Molecular mechanisms of receptor desensitization using the beta-adrenergic receptor-coupled adenylate cyclase system as a model

N-glycosylation of SnRK2s affects NADPH maintenance in peroxisomes during prolonged ABA signalling

Unfavourable conditions, such as prolonged drought and high salinity, pose a threat to the survival and agricultural yield of plants. The phytohormone ABA plays a key role in the regulation of plant stress adaptation and is often maintained at high levels for extended periods. While much is known about ABA signal perception and activation in the early signalling stage, the molecular mechanism underlying desensitization of ABA signalling remains largely unknown. Here we demonstrate that in the endoplasmic reticulum (ER)-Golgi network, the key regulators of ABA signalling, SnRK2.2/2.3, undergo N-glycosylation, which promotes their redistribution from the nucleus to the peroxisomes in Arabidopsis roots and influences the transcriptional response in the nucleus during prolonged ABA signalling. On the peroxisomal membrane, SnRK2s can interact with glucose-6-phosphate (G6P)/phosphate translocator 1 (GPT1) to maintain NADPH homeostasis through increased activity of the peroxisomal oxidative pentose phosphate pathway (OPPP). The resulting maintenance of NADPH is essential for the modulation of hydrogen peroxide (H2O2) accumulation, thereby relieving ABA-induced root growth inhibition. The subcellular dynamics of SnRK2s, mediated by N-glycosylation suggest that ABA responses transition from transcriptional regulation in the nucleus to metabolic processes in the peroxisomes, aiding plants in adapting to long-term environmental stress.

Unraveling the complex pathophysiology of heart failure: insights into the role of renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS)

Heart failure (HF) is a widespread disease with significantly elevated mortality, morbidity, and hospitalization rates. Dysregulation of the sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) are both postulated to be significant regulators of cardiovascular function, thereby playing a pivotal role in its pathophysiology. The RAAS is a sophisticated hormonal system that controls electrolyte homeostasis, fluid balance, and blood pressure. Angiotensin II, which operates to constrict blood vessels and raise blood pressure, is its principal effector molecule. The RAAS is frequently hyperactive in HF, which increases fluid retention and worsens cardiac function. The SNS is frequently hyperactive in heart failure, which increases the workload on the heart and worsens symptoms. This review will discuss what is currently known about the pathophysiology of heart failure, specifically in the context of RAAS and the SNS, in-depth to emphasize the knowledge gap that necessitates more research.

Structure-Activity Relationship and Evaluation of Phenethylamine and Tryptamine Derivatives for Affinity towards 5-Hydroxytryptamine Type 2A Receptor

Among 14 subtypes of serotonin receptors (5-HTRs), 5-HT_2AR plays important roles in drug addiction and various psychiatric disorders. Agonists for 5-HT_2AR have been classified into three structural groups: phenethylamines, tryptamines, and ergolines. In this study, the structure-activity relationship (SAR) of phenethylamine and tryptamine derivatives for binding 5-HT_2AR was determined. In addition, functional and regulatory evaluation of selected compounds was conducted for extracellular signal-regulated kinases (ERKs) and receptor endocytosis. SAR studies showed that phenethylamines possessed higher affinity to 5-HT_2AR than tryptamines. In phenethylamines, two phenyl groups were attached to the carbon and nitrogen (R³) atoms of ethylamine, the backbone of phenethylamines. Alkyl or halogen groups on the phenyl ring attached to the β carbon exerted positive effects on the binding affinity when they were at para positions. Oxygen-containing groups attached to R³ exerted mixed influences depending on the position of their attachment. In tryptamine derivatives, tryptamine group was attached to the β carbon of ethylamine, and ally groups were attached to the nitrogen atom. Oxygen-containing substituents on large ring and alkyl substituents on the small ring of tryptamine groups exerted positive and negative influence on the affinity for 5-HT_2AR, respectively. Ally groups attached to the nitrogen atom of ethylamine exerted negative influences. Functional and regulatory activities of the tested compounds correlated with their affinity for 5-HT_2AR, suggesting their agonistic nature. In conclusion, this study provides information for designing novel ligands for 5-HT_2AR, which can be used to control psychiatric disorders and drug abuse.

Biosensor-based profiling to track cellular signalling in patient-derived models of dilated cardiomyopathy

Dilated cardiomyopathies (DCM) represent a diverse group of cardiovascular diseases impacting the structure and function of the myocardium. To better treat these diseases, we need to understand the impact of such cardiomyopathies on critical signalling pathways that drive disease progression downstream of receptors we often target therapeutically. Our understanding of cellular signalling events has progressed substantially in the last few years, in large part due to the design, validation and use of biosensor-based approaches to studying such events in cells, tissues and in some cases, living animals. Another transformative development has been the use of human induced pluripotent stem cells (hiPSCs) to generate disease-relevant models from individual patients. We highlight the importance of going beyond monocellular cultures to incorporate the influence of paracrine signalling mediators. Finally, we discuss the recent coalition of these approaches in the context of DCM. We discuss recent work in generating patient-derived models of cardiomyopathies and the utility of using signalling biosensors to track disease progression and test potential therapeutic strategies that can be later used to inform treatment options in patients.

Inflammatory Cytokine Profile and Plasticity of Brain and Spinal Microglia in Response to ATP and Glutamate

Microglia are the primary cells in the central nervous system that identify and respond to injury or damage. Such a perturbation in the nervous system induces the release of molecules including ATP and glutamate that act as damage-associated molecular patterns (DAMPs). DAMPs are detected by microglia, which then regulate the inflammatory response in a manner sensitive to their surrounding environment. The available data indicates that ATP and glutamate can induce the release of pro inflammatory factors TNF (tumor necrosis factor), IL-1β (interleukin 1 beta), and NO (nitric oxide) from microglia. However, non-physiological concentrations of ATP and glutamate were often used to derive these insights. Here, we have compared the response of spinal cord microglia (SM) relative to brain microglia (BM) using physiologically relevant concentrations of glutamate and ATP that mimic injured conditions in the central nervous system. The data show that ATP and glutamate are not significant modulators of the release of cytokines from either BM or SM. Consistent with previous studies, spinal microglia exhibited a general trend toward reduced release of inflammatory cytokines relative to brain-derived microglia. Moreover, we demonstrate that the responses of microglia to these DAMPs can be altered by modifying the biochemical milieu in their surrounding environment. Preconditioning brain derived microglia with media from spinal cord derived mixed glial cultures shifted their release of IL-1ß and IL-6 to a less inflammatory phenotype consistent with spinal microglia.

Circadian variations in pathogenesis of ST-segment elevation myocardial infarction: an optical coherence tomography study

Previous studies have reported a circadian variation in the onset of ST-segment elevation myocardial infarction (STEMI). However, underlying mechanisms for the circadian variation have not been fully elucidated. We investigated the relationship between onset of STEMI and the underlying pathology using optical coherence tomography (OCT). Patients with a diagnosis of STEMI were selected from a multicenter OCT registry. Patients were divided into 4 groups based on the estimated time of onset (00:00-05:59, 06:00-11:59, 12:00-17:59, or 18:00-23:59). Underlying pathologies of MI (plaque rupture, plaque erosion, and calcified plaque) were compared among the 4 groups. Among 648 patients, plaque rupture was diagnosed in 386 patients (59.6%), plaque erosion in 197 patients (30.4%), and calcified plaque in 65 patients (10.0%). A marked circadian variation was detected in the incidence of plaque rupture with a peak at 09:00, whereas it was not evident in plaque erosion or calcified plaque. The probability of plaque rupture significantly increased in the periods of 06:00-11:59 [odds ratio (OR) 2.13, 95% confidence interval (CI) 1.30-3.49, p = 0.002] and 12:00-17:59 (OR 2.10, 95% CI 1.23-3.58, p = 0.005), compared to the period of 00:00-05:59. This circadian pattern was observed only during weekdays (p = 0.010) and it was not evident during the weekend (p = 0.742). Plaque rupture occurred most frequently in the morning and this circadian variation was evident only during weekdays. Acute MI caused by plaque rupture may be related to catecholamine surge.

Cardiac voltage gated calcium channels and their regulation by β-adrenergic signaling

Voltage-gated calcium channels (VGCCs) are the predominant source of calcium influx in the heart leading to calcium-induced calcium release and ultimately excitation-contraction coupling. In the heart, VGCCs are modulated by the β-adrenergic signaling. Signaling through β-adrenergic receptors (βARs) and modulation of VGCCs by β-adrenergic signaling in the heart are critical signaling and changes to these have been significantly implicated in heart failure. However, data related to calcium channel dysfunction in heart failure is divergent and contradictory ranging from reduced function to no change in the calcium current. Many recent studies have highlighted the importance of functional and spatial microdomains in the heart and that may be the key to answer several puzzling questions. In this review, we have briefly discussed the types of VGCCs found in heart tissues, their structure, and significance in the normal and pathological condition of the heart. More importantly, we have reviewed the modulation of VGCCs by βARs in normal and pathological conditions incorporating functional and structural aspects. There are different types of βARs, each having their own significance in the functioning of the heart. Finally, we emphasize the importance of location of proteins as it relates to their function and modulation by co-signaling molecules. Its implication on the studies of heart failure is speculated.

β-adrenergic signaling broadly contributes to LTP induction

Long-lasting forms of long-term potentiation (LTP) represent one of the major cellular mechanisms underlying learning and memory. One of the fundamental questions in the field of LTP is why different molecules are critical for long-lasting forms of LTP induced by diverse experimental protocols. Further complexity stems from spatial aspects of signaling networks, such that some molecules function in the dendrite and some are critical in the spine. We investigated whether the diverse experimental evidence can be unified by creating a spatial, mechanistic model of multiple signaling pathways in hippocampal CA1 neurons. Our results show that the combination of activity of several key kinases can predict the occurrence of long-lasting forms of LTP for multiple experimental protocols. Specifically Ca²⁺/calmodulin activated kinase II, protein kinase A and exchange protein activated by cAMP (Epac) together predict the occurrence of LTP in response to strong stimulation (multiple trains of 100 Hz) or weak stimulation augmented by isoproterenol. Furthermore, our analysis suggests that activation of the β-adrenergic receptor either via canonical (G_s-coupled) or non-canonical (G_i-coupled) pathways underpins most forms of long-lasting LTP. Simulations make the experimentally testable prediction that a complete antagonist of the β-adrenergic receptor will likely block long-lasting LTP in response to strong stimulation. Collectively these results suggest that converging molecular mechanisms allow CA1 neurons to flexibly utilize signaling mechanisms best tuned to temporal pattern of synaptic input to achieve long-lasting LTP and memory storage.

Long-term potentiation of the strength of synaptic connections is a mechanism of learning and memory storage. One of the most confusing aspects of hippocampal synaptic potentiation is that numerous experiments have revealed the requirement for a plethora of signaling molecules. Furthermore the degree to which molecules activated by the stress response modify hippocampal synaptic potentiation and memory is still unclear. We used a computational model to demonstrate that this molecular diversity can be explained by considering a combination of several key molecules. We also show that activation of β-adrenergic receptors by the stress response appears to be involved in most forms of synaptic potentiation, though in some cases unconventional mechanisms are utilized. This suggests that novel treatments for stress-related disorders may have more success if they target unconventional mechanisms activated by β-adrenergic receptors.

Multifactorial Regulation of G Protein-Coupled Receptor Endocytosis

Endocytosis is a process by which cells absorb extracellular materials via the inward budding of vesicles formed from the plasma membrane. Receptor-mediated endocytosis is a highly selective process where receptors with specific binding sites for extracellular molecules internalize via vesicles. G protein-coupled receptors (GPCRs) are the largest single family of plasma-membrane receptors with more than 1000 family members. But the molecular mechanisms involved in the regulation of GPCRs are believed to be highly conserved. For example, receptor phosphorylation in collaboration with β-arrestins plays major roles in desensitization and endocytosis of most GPCRs. Nevertheless, a number of subsequent studies showed that GPCR regulation, such as that by endocytosis, occurs through various pathways with a multitude of cellular components and processes. This review focused on i) functional interactions between homologous and heterologous pathways, ii) methodologies applied for determining receptor endocytosis, iii) experimental tools to determine specific endocytic routes, iv) roles of small guanosine triphosphate-binding proteins in GPCR endocytosis, and v) role of post-translational modification of the receptors in endocytosis.

Endotoxemia-related attenuation of interleukin-1 secretion in thermally injured patients

The present study examines the effect of post-burn endotoxemia on the capacity for the in vitro induction of interleukin-1 (IL-1)β synthesis by either inflammatory or non-inflammatory stimuli. Adherent cell (AC) cultures from patients with severe burns (n = 14, 25-65% total body surface area) were stimulated with LPS, phorbol ester (TPA) or IL-2 and studied simultaneously with intact or LPS-pretreated preparations from normal donors (n = 9). Levels of spontaneously released IL-1β in unstimulated AC cultures from patients and in LPS-pretreated preparations from normal individuals were highly elevated. However, LPS- and IL-2-related IL-1β production in such cultures was significantly decreased (P < 0.01-0.05). In contrast, in the majority of patients' cultures and LPS-pretreated normal AC preparations, TPA-induced IL-1β production remained relatively unaffected. In all patients studied, reduced capacity for the LPS-induced IL-1 production was observed concurrently with a significant (P < 0.05) elevation in plasma endotoxin content. Diminished secretion of IL-1β coincided also with a profound reduction of IL-2-dependent IFNγ production in patient cultures and in LPS-pretreated normal cultures. Thus, in the burn patient, endotoxemia-related specific desensitization may develop and, combined with other intrinsic mechanisms, restrict the pathophysiological sequelae of continuous bacterial stimulation.

Long-term exposure to PGE2 causes homologous desensitization of receptor-mediated activation of protein kinase A

Background

Acute exposure to prostaglandin E₂ (PGE₂) activates EP receptors in sensory neurons which triggers the cAMP-dependent protein kinase A (PKA) signaling cascade resulting in enhanced excitability of the neurons. With long-term exposure to PGE₂, however, the activation of PKA does not appear to mediate persistent PGE₂-induced sensitization. Consequently, we examined whether homologous desensitization of PGE₂-mediated PKA activation occurs after long-term exposure of isolated sensory neurons to the eicosanoid.

Methods

Sensory neuronal cultures were harvested from the dorsal root ganglia of adult male Sprague-Dawley rats. The cultures were pretreated with vehicle or PGE₂ and used to examine signaling mechanisms mediating acute versus persistent sensitization by exposure to the eicosanoid using enhanced capsaicin-evoked release of immunoreactive calcitonin gene-related peptide (iCGRP) as an endpoint. Neuronal cultures chronically exposed to vehicle or PGE₂ also were used to study the ability of the eicosanoid and other agonists to activate PKA and whether long-term exposure to the prostanoid alters expression of EP receptor subtypes.

Results

Acute exposure to 1 μM PGE₂ augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89. After 5 days of exposure to 1 μM PGE₂, administration of the eicosanoid still augments evoked release of iCGRP, but the effect is not attenuated by inhibition of PKA or by inhibition of PI3 kinases. The sensitizing actions of PGE₂ after acute and long-term exposure were attenuated by EP2, EP3, and EP4 receptor antagonists, but not by an EP1 antagonist. Exposing neuronal cultures to 1 μM PGE₂ for 12 h to 5 days blocks the ability of PGE₂ to activate PKA. The offset of the desensitization occurs within 24 h of removal of PGE₂ from the cultures. Long-term exposure to PGE₂ also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA.

Conclusions

Long-term exposure to PGE₂ results in homologous desensitization of EP4 receptor activation of PKA, but not to neuronal sensitization suggesting that activation of PKA does not mediate PGE₂-induced sensitization after chronic exposure to the eicosanoid.

Differential regulation of the β-adrenoceptor density and cyclic AMP level with age and sex in turkey cardiac chambers

Decreased responses of the heart to β-adrenoceptor stimulation with aging have been shown to occur merely in selected heart chambers in relation to increased catecholamine levels. However, there are no systematic studies that investigate all cardiac chambers with regard to receptor density and cAMP (adenosine 3', 5'-cyclic monophosphate) responses. We used meat-type turkey poults (British United Turkey (B.U.T.) Big 6) with increasing age because their heart seems to decrease in weight in relation to body weight and they are often used as an animal model for heart failure. The receptor density and distribution were quantified by radioligand binding analysis using (-)-[(125)I]-iodocyanopindolol and β-adrenoceptor subtype-specific antagonists (ICI 118.551 and CGP 20712 A) in membranes of four cardiac chambers (right and left atria and ventricles) of 6-week-, 12-week-, 16/21-week-, and 57-week-old B.U.T. BIG 6 turkeys. Receptor function was determined by measuring basal and stimulated cAMP production. In both sexes, the β-adrenoceptor density decreased significantly in all chambers with age without altered β-adrenoceptor subtype distribution. The receptor affinity (KD) to the radioligand was similar in hearts of all age groups. β-adrenoceptor-(isoproterenol and guanosine 5'-triphosphate), G-protein-(NaF) and catalytic unit of adenylate cyclase (forskolin, Mn(2+)) mediated cAMP responses were not chamber-dependent. Indeed, the cAMP level was significantly lower in 57-week-old hearts than in 6-week-, 12-week-, 16/21-week-old hearts. These data suggest that with increasing age and body weight, the β-adrenoceptor signal transduction pathway was highly blunted in all cardiac chambers, occurring by decreased receptor density and cAMP responses.

Estradiol and angiotensin II crosstalk in hydromineral balance: Role of the ERK1/2 and JNK signaling pathways

The angiotensin II (ANGII) receptor AT1 plays an important role in the control of hydromineral balance, mediating the dipsogenic and natriorexigenic effects and neuroendocrine responses of ANGII. While estradiol (E2) is known to modulate several actions of ANGII in the brain, the molecular and cellular mechanisms of the interaction between E2 and ANGII and its physiological role in the control of body fluids remain unclear. We investigated the influence of E2 (40 μg/kg) pretreatment and extracellular-signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) cell signaling on the dipsogenic and natriorexigenic effects, as well as the neuroendocrine responses to angiotensinergic central stimulation in ovariectomized rats (OVX). We showed that the inhibitory effect of E2 on ANGII-induced water and sodium intake requires the ERK1/2 and JNK signaling pathways. On the other hand, E2 pretreatment prevents the ANGII-induced phosphorylation of ERK and JNK in the lamina terminalis. E2 therapy decreased oxytocin (OT) and vasopressin (AVP) secretion and decreased ERK1/2 phosphorylation in the supraoptic and paraventricular nuclei (SON and PVN, respectively). We found that the AVP secretion induced by ANGII required ERK1/2 signaling, but OT secretion did not involve ERK1/2 signaling. Taken together, these results demonstrate that E2 modulates ANGII-induced water and sodium intake and AVP secretion by affecting the ERK1/2 and JNK pathways in the lamina terminalis and ERK1/2 signaling in the hypothalamic nuclei (PVN and SON) in OVX rats.

A dynamic interface between ubiquitylation and cAMP signaling

Phosphorylation waves drive the propagation of signals generated in response to hormones and growth factors in target cells. cAMP is an ancient second messenger implicated in key biological functions. In mammals, most of the effects elicited by cAMP are mediated by protein kinase A (PKA). Activation of the kinase by cAMP results in the phosphorylation of a variety of cellular substrates, leading to differentiation, proliferation, survival, metabolism. The identification of scaffold proteins, namely A-Kinase Anchor proteins (AKAPs), that localize PKA in specific cellular districts, provided critical cues for our understanding of the role played by cAMP in cell biology. Multivalent complexes are assembled by AKAPs and include signaling enzymes, mRNAs, adapter molecules, receptors and ion channels. A novel development derived from the molecular analysis of these complexes nucleated by AKAPs is represented by the presence of components of the ubiquitin-proteasome system (UPS). More to it, the AKAP complex can be regulated by the UPS, eliciting relevant effects on downstream cAMP signals. This represents a novel, yet previously unpredicted interface between compartmentalized signaling and the UPS. We anticipate that impairment of these regulatory mechanisms could promote cell dysfunction and disease. Here, we will focus on the reciprocal regulation between cAMP signaling and UPS, and its relevance to human degenerative and proliferative disorders.

The novel prostaglandin I2 mimetic ONO-1301 escapes desensitization in an antiplatelet effect due to its inhibitory action on thromboxane A2 synthesis in mice

ONO-1301 [(E)-[5-[2-[1-phenyl-1-(3-pyridyl)methylidene-aminooxy]ethyl]-7,8-dihydronaphthalene-1-yloxy]acetic acid] is a novel prostaglandin (PG) I2 mimetic with inhibitory activity on the thromboxane (TX) A2 synthase. Interestingly, ONO-1301 retains its inhibitory effect on platelet aggregation after repeated administration, while beraprost, a representative agonist for the PGI2 receptor (IP), loses its inhibitory effect after repeated administration. In the present study, we intended to clarify the mechanism by which ONO-1301 escapes desensitization of an antiplatelet effect. In platelets prepared from wild-type mice, ONO-1301 inhibited collagen-induced aggregation and stimulated cAMP production in an IP-dependent manner. In addition, ONO-1301 inhibited arachidonic acid-induced TXA2 production in platelets lacking IP. Despite the decrease in stimulatory action on cAMP production, the antiplatelet effect of ONO-1301 hardly changed after repeated administration for 10 days in wild-type mice. Noteworthy, beraprost could retain its antiplatelet effect after repeated administration in combination with a low dose of ozagrel, a TXA2 synthase inhibitor. Therefore, we hypothesized that chronic IP stimulation by beraprost induces an increase in TXA2 production, leading to reduction in the antiplatelet effect. As expected, repeated administration of beraprost increased the plasma and urinary levels of a TXA2 metabolite, while ONO-1301 did not increase them significantly. In addition, beraprost could retain the ability to inhibit platelet aggregation after repeated administration in mice lacking the TXA2 receptor (TP). These results indicate that TP-mediated signaling participates in platelet desensitization against IP agonists and that simultaneous inhibition of TXA2 production confers resistance against desensitization on IP agonists.

Phosphorylation of the deubiquitinase USP20 by protein kinase A regulates post-endocytic trafficking of β2 adrenergic receptors to autophagosomes during physiological stress

Ubiquitination by the E3 ligase Nedd4 and deubiquitination by the deubiquitinases USP20 and USP33 have been shown to regulate the lysosomal trafficking and recycling of agonist-activated β2 adrenergic receptors (β2ARs). In this work, we demonstrate that, in cells subjected to physiological stress by nutrient starvation, agonist-activated ubiquitinated β2ARs traffic to autophagosomes to colocalize with the autophagy marker protein LC3-II. Furthermore, this trafficking is synchronized by dynamic posttranslational modifications of USP20 that, in turn, are induced in a β2AR-dependent manner. Upon β2AR activation, a specific isoform of the second messenger cAMP-dependent protein kinase A (PKAα) rapidly phosphorylates USP20 on serine 333 located in its unique insertion domain. This phosphorylation of USP20 correlates with a characteristic SDS-PAGE mobility shift of the protein, blocks its deubiquitinase activity, promotes its dissociation from the activated β2AR complex, and facilitates trafficking of the ubiquitinated β2AR to autophagosomes, which fuse with lysosomes to form autolysosomes where receptors are degraded. Dephosphorylation of USP20 has reciprocal effects and blocks trafficking of the β2AR to autophagosomes while promoting plasma membrane recycling of internalized β2ARs. Our findings reveal a dynamic regulation of USP20 by site-specific phosphorylation as well as the interdependence of signal transduction and trafficking pathways in balancing adrenergic stimulation and maintaining cellular homeostasis.

Novel roles for β-arrestins in the regulation of pharmacological sequestration to predict agonist-induced desensitization of dopamine D3 receptors

BACKGROUND AND PURPOSE

In addition to typical GPCR kinase (GRK)-/β-arrestin-dependent internalization, dopamine D3 receptor employed an additional GRK-independent sequestration pathway. In this study, we investigated the molecular mechanism of this novel sequestration pathway.

EXPERIMENTAL APPROACH

Radioligand binding, flow cytometry and cell surface biotinylation assay were used to characterize trafficking properties of D2 and D3 receptors. Serine/threonine and N-linked glycosylation mutants of the D3 receptor were utilized to locate receptor regions involved in pharmacological sequestration and desensitization. Various point mutants of the D2 and D3 receptors, whose sequestration and desensitization properties were altered, were combined with knockdown cells of GRKs or β-arrestins to functionally correlate pharmacological sequestration and desensitization.

KEY RESULTS

The D3 receptor, but not the D2 receptor, showed characteristic trafficking behaviour in which receptors were shifted towards the more hydrophobic domains within the plasma membrane without translocation into other intracellular compartments. Among various amino acid residues tested, S145/S146, C147 and N12/19 were involved in pharmacological sequestration and receptor desensitization. Both pharmacological sequestration and desensitization of D3 receptor required β-arrestins, and functional relationship was observed between two processes when it was tested for D3 receptor variants and agonists.

CONCLUSIONS AND IMPLICATIONS

Pharmacological sequestration of D3 receptor accompanies movement of cell surface receptors into a more hydrophobic fraction within the plasma membrane and renders D3 receptor inaccessible to hydrophilic ligands. Pharmacological sequestration is correlated with desensitization of the D3 receptor in a Gβγ- and β-arrestin-dependent manner. This study provides new insights into molecular mechanism governing GPCR trafficking and desensitization.

Different mechanisms of homologous and heterologous μ-opioid receptor phosphorylation

The efficiency of μ-opioid receptor signalling is tightly regulated and ultimately limited by the coordinated phosphorylation of intracellular serine and threonine residues. Here, we review and discuss recent progress in the generation and application of phosphosite-specific μ-opioid receptor antibodies, which have proved to be excellent tools for monitoring the spatial and temporal dynamics of receptor phosphorylation and dephosphorylation. Agonist-induced phosphorylation of μ-opioid receptors occurs at a conserved 10 residue sequence (370) TREHPSTANT(379) in the receptor's carboxyl-terminal cytoplasmic tail. Diverse opioids induce receptor phosphorylation at S375, present in the middle of this sequence, but only high-efficacy opioids have the ability to drive higher order phosphorylation on flanking residues (T370, T376 and T379). S375 is the initiating residue in a hierarchical phosphorylation cascade. In contrast, agonist-independent heterologous μ-opioid receptor phosphorylation occurs primarily at T370. The combination of phosphosite-specific antibodies and siRNA knockdown screening also facilitated the identification of relevant kinases and phosphatases. In fact, morphine induces a selective S375 phosphorylation that is predominantly catalysed by GPCR kinase 5 (GRK5), whereas multisite phosphorylation induced by high-efficacy opioids specifically requires GRK2/3. By contrast, T370 phosphorylation stimulated by phorbol esters or heterologous activation of Gq -coupled receptors is mediated by PKCα. Rapid μ-opioid receptor dephosphorylation occurs at or near the plasma membrane and is catalysed by protein phosphatase 1γ (PP1γ). These findings suggest that there are distinct phosphorylation motifs for homologous and heterologous regulation of μ-opioid receptor phosphorylation. However, it remains to be seen to what extent different μ-opioid receptor phosphorylation patterns contribute to the development of tolerance and dependence in vivo.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

GNAS gene variants affect β-blocker-related survival after coronary artery bypass grafting

BACKGROUND

Cardiac overexpression of the β-adrenoreceptor (βAR)-coupled stimulatory G-protein subunit Gαs enhances inotropic responses to adrenergic stimulation and improves survival in mice under βAR blockade. The authors recently identified three common haplotypes in the GNAS gene encoding Gαs, with the greatest Gαs protein expression and signal transduction in haplotype *3 carriers and less in haplotype *2 and *1 carriers. The authors tested the hypothesis that these GNAS variants result in altered mortality in patients after coronary artery bypass graft surgery, particularly in those receiving βAR blockade.

METHODS

This prospective analysis included 1,627 European ancestry patients undergoing primary coronary artery bypass graft surgery. Patients were genotyped for two GNAS haplotype tagging single-nucleotide polymorphisms defining three major haplotypes. Up to 5-yr all-cause mortality was estimated using a Cox proportional hazard model; hazard ratios and 95% CIs were calculated while adjusting for demographics, clinical covariates, and the new EuroSCORE II.

RESULTS

Univariate analysis revealed haplotype-dependent 5-yr mortality rates (*1/*1: 18.9%, *2/*1: 13.7%, *2/*2: 9.3%, *3/*1: 10.6%, *3/*2: 9.1%, and *3/*3: 9.6%; P = 0.0006). After adjustment for other predictors of death, homozygote haplotype *1 carriers showed a doubled risk for death (hazard ratio, 2.2; 95% CI, 1.2 to 3.8; P = 0.006). Considering only patients receiving βAR blockers (n = 1,267), the adjusted risk of death even tripled (hazard ratio, 3.0; 95% CI, 1.5 to 6.1; P = 0.002).

CONCLUSIONS

GNAS haplotypes independently associate with an increased risk of death after primary coronary artery bypass graft surgery. These results are most pronounced in patients receiving βAR blockers, strengthening the rationale for personalized treatment, to decrease medication side effects and improve outcomes.

Arrestin interactions with G protein-coupled receptors

G-protein-coupled receptors (GPCRs) are the primary interaction partners for arrestins. The visual arrestins, arrestin1 and arrestin4, physiologically bind to only very few receptors, i.e., rhodopsin and the color opsins, respectively. In contrast, the ubiquitously expressed nonvisual variants β-arrestin1 and 2 bind to a large number of receptors in a fairly nonspecific manner. This binding requires two triggers, agonist activation and receptor phosphorylation by a G-protein-coupled receptor kinase (GRK). These two triggers are mediated by two different regions of the arrestins, the "phosphorylation sensor" in the core of the protein and a less well-defined "activation sensor." Binding appears to occur mostly in a 1:1 stoichiometry, involving the N-terminal domain of GPCRs, but in addition a second GPCR may loosely bind to the C-terminal domain when active receptors are abundant.Arrestin binding initially uncouples GPCRs from their G-proteins. It stabilizes receptors in an active conformation and also induces a conformational change in the arrestins that involves a rotation of the two domains relative to each other plus changes in the polar core. This conformational change appears to permit the interaction with further downstream proteins. The latter interaction, demonstrated mostly for β-arrestins, triggers receptor internalization as well as a number of nonclassical signaling pathways.Open questions concern the exact stoichiometry of the interaction, possible specificity with regard to the type of agonist and of GRK involved, selective regulation of downstream signaling (=biased signaling), and the options to use these mechanisms as therapeutic targets.

Bronchoprotection by olodaterol is synergistically enhanced by tiotropium in a guinea pig model of allergic asthma

The novel once-daily β₂-agonist bronchodilator drug olodaterol has recently been shown to be effective in patients with allergic asthma for >24 hours. An increased cholinergic tone common to these patients may decrease the effectiveness of β₂-agonists. This could provide a rationale for combination therapy with olodaterol and the long-acting anticholinergic tiotropium to aim for a once-daily treatment regimen. In guinea pigs, we evaluated the protective effects of olodaterol, alone and in combination with tiotropium, on airway responsiveness to histamine, which is partially mediated by a cholinergic reflex mechanism. In addition, using a guinea pig model of acute allergic asthma, we examined the cooperative effects of these bronchodilators on allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyper-responsiveness (AHR) to histamine, and airway inflammation. It was demonstrated that the protective effect of olodaterol against histamine-induced bronchoconstriction was synergistically enhanced and prolonged in the presence of tiotropium. In addition, tiotropium synergistically augmented both the reversal of and the protection against the allergen-induced AHR after the EAR by olodaterol. Olodaterol and tiotropium were highly effective in inhibiting the magnitude of the allergen-induced EAR and LAR, and both reactions were fully inhibited by the combination of these drugs. It is remarkable that these effects were not associated with an effect on inflammatory cell infiltration in the airways. In conclusion, the results indicate that combination therapy with olodaterol and tiotropium may be highly effective in the treatment of allergen-induced asthmatic reactions and AHR.

Sleep allostasis in chronic sleep restriction: the role of the norepinephrine system

Sleep responses to chronic sleep restriction may be very different from those observed after acute total sleep deprivation. Specifically, when sleep restriction is repeated for several consecutive days, animals express attenuated compensatory increases in sleep time and intensity during daily sleep opportunities. The neurobiological mechanisms underlying these adaptive, or more specifically, allostatic, changes in sleep homeostasis are unknown. Several lines of evidence indicate that norepinephrine may play a key role in modulating arousal states and NREM EEG delta power, which is widely recognized as a marker for sleep intensity. Therefore, we investigated time course changes in brain adrenergic receptor mRNA levels in response to chronic sleep restriction using a rat model. Here, we observed that significantly altered mRNA levels of the α1- adrenergic receptor in the basal forebrain as well as α2- and β1-adrenergic receptor in the anterior cingulate cortex only on the first sleep restriction day. On the other hand, the frontal cortex α1-, α2-, and β1-adrenergic receptor mRNA levels were reduced throughout the period of sleep restriction. Combined with our earlier findings on EEG that sleep time and intensity significantly increased only on the first sleep restriction days, these results suggest that alterations in the brain norepinephrine system in the basal forebrain and cingulate cortex may mediate allostatic changes in sleep time and intensity observed during chronic sleep restriction.

Muscarinic receptors on airway mesenchymal cells: novel findings for an ancient target

Since ancient times, anticholinergics have been used as a bronchodilator therapy for obstructive lung diseases. Targets of these drugs are G-protein-coupled muscarinic M(1), M(2) and M(3) receptors in the airways, which have long been recognized to regulate vagally-induced airway smooth muscle contraction and mucus secretion. However, recent studies have revealed that acetylcholine also exerts pro-inflammatory, pro-proliferative and pro-fibrotic actions in the airways, which may involve muscarinic receptor stimulation on mesenchymal, epithelial and inflammatory cells. Moreover, acetylcholine in the airways may not only be derived from vagal nerves, but also from non-neuronal cells, including epithelial and inflammatory cells. Airway smooth muscle cells seem to play a major role in the effects of acetylcholine on airway function. It has become apparent that these cells are multipotent cells that may reversibly adopt (hyper)contractile, proliferative and synthetic phenotypes, which are all under control of muscarinic receptors and differentially involved in bronchoconstriction, airway remodeling and inflammation. Cholinergic contractile tone is increased by airway inflammation associated with asthma and COPD, resulting from exaggerated acetylcholine release as well as increased expression of contraction related proteins in airway smooth muscle. Moreover, muscarinic receptor stimulation promotes proliferation of airway smooth muscle cells as well as fibroblasts, and regulates cytokine, chemokine and extracellular matrix production by these cells, which may contribute to airway smooth muscle growth, airway fibrosis and inflammation. In line, animal models of chronic allergic asthma and COPD have recently demonstrated that tiotropium may potently inhibit airway inflammation and remodeling. These observations indicate that muscarinic receptors have a much larger role in the pathophysiology of obstructive airway diseases than previously thought, which may have important therapeutic implications.

GPCR and voltage-gated calcium channels (VGCC) signaling complexes

Voltage-gated ion channels are transmembrane proteins that control nerve impulses and cell homeostasis. Signaling molecules that regulate ion channel activity and density at the plasma membrane must be specifically and efficiently coupled to these channels in order to control critical physiological functions such as action potential propagation. Although their regulation by G-protein receptor activation has been extensively explored, the assembly of ion channels into signaling complexes of GPCRs plays a fundamental role, engaging specific downstream -signaling pathways that trigger precise downstream effectors. Recent work has confirmed that GPCRs can intimately interact with ion channels and serve as -chaperone proteins that finely control their gating and trafficking in subcellular microdomains. This chapter aims to describe examples of GPCR-ion channel co-assembly, focusing mainly on signaling complexes between GPCRs and voltage-gated calcium channels.

THE ROLE OF β-ADRENERGIC RECEPTORS IN HEART FAILURE: DIFFERENTIAL REGULATION OF CARDIOTOXICITY AND CARDIOPROTECTION

β-adrenergic receptor blockers have demonstrated significant survival benefit and have become standard therapy for adults with dilated cardiomyopathy, although their efficacy in pediatric patients is still unproven. Recent data suggests that the two major cardiac β-adrenergic receptor subtypes (β1 and β2) couple differentially to intracellular signaling pathways regulating contractility and remodeling. This has led some to suggest that the β1 receptor is the "cardiotoxic subtype" whereas the β2 receptor is "cardioprotective." Given this paradigm, there could be situations where subtype selective β-blockade or even subtype selective β-stimulation might be beneficial. However, since most of these studies have been performed in isolated cardiomyocytes, their application to clinical practice is unclear. To better understand the roles of β1- vs. β2-receptors in the pathogenesis of clinical cardiomyopathy, we and others have taken advantage of several well-characterized murine models of cardiovascular disease. These studies demonstrate that β-receptor regulation of the balance between cardioprotection and cardiotoxicity is even more complex than previously appreciated: the role of each β-receptor subtype may vary depending on the specific cardiac stressor involved (e.g. ischemia, pressure overload, genetic mutation, cardiotoxin). Furthermore, the remodeling effects of β-receptor signaling have a temporal component, depending on whether a cardiac stress is acute vs. chronic.

From pharmacokinetics to therapeutics

Whilst pharmacokinetics describe the relationship between dose levels and concentration-time profiles of a drug in the body and pharmacodynamics describe the concentration-response relationships, pharmacokinectics-pharmacodynamics(PK-PD) models link these two items providing a framework for modelling the time course of drug response. In this chapter, PK-PD models, describing the therapeutic effects of drugs used for the therapy of allergic diseases have been reviewed. Emphasis was given also to the description of the receptor occupancy, which is tightly related to the downstream clinical response. PK - PD models describing unwanted effects were also commented. An integrated use of these models allows choosing appropriate dosing regimens and providing an objective evaluation of the benefit/risk balance.

Ethanol blocks adenosine uptake via inhibiting the nucleoside transport system in bronchial epithelial cells

BACKGROUND

Adenosine uptake into cells by nucleoside transporters plays a significant role in governing extracellular adenosine concentration. Extracellular adenosine is an important signaling molecule that modulates many cellular functions via 4 G-protein-coupled receptor subtypes (A(1), A(2A), A(2B), and A(3)). Previously, we demonstrated that adenosine is critical in maintaining airway homeostasis and airway repair and that airway host defenses are impaired by alcohol. Taken together, we hypothesized that ethanol impairs adenosine uptake via the nucleoside transport system.

METHODS

To examine ethanol-induced alteration on adenosine transport, we used a human bronchial epithelial cell line (BEAS-2B). Cells were preincubated for 10 minutes in the presence and absence of varying concentrations of ethanol (EtOH). In addition, some cells were pretreated with S-(4-Nitrobenzyl)-6-thioinosine (100 microM: NBT), a potent adenosine uptake inhibitor. Uptake was then determined by addition of [(3)H]-adenosine at various time intervals.

RESULTS

Increasing EtOH concentrations resulted in increasing inhibition of adenosine uptake when measured at 1 minute. Cells pretreated with NBT effectively blocked adenosine uptake. In addition, short-term EtOH revealed increased extracellular adenosine concentration. Conversely, adenosine transport became desensitized in cells exposed to EtOH (100 mM) for 24 hours. To determine the mechanism of EtOH-induced desensitization of adenosine transport, cAMP activity was assessed in response to EtOH. Short-term EtOH exposure (10 minutes) had little or no effect on adenosine-mediated cAMP activation, whereas long-term EtOH exposure (24 hours) blocked adenosine-mediated cAMP activation. Western blot analysis of lysates from unstimulated BEAS-2B cells detected a single 55 kDa band indicating the presence of hENT1 and hENT2, respectively. Real-time RT-PCR of RNA from BEAS-2B revealed transcriptional expression of ENT1 and ENT2.

CONCLUSIONS

Collectively, these data reveal that acute exposure of cells to EtOH inhibits adenosine uptake via a nucleoside transporter, and chronic exposure of cells to EtOH desensitizes the adenosine transporter to these inhibitory effects of ethanol. Furthermore, our data suggest that inhibition of adenosine uptake by EtOH leads to an increased extracellular adenosine accumulation, influencing the effect of adenosine at the epithelial cell surface, which may alter airway homeostasis.

Prostacyclin primes pregnant human myometrium for an enhanced contractile response in parturition

An incomplete understanding of the molecular events that regulate the myometrial transition from the quiescent pregnant state to the active contractile state during labor has hindered the development of improved therapies for preterm labor. During myometrial activation, proteins that prime the smooth muscle for contraction are upregulated, allowing maximal responsiveness to contractile agonists and thereby producing strong phasic contractions. Upregulation of one such protein, COX-2, generates PGs that induce contractions. Intriguingly, the predominant myometrial PG produced just prior to labor is prostacyclin (PGI2), a smooth muscle relaxant. However, here we have shown that activation of PGI2 receptor (IP) upregulated the expression of several contractile proteins and the gap junction protein connexin 43 through cAMP/PKA signaling in human myometrial tissue in organ and cell culture. Functionally, these IP-dependent changes in gene expression promoted an enhanced contractile response to oxytocin in pregnant human myometrial tissue strips, which was inhibited by the IP antagonist RO3244794. Furthermore, contractile protein induction was dependent on the concentration and time of exposure to the PGI2 analog iloprost and was blocked by both RO3244794 and PKA knockdown. We therefore propose that PGI2-mediated upregulation of contractile proteins and connexin 43 is a critical step in myometrial activation, allowing for a maximal contractile response. Our observations have important implications regarding activation of the myometrium prior to the onset of labor.

Accommodation in organ transplantation

PURPOSE OF REVIEW

We review recent insights into the mechanisms and prevalence of accommodation. Accommodation refers to an acquired resistance of an organ graft to humoral injury and rejection.

RECENT FINDINGS

Accommodation has been postulated to reflect changes in antibodies, control of complement and/or acquired resistance to injury by antibodies, complement or other factors. We discuss the importance of these mechanisms, highlighting new conclusions.

SUMMARY

Accommodation may be a common, perhaps the most common, outcome of organ transplantation and, in some systems, a predictable outcome of organ xenotransplantation. Further understanding of how accommodation is induced and by what mechanisms it is manifest and maintained could have a profound impact on transplantation in general and perhaps on other fields.

Cell membrane changes of structure and function in protein kinase inhibitor-induced polyploid cells

Exogenous cyclic AMP has been thought to be a chemical without marked pharmacological effect until now, as it is not capable of penetrating the cell membrane in most eucaryotic cells. The present study obtained results consistent with those of most previous studies, showing that exogenous cyclic AMP itself did not interfere with the cell cycle even at the high dose of 100 microM. However, it was found that K252a, a potent inhibitor of protein kinases including protein kinase C, induced DNA re-replication, i.e. DNA synthesis at a elevated DNA ploidy in cells that had not undergone cytokinesis (leading to polyploidization), and that exogenous cyclic AMP markedly potentiated the K252a-induced polyploidization at a very low dose similar to the effective dose of membrane-permeable cyclic AMP analogue dibutyryl cyclic AMP. These findings suggested that the cell membrane changed during the formation of polyploid cells. This supposition was confirmed by scanning electron microscopy to observe structural changes and by determination of cellular attachment to investigate functional changes.

Cardiac GPCRs: GPCR signaling in healthy and failing hearts

G protein-coupled receptors (GPCRs) are widely implicated in human heart disease, making them an important target for cardiac drug therapy. The most commonly studied and clinically targeted cardiac GPCRs include the adrenergic, angiotensin, endothelin, and adenosine receptors. Treatment options focusing on the complex and integrated signaling pathways of these GPCRs are critical for the understanding and amelioration of heart disease. The focus of this review is to highlight the most commonly studied and clinically targeted cardiac GPCRs, placing emphasis on their common signaling components implicated in cardiac disease.

Mathematical Assessment of Properties of Precursor-Dependent Indirect Pharmacodynamic Response Models

Precursor-dependent indirect response (PDIDR) models may describe the tolerance and rebound phenomenon observed for many pharmacodynamic responses where these characteristics are manifested due to the depletion or accumulation of a physiological precursor or cofactor pool responsible for generating drug effects. The purpose of this report is to extend the concepts and applications of these models and to approximate responses and limiting conditions for very large doses of drugs. Asymptotic analysis was performed for qualitative determination of various parameters, such as maximum response (Rmax) and rebound (RBmax), time to maximum response and rebound (TRmax and TRBmax), and area under the effect and rebound curve (ABEC and ABRC) for large doses. Computer simulations were performed to assess the role of dose for both cases where drugs act either by depleting (Model V) or by blocking (Model VI) the endogenous precursor. Simulations showed that Rmax, RBmax, TRBmax, ABEC and ABRC increase with dose, eventually reaching a plateau when Dose/V is very large compared to the efficacy parameters (SC50 or IC50) of the drug. However, TRmax either increased or decreased with dose depending on various system and drug parameters. The limits for these parameters at large doses qualitatively determined by asymptotic analysis closely approximated the plateaus observed from the simulated curves. At large doses, the drug response could be approximated by a Bateman-like function for both Models V and VI. Qualitative analyses along with simulation studies provide a fundamental basis for understanding the temporal aspects of the PDIDR models especially at large doses to describe the tolerance and rebound phenomenon.

Risperidone irreversibly binds to and inactivates the h5-HT7 serotonin receptor

Risperidone displays a novel mechanism of antagonism of the h5-HT7 receptor. Pretreatment of the cells with 5 or 20 nM risperidone, followed by removal of the drug from the media, renders the 5-HT7 receptors unresponsive to 10 microM 5-HT for at least 24 h. Thus, risperidone seems to be producing a rapid, long-lasting inactivation of the h5-HT7 receptor. Whole-cell radioligand binding studies indicate that risperidone interacts in an irreversible or pseudo-irreversible manner with the h5-HT7 receptor, thus producing the inactivation. Internalization of the h5-HT7 receptor was not detected by monitoring green fluorescent protein-labeled fluorescent forms of the h5-HT7 receptor exposed to 20 nM risperidone. Ten other antagonists were tested for h5-HT7-inactivating properties, and only 9-OH-risperidone and methiothepin were found to demonstrate the same anomalous properties as risperidone. These results indicate that the h5-HT7 receptor may possess unique structural features that allow certain drugs to induce a conformation resulting in an irreversible interaction in the intact membrane environment. This may indicate that the h5-HT7 receptor is part of a subfamily of G-protein-coupled receptors (GPCRs) possessing this property or that many GPCRs have the potential to be irreversibly blocked, but only select drugs can induce this effect. At the very least, the possibility that highly prescribed drugs, such as risperidone, are irreversibly antagonizing GPCR function in vivo is noteworthy.

Protein kinase C potentiates homologous desensitization of the beta2-adrenoceptor in bovine tracheal smooth muscle

Preincubation (30 min) of bovine tracheal smooth muscle with various concentrations (0.1, 1 and 10 microM) of fenoterol decreased isoprenaline-induced maximal relaxation (E(max)) of methacholine-contracted preparations in a concentration dependent fashion, indicating desensitization of the beta(2)-adrenoceptor. Preincubation with 1 microM of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) caused a small but significant decrease in isoprenaline-induced E(max), indicating activated PKC-mediated heterologous beta(2)-adrenoceptor desensitization. To investigate the capacity of activated PKC to regulate homologous desensitization, we incubated the smooth muscle strips with the combination of both 1 microM PMA and 1 microM fenoterol. This combined treatment synergistically decreased the isoprenaline-induced maximal relaxation, as compared to the individual effects of PMA and fenoterol alone, indicating a common pathway for heterologous and homologous desensitization. Moreover, the specific PKC-inhibitor 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl) maleimide (GF 109203X) markedly increased the potency and E(max) of isoprenaline for all conditions used, including control conditions, and the synergistic effects of PMA and fenoterol were completely prevented. In conclusion, the present study demonstrates that homologous desensitization of the beta(2)-adrenergic receptor can be enhanced by PKC activation. For the first time we have provided evidence that this concept is functionally operative in airway smooth muscle, and it may explain the reduced bronchodilator response to beta(2)-adrenoceptor agonists in patients with asthma during a severe exacerbation.

Gene expression profiling of exercise-induced cardiac hypertrophy in rats

AIMS

Exercise training causes physiological cardiac hypertrophy, which acts to enhance cardiac function during exercise. However, the underlying molecular mechanisms are unclear. We investigated gene expression profile of exercise training-induced cardiac hypertrophy using left ventricle (LV) excised from exercise-trained and sedentary control rats (12-week old).

METHOD

Rats in the training group exercised on a treadmill for 8-week.

RESULTS

Left ventricular mass index and wall thickness in the exercise-trained group were significantly greater than that in the control group, indicating that the trained rats developed cardiac hypertrophy. Of the 3800 genes analysed in the microarray analyses, a total of 75 relevant genes (upregulation of 33 genes and downregulation of 42 genes) displayed alterations with exercise training. Among these genes, we focused on glycogen synthase kinase (GSK)-3beta, calcineurin-inhibitor (Cain), and endothelin (ET)-1 for their implicated roles in pathological cardiac hypertrophy, and confirmed the results of microarray analysis at mRNA and protein/peptide levels using quantitative PCR, Western blot, and EIA analyses. The gene expression of GSK-3beta decreased significantly and those of Cain and ET-1 increased significantly with exercise training. Furthermore, LV mass index was significantly correlated with GSK-3beta protein activity (r = -0.70, P < 0.01) and tissue ET-1 concentration (r = 0.52, P < 0.05). There were no changes in gene expressions in brain natriuretic peptide (BNP), angiotensin-correcting enzyme (ACE), interleukin-6, and vascular cell adhesion molecule (VCAM)-1.

CONCLUSION

These findings suggest that physiological and pathological LV hypertrophy may share some of the same molecular mechanisms in inducing LV hypertrophy (e.g. GSK-3beta, Cain, and ET-1) and that other genes (e.g. BNP, ACE) may differentiate physiological from pathological LV hypertrophy.

Biochemical purification and functional analysis of complexes between the G-protein subunit Gbeta5 and RGS proteins

Regulator of G-protein signaling (RGS) proteins of the R7 subfamily (RGS6, 7, 9, and 11) contain a unique Ggamma-like (GGL) domain that enables their association with the G-protein beta subunit Gbeta5. The existence of these complexes was demonstrated by their purification from native tissues as well as by reconstitution in vitro. According to pulse-chase analysis, Gbeta5 and RGS7 monomers undergo rapid proteolytic degradation in cells, whereas the dimer is stable. Studies of the functional role of Gbeta5-RGS dimers using GTPase activity, ion channel, and calcium mobilization assays showed that, similarly to other RGS proteins, they can negatively regulate G-protein-mediated signal transduction. Protein-protein interactions involving the Gbeta5-RGS7 complex can be studied in cells using fluorescence resonance energy transfer utilizing Gbeta5, RGS, and Galpha subunits fused to the cyan and yellow versions of green fluorescent protein.

Down-regulation of dopamine D1 and D2 receptors in the basal ganglia of PTZ kindling model of epilepsy: effects of angiotensin IV

The present study examined the effect of pentylenetetrazol (PTZ) induced kindling as well as the action of the hexapeptide angiotensin IV (ANG IV) on the dopamine (DA) D1 and D2 receptor binding in the basal ganglia of the mouse brain. By using quantitative receptor autoradiography, it was found that PTZ kindling led to a decrease in DA D2 receptor density (about 20%) in all regions of the neostriatum (NS) as well as in the olfactory tubercle (OT), the nucleus accumbens (NA) and the globus pallidus, which persisted 24 h and 7 days after the kindling procedure. PTZ induced kindling also elicited a decrease in DA D1 receptor binding sites (about 10%), which however was, restricted to the rostral NS (rNA) and NA. ANG IV (0.2 mg/kg), injected prior to PTZ, not only prevented the development of the kindling process but it also reversed the kindling-induced down-regulation of both DA receptors to the control levels. Furthermore ANG IV induced an area-specific increase of DA D1 receptor density above control levels in the dorsal part of rNS. These findings suggest that DA D2 receptors could mainly contribute to epileptogenesis in the PTZ kindling model, whereas the role of DA D1 receptors is limited to particular regions in the basal ganglia. The anticonvulsant effect of ANG IV pretreatment might be influenced by a DA-related mechanism and particularly by preventing D2 receptor down-regulation as well as by an adaptive area-specific increase in DA D1 receptors.

Up-regulation of adenosine A1 receptor binding in pentylenetetrazol kindling in mice: effects of angiotensin IV

The effects of the hexapeptide angiotensin II (3-8) ANG IV, the selective A(1) receptor agonist cyclohexyladenosine (CHA) and the combination of ANG IV + CHA on pentylenetetrazol (PTZ)-generalized seizures; kindling development and maintenance were studied. By using in vitro quantitative receptor autoradiography, the regulation of adenosine A(1) receptor density at different time points during the kindling procedure and postkindling period was determined. ANG IV and CHA effectively reduced clonic seizures in PTZ-generalized seizure model, in PTZ-kindled mice as well as during kindling development and a week later by rechallenge with PTZ. Furthermore, coadministration of ANG IV and CHA had a strong anticonvulsant effect, both compounds acting synergistically. A significant increase of adenosine A(1) receptor density was detected in somatosensory cortex, hippocampus, amygdala and geniculate nuclei early in the kindling procedure (after the 3rd injection), which persisted at least 1 month after the end of kindling procedure. In addition, a delayed up-regulation of adenosine A(1) receptor binding was observed a week after kindling in the mamillary bodies and a month later in the motor cortex. The pretreatment with ANG IV caused a down-regulation of adenosine A(1) receptor density to the control level in most time points and brain areas. In conclusion, PTZ kindling-induced increase of adenosine A(1) receptor binding at different time points and in specific brain structures might represent an adaptive mechanism for coping with the hyperexcitability typical for this phenomenon. The antiepileptogenic effect of ANG IV could be realized partly through an adenosine-dependent mechanism.