The oxytocin receptor antagonist, Atosiban, activates pro-inflammatory pathways in human amnion via Gαi signalling

Oxytocin (OT) plays an important role in the onset of human labour by stimulating uterine contractions and promoting prostaglandin/inflammatory cytokine synthesis in amnion via oxytocin receptor (OTR) coupling. The OTR-antagonist, Atosiban, is widely used as a tocolytic for the management of acute preterm labour. We found that in primary human amniocytes, Atosiban (10 μM) signals via PTX-sensitive Gαi to activate transcription factor NF-κB p65, ERK1/2, and p38 which subsequently drives upregulation of the prostaglandin synthesis enzymes, COX-2 and phospho-cPLA2 and excretion of prostaglandins (PGE2) (n = 6; p < 0.05, ANOVA). Moreover, Atosiban treatment increased expression and excretion of the inflammatory cytokines, IL-6 and CCL5. We also showed that OT-simulated activation of NF-κB, ERK1/2, and p38 and subsequent prostaglandin and inflammatory cytokine synthesis is via Gαi−2 and Gαi−3 but not Gαq, and is not inhibited by Atosiban. Activation or exacerbation of inflammation is not a desirable effect of tocolytics. Therefore therapeutic modulation of the OT/OTR system for clinical management of term/preterm labour should consider the effects of differential G-protein coupling of the OTR and the role of OT or selective OTR agonists/antagonists in activating proinflammatory pathways

Single molecule analysis of functionally asymmetric G protein-coupled receptor (GPCR) oligomers reveals diverse spatial and structural assemblies.

Formation of G protein-coupled receptors (GPCRs) into dimers and higher order oligomers represents a key mechanism in pleiotropic signaling, yet how individual protomers function within oligomers remains poorly understood. We present a super-resolution imaging approach, resolving single GPCR molecules to ∼ 8 nm resolution in functional asymmetric dimers and oligomers using dual-color photoactivatable dyes and localization microscopy (PD-PALM). PD-PALM of two functionally defined mutant luteinizing hormone receptors (LHRs), a ligand-binding deficient receptor (LHR(B-)) and a signaling-deficient (LHR(S-)) receptor, which only function via intermolecular cooperation, favored oligomeric over dimeric formation. PD-PALM imaging of trimers and tetramers revealed specific spatial organizations of individual protomers in complexes where the ratiometric composition of LHR(B-) to LHR(S-) modulated ligand-induced signal sensitivity. Structural modeling of asymmetric LHR oligomers strongly aligned with PD-PALM-imaged spatial arrangements, identifying multiple possible helix interfaces mediating inter-protomer associations. Our findings reveal that diverse spatial and structural assemblies mediating GPCR oligomerization may acutely fine-tune the cellular signaling profile

Targeting GLP-1 receptor trafficking to improve agonist efficacy

Glucagon-like peptide-1 receptor (GLP-1R) activation promotes insulin secretion from pancreatic beta cells, causes weight loss, and is an important pharmacological target in type 2 diabetes (T2D). Like other G protein-coupled receptors, the GLP-1R undergoes agonist-mediated endocytosis, but the functional and therapeutic consequences of modulating GLP-1R endocytic trafficking have not been clearly defined. Here, we investigate a series of biased GLP-1R agonists with variable propensities for GLP-1R internalization and recycling. Compared to a panel of FDA-approved GLP-1 mimetics, compounds that retain GLP-1R at the plasma membrane produce greater long-term insulin release, which is dependent on a reduction in β-arrestin recruitment and faster agonist dissociation rates. Such molecules elicit glycemic benefits in mice without concomitant increases in signs of nausea, a common side effect of GLP-1 therapies. Our study identifies a set of agents with specific GLP-1R trafficking profiles and the potential for greater efficacy and tolerability as T2D treatments

Prostaglandin F2α requires activation of calcium-dependent signalling to trigger inflammation in human myometrium

IntroductionPreterm birth is one of the major causes of neonatal morbidity and mortality across the world. Both term and preterm labour are preceded by inflammatory activation in uterine tissues. This includes increased leukocyte infiltration, and subsequent increase in chemokine and cytokine levels, activation of pro-inflammatory transcription factors as NF-κB and increased prostaglandin synthesis. Prostaglandin F2α (PGF2α) is one of the myometrial activators and stimulators.MethodsHere we investigated the role of PGF2α in pro-inflammatory signalling pathways in human myometrial cells isolated from term non-labouring uterine tissue. Primary myometrial cells were treated with G protein inhibitors, calcium chelators and/or PGF2α. Nuclear extracts were analysed by TranSignal cAMP/Calcium Protein/DNA Array. Whole cell protein lysates were analysed by Western blotting. mRNA levels of target genes were analysed by RT-PCR.ResultsThe results show that PGF2α increases inflammation in myometrial cells through increased activation of NF-κB and MAP kinases and increased expression of COX-2. PGF2α was found to activate several calcium/cAMP-dependent transcription factors, such as CREB and C/EBP-β. mRNA levels of NF-κB-regulated cytokines and chemokines were also elevated with PGF2α stimulation. We have shown that the increase in PGF2α-mediated COX-2 expression in myometrial cells requires coupling of the FP receptor to both Gαq and Gαi proteins. Additionally, PGF2α-induced calcium response was also mediated through Gαq and Gαi coupling.DiscussionIn summary, our findings suggest that PGF2α-induced inflammation in myometrial cells involves activation of several transcription factors – NF-κB, MAP kinases, CREB and C/EBP-β. Our results indicate that the FP receptor signals via Gαq and Gαi coupling in myometrium. This work provides insight into PGF2α pro-inflammatory signalling in term myometrium prior to the onset of labour and suggests that PGF2α signalling pathways could be a potential target for management of preterm labour

Agonist-induced membrane nanodomain clustering drives GLP-1 receptor responses in pancreatic beta cells

The glucagon-like peptide-1 receptor (GLP-1R), a key pharmacological target in type 2 diabetes (T2D) and obesity, undergoes rapid endocytosis after stimulation by endogenous and therapeutic agonists. We have previously highlighted the relevance of this process in fine-tuning GLP-1R responses in pancreatic beta cells to control insulin secretion. In the present study, we demonstrate an important role for the translocation of active GLP-1Rs into liquid-ordered plasma membrane nanodomains, which act as hotspots for optimal coordination of intracellular signaling and clathrin-mediated endocytosis. This process is dynamically regulated by agonist binding through palmitoylation of the GLP-1R at its carboxyl-terminal tail. Biased GLP-1R agonists and small molecule allosteric modulation both influence GLP-1R palmitoylation, clustering, nanodomain signaling, and internalization. Downstream effects on insulin secretion from pancreatic beta cells indicate that these processes are relevant to GLP-1R physiological actions and might be therapeutically targetable

Agonist-induced membrane nanodomain clustering drives GLP-1 receptor responses in pancreatic beta cells

The glucagon-like peptide-1 receptor (GLP-1R), a key pharmacological target in type 2 diabetes (T2D) and obesity, undergoes rapid endocytosis after stimulation by endogenous and therapeutic agonists. We have previously highlighted the relevance of this process in fine-tuning GLP-1R responses in pancreatic beta cells to control insulin secretion. In the present study, we demonstrate an important role for the translocation of active GLP-1Rs into liquid-ordered plasma membrane nanodomains, which act as hotspots for optimal coordination of intracellular signaling and clathrin-mediated endocytosis. This process is dynamically regulated by agonist binding through palmitoylation of the GLP-1R at its carboxyl-terminal tail. Biased GLP-1R agonists and small molecule allosteric modulation both influence GLP-1R palmitoylation, clustering, nanodomain signaling, and internalization. Downstream effects on insulin secretion from pancreatic beta cells indicate that these processes are relevant to GLP-1R physiological actions and might be therapeutically targetable

The GPR120 agonist TUG‐891 promotes metabolic health by stimulating mitochondrial respiration in brown fat

Brown adipose tissue (BAT) activation stimulates energy expenditure in human adults, which makes it an attractive target to combat obesity and related disorders. Recent studies demonstrated a role for G protein‐coupled receptor 120 (GPR120) in BAT thermogenesis. Here, we investigated the therapeutic potential of GPR120 agonism and addressed GPR120‐mediated signaling in BAT. We found that activation of GPR120 by the selective agonist TUG‐891 acutely increases fat oxidation and reduces body weight and fat mass in C57Bl/6J mice. These effects coincided with decreased brown adipocyte lipid content and increased nutrient uptake by BAT, confirming increased BAT activity. Consistent with these observations, GPR120 deficiency reduced expression of genes involved in nutrient handling in BAT. Stimulation of brown adipocytes in vitro with TUG‐891 acutely induced O2 consumption, through GPR120‐dependent and GPR120‐independent mechanisms. TUG‐891 not only stimulated GPR120 signaling resulting in intracellular calcium release, mitochondrial depolarization, and mitochondrial fission, but also activated UCP1. Collectively, these data suggest that activation of brown adipocytes with the GPR120 agonist TUG‐891 is a promising strategy to increase lipid combustion and reduce obesity