Visualization of endogenous G proteins on endosomes and other organelles.

Classical G protein-coupled receptor (GPCR) signaling takes place in response to extracellular stimuli and involves receptors and heterotrimeric G proteins located at the plasma membrane. It has recently been established that GPCR signaling can also take place from intracellular membrane compartments, including endosomes that contain internalized receptors and ligands. While the mechanisms of GPCR endocytosis are well understood, it is not clear how internalized receptors are supplied with G proteins. To address this gap we use gene editing, confocal microscopy, and bioluminescence resonance energy transfer to study the distribution and trafficking of endogenous G proteins. We show here that constitutive endocytosis is sufficient to supply newly internalized endocytic vesicles with 20-30% of the G protein density found at the plasma membrane. We find that G proteins are present on early, late, and recycling endosomes, are abundant on lysosomes, but are virtually undetectable on the endoplasmic reticulum, mitochondria, and the medial Golgi apparatus. Receptor activation does not change heterotrimer abundance on endosomes. Our results provide a detailed subcellular map of endogenous G protein distribution, suggest that G proteins may be partially excluded from nascent endocytic vesicles, and are likely to have implications for GPCR signaling from endosomes and other intracellular compartments.

Longitudinal Metabolite Changes in Progressive Multiple Sclerosis: A Study of 3 Potential Neuroprotective Treatments.

BACKGROUND: 1 H-magnetic resonance spectroscopy (1 H-MRS) may provide a direct index for the testing of medicines for neuroprotection and drug mechanisms in multiple sclerosis (MS) through measures of total N-acetyl-aspartate (tNAA), total creatine (tCr), myo-inositol (mIns), total-choline (tCho), and glutamate + glutamine (Glx). Neurometabolites may be associated with clinical disability with evidence that baseline neuroaxonal integrity is associated with upper limb function and processing speed in secondary progressive MS (SPMS). PURPOSE: To assess the effect on neurometabolites from three candidate drugs after 96-weeks as seen by 1 H-MRS and their association with clinical disability in SPMS. STUDY-TYPE: Longitudinal. POPULATION: 108 participants with SPMS randomized to receive neuroprotective drugs amiloride [mean age 55.4 (SD 7.4), 61% female], fluoxetine [55.6 (6.6), 71%], riluzole [54.6 (6.3), 68%], or placebo [54.8 (7.9), 67%]. FIELD STRENGTH/SEQUENCE: 3-Tesla. Chemical-shift-imaging 2D-point-resolved-spectroscopy (PRESS), 3DT1. ASSESSMENT: Brain metabolites in normal appearing white matter (NAWM) and gray matter (GM), brain volume, lesion load, nine-hole peg test (9HPT), and paced auditory serial addition test were measured at baseline and at 96-weeks. STATISTICAL TESTS: Paired t-test was used to analyze metabolite changes in the placebo arm over 96-weeks. Metabolite differences between treatment arms and placebo; and associations between baseline metabolites and upper limb function/information processing speed at 96-weeks assessed using multiple linear regression models. P-value<0.05 was considered statistically significant. RESULTS: In the placebo arm, tCho increased in GM (mean difference = -0.32 IU) but decreased in NAWM (mean difference = 0.13 IU). Compared to placebo, in the fluoxetine arm, mIns/tCr was lower (ß = -0.21); in the riluzole arm, GM Glx (ß = -0.25) and Glx/tCr (ß = -0.29) were reduced. Baseline tNAA(ß = 0.22) and tNAA/tCr (ß = 0.23) in NAWM were associated with 9HPT scores at 96-weeks. DATA CONCLUSION: 1 H-MRS demonstrated altered membrane turnover over 96-weeks in the placebo group. It also distinguished changes in neuro-metabolites related to gliosis and glutaminergic transmission, due to fluoxetine and riluzole, respectively. Data show tNAA is a potential marker for upper limb function. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 4.

In-Cell Arrestin-Receptor Interaction Assays.

G protein-coupled receptors (GPCRs) represent ∼30% of current drug targets. Ligand binding to these receptors activates G proteins and arrestins, which function in different signaling pathways. Given that functionally selective or biased ligands preferentially activate one of these two groups of pathways, they may be superior medications for certain disease states. The identification of such ligands requires robust drug screening assays for both G protein and arrestin activity. This unit describes protocols for assays that monitor reversible arrestin recruitment to GPCRs in living cells using either bioluminescence resonance energy transfer (BRET) or nanoluciferase complementation (NanoLuc). Two types of assays can be used: one configuration directly measures arrestin recruitment to a GPCR fused to a protein tag at its intracellular C-terminus, whereas the other configuration detects arrestin translocation to the plasma membrane in response to activation of an unmodified GPCR. Together, these assays are powerful tools for studying dynamic interactions between GPCRs and arrestins. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Receptor-arrestin BRET assay to measure ligand-induced recruitment of arrestin to receptors Basic Protocol 2: Receptor-arrestin NANOBIT assay to measure ligand-induced recruitment of arrestin to receptors Alternative Protocol 1: BRET assay to measure ligand-induced recruitment of arrestin to the plasma membrane Alternative Protocol 2: NANOBIT assay to measure ligand-induced recruitment of arrestin to the plasma membrane Support Protocol 1: Optimization of polyethylenimine (PEI) concentration for transfection.

Sequence-directed concentration of G protein-coupled receptors in COPII vesicles.

G protein-coupled receptors (GPCRs) constitute the largest superfamily of plasma membrane signaling proteins. However, virtually nothing is known about their recruitment to COPII vesicles for forward delivery after synthesis in the endoplasmic reticulum (ER). Here, we demonstrate that some GPCRs are highly concentrated at ER exit sites (ERES) before COPII budding. Angiotensin II type 2 receptor (AT2R) and CXCR4 concentration are directed by a di-acidic motif and a 9-residue domain, respectively, and these motifs also control receptor ER-Golgi traffic. We further show that AT2R interacts with Sar1 GTPase and that distinct GPCRs have different ER-Golgi transport rates via COPII which is independent of their concentration at ERES. Collectively, these data demonstrate that GPCRs can be actively captured by COPII via specific motifs and direct interaction with COPII components that in turn affects their export dynamics, and provide important insights into COPII targeting and forward trafficking of nascent GPCRs.

GLP-1R signaling neighborhoods associate with the susceptibility to adverse drug reactions of incretin mimetics.

G protein-coupled receptors are important drug targets that engage and activate signaling transducers in multiple cellular compartments. Delineating therapeutic signaling from signaling associated with adverse events is an important step towards rational drug design. The glucagon-like peptide-1 receptor (GLP-1R) is a validated target for the treatment of diabetes and obesity, but drugs that target this receptor are a frequent cause of adverse events. Using recently developed biosensors, we explored the ability of GLP-1R to activate 15 pathways in 4 cellular compartments and demonstrate that modifications aimed at improving the therapeutic potential of GLP-1R agonists greatly influence compound efficacy, potency, and safety in a pathway- and compartment-selective manner. These findings, together with comparative structure analysis, time-lapse microscopy, and phosphoproteomics, reveal unique signaling signatures for GLP-1R agonists at the level of receptor conformation, functional selectivity, and location bias, thus associating signaling neighborhoods with functionally distinct cellular outcomes and clinical consequences.

Profile of Ankle Isokinetic Strength and Proprioception in Elite Female Handball Players / Perfil de Fuerza Isokinética del Tobillo y Propiocepción en Jugadoras de Balonmano de Élite

SUMMARY: The evaluation of the invertor and evertor muscle strength and proprioception are important in terms of determining the risk of injury in handball players. The aim of this study was to determine the isokinetic strength and proprioception profile of the ankle invertor and evertor muscles of elite female handball players. Fifteen elite female handball players were included. Ankle invertor and evertor muscle strength and proprioception were evaluated using the isokinetic system. The isokinetic strength test was performed in concentric mode at 30°/s (5 repetitions) and 120°/s (10 repetitions). Proprioception sense was evaluated as active joint position sense. There was no statistically significant difference between the dominant and nondominant sides in terms of invertor and evertor muscle strength, evertor/invertor (Ever/Inver) ratio, and active joint position sense at both angular speeds (p>0.05). The Ever/Inver ratio on both sides was lower than normal values. It was concluded that the female handball players showed bilateral symmetry in the invertor and evertor muscles. However, the fact that the Ever/Inver strength ratio was lower than normal values on both sides suggested that caution should be exercised in terms of risks such as ankle sprain or chronic ankle instability. Pre-season evaluations should be made and it would be beneficial to add strengthening exercises to related muscle groups in training programs to normalize the unilateral ratios in these athletes.

La evaluación de la fuerza muscular inversora y eversora y la propiocepción son importantes para determinar el riesgo de lesión en los jugadores de balonmano. El objetivo de este estudio fue determinar la fuerza isocinética y el perfil de propiocepción de los músculos inversores y eversores del tobillo de jugadoras de balonmano de élite. Se incluyeron 15 jugadoras de élite de balonmano. La fuerza muscular inversora y eversora del tobillo y la propiocepción se evaluaron mediante el sistema isocinético. El test de fuerza isocinética se realizó en modo concéntrico a 30º/s (5 repeticiones) y 120º/s (10 repeticiones). El sentido de propiocepción se evaluó como sentido activo de posición articular. No hubo diferencias estadísticamente significativas entre los lados dominante y no dominante en términos de fuerza muscular inversora y eversora, relación eversor/inversor (Ever/ Inver) y sentido activo de la posición de la articulación en ambas velocidades angulares (p>0.05). La relación Ever/Inver en ambos lados fue inferior a los valores normales. Se concluyó que las jugadoras de balonmano presentaron simetría bilateral en los músculos inversores y eversores. Sin embargo, el hecho de que la relación de fuerza Ever/Inver fuera inferior a los valores normales en ambos lados sugirió que se debe tener precaución en términos de riesgos como el esguince de tobillo o la inestabilidad crónica de tobillo. Se deben realizar evaluaciones de pretemporada y sería beneficioso agregar ejercicios de fortalecimiento a los grupos musculares relacionados en los programas de entrenamiento para normalizar las proporciones unilaterales en estas atletas.

Pathway selectivity in Frizzleds is achieved by conserved micro-switches defining pathway-determining, active conformations.

The class Frizzled of G protein-coupled receptors (GPCRs), consisting of ten Frizzled (FZD1-10) paralogs and Smoothened, remains one of the most enigmatic GPCR families. This class mediates signaling predominantly through Disheveled (DVL) or heterotrimeric G proteins. However, the mechanisms underlying pathway selection are elusive. Here we employ a structure-driven mutagenesis approach in combination with an extensive panel of functional signaling readouts to investigate the importance of conserved state-stabilizing residues in FZD5 for signal specification. Similar data were obtained for FZD4 and FZD10 suggesting that our findings can be extrapolated to other members of the FZD family. Comparative molecular dynamics simulations of wild type and selected FZD5 mutants further support the concept that distinct conformational changes in FZDs specify the signal outcome. In conclusion, we find that FZD5 and FZDs in general prefer coupling to DVL rather than heterotrimeric G proteins and that distinct active state micro-switches in the receptor are essential for pathway selection arguing for conformational changes in the receptor protein defining transducer selectivity.

A Non-Systemic Phosphodiesterase-5 Inhibitor Suppresses Colon Proliferation in Mice.

Phosphodiesterase-5 inhibitors (PDE5i) are under investigation for repurposing for colon cancer prevention. A drawback to conventional PDE5i are their side-effects and drug-drug interactions. We designed an analog of the prototypical PDE5i sildenafil by replacing the methyl group on the piperazine ring with malonic acid to reduce lipophilicity, and measured its entry into the circulation and effects on colon epithelium. This modification did not affect pharmacology as malonyl-sildenafil had a similar IC50 to sildenafil but exhibited an almost 20-fold reduced EC50 for increasing cellular cGMP. Using an LC-MS/MS approach, malonyl-sildenafil was negligible in mouse plasma after oral administration but was detected at high levels in the feces. No bioactive metabolites of malonyl-sildenafil were detected in the circulation by measuring interactions with isosorbide mononitrate. The treatment of mice with malonyl-sildenafil in the drinking water resulted in a suppression of proliferation in the colon epithelium that is consistent with results previously published for mice treated with PDE5i. A carboxylic-acid-containing analog of sildenafil prohibits the systemic delivery of the compound but maintains sufficient penetration into the colon epithelium to suppress proliferation. This highlights a novel approach to generating a first-in-class drug for colon cancer chemoprevention.

Serotonin 5-HT7 receptor slows down the Gs protein: a single molecule perspective.

The 5-hydroxytryptamine (serotonin) receptor type 7 (5-HT7R) is a G protein-coupled receptor present primarily in the nervous system and gastrointestinal tract, where it regulates mood, cognition, digestion, and vasoconstriction. 5-HT7R has previously been shown to bind to its cognate stimulatory Gs protein in the inactive state. This phenomenon, termed "inverse coupling," is thought to counteract the atypically high intrinsic activity of 5-HT7R. However, it is not clear how active and inactive 5-HT7 receptors affect the mobility of the Gs protein in the plasma membrane. Here, we used single-molecule imaging of the Gs protein and 5-HT7R to evaluate Gs mobility in the membrane in the presence of 5-HT7R and its mutants. We show that expression of 5-HT7R dramatically reduces the diffusion rate of Gs. Expression of the constitutively active mutant 5-HT7R (L173A) is less effective at slowing Gs diffusion presumably due to the reduced ability to form long-lasting inactive complexes. An inactive 5-HT7R (N380K) mutant slows down Gs to the same extent as the wild-type receptor. We conclude that inactive 5-HT7R profoundly affects Gs mobility, which could lead to Gs redistribution in the plasma membrane and alter its availability to other G protein-coupled receptors and effectors.

The role of G protein conformation in receptor-G protein selectivity.

G protein-coupled receptors (GPCRs) selectively activate at least one of the four families of heterotrimeric G proteins, but the mechanism of coupling selectivity remains unclear. Structural studies emphasize structural complementarity of GPCRs and nucleotide-free G proteins, but selectivity is likely to be determined by transient intermediate-state complexes that exist before nucleotide release. Here we study coupling to nucleotide-decoupled G protein variants that can adopt conformations similar to receptor-bound G proteins without releasing nucleotide, and are therefore able to bypass intermediate-state complexes. We find that selectivity is degraded when nucleotide release is not required for GPCR-G protein complex formation, to the extent that most GPCRs interact with most nucleotide-decoupled G proteins. These findings demonstrate the absence of absolute structural incompatibility between noncognate receptor-G protein pairs, and are consistent with the hypothesis that transient intermediate states are partly responsible for coupling selectivity.

Time- and cost-efficient bacterial expression and purification of potato apyrase.

Apyrase from potato (Solanum tuberosum) is a divalent metal ion-dependent enzyme that catalyzes the hydrolysis of nucleoside di- and tri-phosphates with broad substrate specificity. The enzyme is widely used to manipulate nucleotide levels such as in the G protein-coupled receptor (GPCR) field where it is used to deplete guanine nucleotides to stabilize nucleotide-free ternary agonist-GPCR-G protein complexes. Potato apyrase is available commercially as the native enzyme purified from potatoes or as a recombinant protein, but these are prohibitively expensive for some research applications. Here, we report a relatively simple method for the bacterial production of soluble, active potato apyrase. Apyrase has several disulfide bonds, so we co-expressed the enzyme bearing a C-terminal (His)6 tag with the E. coli disulfide isomerase DsbC at low temperature (18 °C) in the oxidizing cytoplasm of E. coli Origami B (DE3). This allowed low level production of soluble apyrase. A two-step purification procedure involving Ni-affinity followed by Cibacron Blue-affinity chromatography yielded highly purified apyrase at a level of ∼0.5 mg per L of bacterial culture. The purified enzyme was functional for ATP hydrolysis in an ATPase assay and for GTP/GDP hydrolysis in a GPCR-G protein coupling assay. This methodology enables the time- and cost-efficient production of recombinant apyrase for various research applications.

S-nitrosylation is required for ß2AR desensitization and experimental asthma.

The ß2-adrenergic receptor (ß2AR), a prototypic G-protein-coupled receptor (GPCR), is a powerful driver of bronchorelaxation, but the effectiveness of ß-agonist drugs in asthma is limited by desensitization and tachyphylaxis. We find that during activation, the ß2AR is modified by S-nitrosylation, which is essential for both classic desensitization by PKA as well as desensitization of NO-based signaling that mediates bronchorelaxation. Strikingly, S-nitrosylation alone can drive ß2AR internalization in the absence of traditional agonist. Mutant ß2AR refractory to S-nitrosylation (Cys265Ser) exhibits reduced desensitization and internalization, thereby amplifying NO-based signaling, and mice with Cys265Ser mutation are resistant to bronchoconstriction, inflammation, and the development of asthma. S-nitrosylation is thus a central mechanism in ß2AR signaling that may be operative widely among GPCRs and targeted for therapeutic gain.

GPCR-mediated ß-arrestin activation deconvoluted with single-molecule precision.

ß-arrestins bind G protein-coupled receptors to terminate G protein signaling and to facilitate other downstream signaling pathways. Using single-molecule fluorescence resonance energy transfer imaging, we show that ß-arrestin is strongly autoinhibited in its basal state. Its engagement with a phosphopeptide mimicking phosphorylated receptor tail efficiently releases the ß-arrestin tail from its N domain to assume distinct conformations. Unexpectedly, we find that ß-arrestin binding to phosphorylated receptor, with a phosphorylation barcode identical to the isolated phosphopeptide, is highly inefficient and that agonist-promoted receptor activation is required for ß-arrestin activation, consistent with the release of a sequestered receptor C tail. These findings, together with focused cellular investigations, reveal that agonism and receptor C-tail release are specific determinants of the rate and efficiency of ß-arrestin activation by phosphorylated receptor. We infer that receptor phosphorylation patterns, in combination with receptor agonism, synergistically establish the strength and specificity with which diverse, downstream ß-arrestin-mediated events are directed.

An online pilates exercise program is effective on proprioception and core muscle endurance in a randomized controlled trial.

BACKGROUND: Proprioception is important for stability of body segments, postural control, and functionality. However, there are no studies in literature showing effects of online Pilates exercises that create proprioceptive inputs on vertebra on trunk proprioception. AIMS: This study aims to reveal effect of online Pilates exercises conducted on trunk proprioception and core muscle endurance in healthy individuals. METHODS: We included thirty-three healthy individuals between ages of 18 and 25 in study. Individuals were randomly divided into two groups. There were 17 individuals in Pilates group (PG), and 16 individuals in control group (CG). The PG was given online Pilates exercises by the physiotherapist in groups 3 days a week for 6 weeks, 1 h a day. There was no exercise program recommended for individuals in CG. We evaluated trunk proprioception with an inclinometer, core muscle endurance with three core endurance tests created by McGill, and prone bridge tests. All evaluations completed just before start of study and 2 days after 6-week training. RESULTS: Two groups had similar demographic characteristics, and there was no difference between baseline measurements (p > 0.05). While improvement observed in PG in trunk proprioception and all of core muscle endurance tests (p < 0.05), no statistically significant difference reported in CG (p > 0.05). CONCLUSIONS: We revealed that online Pilates exercises performed at mat level for 6 weeks in healthy individuals had positive effects on trunk proprioception and core muscle endurance with this study. Contribution of Pilates exercises to development of both muscular endurance and proprioceptive senses, even if performed at a distance, is important.

The relationship among aging in place, loneliness, and life satisfaction in the elderly in Turkey.

PURPOSE: This study was conducted to determine the relationship between aging in place, loneliness, and life satisfaction in older people. DESIGN AND METHODS: The descriptive and cross-sectional study has used the Aging in Place Scale (APS), the Life Satisfaction Scale (LSS), and the Loneliness Scale for the Elderly (LSFE). The study was examined the correlation among APS, LSS, and LSFE. FINDING: In our study, when we examined the subscales of the APS scale, we found that the perceived social support, physical competence, and achievable social support of the elderly were at a high level. These high levels led to increased life satisfaction and decreased loneliness. PRACTICE IMPLICATIONS: The results obtained in this study are particularly important for highlighting the importance of aging in place in reducing loneliness, which has a negative impact on the mental health of the elderly, and in shedding light on increasing life satisfaction in the later stages of life.

Respiratory muscle strength in volleyball players suffered from COVID-19.

BACKGROUND: Symptoms related to Coronavirus-19 disease (COVID-19) and quarantine measures have caused pulmonary function abnormality and impaired respiratory mechanics. However, no studies are evaluating pulmonary functions and respiratory muscle strength in female volleyball players according to COVID-19 status in the pandemic. AIMS: This study aims to compare pulmonary functions and respiratory muscle strength in female players with and without COVID-19. METHODS: Seventeen players (23.47 ± 5.89 years) who were recovered from COVID-19 and 25 female volleyball players (20.48 ± 5.05 years) who were not infected by SARS-CoV-2 were included in the study. Maximal inspiratory and expiratory pressure, pulmonary functions, body composition, symptom severity, and perceptions of performance were evaluated. RESULTS: Measured and predicted percent maximal inspiratory pressure and measured maximal expiratory pressure values of COVID-19 players were statistically significantly lower than non-COVID-19 players (p < 0.05). Dynamic lung volumes were similar in groups (p > 0.05). CONCLUSIONS: Inspiratory and expiratory muscle strength in COVID-19 players were more affected compared with non-COVID-19 players. Pulmonary functions were mostly preserved in COVID-19 players. Respiratory muscle weakening can affect the performance of female players. Therefore, respiratory muscle strength training could be suggested in female players with COVID-19 to increase respiratory muscle strength and prevent deterioration in performance. TRIAL REGISTRATION (CLINICALTRIALS.GOV): Registration ID: NCT04789512.

Team Strategies and Tools to Enhance Performance and Patient Safety at primary healthcare units: Effect on patients' outcomes.

The purpose of this study was to examine the effect of application of team strategies and tools to enhance performance and patient safety at primary healthcare units on patients' safety and outcomes. Team Strategies and Tools to Enhance Performance and Patient Safety (Team STEPPS) are specially intended to enhance patient safety through effective communication and teamwork skills. To examine, a quasi-experimental (pre-posttest) design was utilized. Six primary healthcare centers in Egypt were selected. The subjects included composed of two groups: (1) All-available healthcare providers (114) and (2) convenience sample of 108 clients. Four questionnaires were used, namely; the Hospital Survey on Patient Safety Culture (HSPSC), Perception of Teamwork Questionnaire, the Short Assessment of Patient Satisfaction Scale, and Patient's Adverse Events Questionnaire. Results showed that there was a highly significant decrease in the level of weakness and the need for potential improvement of all 11 domains of the HSPSC survey except the staffing domain (p < 0.001). The teamwork perceptions scores showed significant improvement post intervention (p < 0.001). In addition, a highly significant decrease in the frequency of patient-reported adverse events compared to a significant increase in patient satisfaction level was proved (p < 0.001). It may, hence, be concluded that Team STEPPS implementation had improved patient safety culture among healthcare providers and significantly improved patient outcomes.

BRET-based effector membrane translocation assay monitors GPCR-promoted and endocytosis-mediated Gq activation at early endosomes.

G protein-coupled receptors (GPCRs) are gatekeepers of cellular homeostasis and the targets of a large proportion of drugs. In addition to their signaling activity at the plasma membrane, it has been proposed that their actions may result from translocation and activation of G proteins at endomembranes-namely endosomes. This could have a significant impact on our understanding of how signals from GPCR-targeting drugs are propagated within the cell. However, little is known about the mechanisms that drive G protein movement and activation in subcellular compartments. Using bioluminescence resonance energy transfer (BRET)-based effector membrane translocation assays, we dissected the mechanisms underlying endosomal Gq trafficking and activity following activation of Gq-coupled receptors, including the angiotensin II type 1, bradykinin B2, oxytocin, thromboxane A2 alpha isoform, and muscarinic acetylcholine M3 receptors. Our data reveal that GPCR-promoted activation of Gq at the plasma membrane induces its translocation to endosomes independently of ß-arrestin engagement and receptor endocytosis. In contrast, Gq activity at endosomes was found to rely on both receptor endocytosis-dependent and -independent mechanisms. In addition to shedding light on the molecular processes controlling subcellular Gq signaling, our study provides a set of tools that will be generally applicable to the study of G protein translocation and activation at endosomes and other subcellular organelles, as well as the contribution of signal propagation to drug action.

Constitutive G protein coupling profiles of understudied orphan GPCRs.

A large number of GPCRs are potentially valuable drug targets but remain understudied. Many of these lack well-validated activating ligands and are considered "orphan" receptors, and G protein coupling profiles have not been defined for many orphan GPCRs. Here we asked if constitutive receptor activity can be used to determine G protein coupling profiles of orphan GPCRs. We monitored nucleotide-sensitive interactions between 48 understudied orphan GPCRs and five G proteins (240 combinations) using bioluminescence resonance energy transfer (BRET). No receptor ligands were used, but GDP was used as a common G protein ligand to disrupt receptor-G protein complexes. Constitutive BRET between the same receptors and ß-arrestins was also measured. We found sufficient GDP-sensitive BRET to generate G protein coupling profiles for 22 of the 48 receptors we studied. Altogether we identified 48 coupled receptor-G protein pairs, many of which have not been described previously. We conclude that receptor-G protein complexes that form spontaneously in the absence of guanine nucleotides can be used to profile G protein coupling of constitutively-active GPCRs. This approach may prove useful for studying G protein coupling of other GPCRs for which activating ligands are not available.

Circulating Bile Acids in Liver Failure Activate TGR5 and Induce Monocyte Dysfunction.

BACKGROUND & AIMS: Retention of bile acids in the blood is a hallmark of liver failure. Recent studies have shown that increased serum bile acid levels correlate with bacterial infection and increased mortality. However, the mechanisms by which circulating bile acids influence patient outcomes still are elusive. METHODS: Serum bile acid profiles in 33 critically ill patients with liver failure and their effects on Takeda G-protein-coupled receptor 5 (TGR5), an immunomodulatory receptor that is highly expressed in monocytes, were analyzed using tandem mass spectrometry, novel highly sensitive TGR5 bioluminescence resonance energy transfer using nanoluciferase (NanoBRET, Promega Corp, Madison, WI) technology, and in vitro assays with human monocytes. RESULTS: Twenty-two patients (67%) had serum bile acids that led to distinct TGR5 activation. These TGR5-activating serum bile acids severely compromised monocyte function. The release of proinflammatory cytokines (eg, tumor necrosis factor α or interleukin 6) in response to bacterial challenge was reduced significantly if monocytes were incubated with TGR5-activating serum bile acids from patients with liver failure. By contrast, serum bile acids from healthy volunteers did not influence cytokine release. Monocytes that did not express TGR5 were protected from the bile acid effects. TGR5-activating serum bile acids were a risk factor for a fatal outcome in patients with liver failure, independent of disease severity. CONCLUSIONS: Depending on their composition and quantity, serum bile acids in liver failure activate TGR5. TGR5 activation leads to monocyte dysfunction and correlates with mortality, independent of disease activity. This indicates an active role of TGR5 in liver failure. Therefore, TGR5 and bile acid metabolism might be promising targets for the treatment of immune dysfunction in liver failure.