) and were compared to an untrained control (UC) group.

Results

HIIT decreased total granulocytes, CD4+ T-cells, CD4+ naïve T-cells, CD4+ recent thymic emigrants (RTE) and the CD4:CD8 ratio after training, whereas MICT increased total lymphocytes and CD8 effector memory (EM) T-cells. The change in total T-cells, CD4+ naïve T-cells, CD4+ central memory (CM) T-cells and CD4+ RTE was elevated after MICT compared to HIIT. Changes in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{\mathrm{V}}{\mathrm{O}}_{2\max } $$\end{document}V˙O2max after training, regardless of exercise prescription, was inversely related to the change in highly differentiated CD8+ EMRA T-cells and positively related to changes in β2-adrenergic receptor (β2-AR) expression on CM CD4+ and CM CD8+ T-cells. Plasma myokine levels did not change significantly among the groups after training, but individual changes in IL-7 were positively related to changes in the number of β2-AR expressing CD4 naïve T cells in both exercise groups but not controls. Further, CD4 T-cells and CD4 naive T-cells were negatively related to changes in IL-6 and osteonectin after HIIT but not MICT, whereas CD8 EMRA T-cells were inversely related to changes in IL-15 after MICT but not HIIT.

Conclusions

Aerobic exercise training alters the frequency of peripheral T-cells associated with immunosenescence in middle aged/older women at high risk of breast cancer, with HIIT (pro-senescent) and MICT (anti-senescent) evoking divergent effects. Identifying the underlying mechanisms and establishing whether exercise-induced changes in peripheral T-cell numbers can alter the risk of developing breast cancer warrants investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00266-z.

Beta 2-adrenergic receptor mediates noradrenergic action to induce cyclic adenosine monophosphate response element-binding protein phosphorylation in satellite glial cells of dorsal root ganglia to regulate visceral hypersensitivity

ABSTRACT

Sympathoneuronal outflow into dorsal root ganglia (DRG) is suggested to be involved in sympathetically maintained chronic pain, which is mediated by norepinephrine (NE) action on DRG cells. This study combined in vitro and in vivo approaches to identify the cell types of DRG that received NE action and examined cell type-specific expression of adrenergic receptors (ARs) in DRG. Using DRG explants, we identified that NE acted on satellite glial cells (SGCs) to induce the phosphorylation of cAMP response element-binding protein (CREB). Using primarily cultured SGCs, we identified that beta (β)2-adrenergic receptor but not alpha (α)adrenergic receptor nor other βAR isoforms mediated NE-induced CREB phosphorylation and CRE-promoted luciferase transcriptional activity. Using fluorescence in situ hybridization and affinity purification of mRNA from specific cell types, we identified that β2AR was expressed by SGCs but not DRG neurons. We further examined β2AR expression and CREB phosphorylation in vivo in a model of colitis in which sympathetic nerve sprouting in DRG was observed. We found that β2AR expression and CREB phosphorylation were increased in SGCs of thoracolumbar DRG on day 7 after colitis induction. Inhibition but not augmentation of β2AR reduced colitis-induced calcitonin gene-related peptide release into the spinal cord dorsal horn and colonic pain responses to colorectal distention. Prolonged activation of β2AR in naive DRG increased calcitonin gene-related peptide expression in DRG neurons. These findings provide molecular basis of sympathetic modulation of sensory activity and chronic pain that involves β2AR-mediated signaling in SGCs of DRG.

Regulation of hyaluronan production by β2 adrenergic receptor signaling

BACKGROUND

Hyaluronan (HA), the main component of the extracellular matrix, is involved in tissue elasticity and cell scaffolding, and in progression of conditions such as cancer, inflammation and wound healing. Signaling by G protein coupled receptor (GPCR) activation increases expression of hyaluronan synthase (HAS) and HA production. The β2 adrenergic receptor (β2AR) is a catecholamine-liganded GPCR that is involved in cancer progression and wound healing. Since HA and β2AR are involved in a common pathology, we investigated whether β2AR signaling regulates HA production.

METHODS

After stimulating β2AR-expressing cells with a β agonist, the amount of HA in the culture medium was measured and HAS expression was examined by real-time PCR. A variety of signaling molecule inhibitors were used to identify signaling pathways that alter HAS expression.

RESULTS

β2AR activation increased HA production and enhanced HAS2 expression. The increase in HAS2 expression by β2AR activation occurred via the Gs - adenylyl cyclase - PKA - CREB signal transduction pathway.

CONCLUSIONS

Downstream signal transduction by β2AR activation increased HA production by enhancing transcription of the HAS2 gene. This study suggests that β2AR is a GPCR that regulates HA production, and that stimulation with a catecholamine (β2 agonist) can regulate HA production.

GENERAL SIGNIFICANCE

β2AR may function through regulation of HA production in cancer progression and wound healing.

β-arrestin2 recruitment at the β2 adrenergic receptor: A luciferase complementation assay adapted for undergraduate training in pharmacology

In the context of pharmacology teaching, hands-on activities constitute an essential complement to theoretical lectures. Frequently, these activities consist in exposing fresh animal tissues or even living animals to selected drugs and qualitatively or quantitatively evaluating functional responses. However, technological advancements in pharmacological research and the growing concerns for animal experimentation support the need for innovative and flexible in vitro assays adapted for teaching purposes. We herein report the implementation of a luciferase complementation assay (LCA) enabling to dynamically monitor β-arrestin2 recruitment at the β2 adrenergic receptor in the framework of pharmacological training at the faculty of Pharmacy and Biomedical Sciences. The assay allowed students to quantitatively characterize the competitive antagonism of propranolol, and to calculate pEC50 , pKB , and pA2 values after a guided data analysis session. Moreover, the newly implemented workshop delivered highly reproducible results and were generally appreciated by students. As such, we report that the luciferase complementation-based assay proved to be a straightforward, robust, and cost-effective alternative to experiments performed on animal tissues, constituting a useful and flexible tool to enhance and update current hands-on training in the context of pharmacological teaching.

Investigation of Receptor Heteromers Using NanoBRET Ligand Binding

Receptor heteromerization is the formation of a complex involving at least two different receptors with pharmacology that is distinct from that exhibited by its constituent receptor units. Detection of these complexes and monitoring their pharmacology is crucial for understanding how receptors function. The Receptor-Heteromer Investigation Technology (Receptor-HIT) utilizes ligand-dependent modulation of interactions between receptors and specific biomolecules for the detection and profiling of heteromer complexes. Previously, the interacting biomolecules used in Receptor-HIT assays have been intracellular proteins, however in this study we have for the first time used bioluminescence resonance energy transfer (BRET) with fluorescently-labeled ligands to investigate heteromerization of receptors on the cell surface. Using the Receptor-HIT ligand binding assay with NanoBRET, we have successfully investigated heteromers between the angiotensin II type 1 (AT1) receptor and the β2 adrenergic receptor (AT1-β2AR heteromer), as well as between the AT1 and angiotensin II type 2 receptor (AT1-AT2 heteromer).

Autoantibodies against C5aR1, C3aR1, CXCR3, and CXCR4 are decreased in primary Sjogren's syndrome

BACKGROUND

Networks formed of numerous autoantibodies (aabs) directed against G-protein coupled receptors (GPCR) have been suggested to play important role in autoimmune disorders. In present study, we aimed to evaluate the association between anti-GPCR antibodies and primary Sjogren's syndrome (pSS) to determine the potential pathogenic factors.

METHODS

By applying a cell membrane-based ELISA technique, which is capable of detecting aabs against conformational epitopes within GPCR, serum levels of fourteen GPCR were determined in well-characterized patients with pSS (n = 52) and gender-matched healthy controls (n = 54). Comparisons between groups were analyzed by two-tailed Mann-Whitney U test, Bonferroni correction was applied for multiple comparisons. Spearman`s rank correlation coefficients were calculated between variables and visualized by heat map.

RESULTS

Compared to healthy subjects, sera of patients with pSS showed significantly higher binding to β2AR and ETAR, but lower binding to C5aR1, C3aR1, CXCR3, and CXCR4. Autoantibodies against C5aR1, C3aR1, CXCR3, and CXCR4 were also decreased in patients with rheumatoid arthritis. In pSS patients, levels of anti-CXCR3 and anti-CXCR4 antibodies were negatively correlated with circulating lymphocyte counts. Furthermore, correlation signatures of anti-GPCR antibodies changed dramatically in the patients with pulmonary involvement.

CONCLUSIONS

This study demonstrates an association between pSS and autoantibodies recognizing GPCR, especially those functionally involved in immune cell migration and exocrine glandular secretion.

Viewing rare conformations of the β2 adrenergic receptor with pressure-resolved DEER spectroscopy

The β₂ adrenergic receptor (β₂AR) is an archetypal G protein coupled receptor (GPCR). One structural signature of GPCR activation is a large-scale movement (ca. 6 to 14 Å) of transmembrane helix 6 (TM6) to a conformation which binds and activates a cognate G protein. The β₂AR exhibits a low level of agonist-independent G protein activation. The structural origin of this basal activity and its suppression by inverse agonists is unknown but could involve a unique receptor conformation that promotes G protein activation. Alternatively, a conformational selection model proposes that a minor population of the canonical active receptor conformation exists in equilibrium with inactive forms, thus giving rise to basal activity of the ligand-free receptor. Previous spin-labeling and fluorescence resonance energy transfer experiments designed to monitor the positional distribution of TM6 did not detect the presence of the active conformation of ligand-free β₂AR. Here we employ spin-labeling and pressure-resolved double electron-electron resonance spectroscopy to reveal the presence of a minor population of unliganded receptor, with the signature outward TM6 displacement, in equilibrium with inactive conformations. Binding of inverse agonists suppresses this population. These results provide direct structural evidence in favor of a conformational selection model for basal activity in β₂AR and provide a mechanism for inverse agonism. In addition, they emphasize 1) the importance of minor populations in GPCR catalytic function; 2) the use of spin-labeling and variable-pressure electron paramagnetic resonance to reveal them in a membrane protein; and 3) the quantitative evaluation of their thermodynamic properties relative to the inactive forms, including free energy, partial molar volume, and compressibility.

Adult Stress Promotes Purinergic Signaling to Induce Visceral Pain in Rats with Neonatal Maternal Deprivation

Chronic visceral pain is one of the primary symptoms of patients with irritable bowel syndrome (IBS), which affects up to 15% of the population world-wide. The detailed mechanisms of visceral pain remain largely unclear. Our previous studies have shown that neonatal maternal deprivation (NMD) followed by adult multiple stress (AMS) advances the occurrence of visceral pain, likely due to enhanced norepinephrine (NE)-β₂ adrenergic signaling. This study was designed to explore the roles of P2X3 receptors (P2X3Rs) in the chronic visceral pain induced by combined stress. Here, we showed that P2X3Rs were co-expressed in β₂ adrenergic receptor (β₂-AR)-positive dorsal root ganglion neurons and that NE significantly enhanced ATP-induced Ca²⁺ signals. NMD and AMS not only significantly increased the protein expression of P2X3Rs, but also greatly enhanced the ATP-evoked current density, number of action potentials, and intracellular Ca²⁺ concentration of colon-related DRG neurons. Intrathecal injection of the P2X3R inhibitor A317491 greatly attenuated the visceral pain and the ATP-induced Ca²⁺ signals in NMD and AMS rats. Furthermore, the β₂-AR antagonist butoxamine significantly reversed the expression of P2X3Rs, the ATP-induced current density, and the number of action potentials of DRG neurons. Overall, our data demonstrate that NMD followed by AMS leads to P2X3R activation, which is most likely mediated by upregulation of β₂ adrenergic signaling in primary sensory neurons, thus contributing to visceral hypersensitivity.

IgG stimulated β2 adrenergic receptor activation is attenuated in patients with ME/CFS

Background

There is emerging evidence of a network of natural autoantibodies against GPCR which is dysregulated in various diseases. β2 adrenergic and M3 and M4 cholinergic receptor (β2 AdR and M3/4 mAChR) antibodies were found to be elevated in a subset of ME/CFS patients.

Methods

We comparatively analyzed the effects of polyclonal IgG on β2 AdR signaling and immune cell function in vitro. 16 IgG fractions were isolated from serum of 5 ME/CFS patients with elevated (CFS AAB_high) and 5 with normal levels (CFS AAB_norm) of β2 AdR autoantibodies, and from 6 healthy controls (HC). The effect of each IgG on β-arrestin recruitment and cAMP production in β2 AdR and M3/4R reporter cell lines was studied. Further effect of each IgG on human monocyte cytokine production and on T cell proliferation in vitro was analyzed. In addition, studies on cytokine production in β2 AdR wild type and knockout mice splenocytes incubated with IgG fractions were performed.

Results

We found that IgGs from HC could stimulate β-arrestin recruitment and cAMP production in β2 AdR reporter cell lines whereas IgGs from CFS AAB_high had no effect. The IgG-mediated activation of β2 AdR was confirmed in β2 AdR wt and ko mice. In accordance with previous studies IgG fractions from HC inhibited LPS-induced TNFα and stimulated LPS-induced IL-10 production of monocytes. Further IgG fractions from HC enhanced proliferation of T-cells stimulated with anti-CD3/CD28. IgG fractions from CFS AAB_high patients had no significant effect on both cytokine production and T cell proliferation, while IgGs from CFS AAB_norm had an intermediate effect. We could also observe that IgG can modulate the signaling of β2 AdR ligands isoprenline and propranolol.

Conclusions

We provide evidence that IgG can activate β2 AdR. The β2 AdR activation by IgG is attenuated in ME/CFS patients. A dysregulation of β2 AdR function could explain many symptoms of ME/CFS.

Apical splenic nerve electrical stimulation discloses an anti-inflammatory pathway relying on adrenergic and nicotinic receptors in myeloid cells

The autonomic nervous system innervates all lymphoid tissues including the spleen therefore providing a link between the central nervous system and the immune system. The only known mechanism of neural inhibition of inflammation in the spleen relies on the production of norepinephrine by splenic catecholaminergic fibers which binds to β2-adrenergic receptors (β 2-ARs) of CD4⁺ T cells. These CD4⁺ T cells trigger the release of acetylcholine that inhibits the secretion of inflammatory cytokines by macrophages through α7 nicotinic acetylcholine receptor (α7nAchRs) signaling. While the vagal anti-inflammatory pathway has been extensively studied in rodents, it remains to be determined whether it coexists with other neural pathways. Here, we have found that three nerve branches project to the spleen in mice. While two of these nerves are associated with an artery and contain catecholaminergic fibers, the third is located at the apex of the spleen and contain both catecholaminergic and cholinergic fibers. We found that electrical stimulation of the apical nerve, but not the arterial nerves, inhibited inflammation independently of lymphocytes. In striking contrast to the anti-inflammatory pathway mechanism described so far, we also found that the inhibition of inflammation by apical nerve electrical stimulation relied on signaling by both β 2-ARs and α7nAchRs in myeloid cells, with these two signaling pathways acting in parallel. Most importantly, apical splenic nerve electrical stimulation mitigated clinical symptoms in a mouse model of rheumatoid arthritis further providing the proof-of-concept that such an approach could be beneficial in patients with Immune-mediated inflammatory diseases.

Profiling of Differential Expression of Genes in Mice Carrying Both Mutant Presenilin 1 and Amyloid Precursor Protein Transgenes with or without Knockout of B2 Adrenergic Receptor Gene

Alzheimer's disease (AD) is a lifelong progressive neurodegenerativa disease related with accumulation of amyloid β peptide (Aβ) produced by processing of amyloid precursor protein (APP) in the brain. In spite of several-decades effort on AD, there is still no medicine used to intervene with its pathological processes. Our previous studies made in transgenic animal models harboring familial AD genes of mutant presenilin 1 and amyloid precursor protein (APP) showed that β₂AR gene knock-out (β₂AR-KO) is beneficial in senile AD animals. Consistently, an epidemiological study lasted for two decades showed that the sole usage of β blockers as antihypertensive medicines is associated with fewer brain lesions and less brain shrinkage seen in senile AD patients. In order to understand why senile β₂AR-KO AD mice had better learning and memory, genomic effects of β₂AR-KO in the double transgenic AD mice were investigated. In the analysis, major genomic significance of β₂AR-KO was directed to influence protein-processing and presentation involving membrane structure and MHC class I and II protein complex, and lysosome and hydrolase activity for protein degradation, which are critical for accumulation of amyloid β peptide, the hallmark of AD.

Growth inhibition of human hepatocellular carcinoma cells by antagonism of the β2 adrenergic receptor

Previous studies have shown that the activation of the β₂ adrenergic receptor (ADRB2) can stimulate several signaling pathways that promote tumor growth and metastasis. β-adrenergic antagonism may have a beneficial role in cancer treatment; however, little is known about the effect of ADRB2 inhibition on the growth of human hepatocellular carcinoma (HCC) cells. The present study revealed that ADRB2 was highly expressed in HCC cell lines compared with that in a normal liver cell line. Treatment with the ADRB2 antagonists ICI118,551 and metoprolol significantly inhibited the growth of human HCC cells. Annexin V/propidium iodide apoptosis and Hoechst staining assays revealed that treatment with ADRB2 antagonists induced apoptosis in HCC cells. Additionally, cell cycle analysis using propidium iodide staining demonstrated that growth suppression was associated with G₂/M phase cell cycle arrest by ADRB2 antagonism in HCC cells. Treatment with the ADRB2 antagonists suppressed HCC growth, possibly through inhibiting expression of B-cell lymphoma-2 (Bcl-2) and upregulating that of caspase-9 and Bcl-2-associated X, as well as downregulating the expression levels of the G₂/M phase-associated proteins cyclin B1 and cyclin-dependent kinase 1. Therefore, the observations of the present study indicate that ADRB2 blockade inhibited HCC growth, potentially mediated by inducing apoptosis and G₂/M phase cell cycle arrest. ADRB2 antagonists may therefore be a promising therapeutic strategy for HCC.

Fluorophore Labeling, Nanodisc Reconstitution and Single-molecule Observation of a G Protein-coupled Receptor

Activation of G protein-coupled receptors (GPCRs) by agonist ligands is mediated by a transition from an inactive to active receptor conformation. We describe a novel single-molecule assay that monitors activation-linked conformational transitions in individual GPCR molecules in real-time. The receptor is site-specifically labeled with a Cy3 fluorescence probe at the end of trans-membrane helix 6 and reconstituted in phospholipid nanodiscs tethered to a microscope slide. Individual receptor molecules are then monitored over time by single-molecule total internal reflection fluorescence microscopy, revealing spontaneous transitions between inactive and active-like conformations. The assay provides information on the equilibrium distribution of inactive and active receptor conformations and the rate constants for conformational exchange. The experiments can be performed in the absence of ligands, revealing the spontaneous conformational transitions responsible for basal signaling activity, or in the presence of agonist or inverse agonist ligands, revealing how the ligands alter the dynamics of the receptor to either stimulate or repress signaling activity. The resulting mechanistic information is useful for the design of improved GPCR-targeting drugs. The single-molecule assay is described in the context of the β₂ adrenergic receptor, but can be extended to a variety of GPCRs.

The α-Arrestin ARRDC3 Regulates the Endosomal Residence Time and Intracellular Signaling of the β2-Adrenergic Receptor

Arrestin domain-containing protein 3 (ARRDC3) is a member of the mammalian α-arrestin family, which is predicted to share similar tertiary structure with visual-/β-arrestins and also contains C-terminal PPXY motifs that mediate interaction with E3 ubiquitin ligases. Recently, ARRDC3 has been proposed to play a role in regulating the trafficking of G protein-coupled receptors, although mechanistic insight into this process is lacking. Here, we focused on characterizing the role of ARRDC3 in regulating the trafficking of the β2-adrenergic receptor (β2AR). We find that ARRDC3 primarily localizes to EEA1-positive early endosomes and directly interacts with the β2AR in a ligand-independent manner. Although ARRDC3 has no effect on β2AR endocytosis or degradation, it negatively regulates β2AR entry into SNX27-occupied endosomal tubules. This results in delayed recycling of the receptor and a concomitant increase in β2AR-dependent endosomal signaling. Thus, ARRDC3 functions as a switch to modulate the endosomal residence time and subsequent intracellular signaling of the β2AR.